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  • 11451. Zhou, Wei
    et al.
    Yang, Hongxing
    Rissanen, Markku
    Nygren, Bertil
    Yan, Jinyue
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Energiprocesser.
    Decrease of energy demand for bioethanol-based polygeneration system through case study2012Ingår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 95, s. 305-311Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Economic competitiveness of bioethanol production strongly depends on the amount of heat and power consumed during the production process. Integration of different energy conversion processes by polygeneration is one of the solutions to minimize the use of energy resources to best meet user's energy demands. In this study, a biogas generation system, a Fuel Cell system and a green house are integrated in the bioethanol plant to form a polygeneration system. At the same time, in order to further reduce the consumption of external energy sources, possibilities of heat energy integration, which looks for the best utilization of energy flows generated or consumed inside the process, have been investigated. Simulation of the polygeneration system is carried out by Simulink; energy saving potential for the polygeneration plant is analyzed to find the optimum configuration to maximize the electricity production while producing sufficient heat from both the Fuel Cell unit and pellets combustion to satisfy the energy requirements of the whole plant. Based on the simulation results, detailed energy and mass flow processes of the whole polygeneration plant was presented.

  • 11452.
    Zhou, Yang
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Comparison of Chinese Green Building Standard with Western Green Building standards2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    With rapid economic growth and urbanization in China, the Chinese building sector now accounted for a large amount of its energy usage and pollution. In order to minimize the environmental effect, the Ministry of Urban and Rural Development (MOHURD) has set a goal that 30% of all new constructed buildings will be green by 2020.

    This report reviews the Three Star System, the Chinese green building standard developed by the government agency MOHURD in order to promote and regulate green buildings in China. The study is done by comparing the Three Star System with two of its western equivalents, BREEAM and LEED. The technical manual of each standard is studied and compared, results from various researches within the area is also featured in the report.

    The finding of this report is that Three Star System is necessary to fulfill Chinas unique situation with a building sector that consist of high rates of new construction, although the standard is necessary it still need improvement in technical detail and user-friendliness to be at the same level as LEED and BREEAM. Some suggestion are proposed in the report for further development of the Three Star System 

  • 11453.
    Zhou, Yang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Numerical instability investigations for thin membranes2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Membrane structures are commonly used in many fields. The studies of these structures are of increasing interest. The projects in this thesis focus on the evaluations of equilibrium states for pressurized membranes under different problem settings, using finite element methods, and the corresponding instability behaviors.

    The first part of the current work discusses the instability behavior of a thin, planar, circular and initially horizontal membrane subjected to downwards or upwards fluid pressure. The membrane structures exhibit large deformations under pressure. The method for evaluating fluid pressure from gravity was developed in finite element context, and used in numerical simulations. Limit and bifurcation points have been detected for different loading parameters and conditions. The effects on instabilities of parameters, the initial states of the membrane, and the chosen mesh are discussed.

    The second part of the current work discusses instability behavior of a thin, spherical and closed membrane containing gas and fluid, when placed on a horizontal rigid and non-friction plane. A multi-parametric loading is described. By adding practically relevant controlling equations, different classes of equilibrium paths were followed using a generalized path following algorithm. Stability conclusions were made, according to the considered load parameters and the constraints. A generalized eigenvalue analysis was used to evaluate the stability behavior including the constraint effects. Fold line evaluations were performed to analyze the parametric dependence. A solution surface approach is used to visualize the mechanical response under this multi-parametric setting.

    The third part of the current work focuses on instability response of a truncated sphere, containing gas and fluid, and in contact with two vertical rigid and non-friction planes. Different penalty formulations were used and compared. The effects of contact implementations on instability behaviors were investigated. Bifurcation points induced by contacts have been observed. Multi-parametric problems were defined, and generalized paths were followed. The multi-parametric stability was evaluated using generalized eigenvalue analysis, based on the mass and total differential matrices. The effects of augmenting equations on bifurcation points and limit points are discussed.

    The fourth part of the current work analyses the instability response of a truncated sphere, completely filled with fluid, placed on a horizontal plane and spinning around the vertical axis. The loads from fluid pressure and the constraints, e.g., fluid volume, were formulated to generate a symmetric differential matrix. Several mesh patterns with different symmetries were used to simulate the model, and the obtained results are compared. Various problem settings were considered, and generalized paths were followed. The effects of symmetry aspects of the chosen meshes on instability behaviors are discussed, as are the effects of parameters.

  • 11454.
    Zhou, Yang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Parametric stability analyses for fluid-loaded thin membranes2015Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Membrane structures are commonly used in many elds. The studies of thesestructures are of increasing interest. The two projects focus on the evaluations ofequilibrium states for uid-pressurized membranes under dierent loading conditions,and the corresponding instability behavior.The rst part of the current work discusses the instability behavior of a thin,planar, circular and initially horizontal membrane subjected to downwards or upwards uid pressure. The membrane structures exhibit large deformations under uid pressure. Various instability behaviors have been observed for dierent loadingparameters. Limit and bifurcation points have been detected for dierent loadingconditions. Dierent loading parameters have been used to interpret the instabilitybehavior. The eects on instability of parameters, the initial states of the membrane,and the chosen mesh have been discussed.The second part of the current work discusses instability behavior of a thin,spherical and closed membrane containing gas and uid placed on a horizontal rigidand non-friction plane. A multi-parametric loading has been described. By addingthe practically relevant controlling equations, the complex equilibrium paths werefollowed using the generalized path following algorithm, and the stability conclusionswere made dierently, according to the considered load parameters and theconstraints. A generalized eigenvalue analysis was used to evaluate the stabilitybehavior including the constraint eects. Fold line evaluations were performed toanalyze the parametric dependence of the instability behavior. A solution surfaceapproach was used to visualize the mechanical response under this multi-parametricsetting.

  • 11455.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Instability investigation for rotating thin spherical membrane2017Ingår i: International Journal of Non-Linear Mechanics, ISSN 0020-7462, E-ISSN 1878-5638, Vol. 97, s. 96-106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A fluid-filled truncated spherical membrane fixed along its truncated edge to a horizontal, rigid and frictionless plane and spinning around a center axis was investigated. A two-parameter Mooney-Rivlin model was used to describe the material of the membrane. The truncated sphere was modeled in 3D using finite element meshes with different symmetry properties. A quadratic function was used for interpolating hydro-static pressure, giving a symmetric tangent stiffness matrix, thereby reproducing the conservative problem. Various problem settings were considered, related to the spinning, and different instability behaviors were observed. Multi-parametric problems were defined, generalized paths including primary and secondary paths were followed. Stability of the multi parametric problem was evaluated using generalized eigenvalue analysis based on the total differential matrix for the constrained problem. Numerical results showed that mesh symmetry affected the simulated stability behavior. Fold line evaluations showed the parametric effects on critical solutions.

  • 11456.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Instability investigation for rotating thin spherical membranesManuskript (preprint) (Övrigt vetenskapligt)
  • 11457.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Instability of thin circular membranes subjected to hydro-static loads2015Ingår i: International Journal of Non-Linear Mechanics, ISSN 0020-7462, E-ISSN 1878-5638, Vol. 76, s. 144-153Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Membrane structures subjected to hydrostatic load are prone to undergo large deformations and lose stability. This paper investigates different instability phenomena for a thin, circular and initially flat and horizontal membrane. The Mooney-Rivlin hyper-elastic model is used to provide the material description. An axisymmetric and a 3D model have been set up to show the large deformations and instability behavior with different parameter settings. Numerical examples show that the methods developed are capable to describe the deformation dependent loading conditions and the instability phenomena. The numerical simulations show fundamental differences in the response and instability behavior when the horizontal membrane is loaded from above or below. The parameters of fluids and membranes and the means for introducing the pressure are of essence for interpreting the instability behavior.

  • 11458.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Multi-parametric stability investigation for thin membranes with contactsManuskript (preprint) (Övrigt vetenskapligt)
  • 11459.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Multi-parametric stability investigation for thin spherical membranes filled with gas and fluid2016Ingår i: International Journal of Non-Linear Mechanics, ISSN 0020-7462, E-ISSN 1878-5638, Vol. 82, s. 37-48Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The instability behavior of spherical membranes completely or partially filled with fluid, also with internal gas over-pressure, placed on a friction-less rigid plane was investigated. The two-parameter Mooney-Rivlin model was used for material description. A third order penalty function was used to describe the rigid support. Different problem settings were considered, and different instability responses were observed. For the partially fluid-filled membrane, a multi-parametric problem was defined and analyzed. Augmenting equations were introduced to impose control constraints on variables chosen. These equations also affect the instability analysis. A generalized eigenvalue analysis was used for the stability conclusions. Numerical simulations showed that appropriate control constraints are of essence to interpret the instability conclusions. Fold line evaluations were performed to analyze the dependence of the instability behavior on the parameters. A solution surface algorithm was utilized to analyze and visualize the mechanical responses to multi-variable loading.

  • 11460.
    Zhou, Yang
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Multi-parametric stability investigation for thin spherical membranes with contacts2017Ingår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 131-132, s. 334-344Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The instability behavior for a thin truncated spherical membrane completely filled with fluid or containing both gas and fluid, fixed on a circular platform and in contact with two vertical planes was investigated. Different penalty functions for contacts, and symmetry aspects of the discretized model were studied, and gave effects on instability behavior. Stability conclusions for the multi-parametric problems were made using generalized eigenvalue analyses, showing limit points, bifurcation points and turning point. Contact conditions were shown to introduce bifurcations and secondary paths, dependent on the contact implementations and discretizations. Their effects on stability behaviors in connection with various controlling equations are discussed.

  • 11461.
    Zhou, Zhou
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Neuronik.
    Li, Xiaogai
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Neuronik.
    Kleiven, Svein
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Neuronik.
    Biomechanics of acute subdural hematoma in the elderly: A fluid-structure interaction study2019Ingår i: Journal of Neurotrauma, ISSN 0897-7151, E-ISSN 1557-9042, Vol. 36, nr 13, s. 2099-2108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Acute subdural hematoma (ASDH) due to bridging vein (BV) rupture is a frequent and lethal head injury, especially in the elderly. Brain atrophy has been hypothesized to be a primary pathogenesis associated with the increased risk of ASDH in the elderly. Though decades of biomechanical endeavours have been made to elucidate the potential mechanisms, a thorough explanation for this hypothesis appears lacking. Thus, a recently improved finite element head model, in which the brain-skull interface was modelled using a fluid-structure interaction (FSI) approach with special treatment of the cerebrospinal fluid as arbitrary Lagrangian-Eulerian fluid formulation, is used to partially address this understanding gap. Models with various degrees of atrophied brains and thereby different subarachnoid thicknesses are generated and subsequently exposed to experimentally determined loadings known to cause ASDH or not. The results show significant increases in the cortical relative motion and BV strain in the atrophied brain, which consequently exacerbates the ASDH risk in the elderly. Results of this study are suggested to be considered while developing age-adapted protecting strategies for the elderly in the future.

  • 11462. Zhu, B.
    et al.
    Fan, L.
    Deng, H.
    He, Y.
    Afzal, M.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg.
    Dong, W.
    Yaqub, A.
    Janjua, N. K.
    Erratum: Corrigendum to “LiNiFe-based layered structure oxide and composite for advanced single layer fuel cells” (J. Power Sources (2016) 316 (37–43))2016Ingår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 324Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The authors regret that the name of author Yunjuan He was misspelled as ‘Yunjune He’ in the original article. The authors would like to apologise for any inconvenience caused.

  • 11463. Zhu, B.
    et al.
    Lund, P. D.
    Raza, Rizwan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik. COMSATS Institute of Information Technology, Pakistan .
    Ma, Y.
    Fan, L.
    Afzal, Muhammad
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Patakangas, J.
    He, Y.
    Zhao, Y.
    Tan, W.
    Huang, Q. -A
    Zhang, J.
    Wang, H.
    Schottky junction effect on high performance fuel cells based on nanocomposite materials2015Ingår i: Advanced Energy Materials, ISSN 1614-6832, Vol. 5, nr 8, artikel-id 1401895Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel fuel cell device based on integrating the Schottky junction effect with the electrochemical principle is designed, constructed, and verified through experiments. It is found that the Schottky junction has a significant effect on the greatly enhanced device performance, and the fuel cell device incorporating the Schottky junction effect reaches a power output of 1000 mW cm-2 at 550 C.

  • 11464.
    Zhu, Bin
    KTH, Tidigare Institutioner, Kemiteknik. Goeta Technol. Developer Intl, Sweden.
    Advanced ceramic fuel cell R&D2004Ingår i: Fuel Cell Science, Engineering and Technology - 2004, 2004, s. 409-417Konferensbidrag (Refereegranskat)
    Abstract [en]

    Since many years in Swedish national research project and Swedish-Chinese research framework we have carried out advanced ceramic fuel cell research and development, targeting for intermediate and low temperature ceramic or solid oxide fuel cells (ILTCFCs or ILTSOFCs, 300-700°C) based on ceramic-based composite materials. The ceramic composite material developments in Sweden have been experienced from the oxyacid-salts oxide proton-based conductors, non-oxide containment salts, the ceria-based composite electrolytes and nano-composites. Among them the ceria-based composites showed excellent ionic conductivity of 0.01 to 1 Scm-1 and ILTCFCs using these composites as electrolytes have achieved high performances of 200 to 1000 mWcm-2 at temperatures between 400 and 700°C. The excellent ion conduction was resulted from hybrid proton and oxygen ion conduction. The hybrid ion conduction and dual electrode reactions and processes create a new fuel cell system. Advanced ceramic fuel cell aims at developing a new generation to realize the challenges for fuel cell commercialization. This paper reviews our more than 14 years R&D on the field with emphasis on the recent progresses and achievements.

  • 11465.
    Zhu, Bin
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Nanocomposites for Advanced Fuel Cell Technology2011Ingår i: Journal of Nanoscience and Nanotechnology, ISSN 1533-4880, Vol. 11, nr 10, s. 8873-8879Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    NANOCOFC (Nanocomposites for advanced fuel cell technology) is a research platform/network established based on the FP6 EC-China project www.nanocofc.org. This paper reviews major achievements on two-phase nanocomposites for advanced low temperature (300-600 degrees C) solid oxide fuel cells (SOFCs), where the ceria-salt and ceria-oxide composites are common. A typical functional nanocomposite structure is a core-shell type, in which the ceria forms a core and the salt or another oxide form the shell layer. Both of them are in the nano-scale and the functional components. The high resolution TEM analysis has proven a clear interface in the ceria-based two-phase nanocomposites. such interface and interfacial function has resulted in superionic conductivity, above 0.1 S/cm at around 300 degrees C, being comparable to that of conventional SOFC YSZ at 1000 degrees C. Against conventional material design from the structure the advanced nanocomposites are designed by non-structure factors, i.e., the interfaces, and by creating interfacial functionalities between the two constituent phases. These new functional materials show indeed a breakthrough in the SOFC materials with great potential.

  • 11466.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik. Hubei University, 430062, Wuhan, PR China.
    Basile, Angelo
    Tseng, Chung-Jen
    Materials as a player in hydrogen and fuel cell technologies: Preface to the special issue section2017Ingår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 42, nr 34, s. 22090-22090Artikel i tidskrift (Övrigt vetenskapligt)
  • 11467.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi. Hubei University, China.
    Fan, L.
    Deng, H.
    He, Y.
    Afzal, Muhammad
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Dong, W.
    Yaqub, A.
    Janjua, N. K.
    LiNiFe-based layered structure oxide and composite for advanced single layer fuel cells2016Ingår i: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 316, s. 37-43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A layered structure metal oxide, LiNi0.1Fe0.90O2-δ (LNF), is explored for the advanced single layer fuel cells (SLFCs). The temperature dependent impedance profiles and concentration cells (hydrogen concentration, oxygen concentration, and H2/air atmospheres) tests prove LNF to be an intrinsically electronic conductor in air while mixed electronic and proton conductor in H2/air environment. SLFCs constructed by pure LNF materials show significant short circuiting reflected by a low device OCV and power output (175 mW cm-2 at 500°C) due to high intrinsic electronic conduction. The power output is improved up to 640 and 760 mW cm-2, respectively at 500 and 550°C by compositing LNF with ion conducting material, e.g., samarium doped ceria (SDC), to balance the electronic and ionic conductivity; both reached at 0.1 S cm-1 level. Such an SLFC gives super-performance and simplicity over the conventional 3-layer (anode, electrolyte and cathode) FCs, suggesting strong scientific and commercial impacts.

  • 11468.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fan, Liangdong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    He, Y.
    Zhao, Y.
    Wang, H.
    A commercial lithium battery LiMn-oxide for fuel cell applications2014Ingår i: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 126, s. 85-88Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hereby we report first a commercial lithium battery LiMn-oxide (LMO) positive electrode material for fuel cell applications. The obtained LMO can be used for both anode and cathode in a three-layer fuel cell, but displays low electro-catalytic activity and power output. Using a nanocomposite approach we have significantly improved the cell performance from tens mW cm-2 up to 210 mW cm-2, which is technically useful for low temperature (bellow 600 °C) ceramic fuel cells. We also constructed single-layer fuel cell using the LMO/SDC-metal oxide composite and achieved even better performances than those for conventional anode-electrolyte-cathode three-layer fuel cells.

  • 11469.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fan, Liangdong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Lund, Peter
    Breakthrough fuel cell technology using ceria-based multi-functional nanocomposites2013Ingår i: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 106, s. 163-175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent scientific and technological advancements have provided a wealth of new information about solid oxide-molten salt composite materials and multifunctional ceria-based nano-composites for advanced fuel cells (NANOCOFC). NANOCOFC is a new approach for designing and developing of multi-functionalities for nanocomposite materials, especially at 300-600 degrees C. NANOCOFC and low temperature advanced ceramic fuel cells (LTACFCs) are growing as a new promising area of research which can be explored in various ways. The ceria-based composite materials have been developed as competitive electrolyte candidates for low temperature ceramic fuel cells (LTCFCs). In the latest developments, multifunctional materials have been developed by integrating semi- and ion conductors, which have resulted in an emerging insight knowledge concerned with their R&D on single-component electrolyte-free fuel cells (EFFCs) - a breakthrough fuel cell technology. A homogenous component/layer of the semi- and ion conducting materials can realize fuel cell all functions to avoid using three components: anode, electrolyte and cathode, i.e. "three in one" highlighted by Nature Nanotechnology (2011). This report gives a short review and advance knowledge on worldwide activities on the ceria-based composites, emphasizing on the latest semi-ion conductive nanocomposites and applications for new applied energy technologies. It gives an overview to help the audience to get a comprehensive understanding on this new field.

  • 11470.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Li, S.
    Sun, X. L.
    Sun, J. C.
    Fuel Cell and Electrolysis Studies with Dual Phase Proton and Oxide Ion Conduction2012Ingår i: Molten Salts and Ionic Liquids: Never the Twain?, John Wiley & Sons, 2012, s. 407-417Kapitel i bok, del av antologi (Refereegranskat)
  • 11471.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi. Goeta Technology Development International, Sweden .
    Liu, Xiangrong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi. Goeta Technology Development International, Sweden .
    Zhu, Z.
    Ljungberg, R.
    Development of low temperature solid oxide fuel cells2006Ingår i: Proceedings of 4th International ASME Conference on Fuel Cell Science, Engineering and Technology, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    Based on innovative ceria-based composite (CBC) material advantages we have made strong efforts to make technical developments on scaling up material production, fabrication technologies on large cells and stack operated at low temperatures (300 to 600°C). Next generation materials for solid oxide fuel cells (SOFCs) have been developed based on abundant natural resources of the industrial grade mixed rare-earth carbonates named as LCP. Here we show the LCP-based materials used as functional electrolytes to achieve excellent fuel cell performances, 300-800 mWcm2 for low temperatures, exhibiting a great availability for industrialization and commercialization. Copyright

  • 11472.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Lund, Peter
    Aalto Univ, Dept Engn Phys, Sch Sci, FI-00076 Espoo, Finland..
    Advanced fuel cells: from materials and technologies to applications2011Ingår i: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 35, nr 12, s. 1023-1024Artikel i tidskrift (Övrigt vetenskapligt)
  • 11473.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Lund, Peter
    Helsinki Univ Technol, FI-02015 Espoo, Finland..
    Mao, Zongqiang
    Tsinghua Univ, Inst Nucl & New Energy Technol, Beijing 100084, Peoples R China..
    Basile, Angelo
    Univ Calabria, ITM, Italian Natl Res Council, CNR, I-87030 Arcavacata Di Rende, CS, Italy..
    Special IJHE issue from HyForum 2008 conference2010Ingår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 35, nr 7, s. 2579-2579Artikel i tidskrift (Övrigt vetenskapligt)
  • 11474.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Lund, Peter
    Raza, Rizwan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Patakangas, Janne
    Huang, Qiu-An
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fan, Liangdong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Singh, Manish
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    A new energy conversion technology based on nano-redox and nano-device processes2013Ingår i: Nano Energy, ISSN 2211-2855, Vol. 2, nr 6, s. 1179-1185Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrolyte-separator-free fuel cell (EFFC) is a new emerging energy conversion technology. The EFFC consists of a single-component of nanocomposite material which works as a one-layer fuel cell device contrary to the traditional three-layer anode-electrolyte-cathode structure, in which an electrolyte layer plays a critical role. The nanocomposite of a single homogenous layer consists of a mixture of semiconducting and ionic materials that provides the necessary electrochemical reaction sites and charge transport paths for a fuel cell. These can be accomplished through tailoring ionic and electronic (n, p) conductivities and catalyst activities, which enable redox reactions to occur on nano-particles and finally accomplish a fuel cell function.

  • 11475.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Mat, Mahmut D.
    Studies on Dual Phase Ceria-based Composites in Electrochemistry2006Ingår i: International Journal of Electrochemical Science, ISSN 1452-3981, E-ISSN 1452-3981, Vol. 1, nr 8, s. 383-402Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The ceria-based dual-phase composites have been recently developed as functional electrolytes successful for intermediate and low temperature solid oxide fuel cell applications. These composite materials showed many unique advantages over the conventional single-phase electrolytes, such as superionic conduction in two-phase interfaces, dual proton and oxygen ion conduction resulting in extremely high ion conductivity and high current outputs in fuel cell and other applications, e. g. electrolysis. Interfacial superionic conduction is a characteristic for high conducting dual-phase composites. The composite approach can combine or integrate multi-ion functions, typically, dual H(+) and O(2-)conduction together to enhance the material conductivity and device performance. Dual or hybrid H+ and O(2-)conduction is based on a consideration that both proton (H+) and oxygen ion (O(2-)) are the fuel cell source ions. Proton conduction is important for LTSOFCs since it can be activated easier than oxygen ions in the low temperature (LT, 300-600 degrees C) region. The superionic conduction, dual phase proton and oxygen ion transport make significant conduction and electrical contributions for electrochemical devices. This paper makes a review on these recent studies.

  • 11476.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Qin, Haiying
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Raza, Rizwan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Liu, Qinghua
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fan, Liangdong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Patakangas, J
    Lund, P
    A single-component fuel cell reactor2011Ingår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 36, nr 14, s. 8536-8541Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report here a single-component reactor consisting of a mixed ionic and semi-conducting material exhibiting hydrogen-air (oxygen) fuel cell reactions. The new single-component device was compared to a conventional three-component (anode/electrolyte/cathode) fuel cell showing at least as good performance. A maximum power density of 300-600 mW cm(-2) was obtained with a LiNiZn-oxide and ceria-carbonate nanocomposite material mixture at 450-550 degrees C. Adding a redox catalyst element (Fe) resulted in an improvement reaching 700 mW cm(-2) at 550 degrees C.

  • 11477.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Raza, Rizwan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Liu, Qinghua
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Qin, Haiying
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Zhu, Zhigang
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Fan, Liangdong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Singh, Manish
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik.
    Lund, Peter
    A new energy conversion technology joining electrochemical and physical principles2012Ingår i: RSC Advances, ISSN 2046-2069, Vol. 2, nr 12, s. 5066-5070Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report a new energy conversion technology joining electrochemical and physical principles. This technology can realize the fuel cell function but built on a different scientific principle. The device consists of a single component which is a homogenous mixture of ceria composite with semiconducting materials, e.g. LiNiCuZn-based oxides. The test devices with hydrogen and air operation delivered a power density of 760mWcm(-2) at 550 degrees C. The device has demonstrated a multi-fuel flexibility and direct alcohol and biogas operations have delivered 300-500 mW cm(-2) at the same temperature. Device physics reveal a key principle similar to solar cells realizing the function based on an effective separation of electronic and ionic conductions and phases within the single-component. The component material multi-functionalities: ion and semi-conductions and bi-catalysis to H-2 or alcohol (methanol and ethanol) and air (O-2) enable this device realized as a fuel cell.

  • 11478.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Raza, Rizwan
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Qin, Haiying
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Liu, Qinghua
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fan, Liangdong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi.
    Fuel cells based on electrolyte and non-electrolyte separators2011Ingår i: Energy & Environmental Science, ISSN 1754-5692, E-ISSN 1754-5706, Vol. 4, nr 8, s. 2986-2992Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the long-history of fuel cell R&D, the electrolyte is an essential part in a three-component configuration because it separates the anode and cathode to realize the fuel cell's functions. We report here non-electrolyte separator fuel cells (NEFCs) compared with electrolyte based fuel cells (EBFCs). The NEFC consists of single- or dual-components based on mixed ionic and semi-conductors but with no electrolyte separator. A maximum power density of 680 mW cm(-2) has been achieved by the NEFC at 550 degrees C. The NEFCs exhibit performances comparable to, and in some cases even better than, those of conventional EBFCs. The design of NEFCs, new material functionalities and device performances may contribute to new fuel cell R&D.

  • 11479.
    Zhu, Bin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi. Institute of Materials and Technology, Dalian Maritime University, China .
    Sun, J.
    Sun, X.
    Li, S.
    Gao, W.
    Liu, Xiangrong
    KTH, Skolan för industriell teknik och management (ITM), Energiteknik, Kraft- och värmeteknologi. Goeta Technology Development International, Sweden .
    Zhu, Z.
    Compatible cathode materials for high performance low temperature (300-600°C) solid oxide fuel cells2006Ingår i: Proceedings of 4th International ASME Conference on Fuel Cell Science, Engineering and Technology, FUELCELL2006, 2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    We have made extensive efforts to develop various compatible electrode materials for the ceria-based composite (CBC) electrolytes, which have been, reported as most advanced LTSOFC electrolyte materials (Zhu, 2003). The electrode materials we have investigated can be classified as four categories: i) LSCCF (LaSrCoCaFeO) and BSCF perovskite oxides applied for our CBC electrolyte LTSOFCs; ii) LFN (LaFeO-based oxides, e.g. LaFe0.8Ni 0.2O3) perovskite oxides; iii) lithiated oxides: e.g. LiNiOx, LiVOx or LiCuOx are typical cathode examples for the CBC LTSOFCs; iv) other mixed oxide systems, most common in a mixture of two-oxide phases, such CuOx-NiOx, CuO-ZnO etc. systems with or without lithiation are developed for the CBC systems, especially for direct alcohol LTSOFCs. These cathode materials used for the CBC electrolyte LTSOFCs have demonstrated excellent performances at 300-600°C, e.g. 1000 mWcm-2 was achieved at 580°C. The LTSOFCs can be operated with a wide range of fuels, e.g. hydrogen, methanol, ethanol etc with great potential for applications. Copyright

  • 11480.
    Zhu, Jinchao
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Computational Weld Mechanics - estimation of angular distortion and residual stresses2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The present study estimates the angular distortion and the residual stresses using the following methodologies: Thermo-elastic-plastic, Inherent strain (local-global) and Substructuring on two types of welded joints: T-type fillet weld and butt weld. The numerical results are compared with the experimental measurements and these methodologies are evaluated in terms of accuracy and computational time. The influence of welding sequence towards distortion and transverse residual stresses has been studied numerically by implementing Thermo-elastic-plastic and Inherent strain (local-global) methods on T-type fillet weld. It shows that the welding position and welding direction have almost the same influence on angular distortions from Thermo-elastic-plastic method. The Inherent strain (local-global) method can estimate the angular distortion caused by different weld position in good agreement with Thermo-elastic-plastic method. To have a better understanding of where the underestimation of angular distortion in Inherent strain (local-global) method comes from, the study discusses the influence of block length and welding speed towards angular distortion. It is found that for long weld length or slow welding speed, activating the plastic strain gradually by dividing the weld bead into an appropriate number of blocks can reduce the level of underestimation of angular distortion.

  • 11481.
    Zhu, Lailai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Numerical investigation of swimming micro-organisms in complex environments2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
  • 11482.
    Zhu, Lailai
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll.
    Simulation of individual cells in flow2014Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this thesis, simulations are performed to study the motion ofindividual cells in flow, focusing on the hydrodynamics of actively swimming cells likethe self-propelling microorganisms, and of passively advected objects like the red bloodcells. In particular, we develop numerical tools to address the locomotion ofmicroswimmers in viscoelastic fluids and complex geometries, as well as the motion ofdeformable capsules in micro-fluidic flows.

    For the active movement, the squirmer is used as our model microswimmer. The finiteelement method is employed to study the influence of the viscoelasticity of fluid on theperformance of locomotion. A boundary element method is implemented to study swimmingcells inside a tube. For the passive counterpart, the deformable capsule is chosen as the modelcell. An accelerated boundary integral method code is developed to solve thefluid-structure interaction, and a global spectral method is incorporated to handle theevolving cell surface and its corresponding membrane dynamics.

    We study the locomotion of a neutral squirmer with anemphasis on the change of swimming kinematics, energetics, and flowdisturbance from Newtonian to viscoelastic fluid. We also examine the dynamics of differentswimming gaits resulting in different patterns of polymer deformation, as well as theirinfluence on the swimming performance. We correlate the change of swimming speed withthe extensional viscosity and that of power consumption with the phase delay of viscoelasticfluids. Moreover, we utilise the boundary element method to simulate the swimming cells in astraight and torus-like bent tube, where the tube radius is a few times the cell radius. Weinvestigate the effect of tube confinement to the swimming speed and power consumption. Weanalyse the motions of squirmers with different gaits, which significantly affect thestability of the motion. Helical trajectories are produced for a neutralsquirmer swimming, in qualitative agreement with experimental observations, which can beexplained by hydrodynamic interactions alone.

    We perform simulations of a deformable capsule in micro-fluidic flows. We look atthe trajectory and deformation of a capsule through a channel/duct with a corner. Thevelocity of capsule displays an overshoot as passing around the corner, indicating apparentviscoelasticity induced by the interaction between the deformable membrane and viscousflow. A curved corner is found to deform the capsule less than the straight one. In addition, we propose a new cell sorting device based on the deformability of cells. Weintroduce carefully-designed geometric features into the flow to excite thehydrodynamic interactions between the cell and device. This interaction varies andclosely depends on the cell deformability, the resultant difference scatters the cellsonto different trajectories. Our high-fidelity computations show that the new strategy achievesa clear and robust separation of cells. We finally investigate the motion of capsule in awall-bounded oscillating shear flow, to understand the effect of physiological pulsation to thedeformation and lateral migration of cells. We observe the lateral migration velocity of a cellvaries non-monotonically with its deformability.

  • 11483.
    Zhu, Lailai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    The motion of a deforming capsule through a corner2015Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 770, s. 374-397Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A three-dimensional deformable capsule convected through a square duct with a corner is studied via numerical simulations. We develop an accelerated boundary integral implementation adapted to general geometries and boundary conditions. A global spectral method is adopted to resolve the dynamics of the capsule membrane developing elastic tension according to the neo-Hookean constitutive law and bending moments in an inertialess flow. The simulations show that the trajectory of the capsule closely follows the underlying streamlines independently of the capillary number. The membrane deformability, on the other hand, significantly influences the relative area variations, the advection velocity and the principal tensions observed during the capsule motion. The evolution of the capsule velocity displays a loss of the time-reversal symmetry of Stokes flow due to the elasticity of the membrane. The velocity decreases while the capsule is approaching the corner, as the background flow does, reaches a minimum at the corner and displays an overshoot past the corner due to the streamwise elongation induced by the flow acceleration in the downstream branch. This velocity overshoot increases with confinement while the maxima of the major principal tension increase linearly with the inverse of the duct width. Finally, the deformation and tension of the capsule are shown to decrease in a curved corner.

  • 11484.
    Zhu, Lailai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Do-Quang, Minh
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lauga, Eric
    Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Locomotion by tangential deformation in a polymeric fluid2011Ingår i: Physical Reivew E, ISSN 1539-3755, Vol. 83, nr 1, s. 011901-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In several biologically relevant situations, cell locomotion occurs in polymeric fluids with Weissenberg number larger than 1. Here we present results of three-dimensional numerical simulations for the steady locomotion of a self-propelled body in a model polymeric (Giesekus) fluid at low Reynolds number. Locomotion is driven by steady tangential deformation at the surface of the body (the so-called squirming motion). In the case of a spherical squirmer, we show that the swimming velocity is systematically less than that in a Newtonian fluid, with a minimum occurring for Weissenberg numbers of order 1. The rate of work done by the swimmer always goes up compared to that occurring in the Newtonian solvent alone but is always lower than the power necessary to swim in a Newtonian fluid with the same viscosity. The swimming efficiency, defined as the ratio between the rate of work necessary to pull the body at the swimming speed in the same fluid and the rate of work done by swimming, is found to always be increased in a polymeric fluid. Further analysis reveals that polymeric stresses break the Newtonian front-back symmetry in the flow profile around the body. In particular, a strong negative elastic wake is present behind the swimmer, which correlates with strong polymer stretching, and its intensity increases with Weissenberg number and viscosity contrasts. The velocity induced by the squirmer is found to decay in space faster than in a Newtonian flow, with a strong dependence on the polymer relaxation time and viscosity. Our computational results are also extended to prolate spheroidal swimmers and smaller polymer stretching are obtained for slender shapes compared to bluff swimmers. The swimmer with an aspect ratio of two is found to be the most hydrodynamically efficient.

  • 11485.
    Zhu, Lailai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lauga, Eric
    Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Low-Reynolds number swimming in a capillary tube2013Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 726, s. 285-311Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use the boundary element method to study the low-Reynolds-number locomotion of a spherical model microorganism in a circular tube. The swimmer propels itself by tangential or normal surface motion in a tube whose radius is of the order of the swimmer size. Hydrodynamic interactions with the tube walls significantly affect the average swimming speed and power consumption of the model microorganism. In the case of swimming parallel to the tube axis, the locomotion speed is always reduced (respectively, increased) for swimmers with tangential (respectively, normal) deformation. In all cases, the rate of work necessary for swimming is increased by confinement. Swimmers with no force dipoles in the far field generally follow helical trajectories, solely induced by hydrodynamic interactions with the tube walls, and in qualitative agreement with recent experimental observations for Paramecium. Swimmers of the puller type always display stable locomotion at a location which depends on the strength of their force dipoles: swimmers with weak dipoles (small alpha) swim in the centre of the tube while those with strong dipoles (large alpha) swim near the walls. In contrast, pusher swimmers and those employing normal deformation are unstable and end up crashing into the walls of the tube. Similar dynamics is observed for swimming into a curved tube. These results could be relevant for the future design of artificial microswimmers in confined geometries.

  • 11486.
    Zhu, Lailai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lauga, Eric
    Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Self-propulsion in viscoelastic fluids: pushers vs. pullers2012Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 24, nr 5, s. 051902-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use numerical simulations to address locomotion at zero Reynolds number in viscoelastic (Giesekus) fluids. The swimmers are assumed to be spherical, to self-propel using tangential surface deformation, and the computations are implemented using a finite element method. The emphasis of the study is on the change of the swimming kinematics, energetics, and flow disturbance from Newtonian to viscoelastic, and on the distinction between pusher and puller swimmers. In all cases, the viscoelastic swimming speed is below the Newtonian one, with a minimum obtained for intermediate values of the Weissenberg number, We. An analysis of the flow field places the origin of this swimming degradation in non-Newtonian elongational stresses. The power required for swimming is also systematically below the Newtonian power, and always a decreasing function of We. A detail energetic balance of the swimming problem points at the polymeric part of the stress as the primary We-decreasing energetic contribution, while the contributions of the work done by the swimmer from the solvent remain essentially We-independent. In addition, we observe negative values of the polymeric power density in some flow regions, indicating positive elastic work by the polymers on the fluid. The hydrodynamic efficiency, defined as the ratio of the useful to total rate of work, is always above the Newtonian case, with a maximum relative value obtained at intermediate Weissenberg numbers. Finally, the presence of polymeric stresses leads to an increase of the rate of decay of the flow velocity in the fluid, and a decrease of the magnitude of the stresslet governing the magnitude of the effective bulk stress in the fluid.

  • 11487.
    Zhu, Lailai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Rabault, Jean
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    The dynamics of a capsule in a wall-bounded oscillating shear flow2014Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The motion of an initially spherical capsule in a wall-bounded oscillating shear flow is studied via an accelerated boundary integral implementation. Neo-Hookean model is used as the constitutive law of the membrane of capsule. The lateral migration velocity of the capsule varies non-monotonically with its capillary number. It is negatively related with the initial height of the capsule above the wall. A positive correlation between the lateral migration velocity and normal stress difference is identified. The correlation becomes strongest for the capsule with the highest lateral migration velocity. For a fixed capillary number, the lateral migration velocity decreases linearly with the frequency of oscillating shear, and approaches an asymptotic value of zero for high frequency. The deformation of capsule displays a wave-like variation in time and its frequency is twice that of the underlying shear. A phase delay is observed between the variation of capsule deformation with that of the oscillatory flow, more pronounced for a more deformable capsule.

     

  • 11488.
    Zhu, LaiLai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Rabault, Jean
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. Ecole Polytech, F-91128 Palaiseau, France.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    The dynamics of a capsule in a wall-bounded oscillating shear flow2015Ingår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 27, nr 7, artikel-id 071902Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The motion of an initially spherical capsule in a wall-bounded oscillating shear flow is investigated via an accelerated boundary integral implementation. The neo-Hookean model is used as the constitutive law of the capsule membrane. The maximum wall-normal migration is observed when the oscillation period of the imposed shear is of the order of the relaxation time of the elastic membrane; hence, the optimal capillary number scales with the inverse of the oscillation frequency and the ratio agrees well with the theoretical prediction in the limit of high-frequency oscillation. The migration velocity decreases monotonically with the frequency of the applied shear and the capsule-wall distance. We report a significant correlation between the capsule lateral migration and the normal stress difference induced in the flow. The periodic variation of the capsule deformation is roughly in phase with that of the migration velocity and normal stress difference, with twice the frequency of the imposed shear. The maximum deformation increases linearly with the membrane elasticity before reaching a plateau at higher capillary numbers when the deformation is limited by the time over which shear is applied in the same direction and not by the membrane deformability. The maximum membrane deformation scales as the distance to the wall to the power 1/3 as observed for capsules and droplets in near-wall steady shear flows.

  • 11489.
    Zhu, Lailai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Rorai, Cecilia
    Mitra, Dhrubaditya
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    A microfluidic device to sort capsules by deformabilityManuskript (preprint) (Övrigt vetenskapligt)
  • 11490.
    Zhu, Lailai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Centra, SeRC - Swedish e-Science Research Centre. Laboratory of Fluid Mechanics and Instabilities, Switzerland .
    Rorai, Cecilia
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Mitra, Dhrubaditya
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    A microfluidic device to sort capsules by deformability: a numerical study2014Ingår i: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 10, nr 39, s. 7705-7711Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Guided by extensive numerical simulations, we propose a microfluidic device that can sort elastic capsules by their deformability. The device consists of a duct embedded with a semi-cylindrical obstacle, and a diffuser which further enhances the sorting capability. We demonstrate that the device can operate reasonably well under changes in the initial position of the capsule. The efficiency of the device remains essentially unaltered under small changes of the obstacle shape (from semi-circular to semi-elliptic cross-section). Confinement along the direction perpendicular to the plane of the device increases its efficiency. This work is the first numerical study of cell sorting by a realistic microfluidic device.

  • 11491.
    Zhu, Lailai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Stone, Howard A.
    Princeton Univ, Dept Mech & Aerosp Engn, Princeton, NJ 08544 USA..
    Rotation of a low-Reynolds-number watermill: theory and simulations2018Ingår i: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 849, s. 57-75Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent experiments have demonstrated that small-scale rotary devices installed in a microfluidic channel can be driven passively by the underlying flow alone without resorting to conventionally applied magnetic or electric fields. In this work, we conduct a theoretical and numerical study on such a flow-driven 'watermill' at low Reynolds number, focusing on its hydrodynamic features. We model the watermill by a collection of equally spaced rigid rods. Based on the classical resistive force (RF) theory and direct numerical simulations, we compute the watermill's instantaneous rotational velocity as a function of its rod number N, position and orientation. When N >= 4, the RF theory predicts that the watermill's rotational velocity is independent of N and its orientation, implying the full rotational symmetry (of infinite order), even though the geometrical configuration exhibits a lower-fold rotational symmetry; the numerical solutions including hydrodynamic interactions show a weak dependence on N and the orientation. In addition, we adopt a dynamical system approach to identify the equilibrium positions of the watermill and analyse their stability. We further compare the theoretically and numerically derived rotational velocities, which agree with each other in general, while considerable discrepancy arises in certain configurations owing to the hydrodynamic interactions neglected by the RP theory. We confirm this conclusion by employing the RP-based asymptotic framework incorporating hydrodynamic interactions for a simpler watermill consisting of two or three rods and we show that accounting for hydrodynamic interactions can significantly enhance the accuracy of the theoretical predictions.

  • 11492. Zhu, Y.
    et al.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Wang, W.
    Chen, X.
    On the iron oxides between railway wheels and rails using laboratory tests2015Ingår i: CM 2015 - 10th International Conference on Contact Mechanics of Wheel / Rail Systems, International Conference on Contact Mechanics of Wheel , 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    The contact between railway wheels and rails is influenced by various contaminants. Iron oxides present on both wheel and rail surfaces which constantly affects the wheel?rail adhesion and wear. The paper summarizes some laboratory work investigating the iron oxides between the wheel and rai contact which were previous performed in the authors’ group. A comparison of the contact conditions and application regarding the test rig (pin-on-disc and twin-disc) is also given. The influence of iron oxides on the coefficient of friction, adhesion coefficient and wear rate is presented and discussed. Results indicate iron oxides greatly influence the tribological behavior particularly under the wet condition. The author aims to highlight the importance of the iron oxides which may provide some hints to explain the difference between laboratory tests and field measurements. However, a quantitative study is needed based on controlled environmental conditions due to the complexity and fast transition of iron oxides.

  • 11493.
    Zhu, Yaoxuan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Huang, Xiaoting
    IMPROVEMENT OF COMPACTED GRAPHITE IRON DRILLING OPERATIONS WITH CUSTOMIZED CUTTING FLUID2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Inom bilindustrin används ofta kompaktgrafitjärn eftersom det har hög hållfasthet. Att bearbeta kompaktgrafitjärn är utmanade främst pga att det krävs hög temperatur och mycket kraft för att skära/borra materialet. I den här avhandlingen undersöks hur olika skärvätskor påverkar bearbetning av kompaktgrafitjärn under borrning. Skärvätskor där proportionerna mellan den alkaliska delen och oljedelen har anpassats, jämfördes mot traditionella emulsionsvätskor. Oljan i den kundanpassade skärvätskan kan hjälpa till att minska friktionskraften i bearbetningsoperationen. Fasförslitningsmätningen visade att det inte finns någon signifikant skillnad mellan skärvätskorna. Tryckraftsmätningarna visade emellertid att det kundanpassade skärvätskorna effektivt kunde reducera skärkraften med nästan 20%. Genom att använda de anpassade skärvätskorna kan man köra med högre mattningshastighet, reducera cykeltiden eller använda samma processparametrar men med mindre energianvändning.

  • 11494.
    Zhu, Yi
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Adhesion in the wheel-rail contact2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    To attract more customers and compete with other modes of transportation, railway transport needs to ensure safety, punctuality, high comfort, and low cost; wheel–rail adhesion, i.e., the transmitted tangential force in the longitudinal direction during driving and braking, plays an important role in all these aspects. Adhesion needs to be kept at a certain level for railway operation and maintenance. However, wheel−rail contact is an open system contact. Different contaminants can present between the wheel and rail surfaces, forming a third-body layer that affects the adhesion. Prediction of wheel–rail adhesion is important for railway operations and research into vehicle dynamics; however, this prediction is difficult because of the presence of contaminants.

    This thesis deals with wheel–rail adhesion from a tribological perspective. The five appended papers discuss wheel–rail adhesion in terms of dry conditions, lubricated conditions, leaf contamination, iron oxides, and environmental conditions. The research methodologies used are numerical modelling, scaled laboratory experiments, and field tests. The research objective is to understand the mechanisms of the adhesion loss phenomenon. 

    A numerical model was developed to predict wheel–rail adhesion based on real measured 3D surfaces. Computer simulation indicates that surface topography has a larger impact on lubricated than on dry contacts. Plastic deformation in asperities is found to be very important in the model. Ball-on-disc tests indicate that water can give an extremely low adhesion coefficient on smooth surfaces, possibly due to surface oxidation. Investigation of lubricated contacts at low speed indicates that oil reduces the adhesion coefficient by carrying a normal load, while adhesion loss due to water depends on the surface topography, water temperature, and surface oxidation. A field investigation indicates that leaves reduce the friction coefficient because of the chemical reaction between leaves and bulk materials. The thickness of the surface oxide layer was found to be an essential factor determining adhesion reduction. Pin-on-disc experiments found a transition in the friction coefficient with regard to the relative humidity, due to a trade-off between the water molecule film and the hematite on the surface. 

  • 11495.
    Zhu, Yi
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Adhesion in the wheel-rail contact under contaminated conditions2011Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Railway vehicles require a certain level of adhesion between wheel and rail to operate efficiently, reliably, and economically. Different levels of adhesion are needed depending on the vehicle running conditions. In the wheel tread–railhead contact, the dominant problem is low adhesion, as low adhesion on the railhead negatively affects railway operation: on one hand, the vehicle will lose traction resulting in delay when driving on low-adhesion tracks; on the other hand, low adhesion during deceleration will extend the braking distance, which is a safety issue.

    This thesis examines the influence of several contaminants, i.e., water, oil, and leaves, on the adhesion in the wheel tread–railhead contact. This study will improve our knowledge of the low-adhesion mechanism and of how various contaminants influence adhesion. The thesis consists of a summary overview of the topic and three appended papers (AC).

    Papers A and B focus mainly on water and oil contamination examined using two methods, numerical simulation and lab testing. In paper A, real measured wheel and rail surfaces, low- and high-roughness surfaces, along with generated smooth surfaces are used as input to the numerical model for predicting the adhesion coefficient. Water-lubricated, oil-lubricated, and dry contacts are simulated in the model. In the research reported in paper B, scaled testing using a mini traction machine (MTM) was carried out to simulate the wheel–rail contact under lubricated conditions. Two types of disc surfaces of different roughnesses were run at different contact pressures and temperatures. A stylus machine and atomic force microscopy (AFM) were used to measure the surface topography. A study of leaf contamination on the railhead surface, based on field testing, is presented in paper C. Railhead surface samples were cut and the friction coefficient was measured on five occasions over the course of a year. Electron spectroscopy for chemical analysis (ESCA) and glow discharge optical emission spectrometry (GD-OES) were used to detect the chemical composition of the leaf-contamination layer on the railhead surface.

    The main conclusion of the thesis is that different contaminants reduce the adhesion coefficient in different ways. Oil reduces the adhesion coefficient by carrying the normal force due to its high viscosity. Water can reduce the adhesion coefficient to different degrees depending on the surface topography and water temperature. The mixture of an oxide layer and water contamination may have an essential impact. A leaf-formed blackish layer causes low adhesion by means of a chemical reaction between the leaves and bulk material. The thickness of the friction-reducing oxide layer predicts the friction coefficient and the extent of leaf contamination.

  • 11496.
    Zhu, Yi
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi. Zhejiang University, The State Key Lab of Fluid Power Transmission and Control, China .
    Lyu, Yezhe
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Mapping the friction between railway wheels and rails focusing on environmental conditions2015Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 324, s. 122-128Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The coefficient of friction between railway wheels and rails is crucial to the railway adhesion, further greatly affecting railway operation and maintenance. Since the wheel-rail system is an open system, the coefficient of It is significantly influenced not only by various types of contaminants but also by environmental conditions. This paper conducted a set of pin-on-disc tests measuring the coefficient of friction focusing on the influence of environmental conditions (relative humidity and temperature). In addition, influences of iron oxides, leaves and glycol/water mixtures on the coefficient of friction were also studied. The friction results are shown in the form of friction maps. Results indicate that it oxides on the surfaces can prevent the samples from large friction reduction particularly at the low temperature. The friction mechanism is also discussed with the help of scanning electron microscopy photos. On the other hand, effects of leaves in reducing the coefficient of friction become limited with the presence of the glycol/water mixture.

  • 11497.
    Zhu, Yi
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinelement.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinelement.
    An adhesion model for wheel-rail contact at the micro level using measured 3d surfaces2012Ingår i: 9th International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, CM 2012, Southwest Jiaotong University , 2012, s. 550-562Konferensbidrag (Refereegranskat)
    Abstract [en]

    Railway vehicles require a certain level of wheel-rail adhesion for efficient, reliable, and economical operation. A comprehensive wheel-rail contact model is useful for optimizing the adhesion, to simulatevehicle running conditions and to predict wear and rolling contact fatigue. A new contact model using measured 3D surfaces has been developed, comprising normal contact, rolling-sliding contact, flash temperature, and local friction coefficient models. This model can predict the local contact pressure, including the plasticity, local flash temperature, local tangential stress, local friction coefficient, and global adhesion coefficient. The influence of surface topography, creep, and speed on the adhesion coefficient, real contact area, and contact temperature is discussed. Results indicate that, due to increased contact area, the adhesion coefficient decreases with increased surface roughness, although the change is small. Furthermore, increasing speed reduces the adhesion coefficient due to the increasing contact temperature.

  • 11498.
    Zhu, Yi
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinelement.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Maskinelement.
    An adhesion model for wheel-rail contact at the micro level using measured 3d surfaces2014Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 314, nr 1-2, s. 162-170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Railway vehicles require a certain level of wheel-rail adhesion for efficient, reliable, and economical operation. A comprehensive wheel-rail contact model is useful for optimizing the adhesion, to simulate vehicle running conditions and to predict wear and rolling contact fatigue. A new contact model using measured 3D surfaces has been developed, comprising normal contact, rolling-sliding contact, flash temperature, and local friction coefficient models. This model can predict the local contact pressure, including the plasticity, local flash temperature, local tangential stress, local friction coefficient, and global adhesion coefficient. The influence of surface topography, creep, and speed on the adhesion coefficient, real contact area, and contact temperature is discussed. Results indicate that, due to increased contact area, the adhesion coefficient decreases with increased surface roughness, although the change is small. Furthermore, increasing speed reduces the adhesion coefficient due to the increasing contact temperature.

  • 11499.
    Zhu, Yi
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Chen, Hur
    Friction Between Wheel and Rail: A Pin-On-Disc Study of Environmental Conditions and Iron Oxides2013Ingår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 52, nr 2, s. 327-339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The coefficient of friction between railway wheels and rails is crucial to railway operation and maintenance. Since the wheel-rail system is an open system, environmental conditions, such as humidity and temperature, affect the friction coefficient. Pin-on-disc testing was conducted to study the influence of environmental conditions and iron oxides on the coefficient of friction between the wheel and rail. The iron oxides were pre-created in a climate chamber. The surfaces of the tested samples were analysed using X-ray diffraction, scanning electron/focused ion beam microscopy, and Raman spectroscopy. Results indicate that the coefficient of friction decreases with increasing relative humidity (RH) up to a saturation level. Above this level, the coefficient of friction remains low and stable even when the RH increases. In particular, when the temperature is low, a small increase in the amount of water (i.e., absolute humidity) in the air can significantly reduce the coefficient of friction. At high humidity levels, a water molecule film can keep the generated haematite on the surfaces, counterbalancing the effect of rising humidity.

  • 11500.
    Zhu, Yi
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Tribologi.
    Nilsson, R.
    Stockholm public transport AB, Stockholm, Sweden.
    A field test study of leaf contamination on railhead surfaces2014Ingår i: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 228, nr 1, s. 71-84Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Leaves on railway tracks affect the level of adhesion between the wheel and rail, especially in autumn. When crushed by wheels, leaves form a tarnished, low level of adhesion layer that sticks to the railhead and often requires mechanical removal. A Stockholm local traffic track with a long history of adhesion problems was subjected to field tests on railhead contamination. On five occasions under different conditions, spaced over a year, the friction coefficient was measured using a tribometer and samples of the rail were taken. The techniques of electron spectroscopy for chemical analysis and glow discharge optical emission spectrometry were conducted to determine the composition of the top layer of rail contaminants and hardness was measured using the nano-indentation technique. The tarnished layer contains much higher contents of calcium, carbon and nitrogen than do leaf residue layers and uncontaminated samples. These high element contents are generated from the leaf material, which chemically reacts with the bulk material. The hardness of the tarnished layer is one-fifth that of the non-tarnished layer of the same running band. A chemical reaction occurs from the surface to a depth of several microns. The thickness of the friction-reducing oxide layer can be used to predict the friction coefficient and extent of leaf contamination.

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