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  • Public defence: 2018-07-04 10:00 F3, Stockholm
    Castro Flores, José Fiacro
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. IMT Atlantique (École des Mines de Nantes - EMN), Energy Systems and Environment - DSEE.
    Low-temperature based thermal micro-grids: operation and performance assessments2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Energy use in the urban environment is vital for the proper functioning of our society, and in particular, comfort heating –or cooling– is a central element of our energy system often taken for granted. Within this context, district energy systems and especially, district heating (DH) systems must evolve to adapt to the upcoming decades-long transition towards a sustainable energy system. This dissertation seeks to introduce, discuss, and assess from a techno-economic perspective the concept of low-temperature (LT) based thermal micro-grids (subnets) as active distribution thermal networks. It explores the role of the subnet at the system distribution level supervised by an active agent (DH substation), performing tasks of heat supply and demand management (storage and dispatch), as well as coordinating bidirectional flows.


    Here, a mixed methodological approach based on analytical simulation for the assessment of alternatives to evaluate a set of technologies is developed and discussed. This approach covers: the identification of knowledge gaps through the state-of-the-art analysis; a collection of incremental technical and/or economic performance assessments; and the analysis of a measurement data set from an existing LTDH demonstration project.


    Key findings of this work include: an updated and improved model of aggregated heat loads; identification of differences in load and temperature patterns for certain LT subnets; analysis of benefits and drawbacks of active substations with distributed heat sources and/or storage; and the impact on the reduction of the primary network return temperature as a consequence of the increase in the share of LT subnets, leading to lower generation and operating costs.


    These outcomes reveal that the integrated design and operation of the active thermal micro-grid have the potential to improve both the performance of the subnet, and that of the primary network. It further enhances the capability of the overall system to integrate unconventional and distributed heat sources together with energy efficient buildings by increasing the system’s flexibility and controllability. Active thermal distribution networks will likely become a subsequent step in the technological development of DH technologies, to address the matter of providing comfort heating in an effective and cost-efficient manner. This work advances the current DH knowledge by identifying synergies and challenges that arise with these new developments, in order for DH technology to play a key role in the future smart and sustainable energy system.

  • Public defence: 2018-08-29 14:00 Salongen, Stockholm
    Buckley, Jeffrey
    KTH, School of Industrial Engineering and Management (ITM).
    Investigating the role of spatial ability as a factor of human intelligence in technology education: Towards a causal theory of the relationship between spatial ability and STEM education2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Education is a particularly complex discipline due to the numerous variables which impact on teaching and learning. Due to the large effect of human intelligence on the variance in student educational achievement, there is a substantial need to further contemporary understandings of its role in education. Multiple paradigms exist regarding the study of human intelligence. One in particular, the psychometric tradition, has offered many critical findings which have had a substantial impact on STEM education. One of the most significant offerings of this approach is the wealth of empirical evidence which demonstrates the importance of spatial ability in STEM education. However, while categorically identified as important, a causal relationship between spatial ability and STEM is yet to be confirmed

    As there is insufficient evidence to support a causal investigation, this thesis aims to develop an empirically based causal theory to make this possible. Five studies were conducted to achieve this aim and are described in the appended papers. As the research explores spatial ability in technology education, Paper I examines the epistemological position of technology education within STEM education. Based on the evidence showing spatial ability is important in Science, Engineering and Mathematics, Paper II explores its relevance to Technology. Paper III offers an empirically based definition for spatial ability through a synthesis of contemporary research and illustrates empirically where it has been observed as important to STEM learning. Paper IV examines the perceived importance of spatial ability relative to intelligence in STEM education from the perspective of technology education. Finally, Paper V examines the psychometric relationship between spatial ability and fluid intelligence (Gf) based on a hypothesis generated throughout the preceding papers.

    The main results of this thesis illustrate the predictive capacity of visualization (Vz), memory span (MS), and inductive reasoning (I) on fluid intelligence (Gf) which is posited to offer a causal explanation based on the creative, innovative, and applied nature of STEM. Additional findings include the observation that learners use problem solving strategies which align with their cognitive strengths, that external representations of problems can scaffold the use of spatial ability or alleviate the need for it, that the variability of knowledge types across STEM sub-disciplines may affect the nature of reasoning within disciplines, and that for technology education specifically, acquiring an explicit knowledge base is not perceived to denote intelligence while the capacity to reason abstractly to solve novel problems is. This epistemological fluidity and focus on reasoning highlights the unique way in which technology education can provide insight into intelligence in STEM education. The implications of these results are discussed with specific focus on their theoretical validity and potential application in applied educational contexts.

  • Public defence: 2018-09-21 10:00 rum 4301, Stockholm
    Zheng, Weisen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Thermodynamic and kinetic investigation of systems related to lightweight steels2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Lightweight steels have attracted considerable interest for automobile applications due to the weight reduction without loss of high strength and with retained excellent plasticity. In austenitic Fe-Mn-Al-C steels, the nano-precipitation of the κ-carbide within the austenitic matrix significantly contributes to the increase in yield strength. In the present work, the precipitation strengthening simulation has been carried out within the framework of the ICME approach. Thermodynamic assessments of the quaternary Fe-Mn-Al-C system as well as its sub-ternary systems were performed with the CALPHAD method. All available information on phase equilibria and thermochemical properties were critically evaluated and used to optimize the thermodynamic model parameters. By means of the partitioning model, the κ-carbide was described using a five-sublattice model (four substitutional and one interstitial sublattice), which can reflect the ordering between metallic elements and reproduce the wide homogeneity range of the κ-carbide. Based on the present thermodynamic description, a thermodynamic database for lightweight steels was created. Using the database, the phase equilibria evolution in lightweight steels can be satisfactorily predicted, as well as the partition of alloying elements. In order to accelerate the development of a kinetic database for multicomponent systems, a high-throughput optimization method was adopted to optimize the diffusion mobilities. This method may largely reduce the necessary diffusion-couple experiments in multicomponent systems. Based on the developed thermodynamic and kinetic databases for lightweight steels, the precipitation of the κ-carbide was simulated using TC-PRISMA. The volume fraction and particle size were reasonably reproduced. Finally, the precipitation strengthening contribution to the yield strength was predicted. The calculation results show that the anti-phase boundary effect is predominant in the precipitation strengthening. Overall, the relationship between the composition, processing parameters, microstructure and mechanical properties are established in the thesis.