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  • 1. Anton, R.
    et al.
    Jonsson, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ramos, J. C.
    Gomez-Acebo, T.
    Rivas, A.
    Refrigerating Cycle Simulator: System Modelling, Educational Implementation and Assessment2009In: International journal of engineering education, ISSN 0949-149X, Vol. 25, no 2, p. 324-332Article in journal (Refereed)
    Abstract [en]

    To leach and explain system modelling in a Thermal-Fluid application is a challenge: learning how one component or even the surrounding conditions can influence the performance of the rest of the components of the system and the system itself is not all easy task. However a suitable educational implementation may help students gain a deeper understanding not only of the system itself bill of the existing interrelation between the Thermal-Fluid fields: Thermodynamics, Heat Transfer and Fluid Mechanics. In this study a refrigerating cycle simulator is used. The simulator is' prepared in such a way that the interrelation between each component, the system and the surroundings call be analysed by the students. This case study is found to be very useful due of its ability to study system performance. A three-step educational implementation, the simulator being the third step, has been used and found to he enriching both for students and instructors.

  • 2.
    Anton, Raul
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Jonsson, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Moshfegh, Bahram
    University of Gävle.
    Modelling of EMC Screens for Radio Base Stations: Part 2: Evaluation of Turbulence Models2004In: Proc. 9th  InterSociety Conf. on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm 2004), Las Vegas, NV, USA, IEEE Press, 2004, p. 471-478Conference paper (Refereed)
    Abstract [en]

    The objective of this paper is to investigate the performance of five well-known turbulence models and 2 wall treatments, in order to predict the details of the flow patterns through an EMC (ElectroMagnetic Compatibility) screen. The employed turbulence models are investigated in the present study is four different eddy-viscosity models; the standard k-ε model, the renormalization group (RNG) k-ε model, the realizable k-ε model and the k-ω model, as well as the Reynolds stress model, RSM. The commercial finite volume code Fluent 6.1 was used for simulation.

    A steady-state three-dimensional model, which serves as the most accurate representation of the model, was used in order to predict the details of the air flow paths and pressure field. The flow was assumed to be isothermal, turbulent and incompressible.

    The numerical predictions were validated experimentally by using wind tunnel measurements and smoke visualization. The performances of the turbulence models are discussed and the RSM results are compared with other two-equation turbulence models. The result shows that choosing the right turbulence model and wall treatment does not have a great influence on the prediction of pressure drop and the velocity field. The pressure field is over predicted about 15% and the velocity average deviation at several locations before and after the screen is less than 10%. Simulations using a hydraulic impedance surface, i.e. without a detail modeling of the EMC screen, show that the pressure field is also over predicted and great differences are observed in the velocity field.

  • 3.
    Anton, Raul
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Jonsson, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Modeling of Air Conditioning Systems for Cooling of Data Centers2002In: Proc. 8th  InterSociety Conf. on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm 2002), San Diego, CA, USA, IEEE Press, 2002, p. 552-558Conference paper (Refereed)
    Abstract [en]

    Cooling of data centers has emerged as an area of increasing importance in the field of electronics thermal management. As the packaging and power densities are steadily increasing, so will the need for efficient and reliable cooling systems.

    In this paper, a model of an air conditioning unit is described. The model offers considerable flexibility in terms of the ability to choose between different designs of heat exchangers (evaporators and condensers), and working media, and hence the model offers the possibility to optimize the design.

    The model is developed using EES (Engineering Equation Solver), a programming environment that provides the thermo-physical properties for the working media used. The heat transfer and pressure drop in the components are modeled using an integral approach, i.e. the overall behavior of each component is modeled. This approach has been proven to give adequate accuracy.

  • 4.
    Anton Remirez, Raul
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Castiella Sánchez-Ostiz, Miguel
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Jonsson, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Moshfegh, B.
    Smoke and CFD visualization of the flow after an EMC screen in a sub-rack model2005In: Proceeding of the THERMINIC 05, 2005Conference paper (Refereed)
  • 5.
    Anton Remirez, Raul
    et al.
    KTH, Superseded Departments, Energy Technology. University of Gävle, Sweden.
    Jonsson, Hans
    KTH, Superseded Departments, Energy Technology. University of Gävle, Sweden.
    Moshfegh, B.
    Modelling of EMC screens for radio base stations Part 1: Experimental parametric study2004In: ITherm 2004, Vol 1, IEEE , 2004, p. 463-470Conference paper (Refereed)
    Abstract [en]

    Enclosing electronics in sealed metal boxes provides good electromagnetic shielding, but evidently restricts the air movement necessary for adequate cooling. In order to meet ElectroMagnetic Compatibility (EMC) requirements, a perforated plate (an EMC screen) must be used. The design of this screen must provide a sufficient free area ratio for the adequate airflow, but at the same time the holes must be small enough to block electromagnetic radiation. An experimental set-up that represents a Radio Base Station (RBS) subrack was built inside a wind tunnel. The airflow pattern and pressure drop through the EMC screen were investigated experimentally for different subrack geometries, screen porosities and velocities, and the recirculation zones were identified. The study was performed by means of pressure and velocity measurements, together with smoke visualization under isothermal conditions.

  • 6.
    Anton Remirez, Raul
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. TECNUN, University of Navarra, Navarra 31080, Spain .
    Jonsson, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Moshfegh, Bahram
    Compact CFD modelling of EMC screen for radio base stations: a porous media approach and a correlation for the directional loss coefficients2007In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972, Vol. 30, no 4, p. 875-885Article in journal (Refereed)
    Abstract [en]

    A methodology to obtain the directional pressure loss coefficients in a porous media model of an electromagnetically compatible screen of a radio base station model is presented. The directional loss coefficients of this compact model are validated against a detailed computational fluid dynamics model not only by comparing the total pressure drop, but also by evaluating the flow pattern after the screen. The detailed model was validated in an earlier article by the authors. A parametric study is conducted for 174 cases. Seven parameters were investigated: velocity, inlet height, screen porosity, printed circuit board (PCB) thickness, inlet-screen gap, distance between two PCBs and screen thickness. Based on the compact model parametric study, two correlations for the directional loss coefficients are developed as a function of the Reynolds number and the above geometrical parameters. The average disagreement between the compact model that uses the directional loss coefficients from the correlations and the detailed model was of 3% for the prediction of the total pressure drop and less than 6.5% and 9.5% for two coefficients that accurately characterize the flow pattern.

  • 7. Anton Remirez, Raul
    et al.
    Jonsson, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Moshfegh, Bahram
    Detailed CFD modelling of EMC screen for radio base stations: a benchmark study2007In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972, Vol. 30, no 4, p. 754-763Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to investigate the performance of five well-known turbulence models, in order to find a model that predicts the details of the flow patterns through an electromagnetic compatibility (EMC) screen. The turbulence models investigated in the present study are five different eddy-viscosity models; the standard k-ε model, the renormalization group (RNG) k-ε model, the realizable k-ε model, the standard k-ω model, as well as the shear stress transport k-ω model. A steady-state 3-D detailed model, which serves as the most accurate representation of the model, was used in order to evaluate the details of the airflow paths and pressure field. The flow was assumed to be isothermal, turbulent and incompressible. A general model that covers a considerable range of velocities and geometries was validated experimentally by wind tunnel measurements. The result shows that for most of the k-ε models used with correct y+ and mesh strategy, the pressure drop and the velocity field deviation is small compared to experimental data. The k-ω models overpredict the overall pressure drop. When using the RNG k-ε model, the total static pressure drop predicted differs around 5%-10% and the average velocity deviation at several locations before and after the screen is around 5%.

  • 8.
    Anton Remirez, Raul
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Jonsson, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Moshfegh, Bahram
    University of Gävle.
    Detailed CFD Modelling of EMC Screen for Radio Base Stations: A Conjugate Heat Transfer Problem2007In: International Journal of Heat Exchangers, ISSN 1524-5608, Vol. 8, no 1, p. 95-116Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to perform an experimental as well as CFD investigations of the conjugate heat transfer problem in a sub-rack slot model. A steady-state three-dimensional detailed model, which serves as the most accurate representation of the model, was used in order to evaluate the details of the airflow paths and temperature field.

    A general model that covers a considerable range of velocities, screen porosities and heat fluxes was validated experimentally by wind tunnel measurements. The result shows that the RNG k-ε model used with correct y+ and mesh strategy accurately predicts the temperature field. The average temperature deviation at several locations is less than 4% compared to experimental data. The influence of the velocity, screen porosity, heat flux and presence of the EMC screen on the PCB temperature field is commented.

  • 9.
    Anton Remirez, Raul
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Jonsson, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Moshfegh, Bahram
    Detailed CFD modelling of EMC screen for radio base stations: a parametric study2009In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972, Vol. 32, no 1, p. 145-155Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to make a parametric study of the hydraulic resistance and flow pattern of the flow after an electromagnetic compatibility screen and between two printed circuit boards (PCBs) in a model of a 90° subrack cooling architecture. The parametric study is carried out using a detailed 3-D model of a PCB slot. The detailed model was experimentally validated in a previous paper by the authors. Seven parameters were investigated: velocity, inlet height, screen porosity, PCB thickness, distance between two PCBs, inlet-screen gap and screen thickness. A correlation for the static anddynamic pressure drop, the percentage of dimensionless wetted area, Aw*, and the RMS* factor (a function of the flow uniformity along the PCB) after the screen is reported as a function of six geometrical dimensionless parameters and the Reynolds number. The correlations, that are based on 174 three dimensional simulations, yield good results for the total pressure drop, in which the values are predicted within the interval of ±15%. For the, Aw* all the predicted values are within the interval of ±22% of the observed values. Finally, for the RMS* factor, the majority of the values also have a disagreement of less than 20% of the observed values. These last two parameters are believed to provide a correct insight about the flow pattern after the screen.

  • 10.
    Berglund, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Integrated Product Development.
    El Gaidi, Khalid
    KTH, School of Education and Communication in Engineering Science (ECE), Learning.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Hedin, Björn
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Kjellgren, Björn
    KTH, School of Education and Communication in Engineering Science (ECE).
    Kommer det på tentan?: Uppfattningar om motivation och demotivation bland studenter på ingenjörsutbildningar2015Conference paper (Other academic)
    Abstract [en]

    Motivation är en av de viktigaste drivkrafterna bakom människors handlingar. Hur en student klarar sina studier beror till stor del på graden av motivation, men också på graden av demotivation. Vi har i den här studien valt att utforska upplevda källor till studenters motivation och demotivation i ingenjörskurser. Dessa har kodats och kategoriserats i termer av kontext, struktur och lärare, och resultatet har jämförts med en liknande omfattande undersökning från USA. Resultaten visar att frågor rörande kurs ens struktur i högre grad anges som viktiga både för motivation och demotivation för våra studentgrupper, jämfört med den andra undersökningen. Vidare förekommer synpunkter kring lärarens förmåga att förklara och lärarens attityd till studenterna i betydligt högre omfattning än lärarens ämneskompetens i sig, vilket kan ses som stöd för att pedagogisk och didaktisk skicklighet bör vara starkt meriterande för undervisande personal. En slutsats är att lärare har mycket stora möjligheter att påverka studenternas motivation både positivt och negativt, och att det är av stor vikt att lärare är både medvetna om, och har verktyg för att hantera, detta.

     

  • 11.
    Berglund, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Integrated Product Development.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Hedin, Björn
    KTH, School of Electrical Engineering and Computer Science (EECS), Media Technology and Interaction Design, MID.
    Kjellgren, Björn
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Will this be on the exam?: Or, How to Motivate your Students to Learn2017In: KTH SoTL 2017, 2017Conference paper (Refereed)
  • 12.
    Berglund, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Integrated Product Development.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Jerbrant, Anna
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
    Wingård, Lasse
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Andersson, Magnus
    KTH, School of Engineering Sciences (SCI), Physics.
    Hedin, Björn
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Kjellgren, Björn
    KTH, School of Education and Communication in Engineering Science (ECE), Learning, Language and communication.
    THE PEDAGOGICAL DEVELOPERS INITIATIVE: SYSTEMATIC SHIFTS, SERENDIPITIES, AND SETBACKS2017In: 13th International CDIO Conference in Calgary, Canada, June 18-22, 2017, 2017Conference paper (Refereed)
    Abstract [en]

    Pedagogical projects have often, at KTH Royal Institute of Technology, as well as elsewhere, been initiated and managed by individual enthusiasts rather than dedicated teams. This generally decreases the possibility of successful implementation of more ambitious ideas, e.g., changing educational programs, implementing the CDIO syllabus, or strengthening the pedagogical development of larger parts of the faculty. To enable wider and more effective change, KTH top management therefore launched a universityencompassing three-year project in 2014, in which a group of highly motivated teachers from all schools at KTH were appointed part-time pedagogical developers (PDs). The PDs were given the task of promoting pedagogical development and facilitate cooperation and knowledge exchange among faculty members, as described in two previous papers at CDIO conferences. From 2017, the outcomes of this project are supposed to be integrated parts of the KTH line organization. The project has led to numerous actions, which would have been difficult to set in motion unless given the freedom in time to explore and to develop into a collective effort rather than a myriad of individual “stand-alone” examples. By addressing key areas for pedagogical development, our group of dedicated faculty have tried to surpass the suboptimal "lock-in" of strict individual reasoning and to deal with surfaced questions and relevant issues in a broader collective manner. A major insight confirmed by the project and its many sub-projects has indeed been the fundamental importance of collegial discussions and the creation of processes that facilitate and support teacher cooperation. We have also, through discussions with faculty at KTH, confirmed the need for clearly defined, tangible incentives for teachers, motivating them to participate in pedagogical development activities, even if this means less time left for the traditional pathway to rewards within academia, i.e. research. In this paper, we chart changes that have occurred in the educational practices at KTH by describing and discussing the project’s focus on pedagogical development of faculty, actual execution of changes in the engineering educations, lessons learned along the way, and visions yet to be realised.

  • 13.
    Berglund, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Integrated Product Development. KTH.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology. KTH.
    Jerbrant, Anna
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management. KTH.
    Wingård, Lasse
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering. KTH.
    Andersson, Magnus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Hedin, Björn
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES).
    Kjellgren, Björn
    KTH, School of Education and Communication in Engineering Science (ECE), Learning, Language and communication.
    The pedagogical developers initiative - development, implementation and lessons learned from a systematic approach to faculty development2016In: Proceedings of the 12th International CDIO Conference, Turku University of Applied Sciences, Turku, Finland, June 12-16, 2016, Turku University , 2016, p. 497-508Conference paper (Refereed)
    Abstract [en]

    This paper presents a systematic, university--wide approach to creating an encompassing movement towards faculty development. In 2014, KTH Royal Institute of Technology launched the pedagogical developers initiative, appointing part--time pedagogical developers among teachers from all schools of KTH, to implement and strengthen good teaching and learning practices among faculty and students. They are teachers active in different educational programmes, with experience of, and interest in, pedagogical issues. In line with CDIO standard 10, the purpose of the pedagogical developers’ initiative is to facilitate cooperation and knowledge exchange between faculty members, and to establish communities of practice. The paper presents the activities, processes for developing these activities and preliminary results from the initiative’s second year, which focused much on supporting faculty development by putting into place a series of workshops, a format chosen for its combination of active community-building learning and time efficiency. The topics of the workshops emerged to meet faculty needs identified by the pedagogical developers during the first year. The workshops were created by smaller teams of pedagogical developers from different schools of KTH. This enabled a wide array of experiences and perspectives to be incorporated into the workshops. Main focuses of the workshops have been on creating internal discussions in dynamic communities of practice on specific subjects of interest, and on creating forums for exchange of ideas, open to the whole faculty. During Autumn 2015, the workshops have been offered as voluntary add-on parts of the basic course in teaching and learning offered to faculty at KTH. This first round of workshops generated a positive interest from teachers, and participant feedback indicates that they particularly appreciated the opportunity to work directly with their own courses and the opportunity to discuss pedagogical aspects with peers. 

  • 14.
    Berglund, Anders
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Integrated Product Development.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Johansson, Hans Bengt
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Jerbrant, Anna
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Management.
    Andersson, Magnus
    KTH, School of Information and Communication Technology (ICT).
    Hedin, Björn
    KTH, School of Computer Science and Communication (CSC), Media Technology and Interaction Design, MID.
    Soulard, Juliette
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Kjellgren, Björn
    KTH, School of Education and Communication in Engineering Science (ECE).
    The Pedagogical Developers Initiative – Changing Educational Practices and Strengthening CDIO skills2015In: Proceedings of the 11th International CDIO Conference, Chengdu, China, June 8-11 2015, 2015Conference paper (Refereed)
    Abstract [en]

    This paper put emphasis on change agents within the universities and how local initiatives can be systematically approached and ramped up. Rooted in the challenges and constraints that have been addressed in past educational program initiatives, the case consists of specific focus areas to leverage impact. Universities continuously strives to provide the best conditions for an inspiring and prosperous learning environment, and to provide educational programs with teaching of excellent educational quality. KTH is no exception and therefore the university management has initiated a pedagogical program starting in 2014. One of the first thing initiated within the framework of this pedagogical program is the creation of a group of 24 pedagogical developers.

    The focus for the pedagogical developers is to facilitate the opportunities for KTHs faculty to work together and create consensus on educational development in different teaching teams. This paper presents the University's pedagogical developers' initiative as a whole and how this has been outlined in detail to reach specific redesign targets. The School of Industrial Engineering and Management pedagogical group consists of five practicing teachers that besides this new role also engage heavily in various courses of the School's departments. Since the pedagogical initiative is aligned with several important CDIO aspects, e.g. the learning environment, formats of formative feedback, assessment and examination there is also importance to reassure this in the existing Master level programs.

    At KTH the five-year comprehensive Master of Science in Engineering programs concern distinct vocational educations in which the CDIO aspects are very important. At the same time the programs has been divided in a basic level (B.Sc. in Engineering) of three years and a advanced level (M.Sc.) of two years. This has for instance made it harder to align the progression between first cycle level and second cycle level regarding for instance the CDIO efforts (e.g. oral and written communication, teamwork). This paper will therefore discuss and enhance how the pedagogical programme, we as pedagogical developers, can support and strengthen the initiation and implementation of the CDIO aspects in the education.

  • 15.
    Borglund, Dan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Carlsson, Ulf
    KTH, School of Engineering Sciences (SCI).
    Colarieti-Tosti, Massimiliano
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Edström, Simon
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Henriksson, Ann-Sofie
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Hjelm, Niclas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Basic Science.
    Naimi-Akbar, Ida
    KTH, School of Education and Communication in Engineering Science (ECE), Learning, Learning in Engineering Sciences.
    Collaborative Course Evaluation and Development at KTH: Progress, Lessons Learned and Way Forward2017In: 6th USIU Conference, 2017, article id 68Conference paper (Refereed)
  • 16.
    Borglund, Dan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Carlsson, Ulf
    KTH, School of Engineering Sciences (SCI).
    Colarieti-Tosti, Massimiliano
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Edström, Simon
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Hjelm, Niclas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Naimi-Akbar, Ida
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Collaborative course analysis and development at KTH: What's the next step and who needs to do what to make it happen?2017In: KTH SoTL, 2017Conference paper (Refereed)
  • 17.
    Chen, Jianyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Conventional and advanced exergyanalysis of an ejector refrigeration systemManuscript (preprint) (Other academic)
  • 18.
    Chen, Jianyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Investigation of ejectors in refrigeration system: Optimum performance evaluation and ejector area ratios perspectives2014In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 64, no 1-2, p. 182-191Article in journal (Refereed)
    Abstract [en]

    This paper presents an ejector model to determine the optimum performance as well as obtaining the design area ratio of an ejector in a refrigeration system. Working fluid properties and auxiliary dynamic equations are used to model the processes in the ejector. The normal compression shock in the mixing chamber is considered. Experimental data from literature are used to validate the model, and the agreement with the model at optimum operating conditions is very good. The deviation between the model and the experimental data at non-optimum conditions is slightly larger. A study of working conditions for refrigerants R123 and R141b indicates that the condenser temperature has more influence than the generator and evaporator temperatures on the area ratio and the entrainment ratio in the ejector. Furthermore, area ratios need to keep up the pace with the variation of entrainment ratio as operating conditions are changed. A variable-geometry ejector seems a very promising alternative to ensure that the ejector refrigeration system operates at its optimum conditions. Ejector efficiencies play a very important role in the present model, and the influence of the efficiencies on the ejector performance is investigated. This ejector model may be used for parametric analysis and optimum performance evaluation as well as ejector design.

  • 19.
    Chen, Jianyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Parametric analysis of ejector working characteristics in the refrigeration system2014In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 69, no 1-2, p. 130-142Article in journal (Refereed)
    Abstract [en]

    A detailed investigation of ejector working characteristics in terms of refrigeration efficiency, ejector entrainment ratio, and irreversibilities in each ejector component (nozzle, mixing chamber and diffuser) is carried out by using R141b, R245fa and R600a as the working fluids. The aim of this paper is to generalize the interactions and relationships of various ejector parameters to get better understanding of the ejector working characteristics in the refrigeration system. External and internal ejector parameters are studied separately. The operating conditions and ejector component efficiencies have significant influence on the ejector behavior, and different refrigerants perform distinctively different in the ejector refrigeration system. However, effects of superheat of the three working fluids are negligible. The irreversibility related to the shock process dominates in the diffuser and plays an important role in the ejector performance. Further attention is paid on an analysis of quantifying the ejector component efficiencies based on published test data. Correlations are established to estimate the ejector efficiency and to show how ejector parameters interact.

  • 20.
    Chen, Jianyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Screening of working fluids for the ejector refrigeration system2014In: International journal of refrigeration, ISSN 0140-7007, E-ISSN 1879-2081, Vol. 47, p. 1-14Article in journal (Refereed)
    Abstract [en]

    For an ejector refrigeration system, the working fluid significantly influences the ejector behavior and system performance as well as ejector design. There are three categories of working fluids: wet fluids, dry fluids and isentropic fluids. Four wet fluids (R134a, R152a, R290 and R430A), four dry fluids (R245fa, R600, R600a and R1234ze) and one isentropic fluid (R436B) are selected in the paper. Special consideration is paid to the superheat of the ejector primary flow. This superheat is needed not only for wet fluids, but also for dry fluids and isentropic fluids at some cases, to eliminate droplets inside the ejector. A minimum superheat is found, and it is dependent on the used working fluid and the operating temperatures as well as the ejector nozzle efficiency. The comparison among these nine candidates indicates that R600 is a good candidate for the ejector refrigeration system due to a relatively high COP and its low environmental impact.

  • 21.
    Chen, Jianyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Thermoeconomic optimization of an ejector refrigeration system working with isobutane2014In: 11th IIR Gustav Lorentzen Conference on Natural Refrigerants: Natural Refrigerants and Environmental Protection, GL 2014, 2014, p. 286-294Conference paper (Refereed)
    Abstract [en]

    Thermoeconomics is a new branch of thermodynamics and consists of exergy analysis, economic modeling and thermoeconomic analysis on an energy conversion system. In this study, thermoeconomic concepts are applied to an ejector refrigeration system (ERS) that uses natural refrigerant R600a as the working fluid and has 100 kW cooling capacity. The system is investigated from thermodynamic and thermoeconomic perspectives. To optimize such a system, the objective function is defined as the sum of the costs of brine side fluids, electricity, and costs related to capital investment and operation and maintenance expense. The pinch point temperatures in the three heat changers are considered as the decision variables, with two different economic scenarios imposed to the system. An iteration technique is employed to minimize the objective function. It shows that the optimized objective function is reduced by 8.1% and 7.5% respectively compared to the non-optimized cases for the two scenarios.

  • 22. Chen, Jianyong
    et al.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Chen, Y
    An Experimental Study of Vapor Ejectors Working with R245fa2017In: Second Thermal and Fluids Engineering Conference, 2017, p. 925-928Conference paper (Refereed)
    Abstract [en]

    The vapor ejector is the key component in the ejector refrigeration system. The ejector determines the working stability and performance of the whole system. A specific test rig was designed and built with a focus on the performance of ejector itself. Instead of a circulation pump and a generator in the ejector refrigeration system, a compressor was used as the driving source. R245fa was selected as the working fluid. The important parameters, like pressure, temperature and mass flow rate, were measured and recorded. The entrainment ratio was obtained at a maximum value of 0.28. It was found that using ideal gas law and an appropriate value of the ejector nozzle isentropic efficiency could provide reasonable predictions of the mass flow rate through the ejector nozzle. Moreover, the insignificant impact of the superheat of the secondary flow on entrainment ratio was verified.

  • 23.
    Chen, Jianyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Conventional and advanced exergy analysis of an ejector refrigeration system2015In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 144, p. 139-151Article in journal (Refereed)
    Abstract [en]

    This paper presents a comprehensive investigation of an ejector refrigeration system using conventional and advanced exergy analysis. Splitting the exergy destruction within each system component into endogenous/exogenous and avoidable/unavoidable parts provides additional useful information and improves the quality of the exergy analysis. Detailed calculations of the exergy destruction parts are schematically illustrated. Conventional exergy analysis indicates that about half of the total exergy destruction is caused by the ejector and about one quarter occurs in the generator. The advanced exergy analysis reflects the strong interactions between system components. The ejector has the highest priority to be improved, followed by the condenser and then the generator. The temperature difference in the condenser has the largest influence on the exergy destruction compared to that in the generator and the evaporator, and the ejector efficiencies are also very crucial for the exergy destruction. The system performance can be largely enhanced through improvements of the ejector and the condenser as well as the generator.

  • 24.
    Chen, Jianyong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Jarall, Sad
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A review on versatile ejector applications in refrigeration systems2015In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 49, p. 67-90Article, review/survey (Refereed)
    Abstract [en]

    This paper presents a useful knowledge of ejector working principles and the versatility and diversity of its applications in refrigeration technologies. Various ejector refrigeration systems are described with the associated studies, and categorized as conventional ejector refrigeration system, advanced ejector refrigeration systems, combined refrigeration systems and ejector enhanced vapor compression systems. This paper also presents the important elements that affect the optimum performance of the ejector system, and the results of studies that have generally confirmed their energy saving, great potential for large refrigerating temperature scales and performance enhancement.

  • 25.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Applied Thermodynamics: Collection of formulas2014 (ed. 1)Book (Other academic)
  • 26.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Arbetsmaterial till Tillämpad termodynamik2014 (ed. 1)Book (Other academic)
  • 27.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Arranging an exam before the exam – The students love it, and it is easy to do!2015In: KTH SoTL 2015, 2015Conference paper (Refereed)
  • 28.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ch 1: Introduction2011In: Sustainable Energy Utilisation / [ed] Havtun, H., Bohdanowicz, P., Stockholm: KTH Royal Institute of Technology, 2011, 300, p. 1-6Chapter in book (Other academic)
  • 29.
    Havtun, Hans
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Ch 6: Psychrometrics2011In: Sustainable Energy Utilisation / [ed] Havtun, H., Bohdanowicz, P., Stockholm: KTH Royal Institute of Technology, 2011, 300, p. 125-132Chapter in book (Other academic)
  • 30.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Bohdanowicz, Paulina
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Sustainable Building Systems.
    Ch 10: Passive Heating and Cooling Systems2011In: Sustainable Energy Utilisation / [ed] Havtun, H., Bohdanowicz, P., Stockholm: KTH Royal Institute of Technology, 2011, 300, p. 261-272Chapter in book (Other academic)
  • 31.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Bohdanowicz, Paulina
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Sustainable Building Systems.
    Ch 2: Thermal Comfort2011In: Sustainable Energy Utilisation / [ed] Havtun, H., Bohdanowicz, P., Stockholm: KTH Royal Institute of Technology, 2011, 300, p. 7-50Chapter in book (Other academic)
  • 32.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Bohdanowicz, Paulina
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Sustainable Building Systems.
    Ch 3: Heating Demand Calculations2011In: Sustainable Energy Utilisation / [ed] Havtun, H., Bohdanowicz, P., Stockholm: KTH Royal Institute of Technology, 2011, 300, p. 51-82Chapter in book (Other academic)
  • 33.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Bohdanowicz, Paulina
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Sustainable Building Systems.
    Ch 5: Ventilation Requirements2011In: Sustainable Energy Utilisation / [ed] Havtun, H., Bohdanowicz, P., Stockholm: KTH Royal Institute of Technology, 2011, 300, p. 105-124Chapter in book (Other academic)
  • 34.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Bohdanowicz, Paulina
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Sustainable Building Systems.
    Ch 7: Heating Systems, Their Components and Construction2011In: Sustainable Energy Utilisation / [ed] Havtun, H., Bohdanowicz, P., Stockholm: KTH Royal Institute of Technology, 2011, 300, p. 133-172Chapter in book (Other academic)
  • 35.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Bohdanowicz, Paulina
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Sustainable Building Systems.
    Ch 8: Ventilation Systems2011In: Sustainable Energy Utilisation / [ed] Havtun, H., Bohdanowicz, P., Stockholm: KTH Royal Institute of Technology, 2011, 300, p. 173-218Chapter in book (Other academic)
  • 36.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Bohdanowicz, PaulinaKTH, School of Industrial Engineering and Management (ITM), Energy Technology, Sustainable Building Systems.
    Sustainable Energy Utilisation2011Collection (editor) (Other academic)
  • 37.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Hjelm, Niclas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Basic Science.
    An investigation of what students that did not fill in the course questionnaire think of the course2019In: KTH SoTL 2019, 2019Conference paper (Refereed)
  • 38.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Izadi, Roozbeh
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    El Azzi, Charles
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    The Green Room: A Giant Leap in Development of Energy-efficient Cooling Solutions for Datacenters2013In: Sustainability in Energy and Buildings: Proceedings of the 4th International Conference in Sustainability in Energy and Buildings (SEB´12) / [ed] A. Håkansson, M. Höjer, R.J. Howlett, L.C. Jain, Springer Berlin/Heidelberg, 2013, p. 743-755Conference paper (Refereed)
    Abstract [en]

    Nowadays, promoting energy-efficient solutions will have a strong return on investment not only economically but also socially and environmentally. As an added value to economic savings, the carbon footprint of the companies will be reduced and contribute to slowing down the environmental degradation and global warming. The IT-sector is no exception in this aspect. Swedish-Finnish Company TeliaSonera has taken a giant leap in the development of energy reduction by introducing the Green Room Concept which combines not only an energy-efficient cooling production but also an efficient way of distributing the cooling air flow inside the room. Both of these technologies will reduce the energy needed for cooling the equipment on their own, but combining them ensures a very energy-efficient datacenter. Although geothermal cooling or free-cooling would be the preferred choice for cooling production, it is dependent on the geographical location and climate conditions of the site, and investment potential of the company and hence not a possible solution in all cases. For these cases, the Green Room can be installed with a conventional chiller-based cooling production and still reduce the energy consumption. The main feature of the Green Room concept is that the air coolers are installed along the length of the room parallel to the cabinet rows which will minimize the air flow complications in the cold aisle. This delivers cold air to the cabinet in a straight flow path to the racks and hence avoids the conventional raised floor to deliver cold air. One of the downsides of raised floor air-distribution is that it usually suffers from maldistribution of cooling air meaning that some racks suffer from inadequate cooling. The improved air flow distribution of the Green Room concept consequently leads to a more efficient cooling system. By carefully ensuring that no cold air bypasses the racks, any unwanted mixture of hot and cold air is also eliminated. In conventional datacenters, this problem usually occurs because proper hot/cold aisle separation is often neglected during construction. Furthermore, while many conventional datacenters face numerous problems as a result of messy cablings both inside and outside of the cabinets, the Green Room concept has managed to resolve these issues thanks to an effective cable management. The research method in this project was to conduct a series of experimental tests to collect as much necessary data as possible. During tests, temperatures inside the cold and hot aile were monitored and recorded. Special emphasis was put on measuring the temperature distribution in the cold aisle as the temperatures reflect the air distribution. Afterwards, the parameters used to evaluate the efficiency of the system were calculated and in some parts, simulated. Finally, the results were compared with other equivalent data and measurement from other datacenters and conclusions were made based on them. In addition to quantitative results based on a variety of calculations, the qualitative characteristics of this approach are also included to provide the readers with a better outlook on the system while being compared to other solutions currently available for datacenters. To assess the energy efficiency of a datacenter, critical measures such as Power Usage Effectiveness (PUE), defined as the total site power consumption divided by the power consumption of the IT-services, as well as the Coefficient of Performance (COP), defined as the power consumtion of the IT-services divded by the power consumtion needed to operate the cooling system. Results show that the PUE with room operational temperature of 22.5 °C can be as low as 1.05 for for a Green Room with geothermal cooling production, 1.11 for free-cooling, and 1.50 for chiller-based cooling production using old chillers and 1.32 for chiller-based cooling production using modern and more advanced chillers as compared to a PUE of 2.0 for a typical raised floor datacenter.

  • 39.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Naimi-Akbar, Ida
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Nyberg, Sara
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Hjelm, Niclas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Implementation of a course evaluation system: Facilitating faculty and student contributions2018In: ISSoTL 2018, 2018, article id E.11.2Conference paper (Refereed)
  • 40.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Törnqvist, Caroline
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Reducing Ventilation Energy Demand by Using Air-to-Earth Heat Exchangers: Part 1 - Parametric Study2013In: Sustainability in Energy and Buildings: Proceedings of the 4th International Conference on Sustainability in Energy and Buildings (SEB´12) / [ed] A. Håkansson, M. Höjer, R.J. Howlett, L.C. Jain, Springer Berlin/Heidelberg, 2013, p. 717-729Conference paper (Refereed)
    Abstract [en]

    Air-to-Earth heat exchangers (earth tubes) utilize the fact that the temperature in the ground is relatively constant during the year. By letting the air travel through an air-to-earth heat exchanger before reaching the house's ventilation air intake the air gets preconditioned by acquiring heat from the soil in the winter, and by rejecting heat to the soil in the summer. There are few studies showing how large the energy saving would be by using earth tubes. The existing studies and models are adapted to a warm climate like India and Southern Europe. Few studies are made for a Nordic climate. To be able to use earth tubes efficiently, different parameters need to be optimized. The parameters that have the largest effect are length, depth, and diameter of the earth tube, as well as the air velocity inside the tube. To analyze this influence, a numerical model has been created in the simulation program Comsol Multiphysics 4.0a. Weather data for Stockholm, Sweden was used for all simulations. The soil type was chosen to be clay and the material of the duct was polyethylene. The parameters were varied one at a time and compared to a base case consisting of a 10 m long duct placed at a depth of 2 m and with a diameter of 20 cm. The air velocity in the duct for the base case is 2 m/s and the corresponding volumetric flow rate is 60 l/s. Results show that longer heat exchangers with a smaller diameter, lower air velocity and buried at a deeper depth gives a larger energy saving. The increase in efficiency that comes from a deeper placed earth tube levels out at depth over 3.5 m. The decrease in efficiency that comes from an increase of the diameter of the duct levels out at diameters of 60 cm. The total energy saving for one year increased by 70 % for a 20 m long earth tube compared to a 10 m long earth tube. The energy saving for the base case is 525 kWh/year for the heating season and 300 kWh/year for the cooling season. This corresponds to an energy saving of 5 % for heating and 50 % for cooling compared to a case where no earth tube is used.

  • 41.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Törnqvist, Caroline
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Reducing Ventilation Energy Demand by Using Air-to-Earth Heat Exchangers: Part 2 – System Design Considerations2013In: Sustainability in Energy and Buildings: Proceedings of the 4th International Conference on Sustainability and Energy in Buildings (SEB '12) / [ed] A. Håkansson, M. Höjer, R.J. Howlett, L.C. Jain, Springer Berlin/Heidelberg, 2013, p. 731-742Conference paper (Refereed)
    Abstract [en]

    Air-to-Earth heat exchangers (earth tubes) utilize the fact that the temperature in the ground is relatively constant during the year. By letting the air travel through an air-to-earth heat exchanger before reaching the house’s ventilation air intake the air gets preconditioned by acquiring heat from the soil in the winter, and by rejecting heat to the soil in the summer. There are few studies showing how large the energy saving would be by using earth tubes. The existing studies and models are adapted to a warm climate like India and Southern Europe. Few studies are made for a Nordic climate.

    To be able to use earth tubes efficiently, different parameters need to be optimized. A numerical model has been developed using Comsol Multiphysics 4.0.a in order to study earth tubes with multiple ducts. Both the spacing between ducts as well as the number of ducts is simulated. Finally, results have been extrapolated to mimic an installation in a building with a large ventilation demand. Weather data for Stockholm, Sweden was used for all simulations. The soil type was chosen to be clay and the material of the duct was polyethylene.

    For the cases where the duct spacing was investigated, results showed that the outlet temperature of the earth ducts changed only marginally for the three cases simulated. The energy saving per duct showed a slight increase as the spacing was increased. For the cases with different number of ducts, the energy saving increases with increasing number of ducts. However, the increase in energy saving is less than the increase in heat transfer area. The case study considering a building with a large ventilation energy demand, several configurations of earth tube installations have been investigated. Results showed that the best configuration is a case with a small velocity, small duct diameters, long ducts installed at as deep in the earth as possible. However, Once the depth goes below 3.5 m, the increase in energy saving is marginal. For the building having a ventilation air flow demand of 1000 liters/s, a configuration of 33 parallel ducts with a duct diameter of 20 cm and a spacing of 1 meter gave the greatest energy saving. For this configuration, a total energy saving of 34.2 % is possible.

  • 42.
    Havtun, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Wingård, Lars
    KTH, School of Industrial Engineering and Management (ITM), Production Engineering.
    Carlsund, Ninni
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Numerical Analysis, NA.
    Kann, Viggo
    KTH, School of Electrical Engineering and Computer Science (EECS), Theoretical Computer Science, TCS.
    Continuous assessment: Time and effort well spent for students and teachers?2019In: KTH SoTL 2019, 2019Conference paper (Refereed)
  • 43.
    Jonsson, Hans
    KTH, Superseded Departments, Energy Technology.
    Turbulent Forced Convection Air Cooling of Electronics with Heat Sinks Under Flow Bypass Conditions2001Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Air cooling is still the dominant method for dissipating theheat produced by electronic components. In a typical electronicdevice, the components are situated on a Printed Circuit Board(PCB). For most applications natural convection is sufficientto cool the components. However in some cases forced convectionair cooling, which provides more effective cooling, has to beused. In cases with high heat fluxes the switch from natural toforced convection is not enough and in these cases the surfacearea of the components must also be increased by means of aheat sink, i.e. a finned surface. The size of the components isoften considerably smaller than the PCB, and in cases whereheat sinks are used, the heat sink seldom covers the air flowduct formed by two parallel PCBs. Since the air flow is seekingthe path of least resistance, some of it will bypass the heatsink. This air flow bypass has a major impact on theperformance of the heat sink, why knowledge of the amount ofbypass flow is of vital importance.

    The aim of this work has been to investigate the influenceof flow bypass on the performance of heat sinks used forelectronics cooling. The focus has been set on determining theparameters that influence the bypass, and to quantify theirrelative importance using experimental and numericaltechniques.

    Experimentaland numerical parametric studies have beenperformed. The influence of duct dimensions, air velocity, fintype, array arrangement, fin height, and fin-to-fin distance onthe thermal and hydraulic performance of plate fin, strip fin,and pin fin heat sinks have been investigated. The flow wasturbulent, and the Reynolds number was varied between 1 700 and16 000. Measurements have been performed in a wind tunnel. Intotal 42 different heat sinks were tested in seven differentduct configurations. For the plate fin heat sinks and thecircular pin fin heat sinks, numerical predictions have beenperformed by using the finite element code FIDAP and the finitevolume code PHOENICS, respectively. For turbulence modeling therevised RNG k-ε model and the Chen-Kim k-ε model wereused.

    The agreement between the results from the experimental andnumerical investigations was very good, suggesting that acombination of the two methods can be a powerful tool forpredicting the thermal and hydraulic performance of heat sinks.The experimental data can be used to validate the numericalmodel, which in turn can be used for parametric studies.

    The results of the investigations showed that the thermalperformance was most influenced by the duct height, and the airvelocity while the hydraulic performance was dependent on allthe investigated parameters.

    From the experimental and numerical results severalcorrelations have been developed to describe the relativeimportance of the investigated parameters. The agreementbetween the source data and the correlations is very good, aswell as the agreement between the correlations developed withdata from the experimental and the numerical investigationsrespectively.

    Keywords: forced convection, heat transfer, pressuredrop, turbulent, air cooling, bypass, plate, strip, pin, fin,heat sink, electronics, experimental,numerical, CFD

  • 44.
    Jonsson, Hans
    et al.
    KTH, Superseded Departments, Energy Technology.
    Moshfegh, B
    CFD modeling of the cooling performance of pin fin heat sinks under bypass flow conditions2001Conference paper (Other academic)
  • 45.
    Jonsson, Hans
    et al.
    KTH, Superseded Departments, Energy Technology.
    Moshfegh, B
    Modeling and characterisation of plate fin heat sinks under bypass flow conditions using computational fluid dynamics methods2001In: Journal of Electronic Packaging, ISSN 1043-7398, E-ISSN 1528-9044Article in journal (Other academic)
  • 46.
    Jonsson, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Moshfegh, Bahram
    University of Gävle.
    CFD Modeling of the Cooling Performance of Pin Fin Heat Sinks Under Bypass Flow Conditions2001In: Proceedings of IPACK’01 The Pacific Rim/ASME International Electronic Packaging Technical Conference and Exhibition July 8-13, 2001, Kauai, Hawaii, USA, ASME Press, 2001Conference paper (Refereed)
    Abstract [en]

    Three-dimensional CFD models of circular pin fin heat sinksin bypass flow have been developed. The numerical modelshave been validated against experimental data presented earlierby the authors. A parametric study has been performed wherethe inlet velocity, the fin height, the fin-to-fin distance and thepin orientation was varied. For all cases, the duct flow area washeld constant. The flow was turbulent, the Reynolds numbervaried between 6 100 and 15 300. For turbulence modeling theChen-Kim k-ε model was used. Results are presented for theheat transfer coefficient, and the pressure drop, as well as theinfluence of flow bypass, and the leakage from the interfinregion to the bypass regions of the domain. The inlet velocity,the fin height, and the fin-to-fin distance all showed a stronginfluence on the heat transfer coefficient and the pressure drop.

  • 47.
    Jonsson, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Moshfegh, Bahram
    University of Gävle.
    Enhancement of the Cooling Performance of Circular Pin Fin Heat Sinks Under Flow Bypass Conditions2002In: Proc. 8th  InterSociety Conf. on Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm 2002), San Diego, CA, USA, IEEE Press, 2002, p. 425-432Conference paper (Refereed)
    Abstract [en]

    CFD models of circular pin fin heat sinks have beendeveloped. The heat sinks are situated in bypass flow in a duct with constant dimensions. The air velocity was constant,the flow was turbulent, and for turbulence modeling the Chen-Kim k-ε model was used. The influence of increasing fin height in the flow direction, and uneven distribution of the fins in the lengthwise and the spanwise direction are studied.

    In the case of increasing fin height, it was shown that an increase in the heat transfer coefficient can be achieved without an increase in pressure drop when compared at equal mean fin height.

    In the case of uneven distribution of the fins it was shown that the heat transfer coefficient could be increased by an uneven distribution of the fins in the lengthwise direction, using smaller fin spacing at the trailing edge of the heat sink. Results also showed that some cases of unevenly distributed fins in the spanwise direction could achieve an increase inthe heat transfer coefficient. These cases had smaller fin spacing at the center of the heat sink, and the fin height was close to the duct height. The pressure drop was almost thesame as for heat sinks with even distribution of the fins.

  • 48.
    Jonsson, Hans
    et al.
    KTH, Superseded Departments, Energy Technology.
    Moshfegh, Bahram
    Influence of fin spacing, fin thickness and inlet velocity on the performance of plate fin heat sinks under varying bypass conditions using CFD2000In: International journal of heat exchangers, ISSN 1524-5608Article in journal (Other academic)
  • 49.
    Jonsson, Hans
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Moshfegh, Bahram
    University of Gävle.
    Modeling and Enhancement of the Cooling Performance of Pin Fin Heat Sinks in Bypass Flow Using CFD2002In: ScandTherm, 2002, p. 63-74Conference paper (Refereed)
  • 50.
    Jonsson, Hans
    et al.
    KTH, Superseded Departments, Energy Technology.
    Moshfegh, Bahram
    Modeling of the thermal and hydraulic performance of plate fin, strip fin, and pin fin heat sinks: Influence of flow bypass2001In: IEEE transactions on components and packaging technologies (Print), ISSN 1521-3331, E-ISSN 1557-9972, Vol. 24, no 2, p. 142-149Article in journal (Refereed)
    Abstract [en]

    Tests have been conducted in a wind tunnel with seven types of heat sinks including plate fin, strip fin, and pin fin heat sinks. In the case of strip fin, and pin fin heat sinks, both in-line and staggered arrays have been studied. The pin fin heat sinks had circular and square cross-sections, For each type, tests were run with fin heights (H) of 10, 15, and 20 mm while the heat sink width (B) was kept constant and equal to 52.8 mm. In total, 42 different heat sinks were tested, The width of the wind tunnel duct (CB) was varied in such a way that results were obtained for B/CB = 0.84, 0.53, and 0.33. The wind tunnel height (CH) was varied similarly, and data were recorded for H/CH = 1, 0.67, and 0.33 while the duct Reynolds number was varied between 2 000 through 16 500. An empirical bypass correlation has been developed for the different fin designs. The correlation predicts the Nusselt number and the dimensionless pressure drop and takes into account the influence of duct height, duct width, fin height, fin thickness, and fin-to-fin distance. The correlation parameters are individual for each fin design. Further, a physical bypass model for plate fin heat sinks has been developed to describe the bypass effect.

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