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  • 1.
    Chen, Yang
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Carbon dioxide transcritical power cycle discussion2005Report (Other academic)
  • 2.
    Chen, Yang
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Novel cycles using carbon dioxide as working fluid: new ways to utilize energy from low-grade heat sources2006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This licentiate thesis proposes and analyzes three carbon dioxide novel cycles, namely: the carbon dioxide transcritical power cycle, the carbon dioxide Brayton cycle and the carbon dioxide cooling and power combined cycle. Due to the different characteristics of each cycle, the three cycles are suitable for different applications. The CO2 transcritical power cycle is suitable for harvesting energy from low-grade heat sources, near which a low temperature heat sink is accessible. The CO2 Brayton cycle is suitable for harvesting the energy from relatively high-grade heat sources when there is no low temperature heat sink available. The CO2 cooling and power combined cycle is suitable for applications, where both power and cooling are needed (e.g. automobile applications, in which the cycle can utilize the energy in the engine exhaust gasses to produce power and provide cooling/heating to the mobile compartment room at the same time).

    Several models have been developed using the software known as Engineering Equation Solver (EES)1 for both cycle analysis and computer aided heat exchanger design. Different cycle working conditions have been simulated and different working parameters’ influence on the cycle performance has been explained. In addition, Refprop 7.02 is used for calculating the working fluid properties and the CFD tool Femlab has been employed to investigate the particular phenomena influencing the heat exchanger performance.

  • 3.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Analysis of supercritical carbon dioxide heat exchangers in cooling process2006Conference paper (Refereed)
    Abstract [en]

    Carbon dioxide transcritical cycles have become more and more investigated during the last decade. For all systems operating with such a cycle, there will be at least one heat exchanger to either heat or cool the supercritical carbon dioxide. Unlike in the sub-critical region, the supercritical carbon dioxide’s thermophysical properties will have sharp variations in the region close to its critical point. This variation has a significant influence on the shape of the heat exchanger’s temperature profile and the heat transfer performance of the heat exchanger. Therefore, the performance of the heat exchanger used for supercritical carbon dioxide cooling or heating process should be evaluated by taking this effect into account. This paper discusses the heat exchangers used for supercritical carbon dioxide refrigeration process including a suction gas heat exchanger in the cycle. Engineering Equation Solver (EES)1 and Refprop 7.02 are used for cycle calculations and for properties calculations.

  • 4.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    The Co2 Transcritical Power Cycle For Low Grade Heat Recovery-Discussion On Temperature Profiles In System Heat Exchangers2012In: Proceedings of the ASME Power Conference- 2011 Vol 1, ASME Press, 2012, p. 385-392Conference paper (Refereed)
    Abstract [en]

    Carbon dioxide transcritical power cycle has many advantages in low-grade heat source recovery compared to conventional systems with other working fluids. This is mainly due to the supercritical CO2's temperature profile can match the heat source temperature profile better than other pure working fluids and its heat transfer performance is better than the fluid mixtures, which enables a better cycle efficiency. Moreover, the specific heat of supercritical CO2 will have sharp variations in the region close to its critical point, which will create a concave shape temperature profile in the heat exchanger that used for recovering heat from low-grade heat sources. This brings more advantage to carbon dioxide transcritical power systems in low-grade heat recovery.

  • 5.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Lundqvist, Per Gunnar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Carbon dioxide cooling and power combined cycle for mobile applications2006In: Proceedings of 7th IIR-Gustav Lorentzen Conference on Natural Working Fluids, 2006Conference paper (Refereed)
  • 6.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per Gunnar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Johansson, Anders
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Platell, P
    A comparative study of the carbon dioxide transcritical power cycle compared with an organic rankine cycle with R123 as working fluid in waste heat recovery2006In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 17-18, p. 2142-2147Article in journal (Refereed)
    Abstract [en]

    The organic rankine cycle (ORC) as a bottoming cycle1The expression "bottoming cycle" refers to the power cycle that uses waste industrial heat for power generation by supplementing heat from any fossil fuel.1 to convert low-grade waste heat into useful work has been widely investigated for many years. The CO2 transcritical power cycle, on the other hand, is scarcely treated in the open literature. A CO2 transcritical power cycle (CO2 TPC) shows a higher potential than an ORC when taking the behavior of the heat source and the heat transfer between heat source and working fluid in the main heat exchanger into account. This is mainly due to better temperature glide matching between heat source and working fluid. The CO2 cycle also shows no pinch limitation in the heat exchanger. This study treats the performance of the CO2 transcritical power cycle utilizing energy from low-grade waste heat to produce useful work in comparison to an ORC using R123 as working fluid. Due to the temperature gradients for the heat source and heat sink the thermodynamic mean temperature has been used as a reference temperature when comparing both cycles. The thermodynamic models have been developed in EES2EES - Engineering equation solver. The thermodynamic properties for carbon dioxide in EES are calculated by the fundamental equation of state developed by R. Span and W. Wagner, A new equation of state for carbon dioxide covering the fluid region form the triple-point temperature to 1100 K at pressures up to 800 MPa, J. Phys. Chem. Ref. Data, Vol. 25, No. 6, 1996. http://www.fchart.com/ees/ees.shtml.2 The relative efficiencies have been calculated for both cycles. The results obtained show that when utilizing the low-grade waste heat with the same thermodynamic mean heat rejection temperature, a transcritical carbon dioxide power system gives a slightly higher power output than the organic rankine cycle.

  • 7.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Lundqvist, Per Gunnar
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Platell, P.
    Theoretical research of carbon dioxide power cycle application in automobile industry to reduce vehicle's fuel consumption2005In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 25, no 14-15, p. 2041-2053Article in journal (Refereed)
    Abstract [en]

    The current work discusses means to utilize low-grade small-scale energy in vehicle exhaust gases, to reduce the vehicle's fuel consumption and to make it run more environmental friendly. To utilize the energy in the exhaust gas, a CO2 bottoming system in the vehicle's engine system is proposed. Several basic cycles-according to the different design concepts-are presented, and the efficiencies are calculated using Engineering Equation Solver (EES).1 Several thermodynamic models in EES show that after system optimization, in CO2 Transcritical power cycle with a gas heater pressure of 130 bars and 200 °C expansion inlet temperature, about 20% of energy in the exhaust gas can be converted into useful work. Increasing the pressure in the gas heater to 300 bars and with same expansion inlet temperature, about 12% of exhaust gas energy can be converted. When raising the pressure both in the gas cooler and in the gas heater, the cycle runs completely above the critical point, and the efficiency is about 19%. Besides, in the CO2 combined cycle, the system COP is 2.322 and about 5% of exhaust gas energy can be converted.

  • 8.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    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 Nobel Gas-Water Heat Exchanger with Minichannels2008Conference paper (Refereed)
  • 9.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    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.
    A NOVEL GAS-WATER HEAT EXCHANGER WITH MINICHANNELS2009In: HT2008: PROCEEDINGS OF THE ASME SUMMER HEAT TRANSFER CONFERENCE - 2008, VOL 2, NEW YORK: AMER SOC MECHANICAL ENGINEERS , 2009, p. 157-164Conference paper (Refereed)
    Abstract [en]

    In the current study, a novel gas water heat exchanger with minichannels is designed, built and tested. The heat exchanger is mainly composed of a number of concentric ring shaped plates, which are made tip of several heat exchanger tubes. The ring shaped plates are arranged in parallel and placed in a shell. The heat exchanger is designed as a counter current heat exchanger with laminar flow on the heat exchanger's shell-side (gas side) and therefore has a very low pressure drop on the shell side. The heat exchanger was tested with water and hot air on its tube-side and shell-side respectively. All the necessary parameters like inlet and outlet temperatures on tube-side and shell-side as well as the pressure drop, flow rate of fluids, etc. were measured. Different existing correlations were used to calculate the overall heat transfer coefficient and the results were compared with the measured value. The measured results show that the new designed heat exchanger can achieve a good heat transfer performance and also maintain a low pressure drop on shell-side (gas side).

  • 10.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Pridasawas, Wimolsiri
    King Mongkut’s University of Technology Thonburi, Dept. of Chemical Engineering,Bangkok, Thailand.
    Theoretical Study of a Carbon Dioxide Double Loop System2007Conference paper (Refereed)
    Abstract [en]

    In the current research, a carbon dioxide double loop system is proposed. The system contains of two sub systems: a CO2power subsystem and a CO2refrigeration subsystem. The power subsystem is able to utilize the energy from the low-grade heat source to produce power. The power is then transferred to the refrigeration subsystem, partly or totally covering the power consumption of the compressor. Furthermore, it is also possible to take advantage of the temperature glides of both subsystems’ heat rejection processes to produce hot water. Engineering Equation Solver (EES) is employed to analyze the system performance. The results show that the proposed system is a very promising way to provide cooling, heating and hot water in a more efficient way comparing to traditional systems.

  • 11.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Workie, Almaz Bitew
    Second Law Analysis of a Carbon Dioxide Transcritical Power System in Low-grade Heat Source RecoveryArticle in journal (Other academic)
    Abstract [en]

    Employing Carbon dioxide as a working media in power cycles for low-grade heat source utilization has attracted more and more attentions. However, compared to other well-known cycles that employed in low-grade heat source utilizations, the information about CO2power cycle is still very limited. In the current work, the performance of a CO2power cycle in utilizing the low-grade heat sources is simulated and the results are analyzed with a focus on second law thermodynamics (i.e. exergy and entropy). Different system parameters that influencing the system exergy and entropy change are discussed.

    Engineering Equation Solver (EES) is used for simulation. The simulation results show that the matching of the temperature profiles in the system heat exchangers has crucial influences on their exergy destructions and entropy generations. It is also an essential factor that influences the system thermodynamic efficiencies.

  • 12.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Pridasawas, Wimolsiri
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Dynamic simulation of a solar-driven carbon dioxide transcritical power system for small scale combined heat and power production2010In: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 84, no 7, p. 1103-1110Article in journal (Refereed)
    Abstract [en]

    Carbon dioxide is an environmental benign natural working fluid and has been proposed as a working media for a solar-driven power system In the current work, the dynamic performance of a small scale solar-driven carbon dioxide power system is analyzed by dynamic simulation tool TRNSYS 16 (Klein et al., 2004) and Engineering Equation Solver (EES) (Klein, 2004) using co-solving technique Both daily performance and yearly performance of the proposed system have been simulated Different system operating parameters, which will influence the system performance, have been discussed. Under the Swedish climatic condition, the maximum daily power production is about 12 kW h and the maximum monthly power production is about 215 kW h with the proposed system working conditions Besides the power being produced, the system can also produce about 10 times much thermal energy. which can be used for space heating, domestic hot water supply or driving absorption chillers The simulation results show that the proposed system is a promising and environmental benign alternative for conventional low-grade heat source utilization system (C) 2010 Elsevier Ltd All rights reserved.

  • 13.
    Chen, Yang
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Pridasawas, Wimolsiri
    Lundqvist, Per
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Low-grade heat source utilization by carbon dioxide transcritical power cycle2007In: 2007 Proceedings of the ASME/JSME Thermal Engineering Summer Heat Transfer Conference - HT 2007 Volume 1, 2007, p. 519-525Conference paper (Refereed)
    Abstract [en]

    One way to reduce the fossil fuel consumption and mitigate environmental impact is to utilize low-grade heat sources for power production. In this paper, a transcritical carbon dioxide power cycle is analyzed for its potential in utilizing the low-grade heat sources. Solar thermal is selected as a representative of low-grade heat sources. TRNSYS 16(1) and Engineering Equation Solver (EES)(2) are employed using co-solving technique to analyze the dynamic performance of the proposed system. Both daily performance and annual performance of the proposed system under Swedish climate conditions are simulated. The simulation results show that the proposed system can achieve 8% average thermal efficiency and consequently 2.43 kW average power production during the system working period on a randomly selected summer day with a 30 m(2) solar collector. Over the whole year, the maximum daily power production is about 17 kWh and the maximum monthly power production is about 185 kWh.

  • 14.
    Sawalha, Samer
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Chen, Yang
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Investigations of Heat Recovery in Different Refrigeration System Solutions in Supermarkets: Effsys2 project final report2010Report (Other academic)
  • 15.
    Yang, Chen
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Thermodynamic Cycles using Carbon Dioxide as Working Fluid: CO2 transcritical power cycle study2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The interest in utilizing the energy in low‐grade heat sources and waste heat is increasing. There is an abundance of such heat sources, but their utilization today is insufficient, mainly due to the limitations of the conventional power cycles in such applications, such as low efficiency, bulky size or moisture at the expansion outlet (e.g. problems for turbine blades).

    Carbon dioxide (CO2) has been widely investigated for use as a working fluid in refrigeration cycles, because it has no ozonedepleting potential (ODP) and low global warming potential (GWP). It is also inexpensive, non‐explosive, non‐flammable and abundant in nature. At the same time, CO2 has advantages in use as a working fluid in low‐grade heat resource recovery and energy conversion from waste heat, mainly because it can create a better matching to the heat source temperature profile in the supercritical region to reduce the irreversibility during the heating process. Nevertheless, the research in such applications is very limited.

    This study investigates the potential of using carbon dioxide as a working fluid in power cycles for low‐grade heat source/waste heat recovery.

    At the beginning of this study, basic CO2 power cycles, namely carbon dioxide transcritical power cycle, carbon dioxide Brayton cycle and carbon dioxide cooling and power combined cycle were simulated and studied to see their potential in different applications (e.g. low‐grade heat source applications, automobile applications and heat and power cogeneration applications). For the applications in automobile industries, low pressure drop on the engine’s exhaust gas side is crucial to not reducing the engine’s performance. Therefore, a heat exchanger with low‐pressure drop on the secondary side (i.e. the gas side) was also designed, simulated and tested with water and engine exhaust gases at the early stage of the study (Appendix 2).

    The study subsequently focused mainly on carbon dioxide transcritical power cycle, which has a wide range of applications. The performance of the carbon dioxide transcritical power cycle has been simulated and compared with the other most commonly employed power cycles in lowgrade heat source utilizations, i.e. the Organic Rankin Cycle (ORC). Furthermore, the annual performance of the carbon dioxide transcritical power cycle in utilizing the low‐grade heat source (i.e. solar) has also been simulated and analyzed with dynamic simulation in this work.

    Last but not least, the matching of the temperature profiles in the heat exchangers for CO2 and its influence on the cycle performance have also been discussed. Second law thermodynamic analyses of the carbon dioxide transcritical power systems have been completed.

    The simulation models have been mainly developed in the software known as Engineering Equation Solver (EES)1 for both cycle analyses and computer‐aided heat exchanger designs. The model has also been connected to TRNSYS for dynamic system annual performance simulations. In addition, Refprop 7.02 is used for calculating the working fluid properties, and the CFD tool (COMSOL) 3 has been employed to investigate the particular phenomena influencing the heat exchanger performance.

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