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The Co2 Transcritical Power Cycle For Low Grade Heat Recovery-Discussion On Temperature Profiles In System Heat Exchangers
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
2012 (English)In: Proceedings of the ASME Power Conference- 2011 Vol 1, ASME Press, 2012, 385-392 p.Conference paper, Published 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.

Place, publisher, year, edition, pages
ASME Press, 2012. 385-392 p.
Keyword [en]
pinching, specific heat (CP), internal heatexchanger (IHX), efficiency
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-50265ISI: 000320008200050Scopus ID: 2-s2.0-84882637179ISBN: 978-0-7918-4459-5 (print)OAI: oai:DiVA.org:kth-50265DiVA: diva2:461429
Conference
The ASME 2011 Power Conference, POWER2011, July 12-14, 2011, Denver, Colorado, USA
Note

QC 20111206

Available from: 2011-12-06 Created: 2011-12-04 Last updated: 2014-09-11Bibliographically approved
In thesis
1. Thermodynamic Cycles using Carbon Dioxide as Working Fluid: CO2 transcritical power cycle study
Open this publication in new window or tab >>Thermodynamic Cycles using Carbon Dioxide as Working Fluid: CO2 transcritical power cycle study
2011 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology(KTH), 2011. xxii, 128 p.
Series
Trita-REFR, ISSN 1102-0245 ; 11:03
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-50261 (URN)978-91-7501-187-5 (ISBN)
Public defence
2011-12-09, M2, Brinellvägen 64, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20111205Available from: 2011-12-05 Created: 2011-12-04 Last updated: 2011-12-09Bibliographically approved

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