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Novel cycles using carbon dioxide as working fluid: new ways to utilize energy from low-grade heat sources
KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
2006 (English)Licentiate 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.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , viii, 87 p.
Series
Trita-REFR, ISSN 1102-0245 ; 06:50
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4055ISBN: 91-7178-410-1 (print)OAI: oai:DiVA.org:kth-4055DiVA: diva2:10578
Presentation
2006-06-15, Sal MWL74, KTH, Brinellvägen 68, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20101124Available from: 2006-06-16 Created: 2006-06-16 Last updated: 2010-11-24Bibliographically approved
List of papers
1. Theoretical research of carbon dioxide power cycle application in automobile industry to reduce vehicle's fuel consumption
Open this publication in new window or tab >>Theoretical research of carbon dioxide power cycle application in automobile industry to reduce vehicle's fuel consumption
2005 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 25, no 14-15, 2041-2053 p.Article in journal (Refereed) Published
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.

Keyword
Brayton cycle, CO2, Efficiency, Transcritical power cycle
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6007 (URN)10.1016/j.applthermaleng.2005.02.001 (DOI)000230019600002 ()2-s2.0-19944414348 (Scopus ID)
Note
QC 20101004Available from: 2006-06-16 Created: 2006-06-16 Last updated: 2017-12-14Bibliographically approved
2. A comparative study of the carbon dioxide transcritical power cycle compared with an organic rankine cycle with R123 as working fluid in waste heat recovery
Open this publication in new window or tab >>A comparative study of the carbon dioxide transcritical power cycle compared with an organic rankine cycle with R123 as working fluid in waste heat recovery
2006 (English)In: Applied Thermal Engineering, ISSN 1359-4311, E-ISSN 1873-5606, Vol. 26, no 17-18, 2142-2147 p.Article in journal (Refereed) Published
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.

Keyword
CO2; Efficiency; ORC; Transcritical power cycle
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6008 (URN)10.1016/j.applthermaleng.2006.04.009 (DOI)000239984400012 ()2-s2.0-33745233798 (Scopus ID)
Note
QC 20100819Available from: 2006-06-16 Created: 2006-06-16 Last updated: 2017-12-14Bibliographically approved
3. Carbon dioxide cooling and power combined cycle for mobile applications
Open this publication in new window or tab >>Carbon dioxide cooling and power combined cycle for mobile applications
2006 (English)In: Proceedings of 7th IIR-Gustav Lorentzen Conference on Natural Working Fluids, 2006Conference paper, Published paper (Refereed)
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6009 (URN)2-913149-48-0 (ISBN)
Conference
7th IIR-Gustav Lorentzen Conference on Natural Working Fluids, Trondheim, Norway, May 29-31, 2006
Note
QC 20101124Available from: 2006-06-16 Created: 2006-06-16 Last updated: 2011-12-05Bibliographically approved
4. Carbon dioxide transcritical power cycle discussion
Open this publication in new window or tab >>Carbon dioxide transcritical power cycle discussion
2005 (English)Report (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH, 2005
Series
Trita-REFR, ISSN 1102-0245 ; 05/49
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-6010 (URN)
Note
QC 20101124Available from: 2006-06-16 Created: 2006-06-16 Last updated: 2010-11-24Bibliographically approved

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