Solar-Driven Refrigeration Systems with Focus on the Ejector Cycle
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Solar-Driven Refrigeration Systems with Focus on the Ejector Cycle Doctoral Thesis By Wimolsiri Pridasawas Stockholm, October 2006 Division of Applied Thermodynamics and Refrigeration Department of Energy Technology School of Industrial Engineering and Management Royal Institute of Technology, KTH Solar-Driven Refrigeration Systems with Focus on the Ejector Cycle Wimolsiri Pridasawas TRITA REFR Report No 06/55 ISSN 1102-0245 ISRN KTH/REFR/ R06/55 ISBN 91-7178-449-7 Doctoral Thesis by Wimolsiri Pridasawas Division of Applied Thermodynamics and Refrigeration Department of Energy Technology School of Industrial Engineering and Management Royal Institute of Technology, KTH © Wimolsiri Pridasawas 2006 2 Abstract Interest in utilizing solar-driven refrigeration systems for air-conditioning or refrigeration purposes has grown continuously. Solar cooling is com- prised of many attractive features and is one path towards a more sus- tainable energy system. Compared to solar heating, the cooling load, par- ticularly for air-conditioning applications, is generally in phase with solar radiation. The objective of this thesis is to establish a fundamental basis for further research and development within the field of solar cooling. In this thesis, an overview of possible systems for solar powered refrigeration and air- conditioning systems will be presented. The concept of the ‘Solar Cool- ing Path’ is introduced, including a discussion of the energy source to the collector, and choice of cooling cycle to match cooling load. Brief infor- mation and comparisons of different refrigeration cycles are also pre- sented. The performance of solar cooling systems is strongly dependent on local conditions. The performance of a solar divan air-conditioning system in different locations will therefore be compared in this thesis. Solar cooling systems can be efficiently operated in locations where sufficient solar ra- diation and good heat sink are available. A solar-driven ejector refrigeration system has been selected as a case study for a further detailed investigation. A low temperature heat source can be used to drive the ejector refrigeration cycle, making the system suitable for integration with the solar thermal collector. Analysis of the solar driven ejector system is initiated by steady state analysis. System performance depends on the choice of working fluid (refrigerant), oper- ating conditions and ejector geometry. Results show that various kinds of refrigerants can be used. Also, thermodynamic characteristics of the re- frigerant strongly influence the performance of the cycle. An ejector re- frigeration cycle using natural working fluids generates good perform- ance and lower environmental impact, since traditional working fluids, CFC’s and HFC’s are strong climate gases. Further on, exergy analysis is used as a tool in identifying optimum operating conditions and investi- gating losses in the system. Exergy analysis illustrates that the distribu- 3 tion of the irrervsibilities in the cycle between components depends strongly on the working temperatures. The most significant losses in the system are in the solar collector and ejector. Losses in the ejector pre- dominate over total losses within the system. In practice, the cooling load characteristic and solar radiation are not constant. Therefore, a dynamic analysis is useful for determining the characteristics of the system during the entire year, and dimensioning the important components of the solar collector subsystem, such as storage tanks. The final section of the thesis will deal with the ejector, the key compo- nent of the ejector refrigeration cycle. Characteristics of the actual ejector are shown to be quite complicated and its performance difficult to de- termine solely through theoretical analysis. Suggested design procedures and empirical equations for an ejector are offered in this thesis. Prelimi- nary test results for one fixed ejector dimension using R134a as the re- frigerant are also included. Keywords: Solar Cooling; Solar-Driven Refrigeration System; Ejector; Ejector Refrigeration Cycle; Exergy Analysis; Dynamic Analysis 4 Acknowledgements People have often inquired about my decision to stay and continue my studies in Sweden. Any attempt to justify the reason why I chose to come to a country, where the climate and environment are so extremely different from my own native country would be very difficult. Perhaps it can be explained by a burning desire for adventure, destiny, or a combi- nation of both. Nevertheless, I would like to thank whatever forces that have brought me here, but in particular the Energy Conservation and Renew- able Energy Fund, for providing me with a scholarship during my doctoral studies here in Sweden. I would also like to take this opportunity to thank my supervisor, Professor Per Lundqvist. During my time here in Sweden, he has been extremely supportive of my ideas, and has provided an invaluable input to the pro- ject. You are a special person with a boundless capacity for ideas and a great inspiration for me. Thanks also for the brief lecture on classical music while sitting in an exclusive seat at the Konserthuset during a concert by Valerij Gergiev., as well as the sailing trip in to St. Nassa with your wonderful family, Anne, Felix and Max, which was both breathtaking and exciting. Many thanks to the staff at the Division of Applied Thermodynamics and Refrigeration, Professor Björn Palm, Professor Eric Granryd, Benny Sjöberg, Benny Andersson, Anders Johansson, Cecilia Hägg, Bo Johansson, Leif Nilsson (IIP), Bernt Jansson (HPT), Jaime Arias, Åke Melinder, Hans Johansson, Claudi Martín, Dimitra Sakellari, Samer Sawalha, Emilio Navarro, Jan-Erik Nowacki, Getachew Bekele, Joachim Claesson, Shota Nozadze, Peter Hill, Wahib Owhaib, Oxana Samoteeva, Raul Anton, Branko Simanic, Teclemariam Nemariam, Anita Elksne, Nabil Kasem, Birger Söderström, Tony Chapman and Chunhong Sheng, gracious people who have all provided very useful help and advice during my stay here at the lab. A special thanks to Inga Du Rietz, the most con- siderate, kind-hearted and helpful secretary I have ever had the pleasure of encountering. Thanks also for the very enjoyable lunch dates and dis- cussions we had in our lunch group consisting of Susy Mathew, Primal Fernando, Rahmatollah Khodabandeh, Yang Chen, Richard and Dorothy Furberg. Big thanks to Anita Elksne and Damon Lane, for the language corrections and valuable comments in the thesis. 5 I am forever grateful to my family and relatives in Thailand: my parents Chamsri and Wirach, my brother Thanaphon and my grandmother Praphai. I would like to extend a special gratitude to the ‘Hägg’ Family, Gunvor, Lennart, Göran, Hans, Catharina, Anneli, Cecilia, Louise, and Wilhelm, who welcomed me as a family member, and taught me Swedish culture. Christmas Eve celebrations in Brålanda, summers spent together in Son- nebo, and many other occasions were so memorable, that I will cherish them forever. One of the places that most impressed me in Sweden was the Stockholm International Library (Internationella Bilioteket). The books and services here are truly remarkable. This library made the long and dark Stock- holm winters more pleasurable. This section would not be complete if I didn’t mention all of my Thai friends here in Sweden who provided me with delicious food (either new inventions or traditional Thai dishes), endless smiles, laughs, crazy activi- ties and creations. Thanks P’Jom, Mats and Emilie Näslund, P’Aoy and Folke Andersons, P’Nid, Win, P’Tee, Thep, Nong, Nok, Nam, O+, Toey, Tum, Care, Mam, Lor, and Miles. A special thanks to P’Tee, Yang, Samer, Claudi, P’Nom, Sittisak, Manustai and Susy who supported and took good care of me after my knee surgery, and during the following recuperation period. Stockholm, August 2006 6 Publications Journal Papers: Published: Pridasawas, W. and Lundqvist, P. (2004): An Exergy Analysis of a Solar-driven Ejector Refrigeration System, Solar Energy, vol. 76, pp. 369-379. In Review: Pridasawas, W. and Lundqvist, P. (2006): A Dynamic Simulation of a Solar-driven Ejector Refrigeration System. In review process for the International Journal of Refrigeration Conference Papers (Peer Reviewed): Pridasawas, W. and Lundqvist, P. (2002): Working Fluid Selection for an Ejector Refrigeration Cycle, Zero Leakage – Minimum Charge Conference, Joint meeting of the International Institute of Refrigeration Sections B and E, August 26-28, Stockholm, Sweden. Pridasawas, W. and Lundqvist, P. (2003): Natural Working Fluids for a Solar-driven Ejector Refrigeration System, Eurotherm Seminar No. 72, Thermodynamics, Heat and Mass Transfer of Refrigeration Machines and Heat Pumps, March 31 – April 2, Valencia, Spain. Pridasawas, W. and Lundqvist, P. (2003): Feasibility and Efficiency of Solar-driven Refrigeration Systems, 21st IIR International Congress of Refrigeration, August 17-22, Washington D.C., USA. 7 Pridasawas, W. and Lundqvist, P. (2004): Butane as a refrigerant for a solar-driven ejector refrigeration system, Proceedings of the 6th IIR Gustav Lorentzen Natural Working Fluids Conference, August 29th – September 1st, 2004, Glasgow, UK. Conference Papers (Others): Pridasawas, W. and Lundqvist, P. (2003): Technical Options for a Solar-driven Cooling System, ISES Solar World Congress 2003, June 14-19, Göteborg, Sweden. Pridasawas, W. and Lundqvist, P. (2003): A Year-round Simulation of a Solar-Driven Ejector Refrigeration System, Proceedings of the International Conference on Fluid and Thermal Energy