The Experts below are selected from a list of 1188 Experts worldwide ranked by ideXlab platform
K. Sumathy - One of the best experts on this subject based on the ideXlab platform.
-
Performance study on solar assisted heat pump water heater using CO2 in a Transcritical Cycle
Renewable Energy and Power Quality Journal, 2012Co-Authors: M. Raisul Islam, K. Sumathy, Jiawei Gong, Samee U. KhanAbstract:This study reports the numerical analyses of a CO2 Transcritical Cycle on solar assisted heat pump water heating system in which evacuated tube U-pipe solar collector is utilized as an evaporator. This simulation model can predict operating characteristics for moderate meteorological conditions of North Dakota. The main purpose of this work is to simulate the overall performance of the heat pump Cycle by varying compressor speed. From the analysis the coefficient of performance (COP) value is predicted from 1.5 – 2.8 with three different average solar insolation. The results showed that the performance of the system significantly influenced by the compressor speed and solar irradiation. This study also calculated the instantaneous collector efficiency and found in the range of 50 – 55%.
-
Transcritical carbon dioxide heat pump systems a review
Renewable & Sustainable Energy Reviews, 2011Co-Authors: Brian T Austin, K. SumathyAbstract:Carbon dioxide is a safe, economic and environmentally sustainable refrigerant which can be used in heat pump and refrigeration systems. Research into the performance and benefits of a Transcritical heat pump Cycle using carbon dioxide began in the early 1990s. Theoretical and experimental research, as well as commercial system development, has improved Transcritical system performance to a level similar to that of conventional heat pump systems. This paper presents an overview of Transcritical carbon dioxide heat pump systems. The paper begins with a summary of carbon dioxide's use as a refrigerant and the distinctions of the Transcritical Cycle, followed by a numerical analysis of Transcritical Cycle performance. The study will then present a review of research on Transcritical carbon dioxide heat pump systems, which covers system components, configurations and modifications and how these factors affect overall system performance.
Angelo Maiorino - One of the best experts on this subject based on the ideXlab platform.
-
the application of a desiccant wheel to increase the energetic performances of a Transcritical Cycle
Energy Conversion and Management, 2015Co-Authors: Ciro Aprea, A Greco, Angelo MaiorinoAbstract:A desiccant dehumidification system with air can be driven by low grade (<80 °C) waste heat. In this paper, which is based on experimental data, the air flow at the outlet of the gas cooler of a trans-critical Cycle is forced through a desiccant wheel regenerated by the air flow itself. The hybrid trans-critical refrigerator-desiccant system improves COP by approximately 77% as compared to a classical Transcritical. The economical analysis suggests that the investment return-time is acceptable (lower than about 8 years) only at ambient temperature exceeding 35 °C. The ecological analysis indicates that the TEWI of the classical Transcritical Cycle exceeds that of the hybrid system, by approximately 60%.
-
Transcritical Carbon Dioxide Refrigeration as an Alternative to Subcritical Plants
Handbook of Research on Advances and Applications in Refrigeration Systems and Technologies, 2015Co-Authors: Adriana Greco, Ciro Aprea, Angelo MaiorinoAbstract:Carbon dioxide (R744) is as a valid alternative to classical substances such as HFCs used in vapour compression plants. A Transcritical refrigeration Cycle is needed because the critical temperature of carbon dioxide is usually lower than the ambient temperature. In this chapter the performances of a Transcritical Cycle have been evaluated with a prototype R744 system working as a classical spit-systems to cool air. An experimental analysis has been carried out on the effect of: refrigerant charge, internal heat exchanger, heat rejection pressure on the energetic performances of the Transcritical plant. An experimental analysis of a hybrid trans-critical refrigerator-desiccant wheel system has been carried out in order to improve the COP. The experimental Transcritical Cycle has been examined in comparison with a classical vapour compression plant working with the R134a.
-
The application of a desiccant wheel to increase the energetic performances of a Transcritical Cycle
Energy Conversion and Management, 2015Co-Authors: Ciro Aprea, Adriana Greco, Angelo MaiorinoAbstract:A desiccant dehumidification system with air can be driven by low grade (
Li Minxia - One of the best experts on this subject based on the ideXlab platform.
-
Performance study of a Transcritical carbon dioxide Cycle with an expressor
Energy, 2013Co-Authors: Sun Zhili, Han Guangming, Li Minxia, Ma YitaiAbstract:This paper provides an energy efficiency study of Transcritical carbon dioxide systems by comparing six Cycles with and without an expressor (expander–compressor), which serves as an assistant compressor or the main compressor. Several different expander–compressor arrangements in the system are investigated. The mass flow rate and compression ratio of the expander–compressor are affected by these arrangements. The COP (coefficient of performance) of STM (series model of two-stage compression Transcritical CO2 Cycle with an expressor as the main compressor) is found to be the highest. Although the intermediate pressure between the two compressor stages in STS (series model of two-stage compression Transcritical CO2 Cycle with an expressor as an assistant compressor in the second stage) cannot approach the optimum value, its COP approaches that of STM at a high evaporation temperature. PSE (parallel model of single-stage compression CO2 Transcritical Cycle with an expressor) and PSS (parallel model of single-stage compression CO2 Transcritical Cycle with an expressor and gas–liquid separator) may be feasible options for reducing the dimensions of a compressor. And the expander and compressor efficiencies are very important factors for the utilization of an expressor.
-
Some design features of CO2 swing piston expander
Applied Thermal Engineering, 2005Co-Authors: Guan Hai-qing, Ma Yitai, Li MinxiaAbstract:Abstract CO2 is a potential substitute for synthesized refrigerants with favorable environmental properties. To improve the coefficient of performance (COP) of CO2 heat pump systems, a swing piston expander prototype has been developed for replacing the throttling valve based on the thermodynamic analysis of the operating conditions of a CO2 Transcritical Cycle. The measures on reducing the loss of friction and leakage are paramount important to improve the efficiency of the expander. The performance of the CO2 swing expander prototype was actually tested in a CO2 Transcritical Cycle water-to-water heat pump test rig, and the test results illustrate that the isentropic efficiency of the prototype can be more than 28% when running steadily and up to a maximum of about 44%. Some operating characteristics of the swing piston expander are presented according to the analysis of the test results.
-
Development and Experimental Study of CO2 Expander in CO2 Supercritical Refrigeration Cycles
International Journal of Green Energy, 2004Co-Authors: Li Minxia, Haiqing GuanAbstract:Abstract As one of the natural working fluids for the refrigeration system, CO2 has been attracting increasing attention over the last ten years. But CO2 has to work at the supercritical region for the so-called “condensation” process regarding the conventional refrigerants and evaporate at the two-phase region, and therefore results in larger throttling loss for the practical refrigeration application. Consequently, new technologies must be developed to improve the performance efficiency of the CO2 Transcritical Cycle, and make it to be equal or closer to that of the refrigeration system with the conventional refrigerants. In this study, an expander is employed in the CO2 Transcritical Cycle to replace the throttling valve, and as a result the throttling loss can be decreased significantly. The paper presents the development of a rolling piston expander and the activity items in the expander design, including the seal technology, the contact friction control, the suction design, etc. The performance expe...
Guan Hai-qing - One of the best experts on this subject based on the ideXlab platform.
-
Some design features of CO2 swing piston expander
Applied Thermal Engineering, 2005Co-Authors: Guan Hai-qing, Ma Yitai, Li MinxiaAbstract:Abstract CO2 is a potential substitute for synthesized refrigerants with favorable environmental properties. To improve the coefficient of performance (COP) of CO2 heat pump systems, a swing piston expander prototype has been developed for replacing the throttling valve based on the thermodynamic analysis of the operating conditions of a CO2 Transcritical Cycle. The measures on reducing the loss of friction and leakage are paramount important to improve the efficiency of the expander. The performance of the CO2 swing expander prototype was actually tested in a CO2 Transcritical Cycle water-to-water heat pump test rig, and the test results illustrate that the isentropic efficiency of the prototype can be more than 28% when running steadily and up to a maximum of about 44%. Some operating characteristics of the swing piston expander are presented according to the analysis of the test results.
-
Theoretical Research on CO_2-NH_3 Compression/Ejection Cascade Cycle
Fluid Machinery, 2005Co-Authors: Guan Hai-qingAbstract:An ejector could be adopted in refrigeration systems to reduce the irreversible energy loss of throttling process and realize a CO_2-NH_3 compression/ejection cascade Cycle.To improve the energy efficiency ratio(EER) of the CO_2 system with considering the rather large temperature gliding of the heat rejection process in the gas cooler,Based on thermodynamic analysis of the system,a corresponding model is founded.The calculation results show that the temperature of injected working fluid and the condensing temperature in the NH_3 Cycle have great impacts on the injection coefficient.Increasing the temperature of injected working fluid and decreasing the condensing temperature in the NH_3 Cycle are effective ways of improving EER.CO_2-NH_3 compression/ejection cascade Cycle has an advantage over the basic CO_2 Transcritical Cycle when the evaporating temperature and the efficiency of compressor is relatively low.Furthermore,reducing the temperature difference of the generator is helpful for increasing EER.
-
Research and Development of Rolling Piston Expander in CO_2 Transcritical Cycle--Experimental Part
Journal of Tianjin University, 2004Co-Authors: Guan Hai-qingAbstract:The replacement of the throttle valve with CO_2 expander in the system and the expansion work recovery were studied for the improvement of the coefficient of performance of the CO_2 Transcritical Cycle and reduction of the throttling energy loss.The prototypes of two-generation CO_2 rolling piston expanders were designed and developed.Their different characteristics were presented and the experimental comparisons of two expanders are conducted.The test results indicate the operability of the rolling piston expander in the supercritical two-phase region.The results show that the performance of the second generation rolling piston expander is better than the first one due to the improvement,and is that the (activities) measurements for minimum leakage and friction are powerful.There exists the optimal revolution speed of the expander in the CO_2 Transcritical Cycle to make the maximum power output produced from the expander.Hovever, there are still many problems in the design of rolling piston expander,especially the vane.A new type of vane is needed to decrease the friction between the vane and cylinder.
Ma Yitai - One of the best experts on this subject based on the ideXlab platform.
-
Performance study of a Transcritical carbon dioxide Cycle with an expressor
Energy, 2013Co-Authors: Sun Zhili, Han Guangming, Li Minxia, Ma YitaiAbstract:This paper provides an energy efficiency study of Transcritical carbon dioxide systems by comparing six Cycles with and without an expressor (expander–compressor), which serves as an assistant compressor or the main compressor. Several different expander–compressor arrangements in the system are investigated. The mass flow rate and compression ratio of the expander–compressor are affected by these arrangements. The COP (coefficient of performance) of STM (series model of two-stage compression Transcritical CO2 Cycle with an expressor as the main compressor) is found to be the highest. Although the intermediate pressure between the two compressor stages in STS (series model of two-stage compression Transcritical CO2 Cycle with an expressor as an assistant compressor in the second stage) cannot approach the optimum value, its COP approaches that of STM at a high evaporation temperature. PSE (parallel model of single-stage compression CO2 Transcritical Cycle with an expressor) and PSS (parallel model of single-stage compression CO2 Transcritical Cycle with an expressor and gas–liquid separator) may be feasible options for reducing the dimensions of a compressor. And the expander and compressor efficiencies are very important factors for the utilization of an expressor.
-
Performance Analysis of CO2 Transcritical Compression Cycle and Freon Refrigeration Cycle
Fluid Machinery, 2011Co-Authors: Zeng Xianyang, Wang Hongli, Ma YitaiAbstract:Based on refrigerants R134a,R290 and CO2,the performance comparison of three kinds of single stage compression Cycle and two stage Cycle were employed.The results shows that the performances COP of all Cycles are gradually increased with the evaporation temperature and compressor efficiency increasing,and the single stage CO2 Transcritical Cycle has an optimal discharge pressure.Replace the throttle with an expander can significantly improve the system coefficient of performance of CO2 Transcritical Cycle.The low stage compressor efficiency has an important effect on the performance of two stage compression Cycle than the high stage compressor efficiency and the CO2 Transcritical Cycle has a higher optimal intermediate pressure than other Cycles.Some fundamental data were obtained for improving Cycle performance and developing the CO2 refrigeration air-conditioning and heat pump water heater products.
-
Some design features of CO2 swing piston expander
Applied Thermal Engineering, 2005Co-Authors: Guan Hai-qing, Ma Yitai, Li MinxiaAbstract:Abstract CO2 is a potential substitute for synthesized refrigerants with favorable environmental properties. To improve the coefficient of performance (COP) of CO2 heat pump systems, a swing piston expander prototype has been developed for replacing the throttling valve based on the thermodynamic analysis of the operating conditions of a CO2 Transcritical Cycle. The measures on reducing the loss of friction and leakage are paramount important to improve the efficiency of the expander. The performance of the CO2 swing expander prototype was actually tested in a CO2 Transcritical Cycle water-to-water heat pump test rig, and the test results illustrate that the isentropic efficiency of the prototype can be more than 28% when running steadily and up to a maximum of about 44%. Some operating characteristics of the swing piston expander are presented according to the analysis of the test results.
-
Comparison and analysis of the expansion process in a CO 2 Transcritical Cycle
International Journal of Environmental Technology and Management, 2004Co-Authors: Zha Shitong, Ma YitaiAbstract:The isentropic and isenthalpic expansion processes in a CO 2 Transcritical Cycle were analysed thermodynamically. It was found that the effective refrigeration capacity of the Cycle with the isentropic expansion process is higher than the Cycle with the isenthalpic expansion process. The increment is slightly larger than the expansion work recovered because of the Transcritical nature of the Cycle. Further analysis and comparison were made for two decreasing throttling loss methods: using internal heat exchangers and using expanders instead of throttling valves. The results indicate that using high efficiency expanders in the Transcritical Cycle is the better method, and the work recovered by the expander is mainly from the flow work in the supercritical area, and from the internal energy change in the liquid-gas two-phase region. It is recommended that the flashing crash model can be used to simplify the characteristic equations of the liquid-gas two-phase adiabatic expansion process.
