TRANSCRITICAL CO2 REFRIGERATION SYSTEMS: COMPARISON WITH CONVENTIONAL SOLUTIONS AND APPLICATIONS

2012 ◽  
Vol 20 (04) ◽  
pp. 1250017 ◽  
Author(s):  
JAHAR SARKAR
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Comparative Study ◽  
Working Fluid ◽  
Vapor Compression ◽  
Vapor Compression Cycle ◽  
Compression Cycle ◽  
Experimental Researches ◽  
Transfer Properties ◽  
Good Heat

Carbon dioxide (CO2) is one of the natural refrigerants which can be used as working fluid in various refrigeration applications along with the ammonia and hydrocarbons due to its eco-friendliness, higher volumetric capacity, good heat transfer properties, etc. The present article consists of two parts: A detailed comparative study of CO2 -based transcritical refrigeration systems with conventional refrigerants-based systems in terms of both thermodynamic and heat transfer performances, and review of both theoretical and experimental researches on transcritical CO2 vapor compression cycle for various refrigeration applications including commercial product status. Suitability of the CO2 system in specific refrigeration application is also discussed.

scholarly journals Performance Analysis of Solar Combined Ejector-Vapor Compression Cycle Using Environmental Friendly Refrigerants

2013 ◽  
Vol 14 (1) ◽  
Author(s):  
A. B. Kasaeian ◽  
S. Daviran
Keyword(s):  
Internal Heat ◽  
Exergy Efficiency ◽  
Operating Conditions ◽  
Working Fluid ◽  
Vapor Compression ◽  
Refrigeration System ◽  
Environmental Friendly ◽  
Vapor Compression Cycle ◽  
Compression Cycle ◽  
Vapor Compression Refrigeration

In this study, a new model of a solar combined ejector-vapor compression refrigeration system has been considered. The system is equipped with an internal heat exchanger to enhance the performance of the cycle. The effects of working fluid and operating conditions on the system performance including COP, entrainment ratio (ω), compression ratio (rp) and exergy efficiency were investigated. Some working fluids suggested are: R114, R141b, R123, R245fa, R600a, R365mfc, R1234ze(e) and R1234ze(z). The results show that R114 and R1234ze(e) yield the highest COP and exergy efficiency followed by R123, R245fa, R365mfc, R141b, R152a and R600a. It is noticed that the COP value of the new solar ejector-vapor compression refrigeration cycle is higher than that of the conventional ejector cycle with R1234ze(e) for all operating conditions. This paper also demonstrates that R1234ze(e) will be a suitable refrigerant in the solar combined ejector-vapor compression refrigeration system, due to its environmental friendly properties and better performance. ABSTRAK: Kajian ini menganalisa model baru sistem penyejukan mampatan gabungan ejektor-wap solar.Sistem ini dilengkapi dengan penukar haba dalaman untuk meningkatkan prestasi kitaran.Kesan bendalir bekerja dan keadaan operasi pada prestasi sistem termasuk COP, nisbah pemerangkapan (ω), nisbah mampatan (rp) dan kecekapan eksergi telah disiasat.Beberapa bendalir bekerja yang dicadangkan adalah: R114, R141b, R123, R245fa, R600a, R365mfc, R1234ze(e) dan R1234ze(z).Hasil kajian menunjukkan R114 dan R1234ze(e) menghasilkan COP dan kecekapan eksergi tertinggi diikuti oleh R123, R245fa, R365mfc, R141b, R152a dan R600a.Didapati nilai COP kitaran penyejukan mampatan bagi ejektor-wap solar baru adalah lebih tinggi daripada kitaran ejektor konvensional dengan R1234ze(e) bagi semua keadaan operasi.Kertas kerja ini juga menunjukkan bahawa R1234ze(e) boleh menjadi penyejuk yang sesuai dalam sistem penyejukan mampatan gabungan ejektor -wap solar, kerana ianya mempunyai prestasi yang lebih baik serta sifatnya yang lebih mesra alam sekitar. KEYWORDS: environmental friendly refrigerants; solar combined ejector-vapor compression cycle; R1234ze(e)

The Steady-State Modeling and Analysis of a Two-Loop Cooling System for High Heat Flux Removal

2009 ◽  
Author(s):  
Rongliang Zhou ◽  
Juan Catano ◽  
Tiejun Zhang ◽  
John T. Wen ◽  
Greg J. Michna ◽  
...  
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Heat Exchangers ◽  
Cooling System ◽  
High Heat ◽  
System Structure ◽  
High Heat Flux ◽  
Vapor Compression ◽  
Vapor Compression Cycle ◽  
Compression Cycle

Steady-state modeling and analysis of a two-loop cooling system for high heat flux removal applications are studied. The system structure proposed consists of a primary pumped loop and a vapor compression cycle (VCC) as the secondary loop to which the pumped loop rejects heat. The pumped loop consists of evaporator, condenser, pump, and bladder liquid accumulator. The pumped loop evaporator has direct contact with the heat generating device and CHF must be higher than the imposed heat fluxes to prevent device burnout. The bladder liquid accumulator adjusts the pumped loop pressure level and, hence, the subcooling of the refrigerant to avoid pump cavitation and to achieve high critical heat flux (CHF) in the pumped loop evaporator. The vapor compression cycle of the two-loop cooling system consists of evaporator, liquid accumulator, compressor, condenser and electronic expansion valve. It is coupled with the pumped loop through a fluid-to-fluid heat exchanger that serves as both the vapor compression cycle evaporator and the pumped loop condenser. The liquid accumulator of the vapor compression cycle regulates the cycle active refrigerant charge and provides saturated vapor to the compressor at steady state. The heat exchangers are modeled with the mass, momentum, and energy balance equations. Due to the projected incorporation of microchannels in the pumped loop to enhance the heat transfer in heat sinks, the momentum equation, rarely seen in previous refrigeration system modeling efforts, is included to capture the expected significant microchannel pressure drop witnessed in previous experimental investigations. Electronic expansion valve, compressor, pump, and liquid accumulators are modeled as static components due to their much faster dynamics compared with heat exchangers. The steady-state model can be used for static system design that includes determining the total refrigerant charge in the vapor compression cycle and the pumped loop to accommodate the varying heat load, sizing of various components, and parametric studies to optimize the operating conditions for a given heat load. The effect of pumped loop pressure level, heat exchangers geometries, pumped loop refrigerant selection, and placement of the pump (upstream or downstream of the evaporator) are studied. The two-loop cooling system structure shows both improved coefficient of performance (COP) and CHF overthe single loop vapor compression cycle investigated earlier by authors for high heat flux removal.

Rechargeable Personal Air Conditioning Device

2016 ◽  
Author(s):  
Yilin Du ◽  
Jan Muehlbauer ◽  
Jiazhen Ling ◽  
Vikrant Aute ◽  
Yunho Hwang ◽  
...  
Keyword(s):  
Air Conditioning ◽  
Cooling System ◽  
Cooling Capacity ◽  
Comfort Level ◽  
Vapor Compression ◽  
Air Conditioning System ◽  
System A ◽  
Single Person ◽  
Vapor Compression Cycle ◽  
Compression Cycle

A rechargeable personal air-conditioning (RPAC) device was developed to provide an improved thermal comfort level for individuals in inadequately cooled environments. This device is a battery powered air-conditioning system with the phase change material (PCM) for heat storage. The condenser heat is stored in the PCM during the cooling operation and is discharged while the battery is charged by using the vapor compression cycle as a thermosiphon loop. The conditioned air is discharged towards a single person through adjustable nozzle. The main focus of the current research was on the development of the cooling system. A 100 W cooling capacity prototype was designed, built, and tested. The cooling capacity of the vapor compression cycle measured was 165.6 W. The PCM was recharged in nearly 8 hours under thermosiphon mode. When this device is used in the controlled built environment, the thermostat setting can be increased so that building air conditioning energy can be saved by about 5–10%.

Analysis and Operation Optimization of Recompression Supercritical Carbon Dioxide Power Generation System Based on the Power Flow Method

2018 ◽  
Author(s):  
Xia Li ◽  
Qun Chen ◽  
Xi Chen
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Power Generation ◽  
Mass Flow ◽  
Power Flow ◽  
Heat Transfer Process ◽  
Working Fluid ◽  
Generation System ◽  
Fluid Properties ◽  
Power Generation System

Due to the peculiar physical properties, supercritical carbon dioxide (sCO2) is considered as a promising working fluid in power generation cycles with high reliability, simple structure and great efficiency. Compared with the general thermal systems, the variable properties of sCO2 make the system models obtained by the traditional modelling method more complex. Besides, the pressure distribution in the system will affect the distribution of the fluid properties, the fluid properties influencing the heat transfer process will produce an impact on the temperature distribution which will in turn affect the pressure distribution through the mass flow characteristics of all components. This contribution introduces the entransy-based power flow method to analyze and optimize a recompression sCO2 power generation system under specific boundary conditions. About the heat exchanger, by subdividing the heat transfer area into several segment, the fluid properties in each segment are considered constant. Combining the entransy dissipation thermal resistance of each segment and the energy conservation of each fluid in each segment offers the governing equations for the whole heat transfer process without any intermediate segment temperatures, based on which the power flow diagram of the overall heat transfer process is constructed. Meanwhile, the pressure drops are constrained by the mass flow characteristics of each component, and the inlet and outlet temperatures of compressors and turbines are constrained by the isentropic process constraints and the isentropic efficiencies. Combining the governing equations for the heat exchangers and the constraints for turbine and the compressors, the whole system is modeled by sequential modular method. Based on this newly developed model, applying the genetic algorithm offers the maximum thermal efficiency of the system and the corresponding optimal operating variables, such as the mass flow rate of the working fluid in the cycle, the heat capacity rate of the cold source and the recompression mass fraction under the given heat source. Furthermore, the optimization of the system under different boundary conditions is conducted to study its influence on the optimal mass flow rate of the working fluid, the heat capacity of the cold source and the maximum system thermal efficiency. The results proposes some useful design suggestions to get better performance of the recompression supercritical carbon dioxide power generation system.

scholarly journals Dryout avoidance control for multi-evaporator vapor compression cycle cooling

2015 ◽  
Vol 160 ◽  
pp. 266-285 ◽  
Author(s):  
Daniel T. Pollock ◽  
Zehao Yang ◽  
John T. Wen
Keyword(s):  
Vapor Compression ◽  
Vapor Compression Cycle ◽  
Compression Cycle ◽  
Avoidance Control

Performance evaluation of a combined ejector-vapor compression cycle

2013 ◽  
Vol 55 ◽  
pp. 331-337 ◽  
Author(s):  
Jia Yan ◽  
Wenjian Cai ◽  
Lei Zhao ◽  
Yanzhong Li ◽  
Chen Lin
Keyword(s):  
Performance Evaluation ◽  
Vapor Compression ◽  
Vapor Compression Cycle ◽  
Compression Cycle
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