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Performance characteristics of low global warming potential R134a alternative refrigerants in ejector-expansion refrigeration system

Mishra S., Sarkar J.

Archives of Thermodynamics

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2016

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Vol. 37, no. 4

55--72

EN

Performance assessment of ejector-expansion vapor compression refrigeration system with eco-friendly R134a alternative refrigerants (R152a, R1234yf, R600a, R600, R290, R161, R32, and propylene) is presented for air-conditioning application. Ejector has been modeled by considering experimental data based correlations of component efficiencies to take care of all irreversibilities. Ejector area ratio has been optimized based on maximum coefficient of performance (COP) for typical air-conditioner operating temperatures. Selected refrigerants have been compared based on area ratio, pressure lift ratio, entrainment ratio, COP, COP improvement and volumetric cooling capacity. Effects of normal boiling point and critical point on the performances have been studied as well. Using ejector as an expansion device, maximum improvement in COP is noted in R1234yf (10.1%), which reduces the COP deviation with R134a (4.5% less in basic cycle and 2.5% less in ejector cycle). Hence, R1234yf seems to be best alternative for ejector expansion system due to its mild flammability and comparable volumetric capacity and cooling COP. refrigerant R161 is superior to R134a in terms of both COP and volumetric cooling capacity, although may be restricted for low capacity application due to its flammability.

2

Operating characteristics of transcritical CO2 heat pump for simultaneous water cooling and heating

Sarkar J., Bhattacharyya S.

Archives of Thermodynamics

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2012

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Vol. 33, no. 4

23-40

EN

The effects of water-side operating conditions (mass flow rates and inlet temperatures) of both evaporator and gas cooler on the experimental as well as simulated performances (cooling and heating capacities, system coefficient of performance (COP) and water outlet temperatures) of the transcritical CO2 heat pump for simultaneous water cooling and heating the are studied and revised. Study shows that both the water mass flow rate and inlet temperature have significant effect on the system performances. Test results show that the effect of evaporator water mass flow rate on the system performances and water outlet temperatures is more pronounced (COP increases by 0.6 for 1 kg/min) compared to that of gas cooler water mass flow rate (COP increases by 0.4 for 1 kg/min) and the effect of gas cooler water inlet temperature is more significant (COP decreases by 0.48 for given range) compared to that of evaporator water inlet temperature (COP increases by 0.43 for given range). Comparisons of experimental values with simulated results show the maximum deviation of 5% for cooling capacity, 10% for heating capacity and 16% for system COP.

3

Thermodynamic optimization of irreversible heat pumps

Sarkar J., Bhattacharyya S., Ramgopal M.

Archives of Thermodynamics

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2008

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Vol. 29, no. 3

59-68

EN

The performance of an irreversible heat pump for simultaneous cooling and heating applications, for which irreversibilities results from both the finite size and finite rate of heat conduction, as well as compression and expansion, is studied. The relation between optimum system coefficient of performance and optimal rate of combined cooling and heating output has been established. Also relations for optimal cold and hot fluid temperatures have been derived and performance of irreversible heat pump has been discussed. The optimal correlations have been simplified for endoreversible cycle and compared with the relation for only cooling or hearting in the literature. Consequently, optimal relations for heat conductance inventory, residence time and mass distribution between the heat exchangers have been established.