Investigation On Thethermodynamic Performance And Typical Application Of Two Liquid-Vapor Separation Condensers With Different Structures

With energy demand continuous increase and requirement of utilization quality improve continuously, high-efficiency heat transfer technique have become an important part in energy field. Base on the high vapor quality condensation, condensation with liquid-vapor separation is a novel technique to enhanced heat transfer. The study of condensation with liquid-vapor separation will make contribution to the energy saving and emission reduction in air conditioning industry and refrigeration, metallurgical industry and power generation industry.This paper comprehensively studies the thermodynamic performance of liquid-vapor separation microchannel condenser and liquid-vapor separation conventional condenser by theoretical method and experimental method. Basic on the method of sectional calculation, we use tube pass optimization computational procedures to calculate the effect of pass number and tube number per pass on the thermodynamic performance of liquid-vapor separation microchannel condenser (LSMC) and liquid-vapor separation conventional condenser (LSC). After obtaining the optimal tube pass liquid-vapor separation condensers, the thermodynamic of the condensers are tested. Finally, an air conditioning system (1.5 HP) with double-row condenser is used as the original unit and study the effect of liquid-vapor separation condenser on the refrigerating capacity and EER of the air conditioning system.Under refrigerant mass flow rate range of 0.017 kgs-1 to 0.029 kgs-1, refrigerant vapor quality after liquid-vapor separation is 0.75 to 1.0, effect of pass number and tube number per pass on the thermodynamic performance of the LSMC are studied theoretically. The results indicate pass number and tube number per pass have obvious effect on the condensation heat transfer coefficient and total pressure drop of the LSMC. Pass number shows more importance on the condenser optimization. At the same total tube number and heat load, the condensation heat transfer coefficient of optimal 5-pass LSMC are 11.9%～ 13.8% higher than those of optimal 3-pass LSMC, on the other hand, the total pressure drop of optimal 5-pass LSMC are 138.7%～155.8% higher than those of optimal 3-pass LSMC. In addition, the more thoroughly liquid-vapor separation of refrigeration, the better thermodynamic performance of the LSMC, for example, when the vapor quality of the refrigerant from 0.75 raised to 1.0, the condensation heat transfer coefficient of the LSMC increase by 3.1%-5.6%, and the total pressure drop decreased by 7.3%～11.9%.Under constant heat flux, R134a is employed to study the thermodynamic performance of the D-LSMC at refrigerant mass flux 450kgm-2s-1～770 kgm-2s-1 and refrigerant vapor quality 0.27 to 0.73. The results show the condensation heat transfer coefficient of the LSMC exceeds that of common single-row parallel flow microchannel condenser at mass flux of about 570 kgm-2s-1 and average vapor quality of 0.58. At mass flux of about 770 kgm-2s-1, the condensation heat transfer coefficient of the LSMC is 6.7% higher than that of common single-row parallel flow microchannel condenser.Under constant heat flux, R134a is employed to study the thermodynamic performance of the D-LSMC at high refrigerant mass flux (585 kgm-2s-1～874 kgm-2s-1) and high refrigerant vapor quality(about 0.78). The results show the condensation heat transfer coefficient of the D-LSMC is about 14.2% higher than those of common double-row parallel flow microchannel condenser. In addition, the heat transfer uniformity between the front row and the back row of the D-LSMC is better than the common double-row parallel flow microchannel condenser, which the heat load of the back row is 39.4% of the whole condenser. According to the average wall temperatures between both rows, the pressure drop uniformity between both rows of the D-LSMC is better than that of common double-row parallel flow microchannel condenser.R134a is employed to study the thermodynamic performance of the LSC with inner diameter of 7mm and finnd-tube condenser at conditions of constant air mass flow or constant heat flux. The results indicate the condensation heat transfer coefficient of the LSC exceed the common finnd-tube condenser at high refrigerant mass flux (about 560 kgm-2s-1) and high average vapor quality(about 0.7). And the total pressure drop of the LSC is over 30% lower than the finnd-tube condenser. The results also show the effect of liquid-vapor separation on thermodynamic performance of the LSC is weaker than that of the LSMC. Basic on the second law of thermodynamics evaluation criterion, the thermodynamic performance of the LSC is better than that of the common finnd-tube condensers.Finally, an air conditioning system (1.5 HP) with double-row condenser is used as the original unit and study the effect of liquid-vapor separation condenser on the refrigerating capacity and EER of the air conditioning system. Under the condition of GB/T 17758-2010 (outdoor dry bulb/wet bulb is 35℃/24℃, indoor dry bulb/wet bulb is 27℃/19℃), the 1.5 HP air conditioner with L-type double-row liquid-vapor separation condenser (L-DLSC unit) is tested to obtain the optimal refrigerant charge of 1150g and capillary length of 400mm. At GB/T 17758-2010 conditions and outdoor tempareture of 27℃ to 43℃, the compressor power consumption of the L-DLSC unit is lower than that of the original unit, the heat transfer capacity of the L-DLSC is larger, and the EER and cooling capacity of the L-DLSC unit is 9.5% and 4.3% lower than the original unit. The pressure drop of the L-DLSC is much lower than that of the original double-row serpentine condenser, but the heat transfer uniformity between both rows of the L-DLSC is a little worse than that of the "back row inlet and front row outlet" double-row serpentine condenser. Basic on the exergy efficiency evaluation criterion, the exergy efficiency of the L-DLSC unit is 0.7%～2.5% higher than that of the original unit at experimental conditions, which indicates the system performance of the L-DLSC unit is better than that of the original unit.Above all, the thermodynamic performances of liquid-vapor separation microchannel condenser and liquid-vapor separation conventional condenser are better than the common condensers. The refrigerating capacity and EER of the air conditioning system with liquid-vapor separation condensers are better than the original air conditioning system.