Experimental Investigation On Pinch Point And Maximum Temperature Difference Of Zeotropic Refrigerant In Horizontal Tube-in-tube Evaporator

This paper presents an experimental investigation on pinch point and maximum temperature difference of zeotropic refrigerant in horizontal tube-in-tube evaporator. The positions of pinch point and maximum temperature difference are obtained through experimental investigation exactly. And the influence factors on the position of pinch point and maximum temperature difference are also analyzed. In addition, the variable composition of zeotropic refrigerant is investigated by gas chromatograph analysis in different positions along evaporator.Firstly, the experimental system utilizing zeotropic refrigerant as the working fluid is designed and constructed, and its experimental principle is illustrated too. To verify the reliability of experimental result, the heat balance of evaporator and the pressure drop of refrigerant in evaporator are analyzed and estimated.Based on this experimental system, the experiments utilizing R290/R600 (mass fraction 0.15/0.85) and R245fa/R152a (mass fraction 0.6/0.4) as working fluid are carried out. The occurrences of pinch point and maximum temperature difference are observed, and positions of them are found exactly. By comparing experimental result with theoretical prediction result, the phenomenon called the non-linear variation of temperature of heat transfer fluid along the evaporator is discovered, and it influences the position of pinch point and maximum temperature different.Through the experiments in different working conditions, the influence factors of the position of pinch point and maximum temperature difference is revealed. The analysis results show that: the position of pinch point moves to the inlet of refrigerant in evaporator, when the inlet temperature of heat transfer fluid increasing, or the flux of refrigerant increasing, or the flux of heat transfer fluid decreasing.Finally, the experimental and theoretical investigations on the component of zeotropic refrigerant are carried out at different positions of evaporator. By comparative analysis, this paper indicates that the closer the position get to the outlet of refrigerant in evaporator, the lower content of R290 and higher content of R600 the gas phase will have at gas-liquid equilibrium.