Experimental Study On Performance Of Heat Transfer And Pressure Drop Of Fin-and-tube Evaporators In Variable Frequency Air-condition System

At present, variable frequency technology is used generally, heat transfer enhancementtechnology is taken as the main technical means for improving energy efficiency ratio ofair-conditioner. Therefor, in this paper, wind tunnel test technique is uesd to studycharacteristics of heat transfer and pressure drop of wavy and louver fin-and-tube heatexchangers in variable frequency air conditioning system. We intend to provide somesuggestions for improving fin-and-tube evaporators’ performance.After error analysis for used test system, uncertainty of airside heat transfer factor is±10.3%～±7.1%, and uncertainty of friction factor is±4.2%～±1.6%. Threlkeld methodbased on enthalpy difference under wet condition is chose to process test data, then we can getfollowing conclusions:With increase of compressor frequency, both boiling heat transfer coefficient andpressure drop of refrigerant increase, and under same face velocity and same frequency, heattransfer coefficient and pressure drop of wavy fin-and-tube evaporator are all higher thanthese of louver fin-and-tube evaporator. The rate of water condensate forms on both finsurface increases with increase of compressor frequency. When the frequency is30Hz, withincrease of face velocity, water condensate rate of wavy fin decreases, but after30Hz, itincreases. For the louver fin, it shows positive correlation with face velocity when thefrequency is more than40Hz.The friction factors of both fins decrease when compressor frequency increases, f factorof louver fin is about two times than that of wavy fin, and the experimental value of each f isvery close to calculated value of correlation. Both of j factors indicate negative correlationwith compressor frequency, and the j factor of wavy fin decreases clearly, on the contrary,louver fin’s does not change significantly. The experimental value of each j displays moreerror with predicted value.For the evaporator with multi-flow circuits, the flash gas after throttling process canresults in quality of refrigerant at inlet of each circuit being inconsistent, and then causes nonuniform heat exchange, according to this situation, secondary throttling and improvingdegree of supercooling of refrigerant are good solutions.