Relationship between expansion ratio and heat exchanger performance of the plate fin tube type heat exchanger with inner grooved tubes

摘要

Plate fin tube type heat exchangers have been widely used in air conditioners. These heat exchangers consist of mainly aluminum fin stocks and copper tubes, and they are commonly assembled by mechanical expansion of tube inner diameter. This paper describes the investigation results of the influence of expansion ratio on heat transfer performances, and the contact condition between inner grooved copper tubes and aluminum fin stocks. The test heat exchangers were produced by using five sizes of expansion bullets and two collar hole sizes of aluminum fins. The quantification of contact condition was expressed as the electrical contact resistance. Summary of investigation results is as follows (1) The contact condition and the heat transfer performance showed peak values in expansion ratio range of 2～4%. (2) The smaller collar hole size of aluminum fin stocks showed better contact condition, and this phenomena is estimated to be caused by the copper tube's spring back after expansion. (3) The expansion ratio influenced not only the condensation performance, but also evaporation performance which had been assumed small effect because of dewed water.