Design Method Of Small Diameter Tubes Heat Exchanger For Room Air Conditioner

The heat exchanger miniaturization in room air conditioner has many advantages, such as decreasing heat exchanger cost, refrigeration charge and leakage, and as well as improving heat exchanger safety, heat exchange capacity and efficiency. The major way of heat exchanger miniaturization in room air conditioner is to utilize small diameter tubes in heat exchanger. In recent years, 9.52 mm tube is no longer widely used while 7 mm copper tube becomes the most popular tube in room air conditioner. For the promoting action of R410A substituting for R22 and heat exchanger miniaturization, the tube smaller than 7 mm tube has been used in room air conditioner. 5 mm tube heat exchanger is in production while 4 mm tube heat exchanger has been developed and 3 mm tube heat exchanger is in research. After all, the heat exchanger miniaturization is the major direction of room air conditioner research. Therefore, there is a definitely demand to study the characteristics and design method of room air conditioner with small diameter tubes.This paper investigate the characteristics of heat transfer and pressure drop inside and outside small diameter tube under operation condition of room air conditioner, which is based on the existing research inside and outside tube. And then, considering the actual design restraint of room air conditioner heat exchanger, the design method of small diameter tubes heat exchanger as well as the matching method of heat exchangers for room air conditioner is proposed under different restraints. The main works and conclusions are briefly reviewed as follows:(1) Summarize the existing research on heat exchange and pressure drop of refrigeration inside small diameter tube and analyze them under refrigeration property of air conditioner operation condition. The result is obtained that the heat exchange performance inside tube can be improved when small diameter tube is used in heat exchanger, and then, the method to define tube path number of small diameter tube heat exchanger is deduced theoretically and proved experimentally.(2) Summarize the existing research on heat exchange and pressure drop of air flow outside small diameter tube and obtain that there is no research on this subject. The existing fin used for small diameter tube is analyzed on air side heat exchange performance and fin efficiency under air conditioner operation condition. The result is obtained that the existing fin is not suit for small diameter tube. And then, a design method is proposed for louver fin of small diameter tube, and, a designed proposal and its result are also given in this paper.(3) Transform the design objective of small diameter tube heat exchanger into mathematical equations according to the design restrain of room air conditioner. Based on existing heat exchanger simulation and optimization software, the design methods of enumeration method for constant heat exchanger structure and surface response method for variation heat exchanger structure are proposed, and both of them are also confirmed by experimental data. The design process and system match of room air conditioner under single cooling and heat pump is also mentioned.(4) Illustrate the way of how to use small diameter tube in indoor and outdoor unit by an actual room air conditioner, both design process and design result are given in detail. According to the design proposal, the performance of small diameter tube room air conditioner is simulated under single cooling and heat pump, and the influence of different compressor is also analyzed.