An Extension of a Steady-State Model for Fin-and-Tube Heat Exchangers to Include Those Using Capillary Tubes for Flow Control

摘要

A multipath fin-and-tube heat exchanger may use capillary tubes to control the refrigerant distribution among the paths in order to improve the performance of the heat exchanger. The existing heat exchanger models are not developed for those using capillary tubes for flow control, and the existing algorithms for solving the refrigerant distribution among the paths cannot be directly extended to those using capillary tubes for flow control due to the choked characteristics of capillary tubes. In order to extend the existing models for heat exchangers to those using capillary tubes for flow control, two auxiliary equations are introduced for solving the refrigerant distribution among the paths. A share-distribution method is applied for the case that one or several refrigerant flows in capillary tubes are choked during the iteration process for solving the refrigerant distribution among the paths, and a standard-path-based method is applied for the case that all capillary tubes are choked during the iteration process. Experiments are performed for evaluating the extended model and algorithm. The evaluation results show that the difference between the calculated cooling capacity and the experimented one is less than ±5%, while the difference between the calculated refrigerant side pressure drop and experimented one is less than ±15%.