Performance of a counterflow heat exchanger with heat loss through the wall at the cold end

摘要

The performance of high effectiveness heatexchangers used in cryogenic systems is strongly controlled byirreversibilities such as longitudinal heat conduction and heat leakfrom ambient. In all heat exchanger analyses, it is assumed that noheat is lost through the heat exchanger walls. In the case of small J-T refrigerators such as microminiature refrigerators, the heatexchanger cold end is almost directly connected to the evaporator,which may result in a large amount of heat loss through the heatexchanger wall at the cold end. The rate of heat loss through thewall at the cold end is also strongly dependent on the longitudinalthermal resistance of the wall. In this paper, we present therelationship between the effectiveness of a heat exchanger losingheat at the cold end and other resistances such as number oftransfer units (NTU), longitudinal thermal resistance etc. Theperformance of such heat exchangers under different operatingconditions is also discussed.