An Experimental and Numerical Study of an Air-to-Air Heat Exchanger Using Liquid Reservoir Variable Conductance Heat Pipes

摘要

This report documents a study of a prototype air-to-air heat exchanger of which the thermal conductivity is governed by the reservoir temperature of the heat pipes. The work is introduced with a brief review of the basic operating principles of heat pipes and of the various existing schemes for variable conductance. An experimental facility, incorporating a computerized data acquisition system, was developed to investigate the steady state performance characteristics of the heat exchanger over a wide range of air inlet temperatures, mass flow rates, and reservoir temperatures. Some tests were conducted imposing a single operating temperature on all of the heat pipes, while in others the heat pipe rows were allowed to operate independently. The results are expressed in terms of heat exchanger effectiveness versus normalized reservoir temperature for various values of the ratio of the mass flow rates of the air streams. Conclusions are drawn as to the internal behaviour of this type of heat pipes under various operating regimes. An original computer model is presented which combines quasi analytical solution for the air and fin temperature profiles in the heat exchanger with a heat pipe simulation routine based on the hydrodynamic equations involved in the working fluid cycle. Computational results are are shown, and a brief comparison with the experiments is made. Possible modifications that would improve the accuracy and the versatility of the program are discussed.