Experimental investigation on temperature profile and pressure drop in two-phase heat exchanger for mixed refrigerant Joule-Thomson cryocooler

摘要

The heat exchanger of a mixed refrigerant Joule-Thomson (MR J-T) cryocooler forms a very important component of the cycle. The working fluid in such a heat exchanger consists of a mixture of gases which undergo condensation and boiling heat transfer simultaneously. The design of these heat exchangers, therefore, is crucial; however, heat transfer data related to such heat exchangers is not available. In the present work, temperature distributions of hot and cold fluid along the length of the helical coil heat exchanger are measured experimentally. The effect of mixture compositions on the temperature distributions in the heat exchanger is studied. The performance of the heat exchanger is analyzed in terms of overall heat transfer coefficient and the heat transfer rate. It was found that the higher values of overall heat transfer coefficient leads to decreasing cool-down time for MRJ-T cryocooler. However, to achieve lower refrigeration temperatures, the greater part of the heat exchanger should experience two-phase flow and the temperature profiles should be linear. Pressure drop studies reveal that the total pressure drop for the evaporating cold stream is crucial, which strongly depends on the mixture composition and operating conditions.