A review of the development of a precooler for the air-turboramjet expander-cycle (ATREX) engine is given. Three types of precooler for the ATREX engine ground-test model were designed, manufactured, and tested under sea-level static conditions. The results suggested two problems affecting the precooler performance, heat transfer rate and airflow pressure drop. One is nonuniformity of the airflow through the tube banks. The other problem is frost formation on the heat transfer surfaces. Concerning nonuniformity of airflow, the shell configuration was modified based on analysis by computational fluid dynamics calculation. To improve the precooler performance under frosting condition, a new method to add a condensable gas into the airflow was proposed and examined by experiments on a subscale heat exchanger model. Addition of a small quantity of ethanol can effectively restrain the decline of the precooler performance due to frost formation.
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