Heat transfer limit resulting from heat leak in a cryogenic loop heat pipe

Abstract

Cryogenic loop heat pipes (CLHP) are developing rapidly for the increasing demand for both space and terrestrial applications. The heat transfer limits are important features for evaluating the performance of CLHPs. In this paper, a CLHP experimental setup using nitrogen as the working fluid was built, and the temperature distribution of key components and the pressure difference across the evaporator were measured. The heat transfer limit resulting from heat leak is analyzed and compared with other two heat transfer limits, namely, the capillary limit and condenser heat transfer capacity limit. In this experiment, the heat transfer limit resulted from the heat leak rather than the other two factors, and the heat transfer limits were 13.2 W and 17.0 W under the charging pressure of 0.98 MPa and 1.56 MPa. A mathematical model to predict the heat transfer limit is established and experimentally validated. Model-based parametric analysis is conducted to investigate the effects of charging pressure, convection heat transfer coefficient, heat sink temperature and heat leak from the environment on the heat transfer limits of the CLHP.