Challenges and Fundamentals of Modeling Heat Pipes' Startup from a Frozen State

摘要

Alkali metal heat pipes are being used in a variety of space nuclear power applications, including cooling of nuclear reactors and heat rejection radiators. Candidate working fluids for these heat pipes, in an order of increasing operation temperature, are potassium (700-950 K), sodium (800-1100 K), and lithium (1100 K-1600 K), which are frozen at startup conditions. The startup of alkali metal heat pipes from a frozen state poses a number of complex issues and challenges, some of which are reviewed and discussed in this paper. In addition, the selection of the working fluid, wick and wall materials, and the operation limits of the heat pipes are briefly reviewed, including the sonic limit and the change in the vapor flow regimes during the startup from a frozen state. The successive processes occurring during the startup of a radiatively-cooled sodium heat pipe are also presented and discussed.