Design and Thermal-Hydraulic Performance Analysis of a Low-Temperature Heat Pipe Test Facility

Interest in heat pipe microreactors (HPMRs) has recently grown due to several unique advantages compared with other reactor types. These compact and mobile reactors are expected to find applications in a variety of fields to provide carbon-free power in remote or off-grid locations. Experimental work is needed to aid and expedite the design and licensing of future HPMRs, especially on the validation of heat pipe performance as key heat transfer components. A Low-Temperature Heat Pipe Test Facility (LTHPF) was designed and constructed according to previously developed scaling laws to bypass the difficulties of experimenting with liquid-metal working fluids by using surrogate fluids. The design, instrumentation, and experimental capabilities of the facility are described. The testing conditions, including various operating limits and the ranges of the nondimensional parameters used for scaling analysis, are reported. It is found that certain nondimensional parameters could yield a wide range over the operating conditions, whereas some showed minimal variation when water was used as the working fluid. Last, the performance of several types of wicks, including the annulus-screen, groove-screen, and wrapped-screen designs, were investigated for applications in the LTHPF. It is observed that the groove-screen wick structure provided slight improvement in capillary limits at higher temperatures and that the wrapped-screen wick yielded lower capillary limits due to the absence of a low-resistance flow path for the liquid.