Current capabilities of “HPTAM” for modeling high-temperature heat pipes’ startup from a frozen state

Abstract

The Heat Pipe Transient Analysis Model “HPTAM” has been developed at the University of New Mexico’s Institute for Space and Nuclear Power Studies for simulating the transient and steady state operation as well as the startup of alkali-metal and low-temperature heat pipes from a frozen state. This model has been subject to continuous upgrade and verification since the early nineties using experimental data for water, sodium, and lithium heat pipes. Some of the current capabilities of HPTAM include tracking: (a) the progression of the 2-D thaw front in the wick and the transition fronts separating the successive flow regimes (free-molecular, transition, and continuum) in the vapor core; (b) the liquid circulation in the wick and in the annular space that may be incorporated by design between the wick and the heat pipe wall; (c) the formation of the wet point at the wick-vapor interface and its progression toward the condenser; (d) the excess liquid volume resulting from the decrease in density of the working fluid upon thaw and heating up to the operating temperature, and its accumulation at the end of the condenser section; (e) the change in the local radius of curvature of the liquid meniscus in the surface pores of the wick and incipient dryout; (f) the sublimation of the frozen working fluid in the evaporator and resolidification in the adiabatic and condenser sections early during the startup from a frozen state; and (g) the changes in the local vapor velocity and the liquid velocity and temperature distributions. The simulation capabilities of HPTAM are reviewed and examples of the code verification results using experimental data for the startup of sodium and lithium heat pipes from a frozen state are presented and discussed. HPTAM employs a very stable and efficient numerical technique and may run at twice the real time on a 700-MHz PC.