Transient response of a liquid metal heat pipe

Abstract

The purpose of this research was to investigate the transient response of a liquid metal heat pipe under external radiant thermal loading at the condenser section. An experiment was conducted using an Inconel screen wick sodium heat pipe. The external wall axial temperature profile vs time was recorded for various radiant heat fluxes and condenser coverages. A simple one-dimensional model was developed. The theoretically determined temperature vs time profiles compared closely to those obtained experimentally. The analytical model predicts transient vapor mass flow rates and condensation/evaporation rates along the pipe for a variety of condenser heat load conditions. From this information, heat-pipe reversal and incipient failure can be predicted. The model also includes a dryout prediction based on the maximum capillary transport limit. This model can be easily modified for use with a variety of different heat-pipe designs and heat loading conditions. Nomenclature Ac = surface area of the condenser As = surface area of the condenser radiant heat input C = effective thermal capacity h = enthalpy of fluid L = length ra = mass m = mass flow rate me c = evaporation or condensation rate n = number of nodes Pin = equivalent power input at the evaporator Qext = net external heat input rate into a given section grad = heat rejection due to radiation qc = condenser external radiant heat flux T = temperature 7^av = averaged temperature of radiant heater surface / = time X = heat-pipe axial position € = heat-pipe surface emissivity X = latent heat of vaporization ju, = dynamic viscosity p = density a = Stefan-Boltzmann constant a, = liquid sodium surface tension