Characteristics of heat pipes with liquid-metal heat carriers under low-temperature conditions

A method is outlined for the theoretical study of the properties of heat pipes containing liquid-metal heat-transfer agents at low vaporization temperatures. This method takes into account the compressibility and friction of the vapor flow, heat-load nonequilibrium along the length of the vaporization zone, and the temperature dependence of the properties of the heat-transfer agent. It is shown that the capacity of heat pipes in sonic flow regimes depends substantially on the geometric dimensions of the vaporization zone; i.e., the diameter of the vapor duct and the ratio of zone length to diameter. The calculations also indicate that neglect of the friction of the vapor flow leads to errors of $50\%$ or more in determining the sonic limit. The theoretical results are found to be in good agreement with experimental measurements in a vapor duct and with empirical data on the sonic limit of heat transfer. The greatest discrepancy between theory and experiment does not exceed $10\%$.