Simultaneous pressure-temperature measurements in a heat pipe

When a heat pipe operates with a large temperature difference between the two ends, the vapor liquid combination is not in thermodynamic equilibrium. The experiments showed that the vapor liquid mixture is in a higher state of saturation at the condenser as compared to other sections of the pipe. Correlations were obtained that relate the coefficient of thermal coupling alpha to the evaporator flux and mass of NCG (non-condensable gas). As mass of NCG is increased in the heat pipe, the thermal coupling coefficient alpha decreases. The evaporator heat flux is directly proportional to alpha. The coefficient alpha is related to the pressures and temperatures at the evaporator, condenser and the adiabatic sections. In conclusion, for heat pipes that do not operate in thermodynamic equilibrium, correlations were obtained between the operating conditions of the heat pipe, the evaporator heat flux and the mass of NCG.