Analytical and numerical simulation of the thermal performance of `miniʹ gravitational and `microʹ gravitational heat pipes

An analytical model has been developed to investigate the performance of a `miniʹ gravitational heat pipe and two `microʹ gravitational heat pipes of different sizes, using water as the refrigerant. The model has been used to determine the limits of heat transport capacity, which expresses the thermal performance of heat pipes. The model is defined in terms of the physical shape of the heat pipes and evaluates the limits of heat transport capacity as functions of the properties of the working fluid used, the inclination angle and liquid fill level. A numerical model has also been developed and used to investigate the operating characteristics of the heat pipes. The results are presented in terms of the cross-sectional areas, pressures, temperatures and mass flow rates of the liquid and vapour within the heat pipes. In general, the modelling results indicate `microʹ gravitational heat pipes have higher heat transport limits than `miniʹ heat pipes of the same cross-sectional area.