Numerical investigation of hydrodynamics and thermal performance of a specially configured heat pipe for high-temperature thermal energy storage systems

Abstract

In the present study, a complex geometry, high temperature heat pipe was investigated numerically. The heat pipe was designed specifically to improve the performance of the thermal energy storage system incorporated in a concentrated solar power system. Due to the complexity of the heat pipe geometry, a new numerical approach was developed. The heat conduction in the wall and wick regions was included in the two-dimensional axisymmetric model. The compressibility of the working fluid and viscous dissipation were taken into account. Due to the high expansion ratio from adiabatic section to condenser, high speed vapor flow impinges on the condenser wall. The combined vapor jet impingement and condensation on the condenser wall was modeled by attaching a porous layer. This porous layer forces the impinging vapor jet to split out radially while it allows the wall suction. The heat rejection via the vapor condensation was estimated from the mass flux by energy balance at vapor–liquid interface. The heat transfer limits due to heat pipe geometry, working fluid, wick structure, and operational temperature were calculated. The vapor–wick interface temperature predicted by the current simulation agrees very well with the available experimental data. The performance of the heat pipe was evaluated by calculating the corresponding thermal resistance. The results showed that the thermal resistance decreases with the increase of the operating temperature and vapor radius while increases with the increase of the heat input. It was also shown that, for the cases studied, adiabatic section radius of 15 mm is sufficient. Further increase of the radius does not reduce the thermal resistance of the heat pipe.