A mathematical model for estimation of the maximum heat transfer capacity of tubular heat pipes

Abstract

Heat pipes are unique in their extremely high thermal conductivity and have high potential applications in the fields of heat recovery and renewable energy. The maximum heat transfer capacity of a heat pipe is determined by viscous, sonic, capillary, entrainment, and boiling limitations. There are dozens factors affecting the maximum capacity, for instance, the size of heat pipes, the capillary structure, the working fluids, and the operating condition. It would be difficult to design a high capacity heat pipe without a computational-aided tool. In this paper, a simple mathematical model is presented for quick estimation of the maximum heat transfer capacity of tubular water heat pipes with mesh wicks. The model prediction agrees well with other literatures and experimental data. To better understanding of heat pipes, with the model, a case study of a 2 meter long heat pipe for air-to-air heat exchanger application was performed. The influence of the evaporation temperature, the inclination angle, the mesh number, and the mesh layer on the maximum heat transfer capacity (Qmax) was analyzed. Results showed that their trends were nonmonotonic, and highly depending on the evaporation temperature. The simple mathematical model could serve as a handy tool for quick evaluation of Qmax as well as for speedup of a heat pipe design.