Modeling and simulation of large-scale separated heat pipe with low heat flux for spent fuel pool cooling

Highlights: • Numerical model for large-scale separated heat pipe is presented. • Heat transfer capacity of heat pipe varies in a wide range. • Limited by heat pipe filling ratio, vapor quality at condenser exit is always zero. • Water heat pipe performs poorly in long distance heat transport applications. • Ammonia and R134a heat pipes are preferable for long distance applications. -- Abstract: The large-scale separated heat pipe consisting of large-diameter evaporators and condensers and tens of meters of connection tube is a promising approach to cool the spent fuel pool passively within a small temperature difference. In this study, a lumped model for this kind of large-scale separated heat pipe is developed. Ammonia, R134a and water are used as the working fluid. Due to the large diameter and low wall heat flux, flow patterns in the evaporator can be different from those in conventional pipes, which should be considered in the model. The simulation results agree with experimental data well. It is that the heat pipe changes its heat transfer capacity in a wide range with the variation of heat source temperature, and vapor quality at condenser exit is always 0, which indicates that the downcomer is always partially liquid filled. Heat transfer performance of heat pipe in long distance heat transport applications is also presented. In these applications, there exist large pressure losses, especially in the water heat pipe, which causes serious deterioration of heat transfer performance. However, for the ammonia and R134a heat pipe, the influence of heat transport distance is limited.