Simulation Study On The Effects Of Nickel Foam On The Phase Change Process And The Thermal Performance Of The Unit Tube

Storage technology is an important means of energy conservation, which thephase change thermal storage has been widely applied in various fields for its highstorage density, small energy loss and high stability. In the space solar dynamic powersystem, phase change heat storage unit tube is the main unit which performancedirectly affects the efficiency and stability of the system. However, the disadvantage oflow thermal conductivity of phase change material and relatively higher rate of volumechange exists in the course of its work. Foam metal can be very good to improve theseshortcomings. Therefore, it is important to study on how to use metal foam reasonableand the thermal performance of phase change heat storage unit tube.In this paper, the effects of nickel foam on the high temperature phase changeheat storage process and the performance of the unit pipe in the space solar thermaldynamic power system were studied. The model used Haynes188as the material ofphase change heat storage container,80.5LiF-19.5CaF2as phase change materials andthe mixed gas of He-Xe as the circulating working fluid. The physical andmathematical models of the single phase change heat storage containers and the phasechange thermal storage unit tube were established using FLUENT software. The mainworks and achievements are as follows:(1)In the model of single phase change heat storage container, the effects of theporosity, filling volume and filling position of the nickel foam on the entire phasechange process were studied. Phase change materials liquid rate and phase transitiontemperature of the container were analyzed along with the change of parameters ofnickel foam.(2) In the model of phase change heat storage unit tube, the change of liquid rateof phase change material and the temperature of various parts of the unit tube whichfilling the nickel foam or not were analyzed under the influence of the gas. At the sametime, effects of cyclic working fluid inlet velocity and initial temperature on the performance of unit and system were studied.(3) According to the study of the circumferential heat flux boundary condition ofphase change thermal storage unit tube in basic absorber, the corresponding UDF wasprepared. On this basis, the three-dimensional physical and mathematical model of theunit tube was established.(4) In the three dimensional model of the unit tube, the maximum temperature,the liquid rate and the average outlet temperature were compared with the twodimensional model under certain conditions, and the simulation results are morereliable.According to this paper, nickel foam can be used in phase change thermal storagewith a reasonable way and it provides a theoretical basis to improve the performanceof phase change thermal storage unit tube.