Simulation And Optimization Phase Change Thermal Storage Tank

With the aggravation of energy crisis and the environment pollution caused by burning traditional energy, new energy source is in high demand. Solar energy, a new energy, is advantageous in its abundance and it is free of charge, transportation and pollution. Therefore it is attracting more and more attention. However, its application is mainly limited due to its discontinuity, instability as well as mismatch in time and strength of energy supply and consumption. Heat storage technology provides an effective solution for solar energy application. Phase-change heat storage system is advantageous in high heat storage capacity, high efficiency, stability in heat absorption and release as well as ease in control and operation. Hence, it is gradually becoming the first choice in energy storage system, arousing the importance of research in phase-change heat storage.3-dimensional fluid dynamic simulation was carried out on heat storage tank which used wax as phase-change material in this paper. The simulation was more practical and therefore gave comprehensive variation principle of temperature field and phase-change interface in the heat transfer process of heat storage unit because the unsteady heat transfer temperature was considered, the simulation was more practical and therefore gave comprehensive variation principle of temperature field and phase-change interface in the heat transfer process of heat storage unit. Relevant theoretical calculation method was also investigated.(1)In this paper, a three-dimensional, non-steady state, liquid paraffin phase change thermal storage tank model was established, which contains the natural convection. A cylindrical and paraffin containing heat storage unit in this model was selected for study. The heat transfer tubes were in the center of the units and the paraffin was heated by the hot water through the heat transfer tube and their fins. The simulation results show that the paraffin melting process has experienced four stages:the heat conduction process, phase change thermal storage process, natural convection strengthened heat transfer process, and the weakened heat transfer process. The influence of the natural convection on the melting of the paraffin was mainly embodied in the convective heat exchange between the paraffin and the heat transfer tube, which increased the heat transfer coefficient. On the other hand, equivalent thermal conductivity of the liquid paraffin was increased by the natural convection of the liquid region. The melting of the paraffin became faster as the natural convection strengthened.(2)Theoretical calculation formula and method is established and the mathematical model of the heat storage unit is constructed by analyzing the thermal storage process of heat storage unit, accompanying with the comparison with simulation. The performances of the heat storage unit for the heat storage tank can be simulated by this model. Results find that the time of heat storage growths with the increase of the height that is less the critical height, and but this increasing trend will slow down; with the increasing of the characteristic length D, the increasing trend of heat storage time becomes faster. It is found that the influence of the variation of the characteristic length D is larger than that of the variation of the height on the performances of heat storage unit. In addition, the performance of the heat storage unit improved with the increase of fin number. However the improvement ability of fin number is limited. This mathematical model shows significant for the structure design and optimized operation of heat storage tank.