Preparation And Simulation Of Heat Release Performance Of Basalt Melt For Mobilized Thermal Energy Storage

The mobilized thermal energy storage is widely recognized as a flexible and efficient heat transfer technology,which breaks the limit of the short distance of the heating pipe network and the intermittency of renewable energy.This technology effectively solves the supply-demand mismatch of the thermal energy in time and space.However,some unavoidable drawbacks and limitations have restricted the application of conventional materials in the field of mobilized thermal energy storage.Specifically,water is only suitable for the thermal storage below 100 °C,while the molten salt is prone to freeze and corrode.Concrete exhibits unstable chemical properties at high temperature.Besides,thermal decomposition,supercooling and other phenomena are apparently observed over the latent heat materials such as erythritol.The above content indicates that the research on chemical reaction thermal storage materials remains in the experiment stage.This paper elaborates the research progress and application status of mobilized thermal energy storage.It is found that basalt melt displays the characteristics of high storage density,better thermal stability,high strength,excellent corrosion and temperature resistance,which is considered to be an extremely promising thermal storage material.In this paper,based on the mobilized thermal energy storage system of basalt melt as a heat storage material,the following work was carried out:(1)The working principle of the mobilized heat storage tank was described and the preparation process of the basalt melt rod was proposed.The basalt melt was analyzed by DSC(Differential Scanning Calorimetry)to obtain more accurate thermal physical parameters of the three samples.The results were calculated and fitted to provide a theoretical basis for subsequent research.In order to understand the heat release of basalt melt rods in detail,based on the reasonable simplification and assumptions,the corresponding mathematical models was established and the numerical simulation of the heat release process was conducted.Then the rationality of the assumptions and calculation methods made in the simulation was verified by comparing the results of the theoretical calculations and simulation.(2)The evaluation index of the heat release performance of basalt melt was established,including the outlet temperature,heat release power and heat release efficiency.By summarizing the development of the thermocline in the basalt melt heat storage module,it is found that in the thermocline zone,the basalt melt and air continue to radiate heat due to the temperature difference,and the thermocline will gradually move downstream as the heat release process progresses moving.When the thermocline moves to the last row of rod bundles,the temperature of the air outlet begins to decrease.The simulation results shows that when the air inlet flow rate is 0.0258kg/s,the stable heat release time of the heat storage system is 0.57 h and the effective heat release time is 1.14h;the stable heat release power and the effective heat release power are 18.75 k W and 10.07 k W,respectively;the heat release efficiency during the effective heat release time is 82.9%.(3)This paper further simulates the influence of the four parameters of basalt melt thermal conductivity,air inlet velocity,rod diameter and spacing on the heat release performance of the basalt melt rod bundle.The results show that increasing the thermal conductivity by adding steel fibers can increase the heat storage per unit volume of the heat storage module and improve the heat release performance.As the inlet flow rate decreases,the stable heat release time and the effective heat release time increase almost linearly,the heat release efficiency increases slightly,but the maximum heat release power decreases proportionally.The smaller the diameter and spacing of the basalt melt rods,the longer the stable heat release time and the effective heat release time,the higher the heat release efficiency,the thinner the thermocline,the better the heat release performance,but the stable heat release and effective heat release power are almost no effect.(4)The influence of cracks on the temperature distribution of basalt melt during the heat release process was discussed,and the analysis was quantified by calculating the maximum temperature difference between the inside and outside of the melt.It mainly includes four parameters: different fracture direction,location,length and width.For radial cracks growing inside the basalt melt,their different positions,lengths,and widths have little effect on heat transfer,which is consistent with those without cracks.The effect of circumferential cracks is much larger than that of radial cracks.The results reveal that the farther distance between the crack and the center of the rod,the greater length and width of the crack will increase the temperature difference between the inside and outside of the basalt melt,thereby increasing the temperature stress and making the basalt melt body modules are easier to damage and should be replaced in time.