Experimental Measurement And Simulation Of Thermal Storage Performance Of Low-melting-point Alloy

Due to the miniaturization and high integration of electronic chips,the heat and heat flux of electronic chips are increasing,and it is urgently needed to find efficient heat dissipation measures.The energy storage type temperature control unit has a simple structure,high reliability,no moving parts,no power drive,and is not affected by gravity,and is particularly suitable for controlling the temperature of intermittent high-power electronic chips in the aerospace field.The low melting point alloy has the advantages of high thermal conductivity,high heat storage density,and stable performance,and is an excellent phase change energy storage material.The general chip junction temperature is 150?.In order to ensure the normal operation of the chip,its maximum temperature needs to be lower than this temperature value.Taking the thermal resistance of the chip itself,packaging,heat dissipation equipment installation and etc into account,a low-melting alloy with a phase transition temperature of less than 85? is generally selected.In this paper,five low-melting-point alloys with high latent heat of phase transformation were prepared using high-frequency vacuum furnaces.The phase transition temperatures,latent heat of phase change,thermal diffusivity,and density of ow-melting-point alloys were measured by differential scanning calorimetry,laser flashing,and drainage methods,respectively.This provides basic data for the large-scale application of low-melting-point alloys in the energy storage field.The prediction formula of latent heat of phase change of low-melting-point alloy is deduced from the viewpoint of thermodynamics.The latent heat of each component of the low-melting alloy,the difference of the relative heat capacity of the solid and liquid of each component,and the influence of the entropy of mixing on the latent heat of the phase change of the low-melting alloy are considered.The effect of latent heat of each component of the low-melting-point alloy,differences in heat capacity between solid and liquid components and mixed entropy on the latent heat of phase change of the low-melting-point alloy are considered in the formula.In this paper,nine known low-melting eutectic alloys were selected to verify the accuracy of the formula of latent heat of phase change.The calculation results show that the maximum error is 19.35%,the minimum error is 1.86%,and the root mean square error is 17.05%.At the same time,three kinds of low-melting alloys were configured according to certain rules,and then the thermal properties of the alloys were tested.The heat storage performance of the low melting point alloy in practical applications was measured by experiments.An experimental bench was set up to study the effects of the heat flux and heating power of five low-melting alloys with different phase transition temperatures between 40 and 85? on the performance of the energy storage temperature control unit.Combining the measured thermal properties parameters,the simulation of the melting process of the low-melting alloy was performed using CFD software.The simulation results were compared with the experimental results.It was found that the simulation and the experiment were in good agreement.The melting and heat transfer processes of low-melting-point alloys under different heat flux and heating power conditions were analyzed.Cd8.5Sn11.3Pb37.7Bi42.5 has the largest latent heat,high thermal diffusivity and best temperature control performance.Studies have found that both heat flux and heating power have an effect on heat storage performance.Comparing the heat storage performance of the same heating power 24 W,different heat flux density 24.00W/cm~2,6.00W/cm~2,2.67W/cm~2,1.50W/cm~2,0.96W/cm~2,it is found that the heat flux is too large and heat will not be transmitted to the entire energy storage temperature control unit in time.The alloy cannot be melted in time and the energy storage temperature control unit fails.Under the experimental conditions of this paper,when the heat flux is less than 2.67 W/cm~2,the effect of the heat flux density on the performance of the energy storage temperature control unit is negligible.This critical value is related to the specific type of low-melting-point alloy and external conditions.Comparing the heat storage performance of the same heating area,the heating powers of 20 W,24W,28 W,32W and 36 W,it is found that the greater the power,the greater the temperature non-uniformity of the energy storage temperature control unit and the smaller the heat absorption at the time of failure.