Numerical Simulation Of Heat Storage Enhancement Of Phase Change Materials

Since the beginning of the twenty-first century,electronic products have been widely developed around the world.Some commercial electronic products are first introduced into the household.However,with the improvement of people's living standard,the pursuit of electronic products has become higher and higher.People are no longer satisfied with the application of large-volume electronic products,in order to meet the new needs of users,electronic devices are gradually developing towards the direction of small size and integration.As the volume of electronic devices is getting smaller,traditional heat dissipation methods can no longer meet the heat dissipation requirements of some electronic devices with small size,intermittent,variable power operation and pulsed working characteristics,such as LED lights,IGBT components,power batteries,etc.Therefore,seeking new heat dissipation methods has become a key issue in the study of heat dissipation of electronic devices.The solid-liquid phase change process has the characteristics of small volume change,basically constant phase change temperature,and large amount of latent heat release/absorption.Therefore,phase change heat sink devices based on solid-liquid phase change materials(PCMs)are considered to be the most likely to replace traditional heat dissipation devices,so in-depth study on the heat storage capacity of solid-liquid phase change heat sink devices will provide important basis for heat dissipation of electronic devices.In this paper,a three-dimensional physical model embedded metal fins is established.The Fluent software is used to numerically simulate the melting process of the PCM in the three-dimensional phase change heat sink device with needle fins.Firstly,the temperature changes of the heat source under the three cases of adding no PCM,adding the pure PCM,and adding fins to the PCM are compared.Then,the influence of different fin parameters(spacing,height,number)and heat flux on the melting process of the PCM are analyzed.The effect on the heat storage capacity of the phase change heat sink device with embedded metal fins is discussed.Finally,the metal fins were replaced with the same volume of porous media,and the effects on the heat storage capacity of the heat sink device with metal fins and porous media are compared and analyzed.The results show that the heat storage capacity of the heat sink device filled with porous media is better than that of the embedded metal fins with the same volume.Considering the real phase change process,the volume of the PCM becomes smaller after solidification,resulting in a certain space of air layer above the device.The existence of the air layer has a certain impact on the heat storage capacity of the heat sink device.Under this situation,a three-dimensional physical model of heat sink device is established,and the coupling calculation model of VOF(Volume of Fluid)and enthalpy-porous media is adopted.The change in the heat storage capacity of the heat sink device with or without air layer is analyzed,and the heat storage process of the heat sink device with air layer under different heat fluxes,different uniform porosities and gradient porosities are studied.The heat storage process of the solid-liquid phase change and the heat transfer mechanism of the phase change process are in-depth studied.In the case of constant porosity,when the heat flux is 4500W/m~2,the heat storage time can reach 1900s;when the heat flux is 10000W/m~2,the heat storage time is700s.The average heat storage rate of the heat sink device is calculated to further explain that the heat storage capacity under different pore structures is different.The PCM under the positive gradient pore structure has the shortest complete melting time and the fastest average heat storage rate.Compared with uniform pore structure and negative gradient pore structure,the heat storage rate increased by 6.6%and 10.9%,respectively.After processing the simulation result data,we discover that the PCM has a volume expansion rate of 9.2%during the entire phase change process.