Investigation On The Process Of Thermal Heat Storage Of Metal Foam Composite Phase Change Material With Porosity Gradient

Under the energy crisis,new-energy vehicle get rapid development with the supports of the government around the world.Li-ion battery is the key component of electric vehicle(EV),which is one of important factors to influence the performance of the EV.Thus,the investigation of the li-ion battery is significant.The output of the battery is affected apparently by the temperature.The effective thermal management system can keep the temperature in a proper range,which is able to improve the performance and increase the service life of the battery.Phase change thermal management system has a good development prospect,for its advantages of high heat storage density,simple structure,no energy consumption and little temperature change.According to the output of the battery system of the EV,the visualization experiment system of aluminum foam-paraffin composite phase change material(PCM)is established to study the heat storage process of the composite PCM.The experimental results indicate that convection heat transfer has a strong impact on the phase change interface and has a heat transfer deterioration at the bottom of the composite PCM.Temperature difference along the direction of the heat flux is much bigger than that at the vertical direction of the heat flux.The structure of the aluminum foam is adjusted to optimize the heat storage process,according to the experimental phenomena and the experimental data.For the limitation of the experiment,numerical simulation is adopted to investigate the heat storage process of the composite PCM.The tetrakaidecahedron porous model is simplified according to the real structure of the aluminum foam and is verified by the experiment.The numerical result makes a great consistent with the experimental data,which indicate that the simplified porous model can reflect the real structure of the aluminum foam and the data obtained by this model is reliable.The phase change interface,temperature uniformity and the performance of thermal heat storage are investigated in the uniform porosity composite PCM and porosity gradient variation composite PCM.The results indicate that the porosity has a significant impact on the phase change interface.Bigger porosity of the composite PCM leads to a bigger angle of the phase change interface to the heating face.Bigger porosity results in a worse temperature uniformity of the composite PCM.Besides,porosity gradient varying(from the bottom to the top:0.86-0.90-0.94 and 0.86-0.94 linear)can enhance the heat transfer at the bottom,accelerate the melting process of the composite PCM.The temperature difference of the composite PCM with porosity gradient varying is 10.8 ? lower than that of the composite PCM with uniform porosity.The heat storage performance the composite PCM with porosity gradient varying is 142%higher than that of the composite PCM with equivalent porosity.Furthermore,conduction heat transfer dominates the whole process of the heat storage process.