Experimental Study On The Thermal Performance Enhancement Of Phase Change Materials By Filling Copper Foam Partially

Phase change energy storage is a clean energy technology that has greatly improved the utilisation of energy and is widely used in green buildings,industry,medicine and aviation,where phase change materials used for latent heat storage are of great interest due to their large thermal storage potential.However,the efficiency of heat transfer is severely hampered by the low thermal conductivity of phase change materials.In order to enhance the heat transfer rate of phase change materials,the application of copper foam can be a good solution to the problem of low thermal conductivity of phase change materials during the phase change process.Most of the research has been focused on the full filling of copper foam,but there is still a gap in the research on partial filling of copper foam.Therefore,this paper proposes an innovative form of copper foam fins and compares and analyses the experimental images and temperature data.As a result,the main research in this paper is as follows.(1)Firstly,this paper designs an experimental system for a vertical shell-tube heat accumulator.The physical properties of the phase change material and copper foam are tested in the pre-experimental stage and the evaluation indexes used in the experiments are summarised to lay the foundation for the subsequent research.In order to verify the research potential of latent heat accumulators,an experimental comparison between sensible and latent heat accumulators was carried out.While the great heat storage potential of the latent heat accumulator was demonstrated,the lack of heat transfer in the latent heat accumulator was also identified.A further comparison of the latent heat accumulator with copper foam fins was carried out to verify the effective enhancement of heat transfer from the phase change material by copper foam fins.The final experiments demonstrated that the heat storage and heat release of the latent heat accumulator was effectively increased with the addition of copper foam fins,while the thermal efficiency was increased by 10.8%.The internal heat transfer per unit area was also greatly improved,with the average heat flow density increasing by 45.2% to 111.6%during the storage and exothermic phases,and the convective strength within the heat accumulator was also effectively enhanced,with the average Nussle number increasing by 31.9%.(2)Secondly,to further verify the superiority of annular copper foam fins for heat transfer,experiments were conducted to compare the shapes of three types of copper foam fins: annular fins,longitudinal fins and annular longitudinal composite fins.The experimental results demonstrate that the annular copper foam fin accumulator has a higher temperature field uniformity and a thermal efficiency that is 13.3 to 13.8% higher than the other shapes.The average heat flow density is also significantly higher than other heat exchangers,while the average Nussle number is 15.1 to 34.5 % higher than other heat exchangers.And it was found that the biggest heat transfer difficulty of the shell and tube heat accumulator is located at the bottom where the heat transfer demand is higher,and the heat transfer area at the bottom of the heat accumulator should be further enhanced.(3)Secondly,different foam copper ring fin arrangement methods creatively propose the balance between heat transfer and natural convection inside the accumulator.Experiments were carried out with four types of arrangement and the final results show that the dense distribution of the lower copper foam fins improves the natural convection inside the heat exchanger while enhancing the heat transfer in the lower part of the heat exchanger.The dense distribution of copper fins in the lower part of the heat exchanger has a higher heat storage and discharge capacity of the four distribution types,and the thermal efficiency is increased by 4.2-10.8% compared to the other three distribution types.The natural internal convection is greatly improved,with an average Nussle number 22.6 to 91.3 per cent higher than that of the other heat accumulators.This demonstrates that the natural convection heat transfer inside the heat accumulator has great potential for research into the thermal performance enhancement of heat accumulators.(4)Finally,based on the enhancement of heat transfer by natural convection,a creative proposal was made to improve the thermal performance of the heat accumulator by improving the natural convection path inside the heat accumulator in the form of perforated copper foam.The final experiments found that the perforated copper foam heat accumulator achieved higher heat storage and heat release,and that the thermal efficiency was only 3.8% lower than that of a solid copper foam heat accumulator in the exothermic phase with 50% of the heat transfer area missing.It also has a higher contribution to heat transfer per unit area,with an average heat flow density increase of 29.7 to 100.1 %.The perforated path also greatly improves natural convection,with an average Nussle number increase of 37.7%.