Experimental Study On Mid-temperature Latent Thermal Energy Storage Unit With Gradient Porosity Metal Foam

Thermal energy is the world's largest terminal energy utilization mode,heating accounts for about 50% of the global terminal energy consumption,among which,in the industrial sector,more than 74% of the thermal energy is consumed in the form of process heat.At present,the biggest problem restricting the development of phase change heat storage industry is that the thermal conductivity of commercial phase change materials is too low.Therefore,a gradient copper foam with an average porosity of 0.95 was designed in this paper.Homogeneous foamed metal with a porosity of 0.95 and gradient foamed metal were immersed in phase change material Adipic acid(melting point is 153?)to form a composite phase change material.Based on the concept of shell and tube heat exchanger,a phase change heat storage unit is designed,that is,the working medium of heat transfer silicone oil flows through the inner tube,the shell is filled with composite phase change material,and the heat transfer material exchanges the heat stored in the composite phase change material.The shell adopts quartz glass tube to facilitate the observation of phase change process.In order to investigate and compare the thermal performance of different phase change heat storage units,a set of laboratory scale solar energy storage system was built.In order to ensure that the experimental conditions of each heat storage unit are consistent,a flow distributor is designed by CFD so that the heat transfer medium passing through each heat storage unit has the same inlet temperature and flow rate.Assessing the different thermal storage unit in the thermal performance of heat and heat release process,and also explores the different discharge in the thermal environment of the influence of the reservoir.The main results of this paper are as follows:(1)The experimental results show that,compared with homogeneous metal foam,the addition of gradient metal foam in phase change materials can effectively increase the heat transfer rate and improve the temperature uniformity of each latent heat storage unit,no matter in the process of heat charge or heat release.(2)During the heating process,the melting time of the gradient copper foam phase change heat storage unit was 8110 seconds,while the corresponding homogeneous copper foam phase change heat storage unit needed 13010 seconds to complete the melting process.The overall melting time of PCM can be reduced by 37.6%.At the same time,the average power of gradient copper foam phase change heat storage unit is improved compared with that of homogeneous copper foam phase change heat storage unit.(3)The results also show that although increasing the inlet flow can improve the heat filling performance of the heat storage unit,the effect is not obvious.This experiment is the first to demonstrate that the application of gradient porous media can enhance the thermal performance of a tubular phase-change heat storage system.It provides a new way to enhance the heat storage performance of phase change materials.Therefore,this conclusion is very important for latent heat storage and the utilization of solar thermal energy.