Design And Analysis Of Heat Transfer Performance Of A New Phase Change Heat Storage Exchanger(PCHSE)

At present,the technology of developing and utilizing renewable energy has been deeply studied at home and abroad,in order to deal with the crisis of fossil energy and environmental pollution.Solar energy,as one of the renewable energy sources,has advantages of abundant resources,wide distribution,clean and pollution-free,inexhaustible and so on.Photovoltaic power generation technology,as one of solar energy technologies,is promising.However,a higher temperature of the photovoltaic cell decreases the power generation efficiency.Phase change heat storage technology making up for the shortcomings of photovoltaic power generation technology and improving the comprehensive utilization efficiency of solar energy is introduced,and the contradiction between heat supply and demand is solved.Nevertheless,phase change material(PCM)with excellent heat storage performance and heat storage devices with good heat transfer performance are essential to achieve efficient heat storage.The melting process of PCM in reference was numerically simulated under the same conditions before numerical simulation study,in order to valid the correctness of the solution model,calculation method,spatial discrete,numerical simulation results and so on in this paper.It is correct that the solution model,calculation method,spatial discrete and so on by comparing simulation results with experimental results.In this paper,a new Phase Change Heat Storage Exchanger(PCHSE)was designed by referring to the design concept of plate heat exchanger and fully considering the thermophysical performance of PCM.Phase Change Heat Storage Cell(PCHSC)is composed of upper,middle and lower layers.Heat transfer fluid flows through upper and lower layers formed by gaskets between two plates.The middle layer is filled with PCM.The PCHSC can realize heat storage,heat release,heat storage and release at the same time.Whether heat storage and heat release or heat storage and release at the same time,the device can realize that the phase change material layer above is cold fluid,below is thermal fluid.Natural convection will be formed in the condition of solid-liquid density difference and liquid density of PCM variations with the variation of temperature,which enhances the phase change rate of PCM.And rectangular fins in middle layer also accelerates melting or solidification of PCM,further reducing heat storage or heat release time.Physical and mathematical model of PCHSC were developed.Heat storage,heat release,heat storage and release at the same time of operating condition 1 neglecting of natural convection,operating condition 2 considering natural convection and operating condition 3 considering natural convection and rectangular fins set in middle layer were simulated and analyzed utilizing Fluent,in order to study natural convection and fins how to affect the phase change rate of PCM.Then,operating parameters(inlet temperature,inlet velocity)and geometric parameters(length of PCHSC,thickness of phase change layer and thickness of flow channel)were optimized by Fluent.Results reveal that:(1)The phase change rate of PCM of operating condition 3 is greater than that of operating condition 1 and 2,and the phase change rate of PCM of operating condition 2 is greater than that of operating condition 1.Natural convection has an influence on time of phase change,which accelerates the phase change rate of PCM.The influence of natural convection on heat storage is greater than that of heat release,and the effect of natural convection is the strongest during heat storage and release at the same time.The fin extends heat transfer area between PCM and heat transfer fluid,which also speeds up the phase change rate of PCM.Both natural convection and fins can make up for the low thermal conductivity of PCM.(2)Inlet temperature and inlet velocity have a great influence on the complete melting time of PCM.The complete melting time of PCM decreases with increase of inlet temperature and inlet velocity.However,with the increase of inlet temperature and inlet velocity,influence of inlet temperature and inlet velocity on the complete melting time of PCM gradually decreases.In this paper,inlet temperature 348?358 K,inlet velocity 0.2?0.4 m/s were recommended.(3)Longer the PCHSC length is,longer the heat transfer time between heat transfer fluid and PCM is,and lower the temperature of fluid outlet is.With increase of thickness of PCM,the complete melting time of PCM is prolonged,and total heat storage of PCHSC is larger.The complete melting time of PCM increases with increase of the thickness of phase change layer,and the growing rate is larger and larger.The complete melting time of PCM can be shortened by increasing the channel thickness within a certain range.With continuous increase of channel thickness,the complete melting time of PCM almost remains unchanged.