Study On Phase Change Heat Transfer Characteristics Of Tube Bundle Phase Change Storage

The development of phase change heat storage technology is very important to the preservation of clean energy and solving the problem of matching supply and demand of energy.The analysis and optimization of the melting process of phase change material(PCM)is of great significance for improving the energy storage of phase change heat storage system under stable heat source.The research of latent heat storage mainly focuses on how to improve the heat storage efficiency and energy storage rate,which is the key index to evaluate the overall thermal performance of the energy storage system.The study of the factors affecting the enhanced heat transfer of the phase change heat accumulator is of great significance to speed up the heat storage process and improve the heat storage efficiency of the phase change heat accumulator.In this paper,through the combination of experiment and numerical calculation,taking the vertically placed single tube bundle phase change heat accumulator as the research object,studied the effects of different inlet velocity,inlet temperature of heat transfer fluid(HTF)and initial temperature on the heat storage process of phase change heat accumulator.The effects of natural pairing converged heat transfer characteristics of the natural pair of tube-type phase change regenerator were also studied by changing the placement of the experimental segment.In the experiment,the phase change material is OP28 E,uses water as the heat transfer fluid.The enthalpy-porosity method is used in the numerical calculation.In order to facilitate the calculation,the experimental model is reasonably simplified to a two-dimensional axisymmetric model.The main conclusions are as follows:(1)At the beginning of heat storage,the heat in the phase change material area is mainly transferred by heat conduction.When the temperature of the phase change material reaches the phase change temperature,the convective heat transfer begins to occur in the phase change material region.The melting process of the phase change material in the phase change heat storage unit is carried out from the inside to the outside and from top to bottom.(2)The inlet temperature of the heat transfer fluid has a great influence on the heat storage process of the phase change heat accumulator.With the increase of the temperature,the faster the heat storage rate is.When the temperature is low,the increase of temperature can significantly accelerate the heat storage process,but when the inlet temperature rises to a certain extent,the increase of temperature has little effect on the heat storage process of phase change heat accumulator.(3)The inlet flow rate of the heat transfer fluid has no effect on the heat storage process of the phase change heat accumulator.Because the main thermal resistance in the process of heat storage is in the pipe wall and the area of phase change material,increasing the flow rate has no effect on the thermal resistance of the heat conducting fluid.(4)The initial temperature of the phase change heat accumulator also has a great influence on the heat storage process.The higher the initial temperature is,the shorter the heat storage time is and the faster the heat storage speed is.Increasing the initial temperature can accelerate the heat storage process of the phase change heat accumulator,but the initial temperature can’t be increased indefinitely.The physical parameter of the phase change temperature of the phase change materials should be comprehensively considered,and the initial temperature should not exceed the phase change temperature.(5)The heat storage process of phase change heat accumulator is numerically simulated by ANSYS FLUNT software.The simulation results are in good agreement with the experimental results,which proves the correctness of the experimental results.(6)The different tilt placed angles of the phase change regenerator differs from the heat transfer characteristics of the heat storage unit.After comparison,it is found that the regenerator is the fastest storage rate when the level is placed.