| As a kind of energy storage system,phase change energy storage heat exchangers can reduce energy consumption and play an important role in energy saving and emission reduction.How to improve heat transfer efficiency,strengthen heat exchange,and minimize energy consumption is the current heat exchange An important issue in the field of energy-saving devices.In this paper,on the basis of improving the thermal properties of phase change materials,the performance of heat storage heat exchangers filled with paraffin/graphene composite phase change materials will be studied by using numerical simulation methods to study the heat exchanger structure,heat exchange conditions and other factors This will provide theoretical support for the application of heat storage heat exchangers in building energy saving.The 54# paraffin wax with low melting point and 64# paraffin wax with high melting point are mixed in a certain proportion.The results show that when the two paraffin waxes are 6:4,the phase transition temperature is 59.2?and the latent heat of phase transition is 214.37 kJ/kg.When graphene with a mass fraction of 1.5% was added to the mixed paraffin and the paraffin/graphene composite phase change material was prepared,it was found that the latent heat of the phase change of the composite phase change material only decreased by 1.4% and the phase change temperature decreased by2.2?,but its thermal conductivity is improved by 34%,and its stability and uniformity are better,so the material can be filled into a heat storage heat exchanger as a heat storage working medium.In order to verify the accuracy of the numerical simulation,the concentric sleeve model was used to compare the experimental results in the literature with the numerical simulation method,and the phase change material was filled into the concentric sleeve heat exchanger,and hot water was passed into the inner tube The phase changetemperature and melting process of the phase change material in the heat exchanger.The melting point of the phase change material used in the literature is 51?.The results show that the melting process is consistent with the experimental results provided in the literature,indicating that the numerical simulation method used in this article is correct.In order to study the effect of heat exchange area on the heat storage and release of heat exchangers,inner tubes with the same tube diameter and the number of 1,2,3,4were set in the heat exchanger.The results show that the 4-inner tube heat exchanger can significantly enhance the natural convective heat transfer of the composite phase-change material during heat storage and release,and reduce the heat transfer resistance.The device is shortened by 32.5% and 29.74%.At the same time,the water temperature is also an important factor affecting the heat storage and release of the composite phase change material in the heat exchanger.During the heat storage process,the higher the water temperature,the shorter the melting time of the composite phase change material,and the lower the water temperature,the more favorable the composite phase change.The solidification of the material.The tube core distance is an important parameter of the heat exchanger structure.Based on the four inner tube heat exchanger,the composite phase change materials in the heat exchanger are studied when the tube core distance and the tube diameter ratio are 1.3,2.0,2.6,and 3.3,respectively.Heat storage performance.The results show that when the ratio of tube center distance to tube diameter is 2.6,the thermal resistance between the inner tube and the inner tube and the inner wall of the outer tube and the inner wall of the inner tube are more average.The heat storage efficiency is 23.9% and 13.30% higher than the model with a tube center distance to tube diameter ratio of 1.3,respectively.This paper studies the performance of the heat storage heat exchanger when the inner tube is an elliptical tube.When the volume of the elliptical tube and the circular tube are the same,the specific surface area of the elliptical tube is larger than that of the circular tube.When the flow rate of water in the inner tube is the same,the heat storage heat exchanger of the elliptical tube in the inner tube has a heat storage rate of 12.96% and9.20% higher than that of the circular inner tube model.The overall heat transfer performance of the elliptical tube is higher than that of the round tube.The lower the mass flow rate of the water in the inner tube,the greater the PEC factor value of the elliptical tube.Therefore,the elliptical tube is more suitable for the application of low mass flow rate of fluid in the inner tube It shows that the elliptical tube is more suitable as the heat exchange inner tube in the heat storage heat exchanger. |
PDF Full Text Request