| Industry of China will produce a large amount of waste heat resources in the production and manufacturing process,and if not properly recycled,it will cause a huge waste of energy and aggravate the tension between energy supply and demand.Meanwhile,there are still a large number of building areas in northern cities and towns in China being heated by small self-provided coal-fired boilers with low heating efficiency,which will not only result in low energy utilization,but also aggravate environmental pollution,therefore,it is urgent to find a reasonable method to the solve contradictions.Mobile heat storage technology can collect and store industrial waste heat in its own heat storage materials,and transport it to nearby heat users by truck to provide hot water or heating,so it is an ideal method to solve the above problem of heat supply and demand by matching heat supply and demand in time,place and intensity.Mobile phase change heat storage device has become the development direction of mobile heat storage technology because of its advantages such as high heat storage density,stable heat load,safety and reliability,however,because of the low thermal conductivity of its own phase change storage material,the efficiency of heat storage and release is low.In this paper,the experimental and numerical simulation methods are used to study the heat storage and release performance of the phase change storage device,the selection method of high efficiency phase change material and the optimization of the heat storage and release structure of the heat storage unit,striving to lay a foundation for the design of high efficiency mobile phase change heat storage device.The temperature and residual heat generated by the industrial sector may vary at different times,so in order to investigate the influence of temperature and amount of heat source in the process of recovery and utilization of waste heat resource in mobile phase change heat storage device,a small scale experimental bench was set up to simulate the effects of temperature and amount of heat source on the heat storage and release performance of the mobile phase change heat storage device by changing the circulating water temperature and flow rate with using Rubitherm#60 paraffin phase change material as heat storage medium in this paper.It is found that,there are three stages in the melting and solidification process of phase change material,that are solid sensible heat,latent heat and liquid sensible heat storage and release stage.Among them,the temperature of sensible heat storage and release stage changes greatly,the rising rate is fast,and the heat transfer mode is mainly heat conduction.The change of temperature in latent heat storage and release stage is relatively small,and the heat transfer mode gradually changes from heat conduction to convection,with heat conduction as auxiliary.Natural convection occurs in latent heat storage and release stage,which can promote the heat storage process and hinder the heat release process of the phase change material,so it is worth studying.In addition,the dimensionless number is used to characterize the heat storage and release degree of the regenerator,and the magnitude of the heat storage and its variation can be obtained from the histogram.In this paper,the open-hole fin with transverse rib used by experiment is regarded as the research object.The geometric modeling of heat storage unit is built by using ICEM CFD software and meshed by using structured hexahedron mesh,and then the grid independence and reliability verification are completed.The method of selecting phase change heat storage material with the best comprehensive performance was studied.in other words,in order to recycle the industrial waste heat resource of 300?and supply 85? hot water to the heat user,numerical calculation of 10 kinds of phase change materials was carried out.The heat storage,heat storage rate and velocity vector diagram of the 10 kinds of phase change materials are compared and analyzed.Take the 10 kinds of phase change materials into consideration,#5(56%LiNO3-44%NaNO3)phase change material has large heat storage and high heat storage rate,it can be considered as the phase change material studied in this paper.Finally,the optimization scheme of enhanced heat transfer of heat storage unit is studied by means of numerical simulation,including size of fin hole,size of transverse rib,fin spacing and fin thickness.The results show that the principle of enhancing heat transfer performance of fin with opened holes and transverse rib is different.The former is breaking and regenerating the thermal boundary layer and the latter is used to enhance the disturbance of natural convection in the process of heat storage and heat release.The fin spacing and fin thickness affect the heat storage and release performance by changing the average heat transfer thermal resistance of the heat storage unit.Reducing fin spacing and increasing fin thickness have more significant effects than opened holes and transverse ribs.However,considering the possible increase in the weight and the initial investment,a comprehensive consideration is needed.The conclusions obtained in this paper can lay a foundation for the design,optimization and engineering application of mobile phase change heat storage device. |
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