| Latent heat storage refers to the use of phase change materials to absorb or release a large amount of latent heat by changing the state of matter.It is one of the main directions of energy storage technology research.It has potential applications in cooling power electronic devices,industrial waste heat utilization,thermal management of lithium-ion batteries and other fields.Mastering the melting and solidification mechanism of phase change materials is the key to the application of latent heat storage technology.In addition,the introduction of high-efficiency heat transfer enhancement refrigerant nanofluids to further enhance the heat transfer process of phase change materials has hardly been studied.For this reason,the research on the above proble ms will lay a theoretical foundation for the application of phase change energy storage technology in the industrial field.In this paper,the relative thermal conductivity of Al 2O3-water nanofluids is studied by radial basis function(RBF)neural network and response surface methodology(RSM).Among them,the RBF neural network program is compiled by using matlab,and the prediction results of RBF neural network model are compared with those of Maxwell model and Bruggeman et al.model,RBF neural network model is the best.RSM analysis is carried out by using Minitab,and an empirical correlation formula for classification according to concentration is proposed.The prediction results are compared with those of Timofeeva et al.model and Minsta et al.model,the prediction result of this model is the best.Secondly,the melting process of phase change materials(PCM)was studied by using the melting/solidification model in Fluent.Firstly,the effects of flow rate and temperature difference on the complete melting time and liquid phase ratio of PCM with time were studied.The results show that the effect of flow rate on the melting process of paraffin wax is weak,while the effect of temperature difference on the melting process of paraffin wax is severe.Th en through the change of the phase interface position of the axial section,the influence of different temperature difference on the phase interface position,the average flow velocity of liquid paraffin at different time and temperature difference,the heat flux at the coupling interface at different time and temperature difference,the temperature distribution maps of the axial section at different working conditions and different times,and the temperature distribution maps of the axial section at differ ent temperature difference at the same time,the melting mechanism of PCM was studied.The results show that the initial temperature difference,the heat flux at the coupling interface,the temperature distribution in paraffin wax and the heat transfer proc ess in paraffin wax affect each other.Finally,in order to select the content of paraffin better according to the operating conditions in practical application,a full-factor experimental design analysis was carried out using Minitab,and an empirical correlation was established between the complete melting time of paraffin and the inner and outer diameter of concentric casing and the temperature difference.Finally,the effects of temperature difference and nanofluids on the complete solidification time and liquid fraction of paraffin wax with time were studied by solving the melting/solidification and discrete phase(DPM)coupled model.The solidification process of paraffin is divided into four time periods according to the change chart of liquid rate wi th time,and the liquid rate per unit time change rate in each time period is calculated.The whole numerical simulation process is completed in Fluent.The results show that the effects of temperature difference and nanofluids on the solidification proces s of PCM mainly occur in the early stage.By comparing the effects of temperature difference and nanofluids on the solidification process of paraffin wax,it was found that using nanofluids as refrigerant equivalent to increasing the initial temperature difference. |
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