| The phase change energy storage technology focusing on phase change material solves the problems of intermittence and instability in solar heating to a great extent.In practical application,PCM is usually loaded into the unit structure that does not react with it,and then these units are arranged in the energy storage box and combined with the heating system,which not only reduces the waste of energy but also greatly improves the stability and continuity of the system heating.Plate-type phase change unit has the advantages of a large surface to volume ratio,good thermal conductivity in the thickness direction,easy to process,and easy to assemble,so it is widely used.Domestic and foreign scholars have done relevant research on the improvement of the thermal performance of the plate-type unit by tilting the unit and adding fins,but the difficulty of unit placement and processing was also increased,and there is less research on changing the overall structure of the unit.Based on this,the following research work was carried out in this paper:(1)In order to improve the thermal performance of the rectangular plate-type unit,in the case where the unit volume,length,and height are constant,the equation is established based on Nusselt’s boundary layer theory for structural optimization,and the plate-type unit(40mm wide),the wedge-shaped unit(80mm wide)and the optimal trapezoidal unit(12.8mm wide in the upper,67.2mm wide int the lower)are designed.The organic PCM whose main material is paraffin was encapsulated into three units,to conduct the experimental study for the heat storage and release performance by a single control variable method,and the relevant physical and mathematical models were established to analyze the liquid phase rate curve and cloud diagram changes of the three units during the process of the heat storage and release and to explore the phase change heat transfer mechanism of PCM and heat exchange fluid(Heat Transfer Fluid,HTF)with time.It was found from the study that the optimal trapezoidal unit among the three units can make better use of the melting/solidification characteristics of PCM to make it take the lead in completing the heat storage and release process.Increasing the inlet flow rate and increasing the temperature difference between PCM and HTF will improve the heat storage and release efficiency of the plate-type unit.(2)To explore the effects of two kinds of water intake modes(bottom in and top out&top in and bottom out)on the heat release performance of the three plate-type units,combined with experiments and simulation studies,it was found that: under the same conditions,the smaller the height difference between the inlet and the unit,the less the time spent in the liquid sensible heat release process of PCM,and the earlier the latent heat release process begins;under the water inlet mode(bottom in and top out),the solidification effect of PCM in the three units is better.(3)Contrast three types of platelets when vertical placement and horizontally uniformly placed,the vertical placement angles of the units were adjusted to 0 °,45 ° and90 °.It was found via experimental research that the optimal trapezoidal unit takes the least time to complete the heat storage and release process when the vertical placement angle is90 °.In this paper,a new plate-type phase change unit was studied by using the method of theoretical analysis,in combination with experiment and simulation,the practical application was taken into account while improving its thermal performance,which provides a certain theoretical basis and technical reference for the structure optimization of plate-type phase change energy storage device and the storage and utilization of solar energy resources. |
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