Numerical Simulation Of Heat Transfer Process Of Paraffin Phase Change Capsule And Its Energy Storage Wall

Phase change energy storage technology can achieve green and energy-saving wood drying.The phase change problem is a kind of nonlinear problem,which can be solved by using numerical methods.This can help people understand the details of the phase change process.What's more,it can also promote energy saving and emission reduction of wood drying.This subject uses the heat enthalpy method,taking paraffin capsules as the research object.The heat transfer enhancement of phase change capsules and nano-Al2O3 at different scales was numerically studied.In addition,the heat transfer characteristics of dry kiln walls with phase change capsules were also studied.The main research contents and conclusions are as follows:First,the author analyzed the influence of capsule size,wall temperature and other factors on the melting process of phase change capsules by establishing the melting heat transfer model of paraffin capsules.The results show that reducing the particle size and increasing the wall surface temperature will shorten the melting time of the core material.When the particle size is less than 500?m,the natural convection in the core material is negligible.The thermal conductivity of the wall material of the paraffin microcapsules and the thickness of the shell layer have some influence on the phase transformation process of the core material within a certain range.The relationship between the complete melting time of the core material,the particle size and the thickness of the shell and its applicable range are fitted.Second,the author used nano-Al₂O₃ as a modifier and established the melting heat transfer model of two modified paraffin microcapsules based on the distribution of the modifier.The influence of the particle size and number of modifiers on the melting process of paraffin microcapsules was explored.Moreover,the author found that choosing a modifier with high thermal conductivity can shorten the end time of paraffin melting,and there was a critical value for the thermal conductivity.As the particle size and number of modifiers Increased,the average heat storage rate of the microcapsules and the liquefaction rate of the core material increase.When the modifier is distributed in the wall material,the microcapsules have the best heat transfer effect.Fitted the relationship between the end time of the core material melting and the particle size and number of modifiers,and its applicable range.Third,the author studied the effect of modified paraffin microcapsules on the heat transfer of the wood drying kiln wall by establishing phase change microcapsule energy storage wall model,and discussed the heat transfer characteristics of the phase change layer thickness and phase change latent heat on the phase change wall.It was found that the modified paraffin microcapsules had a"peak-shaving and valley-shifting"effect on the wall heat transfer.Furthermore,increading the thickness of the phase change layer and the latent heat of the phase change will reduce the heating rate and the cooling rate of the nodes in the wall,which will improve the insulation performance of the wall.When the phase change temperature drops to 325K,the wall with a phase change layer thickness of 30mm can maximize the utilization rate of phase change materials.This subject uses numerical simulation methods to study the heat transfer of paraffin capsules at different scales,as well as the modification and application of paraffin microcapsules.It provides theoretical guidance for the optimized design,development and application of paraffin capsules,and promotes energy saving and emission reduction of wood drying.