Study On Heat Transfer Performance Of Sugar Alcohol Based Phase Change Heat Storage

With the increasing depletion of fossil fuels and the worsening greenhouse effect,using various clean energy sources to replace fossil fuels is currently the way out and key to solving energy shortages and environmental pollution problems.The latent heat storage technology of phase change materials has relatively small temperature changes during the heat storage process,enabling more stable thermal energy storage and release.At the same time,the heat storage process of phase change materials does not involve the generation and emission of gases,and has the advantages of being more environmentally friendly and maintaining a constant temperature during the phase change process.It has been widely used in building envelope structures,HVAC systems,and solar energy storage fields.Among many latent heat storage methods,solid-liquid phase change is currently one of the most widely used types of phase change heat storage materials in practical applications.However,solid-liquid phase change heat storage materials may have some problems during the heat storage process,such as undercooling and phase separation phenomena,leading to unsatisfactory energy storage.Conducting experimental and simulation studies on solid-liquid phase change heat transfer and designing new and efficient phase change heat exchangers are of great significance for efficient energy utilization.In most phase change heat storage systems,the key to improving the efficiency of phase change heat storage systems is to improve the melting and solidification efficiency of phase change materials.To this end,it is necessary to improve the thermal conductivity of phase change materials during the phase change process,and conduct in-depth research on the charging and discharging performance of heat exchangers.This article aims to improve and optimize the melting and solidification heat transfer structure of phase change materials in heat storage devices,thereby improving the heat storage efficiency of heat storage devices and strengthening the heat transfer characteristics of phase change heat storage.Therefore,two efficient phase change heat storage devices were proposed,and numerical simulation and experimental research were conducted to explore their heat storage performance.Related research can provide theoretical support for the design and thermal management of high proportion solar energy storage and heating systems on the building side.The main research is as follows:1)A rectangular finned tube heat storage device was proposed,and a three-dimensional transient mathematical model of the rectangular finned tube heat storage device was established.A rectangular finned tube heat storage test platform was built to verify the accuracy of numerical simulation.This numerical model was used to analyze the temperature response process inside the device during the melting and solidification process of rectangular finned tubes,as well as the effects of heat transfer fluid flow rate U,heat transfer fluid inlet temperature,fin spacing S,and tube spacing D on the melting and solidification process of rectangular finned tubes.Research has shown that the phase change materials in the fin region exhibit a rapid phase change trend during the charging and discharging processes;Increasing the temperature difference between the heat transfer fluid and the phase change material can accelerate the phase change rate in the non finned area,resulting in a significant improvement in the charging and discharging rates;In turbulent conditions,the influence of flow velocity changes on the heating and heat release rates is relatively small;Under the conditions of 2.5 mm and 10 mm fin spacing,the effect on the heating and heat release processes is relatively small,and the phase change rate in the fin area is significantly higher than that in the non fin area;Under the calculation structure and conditions,the changes in liquid phase rate during the filling and heat release processes of the 26.25 mm and 52.5 mm finned tube heat exchangers with tube spacing are basically consistent,and the phase change rate is faster than that under the 105 mm tube spacing.2)A finned microchannel heat storage device was proposed,and a three-dimensional transient mathematical model of the finned microchannel heat storage device was established.A finned microchannel heat storage experimental platform was built to verify the accuracy of numerical simulation.This numerical model was used to study the temperature variation of the heat storage medium inside the device,and the effects of different fin spacing S and different inlet temperatures of heat transfer fluid on the melting process of finned microchannels were analyzed.The dynamic evolution of the morphology of phase change materials in the device was studied through experiments,and the influence of the inlet temperature and flow rate of different heat transfer fluids on the heat storage process was discussed.Research has shown that during the entire melting process of phase change materials inside the finned microchannel device,the temperature changes of phase change materials inside the fins,near the fins,and far away from the fins are significantly stratified.The average temperature rise rate of phase change materials inside the entire device follows the following law: the temperature rise inside the fins is the fastest when they are close to the fins and far away from the fins;The heat absorption time of phase-change materials in finless devices is much longer than that in finned devices.The time spent in solid-state sensible heat storage,latent heat storage,and molten liquid sensible heat storage is longer than that in finned devices.However,the trend after 50 minutes coincides with that in finned devices.Reducing the fin spacing can shorten the melting time of phase-change materials;The increase in inlet temperature can improve the heating rate of phase change materials to a certain extent,but this process cannot affect the average temperature change trend of phase change materials;The influence of the inlet flow rate of heat transfer fluid on the melting and solidification process of phase change materials is relatively small,with only slight differences.