Study On The Performance Of Bilateral Exothermic Solar Phase Change Kang Heating System

In the rural areas of northern China,the hot Kang is still one of the main heating methods in winter.However,this traditional heating method will not only consume a lot of non renewable resources and cause environmental pollution,but also have some disadvantages,such as uneven temperature distribution on the Kang surface and poor indoor environment.Therefore,it is necessary to transform and innovate the Kang,and vigorously develop the application of renewable resources in Kang heating.For rural areas rich in solar energy resources such as northwest,northeast and North China,domestic and foreign scholars have conducted more research on solar hot water Kang and phase change Kang,and the new solar phase change Kang has also been preliminarily studied.However,the impact of different exothermic forms on solar phase change Kang has not been studied.Therefore,based on the meteorological data during heating period in Xining area,The performance of single side exothermic and double side exothermic solar phase change Kang heating system is studied by numerical simulation.The specific research contents include:Firstly,the operation principle of the new solar phase change Kang heating system is introduced,and the design basis of the Kang body and solar collector is explained.Then,the heat transfer processes of the solar phase change Kang heating system are theoretically analyzed,and the evaluation indexes of the system are given.The three-dimensional heat transfer problem of solar phase change Kang heating system is simplified to a two-dimensional problem.A numerical calculation model is established based on FLUENT software,including mesh generation of geometric model,selection of calculation model,setting of solution parameters and boundary conditions.Through independence verification,a more reasonable mesh density and time step are obtained,Finally,the numerical model is simplified and verified by experiments.Then,the operation effect of one-sided exothermic solar phase change Kang is analyzed from three aspects:the heat storage and release of the Kang,the non temperature control of the upper Kang surface and the heating effect when the temperature is controlled.On this basis,the heating effect differences between two-sided exothermic Kang and one-sided exothermic Kang are compared.The results show that:（1）when the temperature of the upper Kang surface is not controlled,although the unilateral exothermic Kang can maintain the bedding temperature between 29～34℃,the average temperature of the upper Kang surface will be higher than 35℃for a long time in the whole day,and prolonged sitting on the Kang will cause physical discomfort;When controlling the temperature of the upper Kang surface,the bedding temperature of the unilateral exothermic Kang cannot be maintained between29～34℃;（2）Compared with unilateral exothermic Kang,bilateral exothermic Kang is not provided with thermal insulation layer,which can transfer more heat from the lower Kang surface to the indoor environment,and has higher system thermal efficiency.Compared with the unilateral exothermic Kang,the heating rate of the bilateral exothermic Kang in the heating stage is delayed,and the average temperature of the upper Kang surface is lower than 35℃all day.During human sleep,the bedding temperature of the bilateral exothermic Kang fluctuates less and can be maintained between 29～34℃.It can be concluded that the bilateral exothermic Kang is more suitable for the solar phase change Kang heating system in Xining area than the unilateral exothermic Kang.Finally,based on the form of bilateral exothermic Kang,the effects of phase change temperature,phase change latent heat,pipeline flow and outdoor radiation intensity on solar phase change Kang heating system are analyzed.The results show that:（1）increasing the phase change temperature or decreasing the phase change latent heat will gradually increase the average temperature of the upper Kang surface and the bedding temperature,but too large or too small phase change latent heat will lead to the average temperature of the upper Kang surface exceeding 35℃.Based on the calculation conditions in this paper,the phase change material with phase change temperature between 32～35℃and phase change latent heat between 150～200 J·g^-1 is selected,it can achieve better heating effect of Kang body;（2）When the control pipeline flow changes between 0.14～0.186 kg·s^-1,the difference of Kang body heating effect is small.Considering that the smaller the pipeline flow is,the smaller the power consumption of the system circulating water pump is,so the pipeline flow should adopt the smaller value within the specified flow range of the vacuum tubular collector;（3）When the outdoor radiation intensity is too small,the heat storage of the Kang body in the heating stage is insufficient,and the bedding temperature cannot be maintained above 29℃,so it is necessary to control the temperature at night.Based on the obtained temperature control strategy,the temperature control operation of the heating daily working condition with the lowest average radiation intensity in Xining area is analyzed.The results show that the bedding temperature under the heating daily working condition can be maintained above29℃,and the solar contribution rate of the system is 69.65%,which proves that the solar phase change Kang heating system studied in this paper has a good operation effect,It can provide design basis for the application of the system in different regions.