| In most rural areas in northern China,heating in winter mainly depends on burning coal,natural gas and fuelwood.Traditional heating methods not only have disadvantages such as low comfort,poor safety,and bad sanitary environment,but also cause serious pollution to the atmosphere.From the perspective of energy conservation and environmental protection,this paper designs a storage system using solar energy as a heat source,paraffin-expanded perlite composite PCMs(phase change materials)as an energy storage medium with laying carbon fiber cloth to enhance thermal conductivity.It can provide a kind of comfortable and safe heating device in the countryside.Firstly,domestic and foreign literatures related to solar technology,PCMs thermal storage technology,fired-bed technology and carbon fiber cloth application have been referred to determine the operation system of composite PCMs energy storage technology.The thermal load of the experimental room is calculated based on the meteorological parameters of Tianjin area and the heating design temperature.No.35 paraffin and expanded perlite with a particle size of 3～4 mm are used to prepare composite PCMs,an experimental platform is set up,temperature measuring thermocouples are arranged,and an experimental operation scheme is determined.Secondly,the analysis method of thermal performance of energy storage Kang is determined.Thermal performances of pure paraffin energy storage Kang at temperatures of35℃,40℃ and 45℃ are analyzed.The results show that the optimal water supply temperature is obtained at 40℃ for pure paraffin energy storage Kang.At this time,the average surface temperature is 36.19℃,the heating rate is 2.07℃/h,the cooling rate is1.60℃/h,and the uneven surface temperature is 1.81℃.Though the comparative analysis of experiments,it can be show that the composite PCMs energy storage Kang has the best performance when the ratio of paraffin wax to expanded perlite is 1:1 at water supply temperature of 40℃.At this time,the heating rate is 1.08℃/h,the cooling rate is 0.94℃/h,and the unevenness of surface temperature is 1.66℃.The composite PCMs Kang can not only reduce the amount of paraffin with meeting the comfort requirements,saving investment costs and reducing the risk of paraffin leakage during the phase changing period,but also improve the overall safety performance of energy storage Kang.Thirdly,thermal conductivity of the composite PCMs energy storage Kang can be improved by laying carbon fiber cloth.Thermal performances of the energy storage Kang when the carbon fiber cloth is laid at the lower,middle and upper positions are experimentally analyzed at different water supply temperatures.The following conclusions are obtained that thermal conductivity effectiveness of the Kang can be reach to the highest level when the carbon fiber cloth is laid at the lower position.When the water supply temperature is 35℃,the ratio of paraffin to expanded perlite is 1:1,and also when the carbon fiber cloth is laid at the lower position,the energy storage Kang of carbon fiber cloth combined with composite PCMs can reach to optimized condition.It is defined as an optimized operating scheme.At this time,the optimized average temperature of the energy storage system over the whole day is 31.85℃,and the temperature of the sleep layer is 29.79℃.Laying carbon fiber cloth can enhance the thermal conductivity of the energy storage Kang without affecting the phase changing process.Finally,the thermal performance of the optimized composite PCMs energy storage system is used to compare with that of the conventional Kang,and results show that the optimized average phase temperature of the composite PCMs energy storage system is higher and the surface temperature is more stable.The sleeping environment is safer and more comfortable,and the heating method is more economical and environmentally friendly. |
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