基于太阳能牧草干燥的相变蓄热材料热物理特性研究

Study on Thermal Physical Properties of PCM Based on Solar Energy Drying of Forage

太阳能低温干燥技术能够最大限度地减少苜蓿草营养成分的损失。目前,相变蓄热技术在工、农业领域的应用前景广阔,而太阳能相变蓄热技术在牧草干燥领域的研究很少。牧草干燥的中温太阳能蓄热技术研究不多的主要原因是对牧草干燥领域应用的相变材料的基础研究不足,文献获得的物性数据可信度不高,对相变材料的热物理特性参数获取的不准确直接影响相变蓄热装置的开发。为此,在牧草太阳能干燥设备参数和水蓄热研究成果的基础上,初步选择了甘露醇、复合共晶盐和复合赤藻糖醇3种相变蓄热材料作为研究对象,进行了试验研究。试验结果表明:甘露醇和复合赤藻糖醇在中温相变蓄热材料中表现突出,相变潜热值高;但甘露醇和复合赤藻糖醇存在导热系数低的缺点,在应用过程中需进行强化传热。研究成果可为牧草干燥的中温太阳能蓄热技术提供准确的参考依据。

Solar low-temperature drying technology can minimize loss of alfalfa nutrients.Phase change heat storage technology has a wide prospect in the fields of industry and agriculture,while solar energy phase change heat storage technology has little research in the field of herbage drying.The main reason for the lack of research on the heat storage technology of medium-temperature solar energy in herbage drying is that the basic research on the PCM used in the field of pasture drying is insufficient,and the reliability of the physical characteristics data of the PCM obtained in the literature is not high.So the inaccuracy of the parameters of the thermal physical characteristics of the PCM directly affects the development of the phase transition heat storage device.Based on the parameters of solar drying equipment for forage and the results of water heat storage,three phase change heat storage materials of mannitol,compound eutectic salt and compound alginosacol were selected as the research objects.The measured solid-liquid phase change temperature of β-phase mannitol is 162.83℃,the liquid-solid phase transition temperature is 153.87℃,and the phase change latent heat value is 324.1 J/g;The temperature has maintained good thermal stability within 287℃;Its solid thermal conductivity is 0.6 W/(m·℃);The phase change temperature of composite eutectic salt solid-liquid is 142℃,and the potential heat of phase transition is 75.312 J/g;Temperature within 400℃ maintains good thermal stability.The temperature is between 50℃ and 150℃,the thermal conductivity decreases with the increase of the temperature,and the thermal conductivity of the composite eutectic salt increases from 1.06W/(m·℃)to 2.01W/(m·℃),the reduction process is linear.The solid-liquid phase transition temperature of compound alginosaccharide is 118.84℃,and the potential heat of phase transition is 324.9J/g;The temperature has maintained a good thermal stability within 225℃;The thermal conductivity of compound alginol increased from 0.285W/(m·℃)to 0.344W/(m·℃).Furthermore,the experimental results show that mannitol and compound alginosacol are prominent in the medium temperature phase change heat storage materials,and the potential heat value of phase transition is high.However,mannitol and compound alginosacol have a disadvantage of low thermal conductivity,and heat transfer should be enhanced during application.The research results in this paper provide an accurate reference for heat storage technology of medium temperature solar energy for pasture drying.