日光温室保温被保温性能影响因素的分析

日光温室保温被保温性能受多种因素的影响。该文采用日光温室保温被传热理论模型,针对影响保温被传热系数的主要因素进行了模拟分析。结果显示:保温被的上表面红外辐射特性对其保温性能的影响更加显著;当保温被的厚度为40~50 mm时,普通隔热材料作为保温芯材,均可满足设施园艺覆盖材料保温性能要求;保温芯材在不考虑保温被冷风渗透的情况下,当保温被的传热系数较大,上表面发射率较小时,保温被传热系数随室外风速的增大而增大;当保温被的传热系数较小,保温被上表面发射率较大,保温被的传热系数随室外风速的增大而减小。在此基础上,构建了能反映保温被传热系数与各影响因素间的关系的传热系数经验计算式。该文分析结果及成果为保温被的合理开发及应用提供了参考依据。

Analysis on affecting factors of heat preservation properties for thermal insulation covers

Abstract: The thermal insulation properties of solar greenhouse thick cover are affected by many factors, due to the complexity of heat transfer process which include conduction, convection and radiation. There have been some studies on the effects of the outdoor wind speed and infrared characteristic parameters of cover surfaceon the thermal insulation performance of thick cover. However, it is difficult to obtain accurate results due to the site conditions are not easy to control, and there are limited systematic studies on impact factors, which include heat preservation performance of greenhouse thick cover, using heat transfer theory. To master the effects of main influence factors on heat transfer coefficient of thick cover, we analyzed the relationship between surface emissivity of thermal insulation covers, thickness of thick cover, coefficients of insulation materials, wind speed of outside and the heat transfer coefficient of thermal insulation covers using heat transfer theoretical model on thermal thick cover. While the relationship between one factor and heat preservation performance of thick cover was being analyzed, other factors should be considered as constants to eliminate the impact of these factors. Thus the variation trend of relationship between single factor and heat transfer coefficient K can be gained. The results showed that the effect of up surface emissivity of thermal insulation covers on K value was more than 8.9%, and the effect of down surface emissivity of thermal insulation covers on K value was less than 4.5%, when there was fixed film under the thermal thick cover. When there was without fixed film, the effect about down surface emissivity of thermal insulation covers on K value would increase, but it was still lower than that of up surface emissivity on heat transfer coefficient. The increase in thickness and the decrease in conductivity coefficient of thermal thick cover would increase the heat transfer resistance substantially. So the K value would be decreased with thickness increasing or heat conductivity coefficient of thick cover materials reducing. It also showed that all the thermal insulation materials could meet the heat preservation performance requirements of horticultural cover, when the thickness was between 40 mm and 50 mm, based on the analysis of the relationship between K and thickness of thermal thick cover, conductivity coefficient of thermal insulation materials. K value of thermal thick cover was decreased with wind speed increasing (neglecting the heat loss of thick cover overlap joints) when emissivity of the upper surface was high and the heat transfer coefficient was low; K value of thermal thick cover was increased with wind speed increasing when emissivity of the upper surface was low and the heat transfer coefficient was high. An empirical formula on heat transfer coefficient was promoted based on the analysis of the relationship between influence factors and heat transfer coefficient. And the parameters in the formula were obtained by regression method. The empirical formula about K provides theoretical foundation for development and application of thermal thick cover.