Theoretical Analysis And Validation On Heat Transfer Of Covering Layer And Heat Transfer Coefficient

Theoretical analysis method on heat transfer of covering materials was established and test measurement method was used to validate in this paper in order to study on the relations between heat transfer coefficient of covering materials in greenhouse and their thermal property, including infrared emissivity, reflectivity, transmittance etc. as well as their work conditions in situ, including outside temperature, inside temperature, sky temperature, and wind speed. These methods can offer theoretical guidance for evaluating heat transfer coefficient of covering materials, designing environment of greenhouse, studying, analyzing and using greenhouse.Theoretical model on heat transfer of covering materials in greenhouse firstly was established. Secondly energy equilibrium of covering layer was put forwards. And then theoretical calculation formulae on heat transfer coefficient of covering layer were deduced. Covering layer was supposed as arciform surface in theoretical model. At the same time it meets the need of proper predigestion and shows that its construction has effect on model. By analyzing net radiation of covering layer inside and outside, the theoretical method determines expressions on heat transfer of radiation, which show the effect of several factors.Test measurement method was improved on basis of primary test apparatus. A set of operative test procedure and method on dealing with data were provided in this paper. After improved, the test apparatus can simulate real work conditions of covering materials, the test is took under the stable test conditions, the test conditions are comprehensively adjusted to some extent, and the measuring values is exact.Research results show that the effect of transmittance on heat transfer coefficient of covering materials is obvious, effect of emissivity is the second, and effect of reflectivity is steady. Wind speed and sky temperature have different effect on heat transfer coefficient of different covering materials. PE film's is obvious and PC's is almost steady.