Experimental Analysis On Photothermic Property Of New Style Covering Materials PETP Film For Greenhouse

In multi-span greenhouses, the coupling of heat storage and release courses caused by radiation, conduction, convection, wet evaporation, crop rising and condensation and the dynamic change of the outdoor cold weather parameters affect the indoor environment momently. Such aspects of covering materials as light permeation performance, heat preservation performance, endurable performance, anti-aging performance, dew drips resistance performance and intensity are the important indexes to appraise the qualities of the covering films for greenhouses.The main covering materials in existence for greenhouses are glasses, PC hollow board, PVC, PE and EVA plastic films. Each of them has shortcomings. It badly demands researching and developing new agricultural covering materials. Polyethylene terephthalate (PET) is a new type of polymeric plastic materials. With the excellent physics performance, PET has been widely applied into many industries such as chemical industry, packaging industry and medical treatment trade. The paper mainly researches on the photothermic property of PETP film (changed by PET materials) utilizing as agricultural covering materials.Under the indoor steady state, the thermal properties of new type PETP film and several kinds of common covering materials have been measured by the method of one-dimensioned thermal insulated box. After analyzing the thermal transmittance (K) of different materials, the following conclusion is drawn that the heat preservation property of PETP film with 0.lmm thickness is between those of 8mm thick hollow PC hollow board and 0.15mm thick PVC film. Moreover, the heat preservation capability of PETP film will augment with the increase of thickness. The whole spectrums of PETP film and other covering materials have been measured simultaneously. After comparing the spectrums, it is found that in winter during 5~25um, the main radiation extent of inside heat radiation, the heat transmitting rate of PETP film is further less than those of the others. Transmitting rate can reflects the heat preservation performance in a degree. So that can prove, from another aspect, the experimental results of the heat transfer performances of various covering materials. Moreover, PETP film has excellent property of transmitting solar radiation, the chart of which basically tallies with the ideal transmitting chart of covering materials for greenhouses.