Research On The Test Apparatus And Technology For Measuring The Thermal Transmittance Of Greenhouse Covering Materials

The thermal transmittance of greenhouse covering materials is an important parameter both for estimating the performance of heat preservation of them, and designing the thermal environment in a greenhouse. In the past, the measurements, which were used to measure the thermal transmittance of the covering materials, could not provide the conditions that approximate to the real conditions. At the same time there is not a uniform measure criterion and uniform measure apparatus. So the result of these measurements cannot be compared with each other, as a result, the need of production and scientific research cannot be met.In this thesis, the process of heat transferring through covering materials was analyzed, and a mathematic model was set up to calculate the thermal transmittance of covering materials. Some elementary factors are selected from the model, which will be simulated in a test apparatus.The author develops the test apparatus, which is used to measure the thermal transmittance of the greenhouse covering materials in the laboratory. The apparatus is based on the principle of hot-box measurement and steady-state thermal transmission with one dimension. The apparatus can simulate the real conditions under which the covering materials used. These conditions include the temperature inside and outside of the greenhouse, the wind velocity outside, and the sky temperature. It is the first time to simulate the sky temperature and wind velocity outside of greenhouse in the laboratory to measure their infections to the thermal properties of the covering materials.In this thesis, the author introduces the design and manufactures of the main parts of the test apparatus in detail; and made the initial performance check to the apparatus to ensure that the simulated factors are fulfilled. The author also analyses the process of the heat transferring in the apparatus and sets up a mathematic model for the measure system of the apparatus. At last, the author used the apparatus to measure the thermal transmittance of some greenhouse covering materials.The result of the initial check and test shows that the apparatus can steadily simulate the real conditions under which the covering materials used. The conditions include the temperature inside and outside of greenhouse, the wind velocity outside of greenhouse and the sky temperature. So the apparatus can provide the necessary conditions for measuring the thermal properties of the greenhouse covering materials in the laboratory.The test result also conforms that condensation has little infection on the thermal opaque materials, such as glass, while the condensation has great infection on plastic, through which the long thermal ray can transfer.