The Study On Coupled Heat And Moisture Transfer Characteristics Of The Ground Surface In Sunlight Greenhouse

In recent years,with the ecological stress and bad agricultural production environment,how to achieve the crop quality,high efficiency,high yield,has become a new issue of modern solar greenhouse research.This means that the higher requirements should be put forward in greenhouse heat and humidity environment.However,there are few studies on heat and moisture transfer in the surface of soil.Therefore,in this thesis,a building with modern solar greenhouse was used as a test platform to research the surface temperature and humidity fields of the greenhouse.A three-dimensional unsteady numerical model was established to consider soil moisture evaporation.Coupled heat and moisture transfer characteristics of the ground surface in sunlight greenhouse was studied.Firstly,there was a brief introduction in present situation of the study on the surface temperature and humidity fields of the surface of the soil,which includes the establishment of the test platform,the description of the test equipment and the arrangement of the test points.Then,under sunny and cloudy conditions,by continuous testing of the temperature and humidity fields of the north-south surface of the soil,it was shown that there is a change rule with time in the temperature gradient of the north-south surface of the soil and the temperature and water content of the shallow soil.In addition,under the same weather conditions,there was a comparable test in the water evaporation of soil with different water content,which demonstrates the changes of evaporation and condensation rate of different soil moisture.Finally,The CFD software was used to simulate the tuyere installed in the middle,east and west zone and compare the ground surface temperature field of the two different structures.The results showed that:1.It is periodic and similar fluctuation in the surface temperature of the different distance from the back wall.The surface temperature was the lowest at 8am,and reached the peak point at 3pm in the day.Therefore,the distribution of surface temperature in the north and south of the soil is,‘ in the morning,the lower in the middle,slightly higher in the south,and the highest in the north',and in the afternoon,‘the minimum in the south,the highest in the middle,followed by the north".When the distance from the back wall is different,the distribution of soil surface moisture in the north and south is increase from North to South.2.During the daytime,the soil moisture evaporates and absorb heat,at night,the soil temperature near the surface is below to the air dew point temperature,and there is vapour condensation and exothermic phenomenon.Compared with the surface soils with low initial moisture content,the soil water phase transition rate with high moisture content experienced the highest evaporation rate and the lowest rate of condensation in the sunny days.At the same time,the soil water transition rate and evaporation rate is larger in the cloudy days and no difference in the rate of condensation.3.Under sunny and cloudy conditions,the temperature gradient of the middle surface of the soil is largest,and the middle of the soil experienced the highest evaporation and condensation.4.During the daytime,the net radiation intensity of the north-south surface of the soil experienced the largest heat uptake in the middle,the maximum heat absorption in the north and the largest heat uptake in the central again.At night,the surface of the soil release heat and the middle of the soil had the greatest heat release.5.The surface temperature of the soil at the tuyere is shown in the axisymmetric diagram,and the temperature field is clearly stratified in the north-south direction.The surface temperature of the soil is partly highest in the places with tuyere in the east and west directions.The results provide a theoretical basis for the regulation of solar greenhouse environment in northern China.