The Establishment And Application Of A Two-dimension Heat Transfer Model Of Soil In Chinese Solar Greenhouse Based On MATLAB

The solar greenhouse is an important facility for winter vegetable production in China.The solar greenhouse area has expanded quickly in our country these years. It has thecapacity of good heat preservation and heat storage, and it can provide betterenvironmental conditions for winter crop production. But due to the environmentalconditions, facility structure, the different crop cultivations and management levels, thesolar greenhouse production capacity has great differences. Therefore, it is how to chooseand build the appropriate type of solar greenhouse, optimize the environment condition ofgreenhouse, improve the efficiency of greenhouse production that has been the importantproblem faced in the greenhouse production.Aiming at this problem, our country’s researchers have conducted a lot of discussionand researches on the theory of thermal environment of greenhouse; it is found thatgeothermal conditions of solar greenhouse have played a key role in the production. Byresearching and analyzing the greenhouse structure and production conditions based onHebei province, and based on the underground temperature as the research object, the solargreenhouse of underground heat, water and gas is built up coupling of two-dimensionunsteady heat and mass transfer model, which quantitatively analyzes two-dimensiontemperature changes under greenhouse in mainland. Different from the previousgreenhouse thermal environment analysis method, this model introduces a vegetable cropcultivation conditions and related parameters, such as greenhouse irrigation condition, amore accurate analysis of various factors on the greenhouse temperature synthesis. And thegreenhouse tomato cultivation sinking depths by using the new model are analyzed. Thispaper studies the following main contents and conclusions:The system analyzes the greenhouse thermal environment based on the theory ofmathematical modeling, part of the combining previous research results. This paperestablished the equation of solar total radiation in solar greenhouse ground in real timeafter analyzing the factor such as the internal and external environmental conditions ofgreenhouse, greenhouse structure, crop growth parameters including height, plantingdensity.Greenhouse soil heat and mass transfer coupling model was established in this paperafter determining the simulation region and grid, based on the characteristics of solargreenhouse thermal environment changes, and the analysis of three heat transfer waysincluding soil heat conduction, convection and phase transition. The undergroundtemperature distribution was simulated by using MATLAB software to numerical model of the linear system of equations, based on setting the external environment parameters,greenhouse structure, crop growth height, density of crop planting, soil saturation ingreenhouse, and soil physical parameters.The real greenhouse temperature was received by measuring continuously for threemonth in the experiment greenhouse of Baoding (Dingxing). The analysis of realgreenhouse value and the simulation value showed that building model could bettersimulate the cold season solar greenhouse temperature of the underground section. Thedifference of real data and simulation value was0.9℃and the mean relative differencewas7.8%under cloudy weather; however, the difference was only0.4℃and the meanrelative difference was2.8%under sunny weather. The result showed that the modelbuilding can simulate accurately the varies of the ground temperature in greenhouse.By using the model simulation analysis of five different sinking depth of thegreenhouse temperature values, the simulation results for the sinking depth not more than1.0m, sinking deeper, the greater the ground temperature increase, the greater the groundtemperature uniformity; Sinking depth of1.2m in a significant reduction in the effects ofwarming, ground temperature uniformity no increase. The model simulation analysis areused to get that the appropriate sinking depth about planting spring peach tomatoes inwinter in the solar greenhouse of Baoding was1.2m, the plant density was2200plants per667㎡spring peach tomatoes, and the row spacing of each plant was30cm by40cm.