Temperature Field Simulation Of Solar Greenhouse In Winter Based On CFD And Temperature Homogenization Control System

As the main winter agricultural production facilities with high heat preservation in northern China,solar greenhouses can guarantee the temperature of the internal microclimate reach to a certain level and play an important role in the cultivation of vegetables and flowers in the winter,especially for vegetable production providing throughout the year.But in winter,because of the particularity of the greenhouses structure,the temperature distribution inside the greenhouses is more complex.The heat distribution at different positions is not uniform,with low heat energy utilization rate,which would lead to the large difference of growth of crops,as well as the low yield.According to the problem of low yield because of the uneven distribution of temperature in winter,the CFD model of the greenhouses has been constructed,and the test platform of temperature field model has been validated and improved.The high temperature effect is obtained through the test;finally,the temperature homogenization control system has been designed to achieve good environment with well-distributed temperature.This system can be used effectively for temperature homogenization,improving the uniformity of crop growth,and can increase the yield to a certain extent,promoting the development of solar greenhouses.Following are the main research contents and conclusions of this paper:(1)The building of test platform and data preprocessing.To fully understand the greenhouses internal and external environment parameters and the changing law,the test platform has been set up,including multi point temperature monitoring system and outdoor meteorological station.Environmental information in test greenhouse is preliminary collected,including temperature and humidity of the indoor/outdoor air,as well as the soil,and the outdoor wind speed and the light.The data are processed with MATLAB,and the temperature distribution inside the greenhouses is gained,providing boundary conditions for CFD modeling.(2)The construction and simulation of CFD model of temperature field in greenhouses.Firstly,the geometric model of solar greenhouses has been constructed by SolidWorks software,and then grid model of high quality has been meshed using the "Y" type grid by ICEM CFD software.Based on the data of the experimental platform as the initial and boundary conditions of the model,the simulation model has been simulated on the FLUENT platform.About the model simulation results,the precision of the model is tested by experimental data platform and the error is within 2?.(3)Test of temperature homogenization in greenhouses in winter.In order to obtain the highest efficiency of the strategy to improve the temperature uniform of greenhouses environment,the temperature homogenization test of winter greenhouses has been done.With the mean and variance of temperature as the main uniformity index,experimental study has been done in different weather conditions on the fan strategy for the efficient strategy.It is recommended that 4 fans with medium speed running intermittently for sunny and cloudy day,2 fans with low speed running intermittently for rainy and snowy day.And the test has been done with temperature increasing device to analyze temperature homogenization equilibrium and warming effect of greenhouses,in order to improve the arctic weather conditions of greenhouses temperature compensation heat utilization rate.It is recommended that heating 10 minutes intermittently with 2 fans for sunny and rainy/snowy day,heating 10 minutes continuously with 2 fans for cloudy day.(4)Achieving of the automatic temperature homogenization system in solar greenhouses.128 points inside the greenhouses for monitoring the temperature data has been used to collect the temperature data,with the human-machine interactive control terminal processing temperature data.Judgments and decisions has been made based on the temperature model embedded,sending out the control command.The processor control the fan through control module including the number,speed and start/stop strategy of the fans,in order to achieve the purpose of automatic temperature homogenization.This system is stable in the greenhouses with high effect.