| Greenhouse agriculture has obvious advantages over traditional planting because it is less affected by climate conditions.It is a unique type of plant growth in northern China and an indispensable part of rural economic construction.Through reasonable ventilation,the important factors such as temperature,humidity and solar radiation in the greenhouse meet the requirements of plant growth,so as to increase crop yield and efficiency,and it has important practical significance and economic value.In this paper,the combination of field test and numerical simulation is used to carry out the following research on the round arched winter jujube greenhouse:(1)In this paper,the microclimate environment of the round arched winter jujube greenhouse in Dali County of Shaanxi Province was tested.The microclimate environment characteristics of the winter jujube greenhouse in the county were preliminarily studied,and the changing rules were summarized.During the test period(August 10 th to 11 th,2018),the average temperature in the greenhouse reached47?;the highest temperature in the greenhouse at 14:00,up to 47?;In the morning from 01:00 to 07:00,the relative humidity in the greenhouse is the highest,reaching100%.This condition exceeds the appropriate range for the growth of winter jujube.In order to find out the natural ventilation mechanism of the greenhouse,based on the test results,the appropriate assumptions and simplifications of the natural ventilation process in the greenhouse were carried out,and the CFD numerical model of greenhouse ventilation was constructed.The measured results were used to verify the accuracy of the numerical model.(2)In this paper,the distributions of temperature and velocity fields in different cross sections in length,span and height directions are analyzed.It is concluded that thecooling method is to reduce the top temperature and enhance the airflow in plant canopy.(3)Combined with the working principle of the solar chimney greenhouse.,the temperature field and velocity field distribution of the solar chimney greenhouse with seven different positions and structures were analyzed by CFD simulation.The results show that the cooling effect of the greenhouse is obvious after adding solar chimney,and the maximum temperature can reach 4.8 ?.The airflow structure in the SC-VI type is more uniform than other models,so the ventilation effect is the best and the cooling effect is better.Taking SC-VI as the research object,the temperature field and velocity field in greenhouses with different inlet wind speeds,different widths and different heights were simulated,and the results were analyzed.The results show that the wind speed is increased from 0.5m/s to 1.0m/s,and the temperature in the greenhouse is reduced by 2°C on average.Increasing the width to 1.5m will enhance the air flow and continue to increase the air flow no longer.The increase of the height of the greenhouse is close to the chimney.The flow of the air has a promoting effect,but the overall cooling effect does not change significantly,and the average temperature is lowered by0.2 °C.(4)Due to the uncertainty of natural ventilation,in order to ensure proper temperature and relative humidity in the greenhouse,the wet curtain fan can be used as an auxiliary measure for cooling under the condition that natural ventilation is not guaranteed,and the heater is used as insulation measure.The results show that: in the hottest weather in summer,the temperature in the greenhouse exceeds 35 °C from 9:00to 18:00,using solar chimney and wet curtain fan for cooling;natural ventilation is carried out from 18:00 to 21:00;relative humidity in the greenhouse from 21:00 to 9:00exceeds 85%,and dehumidifier is used to dehumidify.In the coldest weather in winter,the downwards mechanical air supply can be used to heat the air. |
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