Design And Environmental Analysis Of Ventilation Pipe Components For Positive Pressure Greenhouse Based On CFD

Compared with traditional glass greenhouses,positive pressure greenhouses can create an environment that is more conducive to crop growth.In recent years,China has begun to introduce,promote and pay attention to the research and application of positive pressure greenhouses.Positive pressure ventilation pipe components are the core components of the supporting equipment for positive pressure greenhouses.Carrying out CFD-based positive pressure greenhouse ventilation pipe component design and greenhouse environment analysis has important theoretical significance and practical value.This paper takes the ventilation pipe components of the positive pressure greenhouse as the research object,and completes the structural design of the positive pressure ventilation pipe components with two length specifications of 120 m and 60 m respectively.The designed positive pressure ventilation pipe with a length of 120 m is subjected to CFD analysis and test inspection to verify the accuracy of the design scheme.The positive pressure ventilation pipe components with a length of 60 m are applied to the actual positive pressure greenhouse,and the ventilation performance test and verification are carried out.Further carry out the experimental research on the environmental regulation of the positive pressure greenhouse,by studying the environmental changes in the greenhouse when the positive pressure greenhouse performs external circulation ventilation and internal circulation ventilation,and analyze the influence of the ventilation pipe components on the environment in the greenhouse under different ventilation modes.Combined with the experimental measurement data,the positive pressure greenhouse is modeled and verified by CFD;the environmental regulation of the positive pressure greenhouse is further simulated and analyzed according to the CFD model,and optimization strategies are proposed.The main research contents of this article are:1.Carry out experimental research on the structure and ventilation performance of positive pressure ventilation pipe components.According to the ventilation volume required for summer cooling in a positive pressure greenhouse with a length of 120 m and 60 m,the structural parameters of the corresponding positive pressure ventilation pipe components are designed respectively,and their applicability is studied through CFD analysis and experiments.1.Carry out experimental research on the structure and ventilation performance of positive pressure ventilation pipe components.According to the ventilation volume required for summer cooling in a positive pressure greenhouse with a length of 120 m and 60 m,the structural parameters of the corresponding positive pressure ventilation pipe components are designed respectively,and their applicability is studied through CFD analysis and experiments.(1)For the design plan of 120 m long positive pressure greenhouse ventilation pipe components,select the appropriate calculation domain and mesh,establish a 120 m long ventilation pipe CFD analysis model to analyze its ventilation performance to verify the accuracy of the design plan.The results of CFD analysis show that the air velocity gradually decreases along the length of the ventilation pipe;the air velocity in the calculation domain is relatively uniform,between 0.35-0.5m/s;the air velocity of the air outlets on the ventilation pipe is basically the same,indicating that the air outlets The flow rate is uniform,and the designed ventilation pipe meets the expected requirements.After the analysis is completed,a 120 m long vent pipe test site is set up to carry out the wind speed measurement test for the center of the designed 120 m long vent pipe and the wind speed at the outlet hole,and the 120 m long vent pipe design scheme and CFD model are tested.The test results show that the wind speed of each outlet is relatively uniform,in the range of 9.5-9.8m/s,and the standard deviation of the wind speed of the outlet is 0.107°C,which meets the design requirements.The experimental value of the wind speed at the center of the ventilation pipe is consistent with the change trend of the simulation value.The wind speed at different measuring points can be better simulated.The 120 m long ventilation pipe CFD model established is effective.(2)Combined with the constructed positive pressure greenhouse CFD model,the simulation analysis of the designed 60 m long ventilation pipe components showed that the wind speed of the air outlet at the front end and the end of the ventilation pipe is basically the same,indicating that the air flow velocity of the air outlets on the ventilation pipe is basically the same.It is uniform and meets the design requirements of ventilation components with a length of 60 meters.Experiments were carried out on 60 m long ventilation pipe components and positive pressure greenhouse,and the ventilation performance of 60 m long ventilation pipe components and the environmental change law in the greenhouse during external circulation ventilation and internal circulation ventilation of positive pressure greenhouse were analyzed.The test results of ventilation components show:The wind speed of the air outlet at each position on the ventilation pipe is uniform,and the standard deviation of the wind speed of the air outlet is 0.082℃,which meets the design requirements.The maximum error between the test value and the simulation value of the central wind speed of the ventilation duct is 0.9m/s,which is within an acceptable range,which proves that the established CFD model is effective.Environmental Analysis.2.CFD modeling and environmental simulation analysis of positive pressure greenhouse.Taking 60 m length specifications of positive pressure ventilation pipe components and positive pressure greenhouses as the research objects,according to the characteristics of the internal structure of the greenhouse,the physical model of the greenhouse is appropriately simplified,and a suitable calculation area is selected for grid division.According to the characteristics of internal airflow changes during ventilation,the DO radiation model,wall function method,k-εturbulence model,and porous media model are determined as the numerical model of the positive pressure greenhouse and the boundary conditions that the model needs to set,and the positive ventilation components are established.Three-dimensional calculation model of pressure greenhouse.The positive pressure greenhouse CFD model is used for simulation analysis,and the simulation results are verified by experimental data.The results show that: for external circulation ventilation,the maximum error between the experimental value and the simulation value is 1.8℃,and the maximum relative error is 6.36%;for internal circulation ventilation,The maximum error is 0.6 ℃,the maximum relative error is 2.34%,the temperature change curve of each measuring point under the two working conditions is basically the same,indicating that the established positive pressure greenhouse CFD model is effective.3.Complete the experimental analysis of the distribution of environmental factors in the positive pressure greenhouse.The environmental measurement test of the positive pressure greenhouse shows that when the positive pressure greenhouse performs external circulation ventilation,due to the obstruction of the crops to the airflow,the temperature in the 1.5m altitude area is relatively high,which is 1-2°C higher than the 2.5m and 3.2m altitude areas.During the test,the outdoor temperature was 18-21°C.When the fan was turned off,the temperature in the greenhouse rose rapidly.The temperature in each altitude area exceeded 32°C,and the highest temperature reached 33.3°C.Before the positive pressure greenhouse is ventilated internally,due to the sun’s radiation,the temperature in the 3.2m altitude area is higher,which is 0.5-1°C higher than the 1.5m altitude area.When the greenhouse is ventilated internally,the temperature of each area in the greenhouse is closer,and the temperature uniformity is higher.4.Use the CFD model of the positive pressure greenhouse to further analyze the change law of the climate environment in the greenhouse under the conditions of external circulation ventilation and internal circulation ventilation in the positive pressure greenhouse.The simulation results show that when the positive pressure greenhouse is externally ventilated,the front and rear parts of the greenhouse are prone to local high temperature areas.Especially for the front of the positive pressure greenhouse,the temperature distribution is uneven.Because the crops have a large obstructive effect on the airflow,The temperature of the crop area above the pipe is also relatively high.When the positive pressure greenhouse is internally circulated and ventilated,the temperature at the rear of the greenhouse is relatively high due to the poor fluidity of the air at the rear.According to the existing problems in the two ventilation conditions of the positive pressure greenhouse,for the external circulation ventilation and the internal circulation ventilation of the positive pressure greenhouse,optimization strategies for changing the inlet wind speed of the ventilation pipe and opening the ventilation holes at the tail of the ventilation pipe were respectively proposed.The analysis results show that: when the improved positive pressure greenhouse performs external circulation ventilation,the wind speed at the inlet of the ventilation pipe is 7m/s,and a better temperature distribution can be obtained.For the circulation ventilation in the positive pressure greenhouse,after opening the ventilation holes at the tail of the ventilation pipe,the air flow effect at the rear of the greenhouse is better,and the temperature distribution in the greenhouse is more even.