Experimental Study And CFD Analysis Of Radiation And Temperature Fields In 6m Shoulder Height Glasshouse

With the development of the scale of facility agriculture,the number of large-shoulder type glass greenhouses in China has increased in recent years.With the increase of the shoulder height of the greenhouse,the trusses of the pillars will also become thicker,resulting in greater non-uniform indoor radiation.In order to improve the uniformity of radiation in the greenhouse,based on measuring the radiation characteristics of the scattering glass,this paper analyzes the changes of the internal radiation field and temperature field under different covering materials,and provides a theoretical reference for the use of scattering glass greenhouses.At the same time,most of the existing shading regulation models are aimed at controlling temperature.Although the use of shading nets reduces the temperature inside the greenhouse,it leads to low indoor radiation intensity and is not conducive to crop growth.In order to optimize the control mode of the shading net and improve the canopy radiation and temperature distribution of crops,the changes of canopy temperature field and radiation field of greenhouse crops under different shading conditions were studied in this paper,which provided a theoretical basis for optimization of shading regulation schemes.In this paper,a 6-meter shoulder-high multi-span glass greenhouse was used as the object.The distribution of greenhouse environmental factors was measured in actual experiments,and a corresponding greenhouse CFD numerical model was established.The validity of the CFD model was verified using experimental test data.On the basis of measuring the radiation characteristics and spectral transmittance of the scattering glass,the CFD model of the greenhouse was used to further study the changes in the canopy radiation field and temperature field of the crop canopy with different covering materials and different shading rates,based on crops.The design of the shading regulation scheme for light and temperature needs and the use of scattering glass greenhouses provide theoretical guidance.First,the radiation characteristics of the scattering glass were measured by means of total radiation,scattered radiation,photosynthetically active radiation,and hyperspectral instruments.The experimental data was processed and the transmittances of the visible and infrared wavelengths of the scattering glass were calculated to be 0.78 and 0.7respectively.The average value of 0.77,the direct scattering transmittance is 0.27;the measured scattering glass values can be used for the subsequent CFD modeling analysis of the scattering glass cover material greenhouse.Secondly,the indoor and outdoor radiation and temperature and humidity values of large shoulder high glass greenhouse were measured,and the effects of the number of shade nets on indoor radiation and temperature were analyzed.When the average outdoor solar radiation is 735W/m²and the outdoor average temperature is 42.1°C,the indoor average solar radiation value is 203W/m² under a sunshade net with a shading rate of70%;corresponding indoor The average photo-quantum flux density is 463.9umol.m^-1s^-1;the average indoor temperature is 37.9°C,and the indoor temperature is 4.2°C lower than the outdoor one.When the average outdoor solar radiation is 532W/m²,the average outdoor temperature is 39.5°C,and the average solar radiation in the two-story sunshade net?one is a shading rate of 70%on and other is a shading rate of 55%?The intensity is57.6 W/m²,and the average photo-quantum flux density in the corresponding room is104umol.m^-1s^-1;the average indoor temperature is 35.7°C,and the indoor temperature is3.8°C lower than the outdoor.It shows that the sunshade net cooling is significant,but the two-story sunshade net makes the indoor radiation value lower,which can not meet the needs of the crop's light temperature,and it needs to optimize the sunshading control scheme.Then,the greenhouse physical model was simplified and a corresponding greenhouse CFD model was established.The standard k-?turbulence model was selected as the numerical simulation method for air flow;the DO model was chosen to solve the radiative heat transfer;the solar ray tracing algorithm was used to calculate the direct solar heat flow;and the steam component transmission model was selected to consider the wet air to the canopy temperature field.Impact;The radiation conversion method was used to simulate the impact of external shading on the indoor environment.The rational setting of porous media was used to simulate the internal shading nets and crops.The boundary conditions were set and the model was solved for convergence.Comparing the simulated values and experimental values of the non-shading,one-layer shade net,and two shade nets respectively.It was found that the simulation results of the radiation value and temperature value without shade net were good,the radiation value error was 4.8%,the temperature field error was 2.3%;there was a layer of shade net under the radiation value error was 19%,the temperature field average error was 3.3%;two layers The shading radiation value error is 18.7%,and the temperature field average error is 4.5%.Within a reasonable error range,the CFD model is effective.Finally,based on the established CFD model,by changing the corresponding boundary conditions,the canopy radiation field and temperature field of greenhouse crops under different glass cover materials,shade nets with different shading rates,and different canopy air relative humidity conditions were analyzed.Variety.The results were as follows:Under a sunshade net with a shading rate of 63%,the average solar radiation intensity was 265 w/m²,and the corresponding photo-quantum flux density was 485.9umol.m^-1s^-1.The average temperature was 38°C.Under the shade of shading rate of 43%,the average solar radiation intensity is 305w/m²,and the corresponding photon flux density is 559.2umol.m^-1s^-1,and the average temperature is 39.3°C.At the same time,the influence of canopy air humidity on crop canopy temperature field was analyzed.Under the same external radiation temperature,when the canopy relative humidity was65%,the indoor average temperature was 37°C and the relative humidity was 95%.The average temperature is 36.2°C,which means that the average difference in the canopy temperature is 0.8°C when the relative humidity differs by 30%.In addition,the solar radiation and temperature distribution under different covering materials were analyzed.It was found that under the same conditions,the internal radiation of the scattering glass covering material was relatively uniform and the average radiation value was 260w/m ²,which was more than the average value of the float glass.Low 30 w/m²;the average canopy temperature of the float glass greenhouse is 43.7°C,and the average canopy temperature of the scattering glass greenhouse is 42.9°C.Based on this analysis,taking the greenhouse cucumber crop as an example,a case of a solar control scheme based on the net photosynthetic rate of crop canopy was given.