Study On Environmental Impact Of Lettuce And LED Light In Plant Factory Based On CFD

Plant factory refers to an efficient agricultural method that realizes the annual continuous production of crops through high-precision environmental control in the facility.It is highly technology-intensive and makes full use of modern engineering,biological,environmental and information means.In recent years,it has been internationally recognized as the highest development stage of facility agriculture.In artificial light plant plants,forced convection under ventilation and air circulation can control the growing environment of crops and keep the stable climate.For the current Computational fluid dynamics(CFD)software is used to simulate the flow field and temperature field in plant factories,which is only carried out in no-load plant factories,ignoring the problems of lettuce plants and LED plant growth lights.The aerodynamic parameters of lettuce and the boundary conditions of LED plant growth lamp were obtained by designing experiments respectively,and the parameters and boundary conditions obtained were applied to the environmental simulation of air flow field and temperature field in plant factories,and the simulation results were compared with the simulation results of empty plant factories.1.Drag coefficient of lettuce canopy(C_D)is determined by using wind tunnel system,and the relationship of lettuce canopy permeability(K)and momentum loss coefficient(C_f)in different leaf area density was obtained under the condition of(L),the relationship between the place lettuce planting plate in the middle of their wind tunnel test section,the static pressure and wind speed of different measuring point locations were measured including the vertical direction and horizontal direction.The viscous resistance coefficient and inertial resistance parameters required for the establishment of lettuce porous media model in CFD modeling are obtained through the obtained parameters.The results showed that:1)The resistance coefficient of lettuce canopy measured in this experiment was C_D=0.02;2)The permeability was 0.04 m~2 and the momentum loss coefficient was 0.13 of mature lettuce(L=32.5 m~2/m~3);3)The values of the nonlinear momentum loss coefficient C_f are 0.1-1.0,and when the leaf area density L was 10,20,and 30 m~2/m~3,the values of the canopy permeability K were 0.25-25.00,0.06-6.25,and0.03-2.78 m~2,respectively;4)Viscous resistance of mature lettuce was 25,inertial resistance factor was1.3.2.In this experiment,a single-layer production system was constructed,and a three-dimensional model was developed and validated.In the model,the LED lamp was divided into a reactor and a lampshade.The reactor was set as the boundary condition of heat source.According to the numbers of red and blue bulbs and the corresponding electro-optical conversion efficiency,the heat dissipation per unit volume was calculated.The lamp shade is a plastic shell on the surface of the LED lamp,which was set as a heat conduction material.The measured values of airflow speed and temperature on the cultivation system were compared with the simulated values.The feasibility of setting LED lamp reactor as heat source and lamp shade as heat conduction material in CFD model was verified.The results showed that:1)The heat dissipation per unit volume of LED lamp in the three-dimensional model of cultivation system was 34166 W/m~3;2)The root-mean-square error of the measured and simulated wind speed values at 30measurement points was 0.06 and the root-mean-square error of the measured and simulated temperature value at 46 measurement points was 2.63.It is feasible to set LED supplementary light reactor as heat source and lamp shade as heat conduction material in CFD simulation of plant factory.3.Since the experimental plant factory has a north-south symmetrical structure,only half of the plant factory was simulated and analyzed in this experiment,and the middle was set as a symmetrical plane.The flow field and temperature field were simulated in two cases.Case 1 was the no-load cultivation rack placed in the plant factory,case 2 considered the heat loss of lettuce canopy and LED lamp.The results show that:through the test and analysis,case 2(the cultivation frame of planted lettuce)was more consistent with the actual situation than case 1(the no-load cultivation frame).Therefore,the influence of crop canopy and LED lamps on the internal airflow field and temperature field should be considered when using CFD to simulate the plant factory environment.