植物工厂导气栽培槽通风对冠层环境影响模拟

    Simulation of the effects of ventilation on canopy environment using cultivation bed with draft tube in a plant factory

    • 摘要: 为了增加植物工厂多层栽培模式中作物冠层内部气流扰动和简化通气管道施工工艺,该研究设计了一种集栽培床和通风管路于一体的导气栽培槽(cultivation bed integrated with draft-tube,CBT)。利用流体计算软件(computational fluid dynamics,CFD)构建了CBT模型,通过模拟和实测入口速度为5.0 m/s时植物冠层内部的气流速度,得到栽培区域几何中心截面速度的模拟值与实测值分布趋势一致,计算模拟值与实测值的均方根误差为0.22 m/s,表明该模型能准确模拟气流速度。利用验证的模型模拟了不同进气速度对作物冠层内部气流分布的影响得到入口速度为6.0 m/s时,植物冠层空间适宜的气流区域体积占比最高,为56.3%,该入口速度下冠层区域的气流平均速度为0.15 m/s。根据模拟结果,选取6.0 m/s为CBT的入口速度,以成熟期生菜作为试验材料,在同一环境条件下对比CBT通风模式和传统通风模式(traditional ventilation control,TVC)下生菜冠层内部微环境,测试通风调温效果。结果表明,CBT处理的冠层内光期温度为22.4 ℃,低于TVC处理的23.7 ℃,暗期处理间温度差异不明显;CBT模式冠层内的光、暗期平均相对湿度分别为65.8%和71.6%,比TVC处理低11.4和3.0个百分点。由此可见,相比于传统通风模式,CBT对冠层内多种微环境参数调控起到了积极作用,降低环控要求,提高了空调温控效率,具有推广价值。

       

      Abstract: Air conditions are usually used to control the environmental parameters in plant factories with artificial light. Among them, the air velocity is generally lower than the optimum range of 0.1-1 m/s that is required for plant growth. The occurrence of tipburn behavior is often observed on the inner and newly developed leaves of lettuce plants, especially during the last days of transplanting. It is very necessary to properly design the airflow in the indoor cultivation systems, thus promoting the growth for less occurrence of tipburn in the lettuce plants. The perforated air tubes can be used to improve the airflow. However, this ventilation scheme is required by the installation of pipelines in the plant factory, inevitably leading to an increase in the installation process and the complexity of the project. In this study, a kind of air-conducting cultivation tank was designed to integrate with the cultivation bed (CBT). The airflow disturbance increased inside the crop canopy in the multi-layer cultivation mode of the plant factory, indicating the simple construction of the ventilation pipe. A model of CBT was also constructed using three-dimensional computational fluid dynamic software (CFD). The airflow velocity was simulated and measured inside the plant canopy with the inlet velocity of 5 m/s. The root mean square error was 0.22 m/s between the calculated and measured airflow velocity. There was a consistent distribution of the simulated and measured geometric center section in the cultivation area, indicating the accurate simulation of the airflow velocity. The validated model was used to simulate the effects of different air inlet velocities on the airflow direction and distribution inside the crop canopy. The simulation results showed that the airflow entered the crop canopy area via the holes of the cultivation pipe, thus forming a regular airflow beam profile. There was a larger airflow area of high velocity in the crop canopy with the increase of the inlet airflow velocity. Once the inlet velocity was 6 m/s, the percentage of volumes was 56.3% inside the plant canopy with the air velocity between 0.1 and 1 m/s, and the volume-weighted average air velocity was 0.15 m/s in the canopy interior. Correspondingly, 6 m/s was selected as the entrance speed of CBT, where the mature lettuce was used as the test material. The microenvironment was compared in the inner part of the lettuce canopy under CBT and traditional ventilation control mode (TVC) under the same environmental conditions. A systematic investigation was carried out to test the effect of ventilation and temperature regulation on the air flow velocity. The results showed that the air temperature was 22.4 ℃ inside the canopy under CBT treatment during the light period, which was lower than the TVC treatment of 23.7 ℃. There was a relatively less significant difference in air temperature in the dark period. The average air relative humidity in the light and dark periods inside the canopy under the CBT treatment was 65.8% and 71.6%, respectively, which were 11.4 and 3.0 percentage points lower than those under the TVC treatment. As such, the CBT greatly contributed to the regulation and control of various micro-environmental parameters inside the crop canopy, compared with the traditional ventilation mode. The finding can provide the promotion value to reduce the requirements of environmental control for the high efficiency of air conditioning temperature.

       

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