植物工厂双通道导气通风模式对生菜冠层热交换的影响

    Impact of dual channel aeration ventilation on lettuce canopy heat exchange in plant factories

    • 摘要: 针对植物栽培空间气流低而导致的植物生长缓慢和生理性病害频发等问题,该研究优化设计了一种装配式双通道导气栽培系统,并在环境较为稳定的植物工厂内开展栽培试验验证系统有效性。试验栽培材料选用生菜(Lactuca sativa cv. Butterhead),试验组采用双通道导气通风模式,冠层气流速度分别设置为0.6 m/s(T1)、0.9 m/s(T2)和1.2 m/s(T3),对照组仍采用植物工厂侧进上出的常规通风模式(CK),冠层气流速度为0.2 m/s,探究不同通风模式对植物生长、叶烧发生率、与周围环境热交换和冠层微环境的影响。结果显示:与CK相比,试验处理组生菜的生长、冠层微环境及与周围环境的热交换均较优;T2处理下,生菜地上部的干、鲜质量比CK处理的分别提高了24%和14%;生菜冠层的微环境及热交换在T3处理下达到最佳;与CK处理组相比,T3处理下的生菜冠层平均相对湿度和温度分别降低了8.8%和2.8℃,生菜冠层光、暗期显热分别提高了48.5%和52.3%,潜热分别提高了52.9%和37.9%;此外,试验处理还可以有效降低植物工厂内生菜叶烧发生率。综上可知,该双通道导气栽培系统能有效改善植物冠层微环境,提高植物产量和品质,促进植物与周围环境的热交换,同时为植物工厂微环境精准调控提供技术支撑。

       

      Abstract: A stagnant airflow area can often occur in the increasing cultivation layers in a plant factory with artificial light, leading to the low growth of the plant, and even physiologic diseases, like tipburn. Furthermore, stagnant airflow can also lead to uneven distribution of environmental factors in the plant canopy, resulting in uneven growth of plants. The optimal air velocity is in the range of 0.3-1.0 m/s in plant canopy. A ventilation system can effectively solve these challenges. Previous studies have focused on the airflow to the plant cultivation spaces. However, these ventilation systems can only provide a single direction of airflow with low penetration, which is heavily obstructed by leaves, resulting in stagnant airflow zones within the canopy. Besides, the devices can also increase the equipment complexity to decrease operational efficiency. In this study, an assembled system of dual channel aeration cultivation was designed to increase the airflow within the plant canopy using simple equipment with operation convenience. A cultivation experiment was conducted in a plant factory. There was one control group (common aeration ventilation of a plant factory generated an airflow velocity of 0.2 m/s within the plant canopy) and three experiment groups (the dual channel aeration ventilation mode generated the airflow velocity of 0.6 (T1), 0.9 (T2) and 1.2 (T3) m/s, respectively). A systematic investigation was made to explore the impact of different ventilation modes on plant growth, tipburn occurrence, heat exchange with the surrounding environment, and the canopy microenvironment. The results showed that the dual channel aeration ventilation outperformed the conventional one, in terms of the lettuce canopy environment, lettuce growth, and heat exchange capacity. Specifically, the best growth for lettuce plants was observed at a canopy airflow velocity of 0.9 m/s, with a shoot fresh weight of 56.7 g. The optimal canopy environment and heat exchange capacity for lettuce were achieved at a canopy airflow velocity of 1.2 m/s. There was a decrease of 8.8% and 2.8 ℃ in average canopy relative humidity and average air temperature, compared with the control group. The airflow regime was first transitioned from the laminar to a transitional flow and then changed to a turbulent flow at an airflow velocity of 0.9 m/s. The convective heat transfer coefficient was also significantly improved with the increasing airflow velocity. The sensible heat flux in the light and dark periods increased by 48.5% and 52.3%, respectively, while the latent heat flux rose by 52.9% and 37.9%, respectively, with the airflow velocity within the plant canopy increased from 0.2 m/s to 1.2 m/s. Besides, there was no tipburn occurred in the experiment groups, while the tipburn occurrence of the control group was 20.9%. It infers that the dual channel aeration ventilation can be expected to effectively alleviate tipburn. In conclusion, compared with the conventional ventilation mode, dual channel aeration ventilation can effectively enhance the plant canopy environment, plant yield, and quality, as well as heat exchange between plants and their surroundings. And the assembled structure can improve transportation and installation efficiency. Furthermore, the integrated structure of ventilation ducts and cultivation tanks also reduced equipment complexity. This mode can provide technical support to precise microenvironment control in plant factories.

       

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