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Computational Fluid Dynamics-Based Simulation of Crop Canopy Temperature and Humidity in Double-Film Solar Greenhouse

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Computational Fluid Dynamics-Based Simulation of Crop Canopy Temperature and Humidity in Double-Film Solar Greenhouse Hindawi Journal of Sensors Volume 2020, Article ID 8874468, 15 pages https://doi.org/10.1155/2020/8874468 Research Article Computational Fluid Dynamics-Based Simulation of Crop Canopy Temperature and Humidity in Double-Film Solar Greenhouse Wei Jiao,1,2 Qi Liu,1 Lijun Gao,1 Kunyu Liu,2 Rui Shi,3,4 and Na Ta 1 1College of Mechanical and Electrical Engineering, Inner Mongolia Agricultural University, Hohhot 010018, China 2Institute of Grassland Research of CAAS, Hohhot 010010, China 3Collage of Grassland, Resources and Environment, Inner Mongolia Agricultural University, Hohhot 010018, China 4Baotou Medical College, Baotou 014040, China Correspondence should be addressed to Na Ta; [email protected] Received 24 July 2020; Revised 14 September 2020; Accepted 19 September 2020; Published 17 October 2020 Academic Editor: Yuan Li Copyright © 2020 Wei Jiao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The microenvironment of the crop area in a greenhouse is the main factor that affects its growth, quality, and pest control. In this study, we propose a double-layer film solar greenhouse microenvironment testing system based on computational fluid dynamics simulations of a celery canopy with a porous medium. A real greenhouse was examined with a sensor system for soil, air, radiation, and carbon dioxide detection to verify the simulation results. By monitoring the internal environment of celery canopies with heights of 0.8 and 1 m during a period of temperature fluctuations, we found the temperature and humidity of the canopy interior changed spatially and differed greatly from the those in the greenhouse under solar radiation conditions. The temperature and humidity of the celery canopy were 4–14°C lower and 10%–30% higher than those of the surroundings. As the canopy grew, the differences in temperature and humidity between the canopy and other parts of the greenhouse increased. The root mean square errors of the temperature and humidity with the 0.8 m high celery canopy were found to be 0.56 and 2.86 during the day and 0.24 and 0.81 at night, respectively; the corresponding values for the 1 m high celery canopy were found to be 0.51 and 2.26 during the day and 0.26 and 0.78 at night. The porous medium model expressed the temperature and humidity characteristics of the celery crop appropriately, and the simulation method was shown to be effective and feasible. With the simulation method proposed in this study, the production of crops in complex microenvironments in greenhouses can be modeled and digitized. 1. Introduction tional fluid dynamics (CFD) simulations of a greenhouse has mainly focused on the greenhouse environment in rela- Solar greenhouses are the most important type of greenhouse tion to the crop growth demand [6–8]. With the rapid devel- used in cold and arid areas of northern China [1]. They are opment of computer technology, CFD-based numerical either closed or semienclosed thermal systems and are com- simulations have been widely used to study the spatial and posed of an enveloped structure, indoor air, crops, and soil. temporal distribution of climate-related characteristics (e.g., The environment in a solar greenhouse is affected by the temperature) of microenvironments in greenhouses [9–12]. external temperature, humidity, solar radiation intensity, In recent years, more scholars have paid attention to the wind speed, greenhouse structure, and planted crops [2]. microenvironment of greenhouse crops. The changes in tem- The microenvironment in which a crop is grown affects the perature and humidity inside greenhouses during crop plant efficiency, healthy growth rate, pest control, greenhouse growth has become a hot research topic [13–15]. Boulard ventilation, irrigation, and other related aspects of the and Roy used a CFD approach to model the micrometeorol- growth. The study of the temperature and humidity distribu- ogy of a closed greenhouse at the canopy level [16]. They tion in crop canopies is important for the crop production visualized the distribution of solar radiation and found good and quality [3–5]. However, research based on computa- agreement between the experimental and simulation 2 Journal of Sensors measurements of crop transpiration. Tadj used the CFD The data were transferred to a laboratory analysis worksta- method to simulate the microclimate in a closed vaulted tion through 4G wireless communication for the simulation greenhouse where tomatoes were grown and discussed the analysis [21, 22]. influence of different heating systems on the microclimate The ATH sensors provide 14 bits air temperature (aTp) of tomatoes in the greenhouse [17]. Yue Zhang developed a and 12 bits air humidity (aHd) measurements. The temper- method to evaluate the microlight climate and thermal per- ature measurement range was from −20 to 85°C with an formance of Liaoshen-type solar greenhouses, including a accuracy of ±0.3°C. The humidity measurement range was detailed 3D tomato canopy structure simulated using a func- from 0% to 100% RH with an accuracy of ±2% RH. The tional–structural plant model [18]. Nebbali simulated the STM sensors measured temperatures between −40 and distributed climate parameters of a ventilated tunnel tomato 80°C and humidity between 0 and 100% RH with accura- greenhouse using a biband discrete ordinate (DO) model cies of ±0.5 and ±3%, respectively. The SR sensors mea- with the plant canopy considered a porous medium [19]. sured the spectral range from 0.3 to 3 μm. The core They considered the impact of the sun position and wind device of the radiation sensor was a high-precision sensor, on the greenhouse microclimate. and a quartz glass cover made using precision optical cold In this study, we investigate the temperature and humid- processing was installed outside the sensor to effectively ity distribution of a celery crop in a solar greenhouse with a prevent environmental factors from affecting its perfor- double-layer cover film using the CFD method. We designed mance. Figure 3 shows the arrangement of the measuring a contrasting experiment with two celery canopies of differ- points in the solar greenhouse and a photograph of the ent heights set as isotropic porous media with different greenhouse sensor system. parameters. Then, we used the ANSYS Fluent to simulate The outdoor temperature, humidity, solar radiation, the crop canopy temperature and humidity. A simple and wind speed, and wind direction were measured by the efficient greenhouse sensor test system was designed to pro- weather station. In order to focus on the crop canopy, vide the boundary and verification conditions required for groups of sensors were arranged at the center of the span the simulation. The accuracy of the CFD model was verified cross-section of the crop canopy at a two-meter (2 m) dis- by comparing the values obtained with the ANSYS Fluent tance on both sides. Each group consisted of four ATH with the measured results. Furthermore, we investigate the sensors arranged in the vertical direction. These sensors distribution of the temperature, and humidity in the celery could be adjusted according to the canopy height. Specifi- crop canopies with different heights is explored. cally, for a 0.8 m canopy height, the sensors could be adjusted to 0.1, 0.4, 0.6, or 0.8 m from the ground level, 2. Materials and Methods and for a 1 m high canopy height, they can be adjusted to 0.1, 0.4, 0.8, and 1 m from the ground level. Seven ATH 2.1. Study Site and Sensor System Settings. The experiment sensors were arranged in the inner arch shed, inner mem- was carried out at the Hailiutu solar greenhouse experimental brane, outer membrane, north and south sides of the ceil- site of the Inner Mongolia Agricultural University. The geo- ing, two meters above the ceiling, and rear wall. These graphic coordinates were as follows: 40.68° N latitude and sensors were used to set the boundary conditions to 111.37° E longitude. Figure 1 shows the study site on the observe aTp and aHd in the greenhouse. Three STM sen- map of Hohhot and a photograph of the studied greenhouse. sors were arranged on the soil surface layer to set the The experiments were performed on a solar greenhouse boundary conditions of the soil surface temperature and with a double-layer cover film. The greenhouse faced south moisture content. The SR sensors were arranged in air from the north and had a length of 70 m and a span of 9 m. and inside the canopy to observe the radiation of the sun The back wall had a brick-and-soil structure and was 1.4 m inside the greenhouse. The CD sensors were arranged in thick and 3.5 m high. As shown in Figure 2, the greenhouse the middle of the canopy and approximately 1.9 m above sensing detection system was composed of three parts: data the ground to observe changes in the carbon dioxide con- acquisition, data storage, and data transmission [20]. Briefly, centration in the canopy and air. carbon dioxide (CD, model: CD10), air temperature and humidity (ATH, model: FLEX1000TH), solar radiation (SR, 2.2. CFD Model Procedure. The CFD simulation of the green- model: YJ-SR200), and soil temperature and moisture house energy dynamics is primarily based on the porous (STM, model: MS10) sensors, provided by Dalian Zheqin medium model, air turbulence model, solar radiation Technology Co., Ltd., were connected to a low-frequency model, and energy component transport model [23]. half-duplex Lora serial port (LG207P) for data collection. Porous media consist of a combination of heterogeneous The Lora data transmission terminal supports the point-to- materials, in which solids serve as the backbone of the point communication protocol with a working frequency media, and liquids or gases are dispersed through the pores.
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