The use of protected agriculture structures in tropical and subtropical countries is the main alternative for intensification of agricultural production selected by producers. In general, in these regions, passive and plastic-covered structures predominate, with natural ventilation as the only method of climate control. This phenomenon has been widely studied in different types of structures using computational fluid dynamics (CFD) simulation. Therefore, this review aimed to collect and analyze the publications generated in this field of knowledge between 2010 and 2020. The search for information included the main academic databases available on the web and the analysis was carried out using bibliometric techniques, from which it was possible to identify details inherent to the scientific production, such as countries of origin, main authors, journals, and citations. Likewise, a detailed breakdown of the relevant technical information of the three phases of numerical simulation, such as preprocessing, processing, and postprocessing, was carried out. A compilation of 118 papers published in 65 journals, written by 256 authors, originating from 24 countries was achieved, where it was evident that Mexico and Colombia were the countries with the highest scientific production in the last decade. These papers analyzed, together, a total of 17 different types of structures where polyethylene-covered greenhouses predominated, with steady state simulations, for daytime climate conditions and without the presence of crops. Within the current and future research trends, the predominance of studies analyzing passive climate control methods, new models of insect-proof mesh-house structures, and, finally, studies focused on the structural analysis of greenhouses was found.

Research on the Microclimate of Protected Agriculture Structures Using Numerical Simulation Tools: A Technical and Bibliometric Analysis as a Contribution to the Sustainability of Under-Cover Cropping in Tropical and Subtropical Countries

The use of covered structures is an alternative increasingly used by farmers to increase crop yields per unit area compared to open field production. In Latin American countries such as Colombia, productive areas are located in with predominantly hillside soil conditions. In the last two decades, farmers have introduced cover structures adapted to these soil conditions, structures for which the behavior of factors that directly affect plant growth and development, such as microclimate, are still unknown. Therefore, in this research work, a CFD-3D model successfully validated with experimental data of temperature and air velocity was implemented. The numerical model was used to determine the behavior of air flow patterns and temperature distribution inside a Colombian passive greenhouse during daytime hours. The results showed that the slope of the terrain affects the behavior of the air flow patterns, generating thermal gradients inside the greenhouse with values between 1.26 and 16.93 °C for the hours evaluated. It was also found that the highest indoor temperature values at the same time were located in the highest region of the terrain. Based on the results of this study, future researches on how to optimize the microclimatic conditions of this type of sustainable productive system can be carried out.

Contribution to the Sustainability of Agricultural Production in Greenhouses Built on Slope Soils: A Numerical Study of the Microclimatic Behavior of a Typical Colombian Structure

In this paper, by exploring photon motion in the region near a Bardeen black hole, we studied the shadow and observed properties of the black hole surrounded by various accretion models. We analyzed the changes in shadow imaging and observed luminosity when the relevant physical parameters are changed. For the different spherical accretion backgrounds, we find that the radius of shadow and the position of the photon sphere do not change, but the observed intensity of shadow in the infalling accretion model is significantly lower than that in the static case. We also studied the contribution of the photon rings, lensing rings and direct emission to the total observed flux when the black hole is surrounded by an optically thin disk accretion. Under the different forms of the emission modes, the results show that the observed brightness is mainly determined by direct emission, while the lensing rings will provide a small part of the observed flux, and the flux provided by the photon ring is negligible. By comparing our results with the Schwarzschild spacetime, we find that the existence or change of relevant status parameters will greatly affect the shape and observed intensity of the black hole shadow. These results support the theory that the change of state parameter will affect the spacetime structure, thus affecting the observed features of black hole shadows.

Shadow images and observed luminosity of the Bardeen black hole surrounded by different accretions

1 LME Laboratory of Mechanics, Department of Mechanical Engineering. University of Laghouat, Laghouat 03000, Algeria 2 LABTHOP Laboratory, Faculty of Sciences, University of El Oued, El Oued 39000, Algeria 3 Kocaeli University, Engineering Faculty, Mechanical Engineering Department, Kocaeli 41001, Turkey 4 Laboratory of Electromechanical Systems, National School of Engineers of Sfax, University of Sfax, Sfax 3038, Tunisia

/pdf/parametric-study-of-the-airflow-structure-in-a-solar-chimney-51bk8kzh81.pdf

Parametric Study of the Airflow Structure in a Solar Chimney

Received: 15 September 2019 Accepted: 12 June 2020 Forced convection is a special type of heat transfer in which fluids are forced to move, in order to increase the heat transfer. The aim of this study is to investigate in a numerical simulation of forced convection in a cubic cavity containing two cylindrical heat sources in the middle. The cavity is subjected to an inflow of air inlet from the left and an outlet flow from the right side with the same dimensions of the opening doors (0.1 H). The walls of the cavity are maintained adiabatic. The conservation equations governing the flow of forced convection are solved using the finite volume method that is used by FLUENT –ANSYS Software. Also, a comparison was performed shows good agreement between the numerical results with those available in the literature (numerical, analytical and experimental). The effect of the dimension of cavity (number of Rayleigh) and the velocity of ventilation of the air (number of Reynolds), as well as the dimension between sources cylindrical are presented and discussed. The results obtained show a strong dependence between the geometrical conditions and the structure of the dynamic and thermal field of the flow of forced convection.

/pdf/3d-forced-convection-in-a-box-containing-two-cylindrical-485fjjp3i0.pdf

3D Forced Convection in a Box Containing Two Cylindrical Heat Sources

Received: 15 September 2019 Accepted: 27 December 2019 In this work, we interested to the numerical simulation of natural convection in a closed model greenhouse heated by tubes. A greenhouse box subjected to different boundary conditions on the roof like the imposed temperature, convective flux and mixed flux was studied. The considered mathematical model is a system of partial differential equations formed by the continuity, the momentum and the energy equations. The commercial Computational Fluid Dynamics (CFD) code Fluent was used for numerical simulations based on a finite volume method. In each case, we have studied the thermal and dynamic flow parameters in the greenhouse, such as the average velocity and the average temperature. The obtained results present a good agreement with the experimental data and show a strong dependence of the air climate in the greenhouse. These results help the farmers to set up a greenhouse with materials and dimensions suitable for external conditions.

Heat and Fluid Flow in an Agricultural Greenhouse

Using the Hamilton-Jacobi method, we study certain optical shadows of rotating Bardeen-AdS black holes in the presence of internal and external field contributions. Precisely, we examine the shadow using one-dimensional real curves. By establishing the equations of motion of such AdS black holes without external dark sectors, we first analyze the shadow configurations in terms of a reduced moduli space involving only internal parameter contributions including the charge of the nonlinear electrodynamics. Among others, we find that this parameter serves as a geometric quantity controlling the shadow shape. Then, we graphically discuss the associated astronomical observables. Enlarging the moduli space, we analyze the behaviors of the quintessential black hole solutions in terms of the involved parameters controlling the dark field sector. Concretely, we observe that the dark energy not only affects the size but also deforms the shadow shape. Finally, we provide a possible link with observations from Event Horizon Telescope by showing certain constraints on the involved moduli space in the light of the M87∗ picture.

Mohammed Benali

Papers

Heat and Fluid Flow in an Agricultural Greenhouse

Optical Shadows of Rotating Bardeen AdS Black Holes