Presentation_4898 cfd analysis of greenhouse vents.pptx

cfd analysis of greenhouse vents

1. СFD analysis of different Greenhouse ventilation designs using ОрenFОАM 9 th International and 49 th National conference of FMFP - 2022 IIT Roorkee| Dec 14-16 Samar Singhal, M.TECH Dr. Ashwini Kumar Yadav, PhD Dr. Ravi Prakash, PhD PhD scholar Assistant professor Professor

2. Introduction A consistent microclimate around crop canopy is an important factor for faster growth plants . The major heat source of greenhouse is solar radiation which leads to indoor greenhouse temperature rise above advised range for optimum plants growth (25-35 ℃) in summer. H ence natural ventilation systems, which are significantly less energy intensive than fan ventilation systems, have been widely adopted.

3. Introduction Many CFD investigation were carried out in the past to investigate the mass air flow rate and temperature distribution inside the greenhouse[1]. The impact of the sun position and wind on the greenhouse microclimate was investigated using a discrete ordinate (DO) model [ 2 ]. As the humidity too plays an important role for plant growth, energy balance simulations to study humidity control in unheated greenhouses were conducted [3] . Dynamic models were developed to predict all the internal greenhouse temperatures for uneven span, even span, single span, vinery, Quonset and arch type green houses from solar radiation availability point of view[4]. CFD study of greenhouse microclimates was carried out using FLOTRAN module of ANSYS for underground heated tubes [5].

4. Objective It is aperient from literature that very few investigation were carried out to study velocity and temperature distribution inside the greenhouse for tropical conditions like India. The aim of this study is to predict the effect vent and roof openings on the greenhouse internal air temperature and ventilation rate, a computational fluid dynamics (CFD) analysis was performed using OpenFOAM . The specific objective was to assess the efficacy of natural ventilation strategies in greenhouse cooling.

5. Methodology The Fig. 1 shows dimensions and vent location of various greenhouses selected for present numerical study.

6. Method The Fig. 2 Boundary conditions and meshing of domain

7. Method Parameter value Density of air (kg/m 3 ) 1.2 Thermal Expansion Factor (1/K) 0.003 Specific heat of air (J/kg) 1005 Prandtl Number 0.7 Dynamic Viscosity ( Kg/m-s) 1e-5 Direct normal radiation on Earth (W/m 2 ) 744 Diffused solar radiation on vertical surface 114 Diffused solar radiation on horizontal surface (W/m 2 ) 100 Table 1: Input parameters for basic directories

8. Method (1)     (3) Continuity Momentum Energy

9. Governing Equations (6)   (5)   (7)   Boussineque approximation Turbulent Kinetic Energy Dissipation Rate

10. Method Solver buoyantSimpleFoam Time dependency Steady State Discretization scheme Gauss upwind Convergence Criteria (Residual tolerance) for pressure, velocity and temperature 1e-7 Table 2: Solution Method

11. Results and Discussions: Temp. and Vel. distribution Figure 3: Contours

12. Results and Discussions: Temp. and Vel. distribution Figure 4: Contours

13. Results and Discussions: Density contours Figure 5: Contours Case 1 Case 2 Case 3 Case 4

14. Results and Discussions Figure 5: Temperature along width at 1.1 m height Figure 6 : Wind velocity along width at 1.1 m height

15. Results and Discussions The Fig. 5 shows temperature and velocity profiles for various configurations. From the contour plots of temperature and wind speed it was observed that wind could not reach to downward region of the entrance in domain and thereby temperature in that region is slightly higher. For all the cases, the air from windward side went deeper into the greenhouse and exit from ridge opening. The cool incoming air initially followed a horizontally trajectory along the floor and as it was heated up during the movement it went up towards the roof vent at the middle of the greenhouse due to stack effect. A minor recirculation zone was also observed in all the cases toward closed vent side (right side) . The Fig. 5 and Fig. 6 show variation of temperature and velocity along width of greenhouse for various cases. The incoming air temperature increased from the inlet side due to greenhouse effect within the domain and reached up-to 307 K near 2 m width of greenhouse . The velocity of incoming air reduced from 1m/s at inlet to 0.1 m/s till the 2 m width and then increased up-to 0.3 m/s due to stack effect.

16. Conclusions The air movement caused by wind and stack effect in greenhouse was an important factor that affected the uniformity of greenhouse temperature. The solar radiation transmitted through the greenhouse was absorbed by the soil and it got heated up. The absorbed heat by soil was transmitted to underground soil by conduction and to adjacent air inside the greenhouse by convection . Hence for all the cases maximum temperature of air was 38 ℃ near the soil. The case-2 greenhouse ventilation system had the most uniform and lowest air temperature at the crop heights of 1.1m which is optimum plants growth temperature (between 25-35 ℃).

17. References [1] R. Nebbali , J. C. Roy, and T. Boulard , “Dynamic simulation of the distributed radiative and convective climate within a cropped greenhouse,”  Renewable Energy , vol. 43, pp. 111–129, 2012. [2] D. Piscia , P. Muñoz, C. Panadès , and J. I. Montero, “A method of coupling CFD and energy balance simulations to study humidity control in unheated greenhouses,” Comput . Electron. Agric., vol. 115, pp. 129–141, 2015, doi : 10.1016/j.compag.2015.05.005. [3] H. G. Mobtaker , Y. Ajabshirchi , S. F. Ranjbar , and M. Matloobi , “Simulation of thermal performance of solar greenhouse in north-west of Iran: An experimental validation,” Renew. Energy, vol. 135, pp. 88–97,2019. [4] Senhaji , A., Mouqallid , M., Majdoubi , H., 2019. CFD Assisted Study of Multi-Chapels Greenhouse Vents Openings Effect on Inside Airflow Circulation and Microclimate Patterns. Open Journal of Fluid Dynamics 09, 119–139. https://doi.org/10.4236/ojfd.2019.92009 [5] Rouboa , A., Monteiro, E., 2007.Computational fluid dynamics analysis of greenhouse microclimates by heated underground tubes, vol. 21, pp. 2196-2204.