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- Title
Wind Tunnel Analysis of the Airflow through Insect-Proof Screens and Comparison of Their Effect When Installed in a Mediterranean Greenhouse.
- Authors
López, Alejandro; Molina-Aiz, Francisco D.; Valera, Diego L.; Peña, Araceli
- Abstract
The present work studies the effect of three insect-proof screens with different geometrical and aerodynamic characteristics on the air velocity and temperature inside a Mediterranean multi-span greenhouse with three roof vents and without crops, divided into two independent sectors. First, the insect-proof screens were characterised geometrically by analysing digital images and testing in a low velocity wind tunnel. The wind tunnel tests gave screen discharge coefficient values of Cd,Φ of 0.207 for screen 1 (10 × 20 threads.cm-2; porosity Φ = 35.0%), 0.151 for screen 2 (13 × 30 threads.cm-2; Φ = 26.3%) and 0.325 for screen 3 (10 × 20 threads.cm-2; porosity Φ = 36.0%), at an air velocity of 0.25 m.s-1. Secondly, when screens were installed in the greenhouse, we observed a statistical proportionality between the discharge coefficient at the openings and the air velocity ui measured in the centre of the greenhouse, ui = 0.856 Cd + 0.062 (R2 = 0.68 and p-value = 0.012). The inside-outside temperature difference ΔTio diminishes when the inside velocity increases following the statistically significant relationship ΔTio = (-135.85 + 57.88/ui)(0.5) (R2 = 0.85 and p-value = 0.0011). Different thread diameters and tension affects the screen thickness, and means that similar porosities may well be associated with very different aerodynamic characteristics. Screens must be characterised by a theoretical function Cd,Φ = [(2eμ/Kpρ).(1/us) + (2eY/Kp0.5)]-0.5 that relates the discharge coefficient of the screen Cd,Φ with the air velocity us. This relationship depends on the three parameters that define the aerodynamic behaviour of porous medium: permeability Kp, inertial factor Y and screen thickness e (and on air temperature that determine its density ρ and viscosity μ). However, for a determined temperature of air, the pressure drop-velocity relationship can be characterised only with two parameters: ΔP = aus2 + bus.
- Subjects
WIND tunnels; AIR flow; GREENHOUSE gases; DIGITAL images; VELOCITY; POROSITY
- Publication
Sensors (14248220), 2016, Vol 16, Issue 5, p690
- ISSN
1424-8220
- Publication type
Article
- DOI
10.3390/s16050690