title: Wind Tunnel Analysis of the Airflow through Insect-Proof Screens and Comparison of Their Effect When Installed in a Mediterranean Greenhouse.
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/Kp(0.5))](-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.
authors.affiliation: Research Centre CIAIMBITAL, University of Almería, Ctra. Sacramento s/n, Almería 04120, Spain. alexlopez@ual.es.
authors.forename: Alejandro
authors.initials: A
authors.lastname: López
authors.affiliation: Research Centre CIAIMBITAL, University of Almería, Ctra. Sacramento s/n, Almería 04120, Spain. fmolina@ual.es.
authors.forename: Francisco D
authors.initials: FD
authors.lastname: Molina-Aiz
authors.affiliation: Research Centre CIAIMBITAL, University of Almería, Ctra. Sacramento s/n, Almería 04120, Spain. dvalera@ual.es.
authors.forename: Diego L
authors.initials: DL
authors.lastname: Valera
authors.affiliation: Research Centre CIAIMBITAL, University of Almería, Ctra. Sacramento s/n, Almería 04120, Spain. apfernan@ual.es.
authors.forename: Araceli
authors.initials: A
authors.lastname: Peña
mesh_terms: D000392:Air Movements; D000818:Animals; D018556:Crops, Agricultural; D004868:Equipment Failure; D007313:Insecta; D013696:Temperature; D014919:Wind
keywords: aerodynamic; greenhouse; insect-proof screen; microclimate; wind tunnel