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Sensors 2016, 16(5), 690; doi:10.3390/s16050690

Wind Tunnel Analysis of the Airflow through Insect-Proof Screens and Comparison of Their Effect When Installed in a Mediterranean Greenhouse

Research Centre CIAIMBITAL, University of Almería, Ctra. Sacramento s/n, Almería 04120, Spain
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Academic Editor: Simon X. Yang
Received: 24 February 2016 / Revised: 5 May 2016 / Accepted: 10 May 2016 / Published: 12 May 2016
(This article belongs to the Special Issue Sensors for Agriculture)
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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 = [(2/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. View Full-Text
Keywords: insect-proof screen; aerodynamic; wind tunnel; greenhouse; microclimate insect-proof screen; aerodynamic; wind tunnel; greenhouse; microclimate
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MDPI and ACS Style

López, A.; Molina-Aiz, F.D.; Valera, D.L.; Peña, A. Wind Tunnel Analysis of the Airflow through Insect-Proof Screens and Comparison of Their Effect When Installed in a Mediterranean Greenhouse. Sensors 2016, 16, 690.

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