Aerodynamic analysis of several insect-proof screens used in greenhouses

Valera, D.L.; Álvarez, A.; Molina, F.D.

doi:10.5424/sjar/2006044-204

Cited by 54 publications

(44 citation statements)

References 11 publications

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“…A low velocity wind tunnel designed and constructed by the Department of Rural Engineering of the University of Almería [16] was adapted to test evaporative pads [17]. This device allows us to control the flows of air and water that pass through the evaporative materials (grid block and pads).…”

Section: Experimental Equipment and Proceduresmentioning

confidence: 99%

Energy Efficiency in Greenhouse Evaporative Cooling Techniques: Cooling Boxes versus Cellulose Pads

2014

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Abstract:Evaporative cooling systems using a combination of evaporative pads and extractor fans require greenhouses to be hermetic. The greatest concentration of greenhouses in the world is located in southeast Spain, but these tend not to be hermetic structures and consequently can only rely on fogging systems as evaporative cooling techniques. Evaporative cooling boxes provide an alternative to such systems. Using a low-speed wind tunnel, the present work has compared the performance of this system with four pads of differing geometry and thickness manufactured by two different companies. The results obtained show that the plastic packing in the cooling unit produces a pressure drop of 11.05 Pa at 2 m·s, which is between 51.27% and 94.87% lower than that produced by the cellulose pads. This pressure drop was not influenced by increases in the water flow. The evaporative cooling boxes presented greater saturation efficiency at the same flow, namely 82.63%, as opposed to an average figure of 65% for the cellulose pads; and also had a lower specific consumption of water, at around 3.05 L·h . Consequently, we conclude that evaporative cooling boxes are a good option for cooling non-hermetic greenhouses such as those most frequently used in the Mediterranean basin.

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Section: Experimental Equipment and Proceduresmentioning

confidence: 99%

Energy Efficiency in Greenhouse Evaporative Cooling Techniques: Cooling Boxes versus Cellulose Pads

2014

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“…Esta puede ser observada mediante un microscopio como una superficie plana. Una de las propiedades geométricas más importantes de estos materiales es su porosidad α (m 2 m -2 ) definida como la superficie ocupada por los orificios con respecto a la superficie total de la malla (Álvarez et al, 2012;Cabrera et al, 2006;Valera et al, 2006) y puede ser calculada por la ecuación (8) para una malla con mismo tipo de hilo en ambas direcciones de tejido.…”

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Características aerodinámicas de mallas anti-insectos usadas en ventanas de invernaderos en México

Vega

Arias

Cruz

2017

Remexca

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ResumenSe analizaron mediante pruebas de microscopía y en túnel de viento, las características geométricas, porosidad y la caída de presión, respectivamente de siete diferentes mallas comúnmente usadas como barreras físicas en ventanas de invernaderos mexicanos para determinar su efecto sobre la tasa de ventilación, la permeabilidad y el factor inercial. Las mallas se analizaron en la Universidad Autónoma Chapingo en mayo de 2013 y fueron: anti-trips (M1), anti-trips bicolor (M2), anti-áfidos (M3), anti-áfidos bicolor (M4), cenital (M5), rompevientos verde-negro (M6) y anti-áfidos blanca (M7), cuyas porosidades fueron 0. 36, 0.35, 0.47, 0.45, 0.54, 0.29 y 0.43 respectivamente. La geometría de las mallas se realizó midiendo las áreas de los poros con un microscopio óptico, para determinar las porosidades y calcular el descenso de la tasa de ventilación. Posteriormente, las características aerodinámicas más importantes; es decir, permeabilidad y factor inercial, se determinaron usando un túnel de viento para medir la relación entre la caída de presión causada por cada malla y la velocidad del flujo de aire. Los resultados mostraron que la malla cenital (M5) presenta la menor resistencia al flujo de aire con 21% de descenso en la tasa de ventilación, mientras que la malla rompevientos verde-negra (M6) fue de 50%. Los invernaderos en México normalmente usan la malla del tipo anti-áfidos con porosidad entre 0.43 y 0.47 para las ventanas laterales y cenitales. AbstractThey were analyzed by tests microscopy and wind tunnel, geometric characteristics, porosity and pressure drop, respectively seven different meshes commonly used as physical barriers windowing Mexican greenhouses to determine its effect on the ventilation rate, permeability and the inertial factor. The meshes were analyzed in the Chapingo in May 2013 were: anti-thrips (M1), antithrips bicolor (M2), anti-aphid (M3), anti-aphid bicolor (M4), zenithal (M5), green-black windbreaker (M6) and anti-aphid white (M7), whose porosities were 0.36, 0.35, 0.47, 0.45, 0.54, 0.29 and 0.43 respectively. The geometry of the meshes is performed by measuring the areas of the pores with an optical microscope to determine the porosities and calculate the decrease in ventilation rate. Subsequently, the most important aerodynamic characteristics; i. e. inertial factor and permeability were determined using a wind tunnel to measure the relationship between the pressure drop caused by each mesh and the speed of the airflow. The results showed that the zenithal mesh (M5) has the least resistance to air flow with 21% decrease in ventilation rate, while the greenblack windbreaker mesh (M6) was 50%. Greenhouses in Mexico typically use anti-aphid mesh with porosity between 0.43 and 0.47 for the side windows and zenithal type.

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“…The ventilation surface S V represented 11.2% of the of the total greenhouse surface area S A . In order to prevent insects entering the greenhouse, insect-proof screens of 13 × 30 threads cm -2 (0.39 porosity, 164.6 µm pore width, 593.3 µm pore height and 165.5 µm thread diameter) were placed on the vents (Valera et al, 2006) …”

Section: Methodsmentioning

confidence: 99%

Determinación de los patrones de flujo de aire en un invernadero multitúnel mediante anemometría sónica

López¹,

Valera²,

Molina-Aiz³

et al. 2012

Span. j. agric. res.

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The present work describes a methodology for studying natural ventilation in Mediterranean greenhouses using sonic anemometry. The experimental work took place in the three-span greenhouse located at the agricultural research farm belonging to the University of Almería. This methodology has allowed us to obtain patterns of natural ventilation of the experimental greenhouse under the most common wind regimes for this region. It has also enabled us to describe how the wind and thermal effects interact in the natural ventilation of the greenhouse, as well as to detect deficiencies in the ventilation of the greenhouse, caused by the barrier effect of the adjacent greenhouse (imply a mean reduction in air velocity close to the greenhouse when facing windward of 98% for u, 63% for u y , and more importantly 88% for u x , the component of air velocity that is perpendicular to the side vent). Their knowledge allows us to improve the current control algorithms that manage the movement of the vents. In this work we make a series of proposals that could substantially improve the natural ventilation of the experimental greenhouse. For instance, install vents equipped with ailerons which guide the air inside, or with vents in which the screen is not placed directly over the side surface of the greenhouse. A different proposal is to prolong the opening of the side vents down to the soil, thus fomenting the entrance of air at crop level.Additional key words: buoyancy; insect-proof screens; natural ventilation; wind effect. ResumenDeterminación de los patrones de flujo de aire en un invernadero multitúnel mediante anemometría sónicaEn este trabajo se ha desarrollado una metodología para estudiar la ventilación natural en invernaderos mediterrá-neos mediante anemometría sónica. Los ensayos se han realizado en un invernadero multitúnel de tres módulos situado en el Campo de Prácticas de la Universidad de Almería. Esta metodología nos ha permitido obtener los patrones de ventilación natural del invernadero experimental para los vientos más comunes de la región. También nos ha permitido describir la interacción entre el efecto eólico y térmico, así como detectar deficiencias en la ventilación natural del invernadero debidas al efecto barrera de otro invernadero adyacente (provocando una reducción media en la velocidad del aire en el exterior de la ventana de barlovento de hasta el 98% para u, 63% para u y y, más importante, 88% para u x , la componente de la velocidad del aire que es perpendicular a la superficie de ventilación lateral). Los conocimientos adquiridos en este trabajo nos permitirán mejorar los algoritmos de control del sistema de ventilación. En este trabajo se realizan una serie de propuestas que podrían mejorar sustancialmente la ventilación natural del invernadero. Por ejemplo, se proponen algunas posibles modificaciones de la configuración de las ventanas laterales, buscando una mayor captación del aire exterior: se podría optar por ventanas dotadas de alerones exteriores que dirijan al aire hacia el inte...

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Aerodynamic analysis of several insect-proof screens used in greenhouses

Cited by 54 publications

References 11 publications

Energy Efficiency in Greenhouse Evaporative Cooling Techniques: Cooling Boxes versus Cellulose Pads

Energy Efficiency in Greenhouse Evaporative Cooling Techniques: Cooling Boxes versus Cellulose Pads

Características aerodinámicas de mallas anti-insectos usadas en ventanas de invernaderos en México

Determinación de los patrones de flujo de aire en un invernadero multitúnel mediante anemometría sónica

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