PRESSURE DROP ACROSS INSECT-PROOF SCREENS

Abstract

Screens can exclude insects from greenhouses and reduce the need for pesticides. They can also be used to createa barrier against the outside environment, to facilitate biological control within the greenhouse. However, the screens have amajor drawback in that they reduce the rate of ventilation because of their resistance to airflow. As air flows through thescreen a static pressure drop occurs across it. This pressure loss is usually specified in the literature by a pressure-losscoefficient, K, which is a function of the porosity of the screen and of the Reynolds number. Numerical simulations show thatthe pressure loss coefficient of a woven screen may also be dependent on the texture of the weave when the spacing betweentwo adjacent threads of the screen is small in comparison with the thread diameter. The simulations show that the velocityfield immediately downstream from the screen is strongly dependent on the weave texture. Under certain conditions, abackflow could develop immediately downstream from the screen, which might hinder insect penetration.