A similitude model for testing greenhouse evaporative cooling pads under the hot-arid conditions of the UAE

A similitude model was constructed at the Faculty of Agricultural Sciences of the U.A.E. University to test the performance of greenhouse evaporative cooling pads under the hot arid conditions of the United Arab Emirates. The model was utilized to assess the performance of two 100 mm thick pads made of date-fronds leaves and fibers as compared to that of a similar thickness "Cel-Dek" pad (a corrugated cellulosic pad most commonly used in the UAE) under several operational conditions. The two pads were: 1- mats of date palm fronds (weaved from 25 mm wide frond leaves), and 2- chopped date fronds (20 mm chip size). The model consisted of a self-contained "pad and fan" evaporative cooling system constructed from a 2.5 m x 0.65m x 0.7m laminated 12mm thick wood tunnel with a 220 mm variable speed, direct drive fan (0.5 to 2.2 m./s), and a controlled circulation, variable-flow wetting water circulation system (0.03 - 0.12 l/s). The model measured variations in dry-and wet-bulb temperatures before and after passing through the pads and consequently calculated the cooling efficiency of the-pad for various air and water flows. Other parameters determined per pad were their water consumption efficiency, permeability and face air speed, and water flow rate through them.