DESIGN AND EVALUATION OF DIFFERENT DEVICES FOR MEASURING AIR DRY-BULB TEMPERATURE IN A FOGGY ENVIRONMENT

Shmroukh, A. N.; Taha, I. M. S.; Abdel-Ghany, A. M.; Attalla, M.

doi:10.21608/jesaun.2012.113135

DESIGN AND EVALUATION OF DIFFERENT DEVICES FOR MEASURING AIR DRY-BULB TEMPERATURE IN A FOGGY ENVIRONMENT

Document Type : Research Paper

Authors

10.21608/jesaun.2012.113135

Abstract

Fogging system has been widely used for cooling and humidification applications such as in greenhouses, cooling towers, factories and conditioning systems. However, measuring the correct air dry bulb temperature by using the conventional psychrometer under a foggy environment may include a significant underestimation error. This is because of the fog wafts in the air introduced to the psychrometer. If the fog adheres to the junction of the thermocouple, measurement of dry bulb temperature is underestimated and sometimes indicates the wet bulb temperature if the fog evaporates. The present study focuses on increasing the accuracy of air dry bulb temperature under the fogging condition. Such estimation is accomplished by equipping the thermocouple junctions with different devices designed mainly to separate the non-evaporated fog before reaching the junction. The proposed devices are: gravity settler, truncated square pyramid, cyclone and cylindrical sudden enlargement. Such devices are experimented in a plexi glass (acrylic) covered box exposed to different values of fogging on-off duration and fogging rate. Air dry bulb temperature is measured by using the proposed devices are compared with free junction positioned in the acrylic covered box and with the conventional psychrometrer device. The results show that the proposed devices improve the measured air dry bulb temperature toward the correct value over that of the free junction. Putting in order: Cyclone device it is found that is better, followed by cylindrical enlargement device, gravity settler and truncated square pyramid. They respectively increased the temperature measured by the free junction in the range from 2.2 to 4.01 C, 1.97 to 3.62 C, 1.89 to 3.52 C and from 1.77 to 3.34 C for different fog on-off duration.

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