Investigation of heat transfer coefficient of spherical element using infrared thermography (IR) and gas - Water droplets (mist) as working medium

Abstract

The changes that do occur in the air ambient properties with increasing concentration of water mist (fog) have a significant influence on heat exchange process between the building and the surrounding medium. In the present paper, the average and local heat transfer coefficient was estimated from surface temperature data obtained using infrared (IR) thermography. In particular, the experiments were performed on steady-state conditions under constant heat flux for a single sphere suspended in cylindrical channel using air as well as air / water droplets as working fluid. The influence of the different factors such as Re numbers and water flux density on heat transfer behaviors are examined. Five cases are tested under range of water flux density (0 -111.68 kg m-2 hr-1). The experimental results confirmed that the heat transfer coefficient significantly increased with increase in water flux density. The heat transfer coefficients are respectively 1%, 19.7%, 90.2% and 134% higher than those in air-cooling. The results also revealed that infrared (IR) thermography it has proven to be very efficient in measuring the surface temperature distribution. The results obtained by infrared thermography (IR) are compared with calibrated thermocouples and the temperature distribution is found to be in close agreement with 2.94% average error.