Heat and Mass Transfer from Moist Air Flowing inside Cold Horizontal Circular Duct II- Experimental Study. (Dept. M)

Heat and mass transfer from moist air flowing inside cold horizontal circular duct is investigated, Experimentally. To perform the experimental study air tunnel is designed and manufactured. The cold horizontal circular duct (test section) is attached to the air tunnel. Moist air is drawn from the surroundings to flow inside the circular duct (250 mm in diameter and 1200 mm long). The evaporator for two separate refrigeration units is made from copper tubes. These copper tubes are warped in counter current around the outer surface of the duct to cool its surface, control and adjust the surface temperature of the duct to the desired value. According to the temperature difference between cold duct surface temperature and the dew-point temperature for the moist air flowing inside it, some of the water vapor from the moist air is condensed. Moist air flow rate and the surface temperature for the test section are controlled and adjusted during the experiments. The amount of condensate through each experiment is measured. Velocity, relative humidity, dry bulb and dew-point temperatures for moist air are taken at different positions along the test section. Reynolds number varies from 1000 to 11000. Heat and mass transfer coefficients are calculated and in turn Nusselt and Sherwood numbers are obtained. Experimental results show that, Nusselt and Sherwood numbers increase with increasing Reynolds number up to a certain value. These increase were found due to the migration of water bubbles with the moist air. Also, results show that heat transfer coefficient decreases with increase of wall temperature, mass transfer coefficient increases with increase of wall temperature. Comparison between the obtained experimental results and the previous works show good agreement. Two empirical correlations for Nusselt and Sherwood numbers are obtained as functions of Reynolds number and other operating parameters