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Non-boiling Heat Transfer in Downward Inclined Gas-liquid Two Phase Flow

John, Tarebi Joseph
Non-boiling heat transfer in downward inclined gas-liquid two phase flow is quite intriguing and is one of the least studied phenomenon in the two phase flow literature. To explore and understand this phenomenon, experiments are carried out to measure the local and averaged non-boiling two phase heat transfer coefficient (hTP) in 0, -5, -10, -20, -30, -45, -60, -75 and -90 degrees of pipe inclinations. The experiments are carried out with uniform wall heat flux boundary condition in 12.5 mm I.D. stainless steel pipe that uses air-water as fluid combination and consists of all flow patterns that covers the gas and liquid superficial Reynolds numbers in a range of 270 to 19000 and 2300 to 17000, respectively. It is observed that an increase in downward pipe inclination from horizontal initially exhibits a decreasing tendency of hTP till -30 degrees and thereafter increases consistently with further increase in the pipe inclination towards vertical downward direction. The general trends of two phase heat transfer coefficients are found to be closely related to the physical structure of the flow patterns and their morphological variations as a function of pipe orientation and phase flow rates. The measured data is compared against some of the relevant non-boiling two phase heat transfer correlations available in the two phase flow literature. Based on this statistical comparison, the relatively top performing correlation is identified and proposal of an improved correlation is presented.