Experimental Study of Free Convection in Coiled Tube Heat Exchanger with Vertical Orientation

Abstract

An experimental study has been conducted on steady-state natural convection heat transfer from helical coil tubes in vertical orientation. Water was used as a bath liquid without any mixing and cold water was used as a coolant fluid. A straight copper tube of 6 mm ID, 8 mm OD and 3 m length was bend to fabricate the helical coil. Four coils are used in this experiment has different curvature ratios and pitches. The data were correlated using tube diameter as the characteristic length. The results show that the overall heat transfer coefficient and Nusselt number increase when the flow rate of coolant and curvature ratio increase. The effect of coil pitch was investigated and the results show that when of the coil pitch (angle of inclination) increases Nusselt number increase. A correlation was presented to calculate the outside average Nusselt number of coil.