Experimental study of forced convection from helical coiled tubes with different parameters

The forced convection from outside surfaces of helical coiled tubes is studied experimentally with a constant wall heat flux. Ten helical coiled-tubes of different parameters with a range of diameter ratio (D/d(o)) ranged from 7.086 to 16.142 and pitch ratio (P/d(o)) ranged from 1.81 to 3.205 are employed in the present study. The experiments are performed in an open-circuit airflow wind tunnel system operated in suction mode. The experiments covered a range of Reynolds number (Re) of 6.6 x 10(2) to 2.3 x 10(3). The experimental results indicated that these parameters (D/d(o) and P/d(o)) have important effects on the average heat transfer coefficient. The average Nusselt number (Nu(m)) increases with the increase of D/d(o) at constant Re and P/d(o). Also, Nu(m) increases with the increase of P/d(o) at constant Re and D/d(o). A considerable agreement between the present experimental data and previous work is achieved. The average Nusselt numbers is correlated with Re, D/d(o) and P/d(o). (C) 2010 Elsevier Ltd. All rights reserved.