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/do) ranged from 7.086 to 16.142 and pitch ratio (P/do) 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 × 102 to 2.3 × 103. The experimental results indicated that these parameters (D/do and P/do) have important effects on the average heat transfer coefficient. The average Nusselt number (Num) increases with the increase of D/do at constant Re and P/do. Also, Num increases with the increase of P/do at constant Re and D/do. A considerable agreement between the present experimental data and previous work is achieved. The average Nusselt numbers is correlated with Re, D/do and P/do.