Experimental Study for Convection Heat Transfer From Helical Coils With the Same Outer Surface Area and Different Coil Geometry

An experimental study is done to study the convection heat transfer from the outer surface of a group of helical coils that have the same external surface area which is 0.1 m². These coils are wrapped to form different helical coils with different geometrical dimensions. Five pipe diameters are used in this study also; the pipes are wrapped by different values of coil diameter ranges 75–300 mm. The effect of the coil pitch on the heat transfer process has been studied, to reach the value that gives the best performance for each coil. The heat source is steam flowing inside the coil. These coils are tested at different airspeeds inside the wind tunnel, which made the Reynolds number (Re) changes from 239 to 3990. The obtained results showed that the Nusselt number enhances with the increase of D/d_o and P/d_o to reach the maximum value at the optimum values of D/d_o and P/d_o, and then, the Nusselt number begins to decrease. The Nusselt number increases with the increase of Reynolds number under all conditions. A correlation for Nusselt number as a function of Reynolds number and the other studied operating parameters is reported. By comparing this work with literature, one can find an acceptable agreement in the results.