Numerical study of heat transfer on using lobed cross sections in helical coil heat exchangers: Effect of physical and geometrical parameters

In this paper, flow characteristics and heat transfer applications of a helical coil with four different lobed cross sections are investigated numerically. The flow is laminar, Reynolds number changes from 1300 to 2500 and the wall of the helical coil in all the simulations has a constant temperature of 373 K. Effects of cross section lobe number (n) on heat transfer rate and pressure drop are studied. The results show that a coil with n = 6 presents the highest Nusselt number (Nu) and the lowest friction factor coefficient (f). In the next step, effects of different geometrical parameters (coil pitch, height, and diameter) and different fluids (Prandtl number) are studied. It is observed that the coil diameter has the greatest effect in comparison to the other geometrical parameters. Last but not the least, the effect of adding Al2O3 nanoparticles to water is discussed. It can be observed that upon using Al2O3-Water nanofluid, the Nusselt number increased 28 percent compared to water as the working fluid. But, it is seen that the friction factor coefficient does not change considerably. Moreover, it can be seen that the higher volume concentrations result in higher heat transfer rates. Finally, a correlation based on the numerical data for predicting Nusselt number is presented.