Comparison of Mixing Performance and Heat Transfer Enhancement in Three Different Coiled Tube Heat Exchangers

Comparison of Mixing Performance and Heat Transfer Enhancement in Three Different Coiled Tube Heat Exchangers

The present work tries to compare the mixing performance and heat transfer enhancement in three different configurations of coiled tube heat exchangers of the same heat-transfer surface area and the same tube length. One of configurations is a convectional helical coil with a fixed axis which produces regular mixing, the other one is a configuration in which there is a periodic change in helical coils configuration and the third one is a configuration with double axes. The Lyapunov exponents are used to identify the presence of chaotic advection in the chaotic configurations. By means of Lagrangian tracing of fluid particles in the flow field and sensitivity to initial condition calculations, it is shown that mixing and heat transfer is increased significantly due to change advection mechanism to chaotic advection. Furthermore, a higher Nusselt number indicates an enhanced heat transfer and a more uniform temperature distribution for the fluid flow in the chaotic configurations. The configuration with the alternative axes also displays a heat transfer enhancement of 16% in terms of the fully developed Nusselt with 4% change in the pressure drop numbers compared to the other configurations.