Mixing and heat transfer enhancement of power-law fluids inside helically coiled tube by chaotic advection

Abstract

In this study, the effect of chaotic advection on mixing and heat transfer of non-Newtonian power-law fluids in a helically coiled heat exchanger is investigated numerically. Two types of coil heat exchanger (normal and chaotic) are studied. The chaotic coil is made by geometrical modification in the normal coil, without any alternation of the coil axis. First, mixing in two both coils was investigated by simulating the flow and tracing of particles. Second, thermal performances of normal and chaotic coils are evaluated by calculation of the Nusselt number and friction factor for a wide range of 0.3<n<1.4, 50<Re<2000 and 2<Pr<200. The numerical results show that the mixing performance in the chaotic coil improves with increasing power-law index and Dean number. The mixing improvement results in heat transfer enhancement in the chaotic coil between 3 and 12% while the friction factor increases to a very slight degree. Besides, the effect of different parameters on heat transfer in the normal and chaotic coils is discussed, and a correlation for the Nusselt number in terms of effective parameters on heat transfer is presented using nonlinear regression analysis.