Heat transfer and fluid mixing enhancement by chaotic advection in a novel sine-helical channel geometry

The objective of this PhD thesis is to present an innovative sine-helical multifunctional heat exchanger reactor that enhances mixing and heat transfer based on the chaotic advection. This novel geometry is constructed by combining a sine-wave channel on a helically coiled channel. The flow structure, passive scalar mixing and the convective heat transfer in the novel heat exchanger are analyzed numerically using the finite volume method implemented in OpenFOAM.. The results are compared to those obtained with a classical helically coiled heat exchanger. The Laminar flow is considered in the present study, with the Reynolds numbers ranging from 100 to 1400 based on the hydraulic diameter and mean flow velocity. Numerical results showed chaotic nature of the flow in the sine-helical geometry, where the periodic change of the centrifugal forces breaks the flow symmetry and leads to chaotic particle trajectories. Lagrangian In this project, we present an innovative sine-helical multi-functional heat exchanger/Reactor that enhances mixing and heat transfer based on the chaotic advection. The flow structure, mixing and the convective heat transfer in the novel heat exchanger are analyzed numerically for laminar flow. Results are compared to those obtained with a helical heat exchanger. Results showed chaotic nature of the flow in the sine-helical geometry, where the periodic change of the centrifugal forces in this channel breaks the flow symmetry and leads to chaotic particle trajectories. The heat transfer enhancement and molecular mixing was proved by Eulerian and Lagrangian indicators. Experimental work was done also for both exchangers, over a Reynolds numbers range Re=100-10000. Results showed higher thermal transfer in the chaotic exchanger, specially at low Reynolds numbers. Consequently, the proposed novel heat exchanger is very promising for many applications with laminar flow regimes.analysis of the particles inside the channel confirmed the effect of chaotic advection on the enhancement of mixing efficiency. The coefficient of variation of the outlet temperature in the sine-helical flow is decreased by about 100% relative to that in the helical channel, highlighting a better temperature homogeneity at the heat exchanger outlet. Moreover, the thermal enhancement factor, measuring the convective heat transfer coefficient at the same pumping power, increases between 5.5 and 20.7% in the since-helical flow relative to the helical channel. Complementary to the numerical analysis, thermal experimental study was conducted on both the helical and the chaotic sine-helical heat exchangers, over a wide range of Reynolds numbers (Re =100 − 10, 000), having both the same heat-transfer surface area. The results proved the superiority of the chaotic heat exchanger against the classical one, especially at low Reynolds numbers. Consequently, the proposed novel heat exchanger is very promising for many applications with laminar flow regimes.