Enhanced heat transfer in a 2D serpentine micro-channel using elastic polymers

TL;DR

This study demonstrates that elastic turbulence in a 2D serpentine micro-channel with dilute polymers significantly enhances heat transfer, with up to 60% improvement at high Weissenberg numbers, while also affecting flow resistance.

Contribution

It provides detailed numerical analysis of heat transfer and flow characteristics in elastic turbulence regimes, revealing regimes of heat transfer enhancement and flow resistance changes.

Findings

Up to 60% heat transfer enhancement at high Wi

Heat transfer increases linearly with Wi in certain regimes

Friction factor can decrease or increase depending on Wi

Abstract

In the presence of elastic forces, even dilute polymer suspensions can exhibit erratic flow fluctuations even when the viscous forces dominate over the inertial forces, which occur at vanishing-low Reynolds numbers (Re). This phenomenon is called Elastic Turbulence (ET). ET can be generated in small-scale laboratory settings and is relevant to enhancing mixing efficiency and heat transfer in microfluidic devices. In this study, we investigate the hydraulic and thermal properties of a dilute polymer solution under ET conditions characterized by inflow conditions of vanishing Re and high Weissenberg numbers (Wi). We carry out extensive direct numerical simulations of the 2D curvilinear channel flow of an Oldroyd-B viscoelastic fluid using Rheotool. We analyze the variations of friction factor and Nusselt numbers along the serpentine channel to reveal the global and local characteristics of ET. Based on Wi, we identify three regimes. First, for 0 < Wi < 3, we observe roughly 10% heat transfer enhancement accompanied by roughly 5% reduction of friction factor compared to laminar flow, known as polymer-induced thermal conductivity enhancement. Second, for 3 < Wi < 5, we observe a sharp linear increase of heat transfer (roughly 30%) at the cost of up to 15% enhanced friction factor. Finally, in the fully developed elastic turbulence regime (Wi > 5), we observe up to 60% heat transfer enhancement accompanied by reduced friction factor. The substantial enhancement of heat transfer with increasing Wi is mainly attributed to the increasing intensity of the elastic instability resulting from the balance between normal stresses and streamlined curvatures.