Experimental investigation of the impact of elastic turbulence on heat transfer in a serpentine channel

Waleed M Abed,Richard D Whalley,David J.C Dennis,Robert J Poole

doi:10.1016/j.jnnfm.2016.03.003

Waleed M Abed, Richard D Whalley + Show 2 more

Open Access

https://doi.org/10.1016/j.jnnfm.2016.03.003

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Abstract

The characteristics of convective heat transfer and fluid flow within a square cross-section serpentine channel are experimentally studied for two groups of polymeric viscoelastic fluids, shear-thinning and constant-viscosity Boger solutions. The elastic turbulence can be created by the non-linear interaction between elastic stresses generated within the flowing high-molecular-weight polymer solutions and the streamline curvature. In order to confirm elastic turbulence in this geometry, pressure drop across the serpentine channel was measured. The findings indicate that the measurements of non-dimensional pressure-drop increase approximately from 1.48 to 4.82 for viscoelastic solutions compared with the Newtonian fluid over a range of Weissenberg number from 4 to 211. The convective heat transfer enhances due to elastic turbulence by up to 200% for low polymer concentration (dilute) solutions and reaches up to 380% for higher polymer concentration (semi-dilute) solutions under creeping-flow conditions in comparison to that achieved by the equivalent Newtonian fluid flow at low Graetz number (up to 14.6). We propose a modified Weissenberg number which is able to approximately collapse the mean Nusselt number data for each solution group.

Highlights

The practical applications of micro-scale systems, such as bioengineering devices, microelectronic devices, cooling systems of computer chips and mini or micro-scale heat exchangers have recently received a great deal of attention due to the development of fabrication technologies for these systems
Elastic turbulence generated in the flow of viscoelastic solutions is shown to augment the convective heat transfer in the serpentine microchannel by approximately 200% for 50-W/GLY and 80-W/SUC and reaches up to 380% for 200-W/GLY and 500-W/SUC under creeping-flow conditions in comparison to that achieved by the equivalent Newtonian fluid flow at identical Graetz number
The normalised values of non-dimensional pressure drop in terms of fRe – essentially the pressure-drop normalised by a viscous stress – for the highly-elastic viscoelastic solutions increase monotonically with increasing Weissenberg number (Wi) and were significantly higher than the Newtonian limit which we attribute to the appearance of so-called “elastic turbulence” at high Wi

Summary

Introduction

The practical applications of micro-scale systems, such as bioengineering devices, microelectronic devices, cooling systems of computer chips and mini or micro-scale heat exchangers have recently received a great deal of attention due to the development of fabrication technologies for these systems. While in the case of the viscoelastic oil solutions, at identical conditions, a good emulsion was observed due to the mixing effects of elastic turbulence Prior to this understanding of elastic turbulence, Hartnett and co-workers conducted a set of experimental [13,14,15] and numerical [16] investigations to study the fundamental characteristics of fully-developed laminar convective heat transfer under different combinations of thermal boundary conditions using various types of viscoelastic fluids in straight ducts. The results indicated that viscoelastic solutions show higher convective heat transfer as compared to Newtonian fluids flow under identical conditions (Re = 314–1974, Pr = 42.9–79) These increases are attributed to secondary flows, arising from the second normal-stress differences imposed on the surfaces boundaries, which occur in viscoelastic fluids in laminar flow through rectangular or square cross-section ducts. We give a more complete account of our experiments on the convective heat transfer in the square serpentine microchannel using elastic turbulence as well as studying the influences of both viscoelasticity and shear-thinning viscosity individually on the convective heat transfer by adjusting the solvent viscosity, polymer concentration and imposed shear rate

Experimental setup

Working fluids preparation and rheological characteristics

Findings

Conclusion