蛇行流路内における粘弾性流体の流動および伝熱特性

Abstract

The heat transfer and fluid flow characteristics of a viscoelastic fluid flow in a serpentine channel are described in this paper. The average heat transfer coefficient, pressure loss, and flow visualization were measured under the Reynolds number conditions of Re = 0.5~2.0. Water solutions of polyacrylamide with sucrose and plain sucrose were employed as viscoelastic fluids and Newtonian fluids, respectively. An increase in the Nusselt number with increasing Reynolds number in the case of the viscoelastic fluid flow was observed in the serpentine channel, while in the case of the Newtonian fluid flow, the Nusselt number remained approximately constant. The visualization results revealed that unsteady flows with a large fluctuation and longitudinal vortex-like secondary flows were generated in the case of the viscoelastic fluid flow, particularly downstream of the inflection point of the serpentine channel. This was believed to be attributed to the increase in the flow instability and the normal stresses produced by the elastic property of the fluids. Further, the Nusselt number increased even in the case of the viscoelastic fluid flow in the straight channel, relative to that in the case of the Newtonian fluid flow. However, this increase moderate in comparison to that in case of the serpentine channel, which indicates that the heat transfer enhancement can be obtained effectively by a combination of the viscoelastic fluid flow and channel geometry. A considerable increase in the pressure loss penalty was observed in the case of the viscoelastic fluid flow. However, the viscoelastic fluid case showed a higher overall performance in terms of the pumping power.