Direct actuation of small-scale motions for enhanced heat transfer in heated channels

Abstract

Flow-effected, enhanced heat transfer in a high aspect ratio rectangular mm-scale channel that models a segment of a high-performance, air-cooled heat-sink is characterized. The present investigation reports a novel approach to enhanced cooling without increasing the channel's characteristically low Reynolds number. Heat transport that is governed by the local heat transfer from the fin surface and by subsequent mixing with the core flow is significantly increased by deliberate shedding of unsteady small-scale vortices that are induced by the vibration of a miniature, planar self-oscillating reed. The present investigation focuses on the heat transfer and fluid mechanics that are associated with the small-scale motions induced by the reed. Performance enhancement by reed actuation is quantified in terms of increased power dissipation over a range of flow rates compared to the baseline flow in the absence of the reed. It is demonstrated that the channel's coefficient of performance can be increased by a factor of 4 while accounting for all the losses associated with the reed actuation.

Air Side Heat Transfer Enhancement with Self Agitators

“…However, for the tests conducted in a 5-channel heatsink, the heat transfer enhancement in Nusselt number varies between a minimum of 53% and a maximum of 69% at lower Reynolds number ranges. The test results shown by Hidalgo et al [17] reported that Nusselt number enhancement increases 43% at Re = 2000 to 88% at 5000 and the pressure drop increment increases from 37% at Re = 2000 to nearly 100% at Re = 4300. Both fluttering reed and AFA are passively driven by air flow through the fluid-structure-interaction process for inducing vortices within the channel to enhance the heat transfer coefficient at the heated wall surface.…”

“…However, for the experiments tested in a 5-channel plate-fin heatsink, the heat transfer augmentation in global Nusselt number varies from 53% to 69% at lower Reynolds number ranges. The test results presented by Hidalgo et al [17] reported that averaged Nusselt number augmentation increases 43% at = 2000 to 88% at = 5000 and the pressure drop increment arises from 37% at = 2000 to nearly 100% at = 4300. Jha and et al…”

“…However, few experimental investigations were conducted on FSI coupled with convective heat transfer [14]. Herrault et al [15] and Hidalgo et al [16][17] reported beneficial effects on heat transfer by inserting elastic fluttering reeds in heatsink fins, which are driven by the air flow. The experimental results reported by Hidalgo et al [16], demonstrated a coefficient of performance enhancement of about 2.4-fold with a reduction in flow velocity of 50% and an increase of about 190% in Nusselt number relative to the base flow in single channel testbed.…”

“…However, they require an additional power supply system to drive the structural oscillation, limiting the range of practical applications. Passive FSI vortex generators for heat transfer enhancement [15][16][17], [36][37] have also been investigated. However, a method to improve the vortex field has not yet been identified.…”

“…Furthermore, it was found that the heat transfer performance was maximized when the reed created large modulations in the boundary layer of the channel according to their studies on the effect of both the Reynolds number and the channel confinement. Herrault et al [15] and Hidalgo et al [16][17] presented beneficial effects on thermal performance by installing fluttering reeds in plate-fin channels, which were driven by the air flow. The experimental results from Hidalgo et al [16] showed a coefficient of performance (COP) increment of around 2.4-fold with a reduction in airflow velocity of 50% and an enhancement of about 190% in Nusselt number compared to the base flow in a single channel setup.…”