Convective Heat Transfer Enhancement With Micro Pin-Fin Surfaces Cooled by a Piezoelectrically-Driven Translational Agitator

2012 ◽  
Author(s):  
Taiho Yeom ◽  
Terrence W. Simon ◽  
Tao Zhang ◽  
Mark T. North ◽  
Tianhong Cui
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Channel Flow ◽  
Convective Heat ◽  
High Frequency ◽  
Single Channel ◽  
Heated Surface ◽  
Large Displacement ◽  
Air Cooling ◽  
Pin Fin

Air cooling of electronic equipment continues to hold many advantages over liquid cooling in terms of simplicity, reliability, cost, etc. Many active and passive air cooling techniques have been developed to meet the thermal challenges of modern, high-power electronics. Active cooling includes such features as piezoelectric flapping fans and synthetic jets that could directly break down and thin the thermal boundary layers on heated surfaces. A microchannel bank of fins, micro pin-fin surfaces, etc. are passive methods for increasing heat transfer area. In the current study, both active and passive methods, piezoelectric translational agitators and micro pin fin arrays, are employed to dramatically enhance convective heat transfer rates. A piezoelectric stack actuator coupled with an oval loop shell displacement amplifier was utilized to generate high-frequency and large-displacement translational agitation over the micro pin fin surface. Two different micro pin-fin surfaces were fabricated using copper and the LIGA process. Heat transfer experiments were performed in a single channel that houses a one-sided, heated surface with attached micro pin fins. The piezoelectric translational agitator oscillates at a high frequency of 596 Hz with a large displacement of up to 1.8 mm. The heat transfer coefficients on the micro pin-fin surface cooled by the agitator and various channel through-flows were compared with those of plain surfaces under the same channel flow rates. A maximum improvement of 222% in the heat transfer rate was achieved when the agitator was operated, the micro pin-fin surface was in place and the channel flow velocity was 11.6 m/sec, compared to that of a non-agitated plain surface case with the same flow rate.

Convective Heat Transfer Enhancement on a Channel Wall With a High Frequency, Oscillating Agitator

2011 ◽  
Author(s):  
Taiho Yeom ◽  
Terrence W. Simon ◽  
Youmin Yu ◽  
Mark T. North ◽  
Tianhong Cui
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Convective Heat ◽  
High Frequency ◽  
Shell Structures ◽  
Transfer Enhancement ◽  
Flow Rates ◽  
Piezoelectric Stack Actuator

Convective heat transfer enhancement on a wall of a narrow channel enhanced by high-frequency, translational oscillation of a thin agitator plate is described. The oscillation is realized using a piezoelectric stack actuator. Small amplitudes of the piezoelectric stack actuator were amplified through oval loop shell structures so that large translational amplitudes are provided to the thin plate agitator. Heat transfer tests were conducted with three operating frequencies resulting from three oval loop shell structures operating at their resonance frequencies. For each operating frequency, four different amplitudes (corresponding to different applied voltages to the piezoelectric stacks) were investigated. Three channel flow rates were tested. They represent laminar, transition, and turbulent flow regimes for a non-agitated channel. Running with agitation and channel flow allows a study of the agitation effect with different channel flow rates. The results show that the oscillating plate with a frequency of about 1,140 Hz raises the convective heat transfer coefficient on the heated surface by 93%, compared to a case with channel flow only. The flow rate was 45 LPM, corresponding to the transitional flow regime in an un-agitated channel. The amplitude of oscillation was about 1.1 mm, peak-to-peak. It was found that the effect of cross flow is minimized with high oscillation frequency agitation regardless of channel flow velocity and flow regime of the un-agitated flow. In addition, numerical simulations were performed to support the experimental results and understand underlying phenomena of translational agitation. Numerical simulation results match well with the experiments and provided good explanations of heat transfer enhancement from the translational agitator. The piezoelectrically-driven oscillating agitator plate coupled with traditional fan cooling shows promising potential for advanced air cooling applications.

Heat Transfer Enhancement of Channel Flow via Vortex-Induced Vibration of Flexible Cylinder

2014 ◽  
Author(s):  
Junxiang Shi ◽  
Jingwen Hu ◽  
Steven R. Schafer ◽  
Chung-Lung (C. L. ) Chen
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Channel Flow ◽  
Convective Heat ◽  
Thermal Performance ◽  
Transfer Rate ◽  
Thermal Boundary Layer ◽  
Flexible Cylinder

Thermal diffusion in a developed thermal boundary layer is considered as an obstacle for improving the forced convective heat transfer rate of a channel flow. In this work, a novel, self-agitating method that takes advantage of vortex-induced vibration (VIV) is introduced to disrupt the thermal boundary layer and thereby enhance the thermal performance. A flexible cylinder is placed at the centerline of a rectangular channel. The vortex shedding due to the cylinder gives rise to a periodic vibration of the cylinder. Consequently, the flow-structure-interaction (FSI) strengthens the disruption of the thermal boundary layer by vortex interaction with the walls, and improves the mixing process. This new concept for enhancing the convective heat transfer rate is demonstrated by a three-dimensional modeling study at different Reynolds numbers (84∼168). The fluid dynamics and thermal performance are analyzed in terms of vortex dynamics, temperature fields, local and average Nusselt numbers, and pressure loss. The channel with the self-agitated cylinder is verified to significantly increase the convective heat transfer coefficient. When the Reynolds number is 168, the channel with the VIV improves the average Nu by 234.8% and 51.4% as opposed to the clean channel and the channel with a stationary cylinder, respectively.

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