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The present work experimentally and numerically investigates the local heat transfer enhancement induced by a piezoelectric fan interacting with a cross flow in a local heated channel. The piezoelectric fan is placed along the flow direction and tested under different amplitudes and flow rates. In the simulations, a spring-based smoothing method and a local remeshing technique are used to handle the moving boundary problems. Hybrid mesh is used to reduce the size of dynamic mesh domain and to improve computational efficiency. The experimental and numerical values of the time-averaged mean Nusselt number are found to be in good agreement, with deviations of less than 10%. The experimental result shows that the heat transfer performance of the heated surfaces is substantially enhanced with a vibrating piezoelectric fan. The numerical result shows that the heat transfer enhancement comes from the strong longitudinal vortex pairs generated by the piezoelectric fan, which significantly promote heat exchange between the main flow and the near-wall flow. In the case of a=0.66 (a is the dimensionless amplitude) and Re=1820, the enhancement ratio of the time-averaged mean Nusselt number reaches 119.9%.

This paper describes an experimental study of the cooling capabilities of microchannel and micro-pin-fin based on-chip cooling systems. The on-chip cooling systems integrated with a micro heat sink, simulated power IC (integrated circuit) and temperature sensors are fabricated by micromachining and silicon-to-silicon direct bonding. Three micro heat sink structures: a microchannel heat sink (MCHS), an inline micro-pin-fin heat sink (I-MPFHS) and a staggered micro-pin-fin heat sink (S-MPFHS) are tested in the Reynolds number range of 79.2 to 882.3. The results show that S-MPFHS is preferred if the water pump can provide enough pressure drop. However, S-MPFHS has the worst performance when the rated pressure drop of the pump is lower than 1.5 kPa because the endwall effect under a low Reynolds number suppresses the disturbance generated by the staggered micro pin fins but S-MPFHS is still preferred when the rated pressure drop of the pump is in the range of 1.5 to 20 kPa. When the rated pressure drop of the pump is higher than 20 kPa, I-MPFHS will be the best choice because of high heat transfer enhancement and low pressure drop price brought by the unsteady vortex street.

The combination of a microchannel and a circular synthetic jet has been proven as a promising cooling technology for microelectronic devices. However, the flow control and heat transfer characteristics of a circular synthetic jet in a microchannel are still not clear. This work numerically investigates the interaction between a circular synthetic jet and a cross flow in a microchannel using an in-house solver based on the finite volume method and analyzes its impact on the heat transfer process to further understand the heat transfer enhancement induced by a circular synthetic jet in a microchannel. The effects of the synthetic jet Reynolds number (Resj = 0 to 324), dimensionless stroke length (L/H = 1.8432 to 92.16), and cross-flow Reynolds number (Rec = 188 to 470) are studied herein. The results show that the main body of the vortex structure generated by the circular impinging synthetic jet during the discharge stage is a hairpin vortex. During the downstream motion of the hairpin vortex, the vortex legs gradually stretch and evolve into a pair of large-scale longitudinal vortex. The heat transfer enhancement induced by a circular synthetic jet can be divided into two parts according to the difference in acting mechanism: an impinging region with severe heat transfer fluctuation and an entraining region with a relatively stable heat transfer performance. The parametric study demonstrates that the enhancements of the time-area-averaged Nusselt number and the total pressure drop are mainly affected by Resj, while the transient heat transfer performance is determined by L/H. Furthermore, the growth rates of the time-area-averaged Nusselt number and the total pressure drop are almost independent of Rec.

Projecte fet en col.laboració amb Zhejiang University