Bio-inspired self-agitator for convective heat transfer enhancement

Abstract

Convective heat transfer plays an important role in both the fundamental research and the development of high-performance heat exchangers. Inspired by blades of grass vibrating in the wind, we developed a self-agitator for convective heat transfer enhancement. Because of fluidstructure interactions, the agitator, with self-sustained vibration, can generate strong vortices to significantly break the thermal boundary layer and improve fluid mixing for enhanced convective heat transfer. In particular, we establish a methodology to link the vorticity field at a preferred frequency to the optimal improvement in the convective heat transfer. To identify the self-agitator preferred frequency, mode analysis is performed with simulation results using dynamic mode decomposition. Experimental results are also obtained to further validate the proposed approach. These results show that the proposed self-agitator design can improve the convective heat transfer by 120% in a conventional heat exchanger without additional pumping power requirements and can achieve a Nusselt number of up to 30 within the laminar flow region, which is improved by 200% with the same Reynolds number compared to the clean channel.

A Biomimetic Approach to Improve Convective Heat Transfer Using Fluid-Induced Vibrations from Self-Excited Flaps

“…Nonetheless, the pressure loss owing to the airflow blockage in the deflected mode eclipsed with an almost 200% increase in Nu number compared to the bare channel at Reynolds numbers higher than 5,000. In another experimental study, the advantage of using two pairs of rectangular flaps over stationary vortex generators was shown, where the convective heat transfer was enhanced by matching the heatsink's preferred frequency mode and the agitator's resonance frequency [18]. An overview of the experimental studies on flap fluttering as a convective heat transfer enhancement method is provided in Table 1.…”

Air Side Heat Transfer Enhancement with Self Agitators

“…Li et al [19] presented a 2D numerical study of a flapping vortex generator mounted on a plate-fin heatsink for air-side heat transfer enhancement, and the results showed a 200% average Nusselt number improvement compared with a clean channel at the same Reynolds number. Inspired by blades of grass vibrating in the wind, Li et al [112] developed a rectangular self-agitator to improve the heat transfer performance of a plate-fin heat exchanger. They conducted a 2D FSI simulation and a dynamic modal decomposition (DMD) analysis and found a preferred frequency of the vorticity mode in a given channel.…”