Vortex generator for an enhanced thermo-hydraulic performance in a microchannel
Toh, Zheng Yong
Date of Issue2018
School of Mechanical and Aerospace Engineering
Longitudinal vortex generators are commonly applied to conventional plate fin heat exchanger due to favorable thermal and hydraulic performance by the vortex generators. However, research into longitudinal vortex generators in microchannel are few and far between. One of the challenges for research into heat transfer in microchannel is the prohibitive cost required to manufacture these channels. In this research, following the implementation by previous researchers, an insert with vortex generators on the surface will be manufactured and placed concentrically into a circular channel. Through this, a 300µm annular channel is produced with vortex generators used to enhance the heat transfer of this channel. The improvements made will be compared to a plain microchannel of the same hydraulic diameter. 4 different inserts have been manufactured for this research to perform a parametric study of the angle of attack of the vortex generators on the thermal and hydraulic efficiencies. The angle of attack being studied in this research is 0°, 15°, 30° and 45°. The results shows that as the angle of attack increases, at the same Reynolds number, the Nusselt number generally increases, except for 30° and 45° at Reynolds number above 3500 where both microchannel have similar heat transfer performance. The pressure drop incurred by the vortex generators also increases with increasing angle of attack. Comparison with the plain microchannel shows that the vortex generator placed at 45° exhibits the highest heat transfer enhancement of 2.42 at a Reynolds number of 2506. When considering the overall thermal and hydraulic efficiency, the vortex generator placed at 30° has the highest efficiency of 1.69 at a Reynolds number of 2777. A numerical simulation has also been conducted for an insert with vortex generator at 15° angle of attack with a flow rate of 6 liters per minute (LPM). The results shows that the vortex generator enhance the heat transfer by mixing the bulk fluid with the boundary layer, resulting in the thinning of the thermal boundary layer and increasing the temperature gradient at the boundary.
Final Year Project (FYP)
Nanyang Technological University