| 1. |
- Wang, Jin, et al.
(author)
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Effects of pin fins and vortex generators on thermal performance in a microchannel with Al2O3 nanofluids
- 2022
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In: Energy. - : Elsevier BV. - 0360-5442. ; 239
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Journal article (peer-reviewed)abstract
- This paper performs a comparative analysis to obtain the optimal cross-section shape and parameters of both pin fins and vortex generators. A novel combined structure with pin fins and vortex generators is proposed to enhance thermal performance of an integrated microchannel heat sink. Effects of nanoparticle diameter and volume fraction are investigated using Al2O3 nanofluid and DI-water as working fluid. Pin fins and vortex generators cause enhancements of flow disturbance and heat transfer on microchannel heat sinks. Results indicate that oval pin fins have better improvements of thermal/hydraulic performance compared to round and diamond pin fins. The oval pin fin with 0.4 mm spacing and 0.1 mm height presents the highest overall performance factor in the Reynolds number range of 340–640. Presence of vortices intensifies the mixing of the hot fluid near bottom surface and cold fluid near top surface. The optimal vortex generator with length of 0.08 mm and height of 0.06 mm provides a 30% increase in overall performance factor compared to the rectangular microchannel at Reynolds number of 340. Mechanism of heat transfer enhancement is analyzed by investigating flow velocity, temperature distribution and field synergy angle distribution in microchannels. Based on the field synergy principle, it is found that a small and uniformly distributed synergy angle is achieved in the integrated microchannel. According to comparisons of the overall performance factor and total thermal resistance, the optimal nanoparticle diameter and Al2O3 volume fraction of nanofluids are 20 nm and 4%, respectively.
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| 2. |
- Ye, Mingzheng, et al.
(author)
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EFFECTS OF ELASTIC PILLARS ON FLUID-FLOW AND HEAT TRANSFER ENHANCEMEN IN A MICRO-CHANNEL
- 2023
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In: Thermal Science. - 0354-9836. ; 27:1, s. 275-287
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Journal article (peer-reviewed)abstract
- In this paper, periodic vortices are generated by a fluid passing a cylindrical obstacle, d, near the micro-channel inlet. Two elastic pillars are arranged on the walls, and the effect of the pillar spacing on heat transfer performance is studied using the Arbitrary Lagrangian-Euler method. With the spacing of 10d, the small pillar amplitude of 2 μm is not conducive to the generation of vortices. The flexible vortex generator has higher heat transfer efficiency and lower pressure loss than the rigid vortex generator. The two pillars with no spacing generate isolated vortices, and the mixing of these vortices is insufficient downstream the pillars. It is found that with the pillar spacing of 5d, the overall performance factor is significantly higher than that with the pillar spacing of 0d and 10d in the Reynolds number range of 800 to 1100. The average Nusselt number with the spacing of 5d increases by 19.2% compared to that with the spacing of 0d at the Reynolds number of 1000. When the Reynolds number is 1100, the overall performance factor is 43% higher than that with a single rigid pillar. The vortices are periodically generated by the two pillars with the 5d spacing, and the disturbance to the boundary layer enhances the heat transfer downstream the region in the micro-channel.
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