Hydrothermal performance of aluminium oxide/water and cupper oxide/water nanofluids in divergent-convergent minichannel heatsink with dimples

• Main Author: Mohamad, Nura Mu'az
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: TJ Mechanical engineering and machinery
• Online Access: http://eprints.utm.my/id/eprint/101918/1/NuraMu%27azMohamadPSKM2021.pdf.pdf; http://eprints.utm.my/id/eprint/101918/; http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:149284

The recent trend in technological advancements in electronic devices offers high-performance compact systems. However, highly concentrated heat flux restricted their efficiency and reduced the Mean time before failure (MTBF). Many researchers exploit different passive heat transfer techniques like geometry modification to alleviate high heat flux. Despite the potential of divergent-convergent minichannel in mixing flow and a higher proportion of surface area to volume than conventional channels, research on it is inadequate. The study aims to develop and examine the influence of combined multi passive heat transfer techniques in an electronic device minichannel heatsink towards further augmenting heat transfer with minimal pressure loss and thermal resistance. This study combines corrugated geometry with innovative high thermal conductive nanofluid as hybrid passive techniques. The experimental validation concerning measured and predicted pressure drop and Heat Transfer Coefficient data indicated a maximum deviation of 19.1% and 13.8%, respectively. The numerical analysis employed a commercial CFD code based on the finite volume method. The investigation of forced convective heat transfer and nanofluids’ flow achieved with single-phase and two-phase mixture models in a divergent-convergent minichannel heatsink (DCMH) having a hydraulic diameter of 1.42mm. The numerical investigation employed Al2O3/water and CuO/water nanofluids with 0 - 2.5 volume%, fluid velocity from 3 – 6 m/s (corresponding to Reynolds number (5000 – 10000), and the inlet temperature 303 K. The two-phase model exhibits better agreement with established correlation than the single-phase model. A numerical analysis of an enhanced geometry with dimples on the minichannel floor was developed to augment the hydrothermal performance. The results found that the effects of principal parameters on the chip heat flux demonstrated the heat transfer coefficient’s growth with a rise in volume fractions and fluid velocity. Both nanofluids indicated better performance enhancement than water. Al2O3/water and CuO/water nanofluids augment over water by about 6.44% and 8.33% for 2.5 vol.%. Also, pressure loss rises when the velocity increases. The pressure loss relative to water at 2.5 vol.% and 5.5 m/s yields 15.14% and 18.56 % for Al2O3/water and CuO/water. The highest pumping power is 0.057 W for all the cases, which indicates the pumping demand is much lower than 1.0 W. The introduction of dimples on DCMH has considerably advanced hydrothermal performance with a PEC of 1.214 over the smooth model. The overall results established that the combined effects of DCMH and nanofluids have significantly improved the heat sink’s hydrothermal performance and can provide the desired heat dissipation from the enclosed chips in compact electronic devices.