Tang, Tsz Loong (2022) An investigation of hydrodynamics and heat transfer correlation of multiple jet impingement by using magnesium oxide-water based nanofluids. Doctoral thesis, Universiti Tun Hussein Onn Malaysia.

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Abstract

The research of convection heat transfer using nanofluids mainly in pipe flows. However, there is a lack of fundamental study on the multiple jet impingements using nanofluid. Thus, MgO-H2O based nanofluid’s heat transfer and hydrodynamic characteristic of multiple jet impingement cooling are investigated experimentally and numerically. The jet array consisted of nozzle diameter, d, of 1.5 mm arranged in 3x3 rectangular arrays with the jet-to-jet spacing, s, from 3.0 to 6.0 mm and nozzle-to-target distance, H, from 3.0 to 9.0 mm. The results covered a range of Reynolds numbers based on nozzle diameter, Red, from 1000 to 10000, and nanofluids volume fractions, , from 0% to 0.15%. The effects of Red, , H,& s are investigated on the average Nusselt number for the impingement surface. The jet arrays were simulated using ANSYS FLUENT software. The present numerical analysis focuses on the jet arrays with H=3.0 mm for all jet-to-jet spacing since the flow under this geometry configuration is in submerged conditions, representing the actual system in electronic cooling. Furthermore, the single phase model is adopted to simulate the nanofluids thermal-physical property. The 3D streamlines, velocity contour, and heat transfer coefficient distribution are presented. The experiment results show that depending upon the combination of Red, , H,& s, the application of nanofluids can achieve a heat transfer enhancement in some cases; conversely, degradation of heat transfer for other combinations may occur. The maximum increase in Nusselt number relative to water is about 19.4% at =0.15%, Red=1001, s=4.5 mm, and H=3.0 mm. In contrast, the maximum decrease of Nusselt number relative to water is about -6.8% at =0.10%, Red=8493, s=6.0 mm, and H=3.0 mm. The numerical results can correctly predict the heat transfer trend, but a large discrepancy is observed compared with nanofluid’s experimental data, especially at high Red, because the single phase model cannot capture the nanoparticle effect. Consequently, a correlation equation is presented combining the impact of the suspended nanoparticles and the flow condition of the multiple jet impingements

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