Correlations for the prediction of natural convection heat transfer of hollow hybrid fin arrays

• Published in: Applied thermal engineering Vol. 254; p. 123885
• Main Authors: Jamilah, Sina, Yang, Hyeon Ho, Noh, Wooheon, Kim, Kyoung Joon
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-10-2024
• Subjects: Hollow hybrid fin; Natural convection; Nusselt number correlation; Orientation; Prediction; Natural convection; Nusselt number correlation; Orientation; Prediction; Hollow hybrid fin
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2024.123885

•Nu correlations are developed for the prediction of natural convection heat transfer around HHFs, HHF arrays, and oriented HHF arrays.•The average discrepancies of the correlation prediction are found to be smaller than 5.5%.•It is found that the convection heat transfer coefficient of the vertical HHF array increases asymptotically with the increase of fin spacing.•The convection heat transfer coefficient of the downward HHF array is found to be greater than that of the sideward case.
A hollow hybrid fin (HHF) array is a staggered array of hollow pin fins concatenated with radially-extruded plate fins. Preceding research for a decade shows that natural convection HHF arrays could yield up to 30 % superior mass-based thermal performance and less orientation dependence compared to natural convection pin fin arrays. Hence, the HHF array could be a potential alternative to conventional pin fin arrays for lightweight high-performance thermal management of microelectronics in natural convection. To demonstrate potential and limitation of the natural convection HHF array, optimization is inevitable, and thus correlations for the prediction of natural convection heat transfer around the HHF arrays should be developed to provide design guidelines for the optimization. Nu correlations are developed for HHFs, HHF arrays, and oriented HHF arrays. Due to broad ranges of physical conditions, 168 cases for the HHF, 48 cases for the vertical HHF array, and 24 cases for the oriented HHF arrays are calculated and validated by the measurement and the literature data. Utilizing CFD thermal data, Nu correlations are formulated. Discrepancies between correlation-predicted and CFD-evaluated Nu values are examined. The results show that average discrepancies are 2.9 % for the vertical HHFs, 4.8 % for the vertical HHF arrays, and 5.5 % for oriented HHF arrays. These reasonable discrepancy values demonstrate the correlation validity. Validated Nu correlations are used to analyze parametric effects on convection heat transfer coefficients, h. It is seen that h increases asymptotically with the increase of fin spacing, S, mainly due to the porosity increase. The parametric study finds that h declines till a certain internal diameter, Di. They are 2 mm for external diameter, Do, of 4 mm, 4 mm for Do of 7 mm, and 6 mm for Do of 10 mm. The parametric study shows that after such Di, h consistently increases until the widest Di. The parametric study for the orientation shows that for the sideward orientation, h increases with the increase of porosity. The result also shows that h of the downward case is greater than that of the sideward case, and the difference is greater at lower Ra values.