Pitch and aspect ratio effects on single-phase heat transfer through microscale pin fin heat sinks. (March 2018)

• Record Type: Journal Article
• Authors: Rasouli, Erfan; Naderi, Cameron; Narayanan, Vinod
• Is Part Of: International journal of heat and mass transfer. Volume 118(2018)
• Page Start: 416
• Page End: 428
• Publication Date: 2018-03
• Subjects: Heat transfer -- Pressure drop -- Single phase -- Pin fin heat sink -- Vortex shedding -- Flow visualization -- Correlation; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2017.10.105
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Aspect and pitch ratio effect on heat transfer in microscale pin fin heat sinks. Transition into unsteady vortex shedding is visualized using high-speed imaging. Unsteady vortex shedding is observed only for α ≥ 1, βT ≥ 2, and βL ≥ 1. Existence of vortex shedding increases the NuLc_Amin at a given ReLc_Amin . Onset of vortex shedding resulted in a decreased dependence of Nu on Pr. Correlations developed for NuLc_Amin in the non-shedding and shedding regimes. Abstract: Heat transfer and pressure drop of single-phase liquid flow is characterized in eight micro pin fin heat sinks with varied pitch and aspect ratios. The pins are diamond shaped with respect to the flow and have transverse pitch-to-diameter ( S T / D h ) and aspect ( H pin / D h ) ratio variations in the range of 1.7–3.0 and 0.7–3.2, respectively. The fluid used is PF-5060 over a Reynolds numbers (based on pin fin hydraulic diameter) range of 8–1189. Flow visualization is performed on all the heat sinks and flow transition into unsteady vortex shedding is observed only in those with specific pitch and aspect ratios. Flow visualization reveals upstream propagation of the onset of vortex shedding along the length of heat sink with an increase in Reynolds number. The existence of vortex shedding in micro pin fin heat sinks affects the prediction error of heat transfer correlations in literature. To address this gap, together with data from a prior study using liquid nitrogen [1], separate correlations are developed to predict Nu in the steady and unsteady regimes. The resulting correlation for the unsteady regime shows significantly decreased dependency of Nusselt on the Prandtl number compared to the non-vortex-shedding condition.