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ACRC Technical Report 137PDF


Title:Heat Transfer Enhancement Using Tip and Junction Vortices
Author(s):Gentry, M.C.; Jacobi, A.M.
Subject(s):air-side heat transfer
Abstract:Single-phase convective heat transfer can be enhanced by modifying the heat transfer surface to passively generate streamwise vortices. The swirling flow of the vortices modifies the temperature field, thinning the thermal boundary layer and increasing surface convection. Tip vortices generated by delta wings and junction vortices generated by hemispherical protuberances were studied in laminar flat-plate and developing channel flows. Local and average convective measurements were obtained, and the structure of the vortices was studied using quantitative flow visualization and vortex strength measurements. The pressure drop penalty associated with the heat transfer enhancement was also investigated. Tip vortices generated by delta wings enhanced local convection by as much as 300% over a flat-plate boundary layer flow. Vortex strength increased with Reynolds number based on chord length, wing aspect ratio, and wing angle of attack. As the vortices were advected downstream, they decayed because of viscous interactions. In the developing channel flow, tip vortices produced a significant local heat transfer enhancement on both sides of the channel. The largest spatially averaged heat transfer enhancement was 55%; it was accompanied by a 100% increase in the pressure drop relative to the same channel flow with no delta-wing vortex generator. Junction vortices created by hemispherical surface protuberances provided local heat transfer enhancements as large as 250%. Vortex strength increased with an increasing ratio of hemisphere radius to local boundary layer thickness on a flat plate. In the developing channel flows, heat transfer enhancements were observed on both sides of the channel. The largest spatially averaged heat transfer enhancement was 50%; it was accompanied by a 90% pressure drop penalty relative to the same channel flow with no hemispherical vortex generator. This research is important in compact heat exchanger design. Enhancing heat transfer can lead to smaller, more efficient heat exchangers in a broad range of applications. A simplified heat exchanger performance evaluation method is considered to explore the heat transfer benefit and pressure-drop penalty of vortex generator enhancements.
Issue Date:1998-03
Publisher:Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Air Conditioning and Refrigeration Center TR-137
Genre:Technical Report
Sponsor:Air Conditioning and Refrigeration Center Project 73
Date Available in IDEALS:2009-05-18

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