Influences of target surface small-scale rectangle roughness on impingement jet array heat transfer. (July 2017)

• Record Type: Journal Article
• Authors: Buzzard, Warren C.; Ren, Zhong; Ligrani, Phillip M.; Nakamata, Chiyuki; Ueguchi, Satoshi
• Is Part Of: International journal of heat and mass transfer. Volume 110(2017)
• Page Start: 805
• Page End: 816
• Publication Date: 2017-07
• Subjects: Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2017.03.061
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Physical effects responsible are increased local mixing, increased local vorticity fluctuations (for laminar and turbulent impingement flows), and increased local turbulent thermal transport (for the turbulent impingement flows). The second physical effect responsible for the measured Nusselt number variations is increased thermal resistance as small roughness height increases. The third physical effect responsible for the measured Nusselt number variations is increased wetted surface area with added roughness. Nusselt number ratios in the present study are as high as 2.5 because of the three physical effects mentioned above. Abstract: The present investigation considers the effects of special roughness patterns on impingement target surfaces to improve the effectiveness and surface heat transfer augmentation levels of impingement jet array cooling. This investigation utilizes various sizes, distributions, shapes, and patterns of surface roughness elements for impingement cooling augmentation. The surface roughness shape considered here is rectangle, in combination with larger rectangular pins. Combinations of small rectangle roughness and large pins are considered together, along with arrays of small rectangular roughness alone. Tests are performed at impingement jet Reynolds numbers of 900, 1500, 5000, and 11, 000. Local and overall impingement cooling performance depends upon the pattern, distribution, arrangement, and height of the roughness elements, as well as upon the jet Reynolds number. Depending upon the magnitude of jet Reynolds number, different behavior and trends are observed for the small rectangle roughness and large pins together, compared with arrays of small rectangular roughness alone. Overall, results demonstrate the remarkable ability of target surface roughness to produce increased surface heat transfer augmentation levels of impingement jet array cooling, relative to target surfaces which are smooth.