International Journal of Thermal Sciences 48 (2009) 1639–1648 Contents lists available at ScienceDirect International Journal of Thermal Sciences www.elsevier.com/locate/ijts The influence of channel height on heat transfer enhancement of a co-angular type rectangular finned surface in narrow channel M.D. Islam a,∗ , K. Oyakawa b , M. Yaga b , I. Kubo a a Department of Mechanical Systems Engineering, The Petroleum Institute, Abu Dhabi, P.O. Box 2533, United Arab Emirates b Department of Mechanical Systems Engineering, Faculty of Engineering, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan article info abstract Article history: Received 21 April 2008 Received in revised form 13 January 2009 Accepted 13 January 2009 Available online 3 February 2009 Keywords: Convective heat transfer Height influence Heat transfer enhancement Infrared image system Co-angular fin pattern An experimental research was conducted to investigate the effect of channel height on heat transfer enhancement of a surface affixed with arrays (7 × 7) of short rectangular fins of a co-angular type pattern in channels. An infrared imaging system with the camera (TVS 8000) measured the temperature distributions to calculate the local heat transfer coefficients of the overall surface (fin base and endwall) of the representative fin regions. Heat transfer experiments were performed for a co-angular type fin pattern varying the channel to fin height ratio ( H d / H f ) from 2 to 5. Friction factors of the finned surfaces were calculated from pressure drop measurements. Relatively larger friction occurs for the smaller channel to fin height ratios and the friction factor slowly decreases with increasing Reynolds number. For the larger channel to fin height ratios, friction factor slowly increases with Reynolds number. The area averaged heat transfer decreases with increasing the channel to fin height ratio and channel aspect ratio, while heat transfer increases with the mainstream velocity. This is because, separation space between the channel wall and the fin top surface has a great influence on the phenomena of flow separated from the fin edge and vortex formation. At a smaller separation space, generated vortex is strongly reflected and vortex structure formation is adequately completed having full strength to interact with fins and endwall surface which leads to larger friction and contributes heat transfer enhancement. A detailed heat transfer analysis and iso-heat transfer coefficient contour gives a clear picture of the heat transfer characteristics of the overall surface. A relative performance graph indicates that the lowest channel to fin height ratio ( H d / H f = 2) has the highest thermal performance out of the channels tested. In addition, significant thermal enhancement, 2.6–3 times the smooth surface value can be achieved at lower Reynolds numbers with a co-angular fin pattern in the channel.  2009 Elsevier Masson SAS. All rights reserved. 1. Introduction The recent development of more powerful chips and the minia- turization of electronic circuits and other compact systems have created a greater demand for development of efficient heat re- moval systems. Fins are widely used as the primary means of heat exchanging devices. With the increasing demand for high perfor- mance heat exchanging devices, researchers are now trying to use the fins as extended surfaces and, additionally, as vortex generators which is an emerging technology in the field of heat transfer. Re- cently, an inclined rectangular fin attached to the endwall is found to be an effective configuration for enhanced heat transfer, because the vortexes, longitudinal and other, produced by this fin maintain their intensity far downstream. It is expected that the heat transfer from the endwall and the fin surface can be improved and hence this configuration is identified as being very promising. The au- * Corresponding author. E-mail address: mdislam02@yahoo.com (M.D. Islam). thors have conducted a series of experimental investigations [1–3] with rectangular fins, using different patterns and arrangements, to study heat transfer enhancement in a rectangular channel. The heat transfer enhancement in arrays of rectangular blocks in a channel has been investigated by other researchers. Sparrow et al. [4,5] studied the heat transfer and pressure drop characteristics of arrays of rectangular modules commonly encountered in electronic equipment and determined the thermal behavior of the arrays in different situations. Heat transfer enhancements exceeding a fac- tor of two were achieved by using multiple fence like barriers, with the interbarrier spacing and the barrier height being varied parametrically with Reynolds number. Molki et al. [6] experimen- tally studied the heat transfer at the entrance region of an array of rectangular heated blocks and presented empirical correlations of the heat transfer for the array. Heat transfer from an array of parallel longitudinal fins to a turbulent air stream passing through the inter fin spaces has been investigated both numerically and experimentally by Kadle and Sparrow [7]. They found that the lo- cal heat transfer coefficients varied along the fins and along the 1290-0729/$ – see front matter  2009 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ijthermalsci.2009.01.006