Thermal characterization of turbulent flow in a channel with isosceles triangular ribs ☆ C. Thianpong ⁎, T. Chompookham, S. Skullong, P. Promvonge Department of Mechanical Engineering, Faculty of Engineering, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand abstract article info Available online 3 May 2009 Keywords: Channel flow Enhanced heat transfer Triangular rib Rectangular duct The article presents an experimental investigation on turbulent heat transfer and friction loss behaviors of airflow through a constant heat-fluxed channel fitted with different heights of triangular ribs. The rib cross- section geometry used in the present study was isosceles triangle. Two rib arrangements, namely, in-line and staggered arrays, were introduced. Measurements were carried out for a rectangular channel of aspect ratio, AR = 10 and height, H = 30 mm with three uniform rib heights, e = 4, 6 and 8 mm (e/H =0.13, 0.2 and 0.26) and one non-uniform rib height, e =4,6 mm (e/H =0.13,0.2) alternately for a single rib pitch, P =40 mm. The flow rate in terms of Reynolds numbers based on the inlet hydraulic diameter of the channel was in a range of 5000 to 22,000. The experimental results show a significant effect of the presence of the ribs on the heat transfer rate and friction loss over the smooth wall channel. The uniform rib height performs better than the corresponding non-uniform one. The in-line rib arrangement provides higher heat transfer and friction loss than the staggered one for a similar mass flow rate. In comparison, the largest e/H rib with inline array yields the highest increase in both the Nusselt number and the friction factor values but the lowest e/H rib with staggered array provides the best thermal performance. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction The use of ribs placing in the cooling channels or channel heat exchangers is one of the commonly used passive heat transfer enhancement technique in single-phase internal flows. Thus, the research work of fluid flow and heat transfer in ribbed channels has been rich so far. This heat transfer enhancement technique has been applied to various types of industrial applications such as shell-and-tube type heat exchangers, electronic cooling devices, thermal regenerators, and internal cooling systems of gas turbine blades. Periodically positioned ribs in the channels interrupt hydrodynamic and thermal boundary layers. Downstream of each rib the flow separates, re- circulates, and impinges on the channel wall and these effects are the main reasons for heat transfer enhancement in such channels. The use of ribs increases not only the heat transfer rate but also substantial the pressure loss. The rib geometry and arrangement in the channel also alter the flow field resulting in different the convective heat transfer distribution. In particular, the angled ribs, the rib cross-section, the rib- to-channel height ratio and the rib pitch-to-height ratio are all parameters that influence both the convective heat transfer coefficient and the overall thermal performance. Several investigations have been conducted to study the effect of these parameters of ribs on heat transfer and friction factor for two opposite roughened surfaces. Han et al. [1,2] studied experimentally the heat transfer in a square channel with different angled rib arrays on two walls for P/e = 10 and e/D =0.0625. They reported that the angled ribs and ‘V’ ribs provided higher heat transfer enhancement than the continuous ribs and the highest value is at the 60° orientation amongst the angled ribs. For heating either only one of the ribbed walls or both of them, or all four channel walls, they reported that the former two conditions resulted in an increase in the heat transfer with respect to the latter one. For using broken ribs in a square channel with e/D = 0.0625 and P/e =10, Han and Zhang [3] also found that 60° broken ‘V’ ribs provide higher heat transfer at about 4.5 times the smooth channel and perform better than the continuous ribs. The performance of square, triangular and semi-circular ribs was experimentally investigated by Liou and Hwang [4,5] using a real time Laser Holographic Interferometry to measure the local as well as average heat transfer coefficients. They found that the square ribs give the best heat transfer performance among them. This is contrary to the experimental result of Ahn [6] indicated that the triangular rib performs better than the square one. Taslim et al. [7] reported that the heat transfer behavior in a ribbed square channel with three e/H ratios (e/H =0.083, 0.125 and 0.167) and a fixed P/e =10 using a liquid crystal technique. The average Nusselt number was increased with the rise in e/H ratio and the best one of the e/H ratios was found to lie between 0.083 and 0.125. Mochizuki et al. [8] studied the effect of rib arrangements on heat transfer in a rib-roughened channel with uniformly heating the four walls. Ribs were placed at 60° with e/H =0.09 and the rib pitch ratio of 10. Experimental data showed an asymmetry of the Nusselt number distribution caused by the secondary flows as already found by previous authors. Murata and Mochizuki [9] studied numerically the heat transfer distribution in a ribbed square channel with e/D = 0.1, P/e =10 and 60° orientation using large eddy simulation. Their International Communications in Heat and Mass Transfer 36 (2009) 712–717 ☆ Communicated by W.J. Minkowycz. ⁎ Corresponding author. E-mail address: ktchinar@kmitl.ac.th (C. Thianpong). 0735-1933/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.icheatmasstransfer.2009.03.027 Contents lists available at ScienceDirect International Communications in Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ichmt