Pressure Loss and Heat Transfer Characterization of a Cam- Shaped Cylinder at Different Orientations A. Nouri-Borujerdi Professor School of Mechanical Engineering, Sharif University of Technology, Tehran, Iran e-mail: anouri@sharif.edu Arash M. Lavasani Professor Science and Research Branch, Islamic Azad University, Tehran, Iran e-mail: a_lavasani@iauctb.ac.ir Pressure drag coefficient and heat transfer are experimentally in- vestigated around a single noncircular cylinder in cross-flow un- der angle of attack 0 deg    360 deg and Reynolds number 1.5  10 4  Re eq  4.8  10 4 based on equivalent diameter of a cir- cular cylinder. The results show that the trend of pressure drag coefficient against the angle of attack has a wavy shape but the wavy trend of the Nusselt number is smoother relative to the drag coefficient behavior. It is found that for l / D eq = 0.4 and over the whole range of the Reynolds number, the pressure drag coefficient has a minimum value of about C D = 0.4 at  = 30 deg, 180 deg, and 330 deg and a maximum value of about C D = 0.9 at  = 90 deg and 270 deg. The corresponding value of the mean Nusselt number to that of the equivalent circular tube is 1.05  Nu cam / Nu cir  1.08 at  = 90 deg and 270 deg as well as 0.87  Nu cam / Nu cir  0.92 at  = 30 deg and 180 deg. DOI: 10.1115/1.2969259 Keywords: pressure drag, surface heat transfer, cam-shaped cylinder, heat exchangers 1 Introduction In contrast to the circular tubes, which cause severe separation and large wake regions to produce high pressure drops, noncircu- lar tubes of streamlined shapes offer high heat transfer and low hydraulic resistance and consequently require less pumping power. Ota et al. 1,2 found that at Re  10 4 maximum and minimum mean heat transfer coefficients around an elliptic cylinder with a major axis parallel to the flow direction with axis ratios of 1:2 and 1:3 occurred in the range of 60 deg    90 deg and 0 deg    30 deg, respectively. The minimum mean heat transfer rate was higher than that of a circular tube with equal circumferential length. The drag coefficient was about 0.12 at Re= 4.8  10 4 and  = 0 deg and increased monotonically with  and reached 1.8 at  =90 deg. Ruth 3 measured pressure drop and heat transfer rate for a lenticular tube bundle in the range of 10 3  Re  5  10 4 with a transverse tube pitch-to-diameter ratio of 2. He found that the drag was reduced by 70% in comparison with a circular tube bundle. Merker and Hanke 4 measured heat transfer and pressure drop along the shell-side of a tube bundle with oval-shaped tubes. They showed that heat exchangers with oval-shaped tubes have consid- erably smaller frontal areas on the shell-side in comparison with circular tubes in the range of 10 3  Re  5  10 4 based on the stream length. Prasad et al. 5 reported heat transfer and pressure drop from an aerofoil NACA-0024 in cross-flow for 2  10 4  Re  5  10 4 based on the equivalent diameter. They concluded that this shape gives higher values of Stanton number to pressure drop coefficient in comparison with a circular, lenticular, and oval tubes at Re  2  10 4 . Badr et al. 6 numerically simulated the unsteady flow over an elliptic cylinder with a major axis parallel to the flow direction at different orientations. They obtained the total drag coefficient equal to 0.8 at Re=3700 and 0.9 at Re=700 with a length ratio of minor-to-major axis equal to 0.6. The form drag was 80–90% of the total drag. Compared with a circular tube, the drag coefficient was reduced between 10% and 20%. Matos et al. 7 numerically and experimentally studied three dimensional of staggered finned circular and elliptic tubes at Re L = 852 and 1065, where subscript L is the swept length of a fixed volume. Circular and elliptic arrangements with the same flow obstruction cross-sectional area were compared on the basis of maximizing the total heat transfer. The results illustrate that the optimal elliptic tube arrangement exhibits higher heat transfer up to 19% in comparison with the optimal circular tube arrangement. The heat transfer gain and the relative total mass reduction of up to 32% show that the elliptical arrangement has a potential to deliver considerably higher global performance and lower cost. Li et al. 8 numerically investigated the heat transfer enhance- ment of three streamlined polymer tubes with fins of lenticular and oval profiles. For Bi  0.3 and 2  10 3  Re  2  10 4 , the heat transfer of oval-shaped tubes was higher than that of the circular tubes. They showed that the teardrop tube had the highest effi- ciency in comparison with the lenticular and oval tubes. Bouris et al. 9 carried out experiments and numerical simula- tions on a novel tube bundle heat exchanger with tube cross sec- tion that contained a parabolic shape in front and a semicircular one at the rear. The Reynolds number was in the range of 2.2  10 3  Re  4.1  10 3 based on the diameter of the bottom circu- lar section of the tube. Their results indicate a higher heat transfer level with 75% lower deposition rate and 40% lower pressure drop. Moharana and Das 10 gave an improvement on the analysis of Li et al. 8. They analyzed conduction through shaped tubes with a circular inner surface and a hydrodynamically shaped outer sur- face by two different techniques. These two techniques were a two-dimensional analysis as well as a one-dimensional approxi- mate technique, which showed a closed agreement with the two- dimensional analysis. Table 1 summarizes the results of the previous works concern- ing the pressure drag coefficient and the Nusselt number around a streamlined single tube or tube bundle. All these noncircular tubes have low pressure drag coefficient and high Nusselt number in comparison with circular tubes with the same circumferential length. Those tubes, which have cross-sectional area similar to a teardrop, have more efficiency than those of the oval and lenticu- lar tubes with less deposition rate of suspension materials on the tube surface. To give better understanding regarding the optimum shape for a noncircular tube in which high heat transfer and/or low drag can be achieved, this study has emphasized on cam-shaped tubes. This shape provides ease of manufacturing and varying flow pattern under different angles of attack in cross-flow. Contributed by the Heat Transfer Division of ASME for publication in the JOUR- NAL OF HEAT TRANSFER. Manuscript received January 4, 2007; final manuscript received June 2, 2008; published online September 22, 2008. Review conducted by S. A. Sherif. Journal of Heat Transfer DECEMBER 2008, Vol. 130 / 124503-1 Copyright © 2008 by ASME Downloaded 29 Aug 2010 to 81.31.171.152. Redistribution subject to ASME license or copyright; see http://www.asme.org/terms/Terms_Use.cfm