Cylinder in crossflow

Figure 6.13 compares Eq. (6-26) with available numerical solutions and experimental data of Hilpert (FI, H4) for heat transfer to air. Agreement is good even for Re as high as 10. The review of Morgan (M12) should be consulted for additional data and discussion on transfer to cylinders in crossflow. 

This idea was first used by Van der Hegge Zijnen (VI) and Douglas and Churchill (D4) in developing correlations for cylinders in crossflow. 

Churchill, S. W., and M. Bernstein A Correlating Equation for Forced Convection from Gases and Liquids to a Circular Cylinder in Crossflow, J. Heat Transfer, vol. 99, pp. 300-306, 1977. 

The flow pattern around a cylinder in crossflow is heavily dependent on the Reynolds number, as Fig. 3.23 clearly shows for a circular cylinder. At low Reynolds numbers Re = w djv < 5, Fig. 3.23a, the flow surrounds the cylin-... 

The equation is the same as that for a cylinder in crossflow, the Nusselt and Reynolds numbers are formed with the length over which the fluid flows, in the example below L = a + b. 

S. W. Churchill and M. Berstein, A correlating equation for forced convection from gases and liquids to a circular cylinder in crossflow, J. Heat Transfer, 99,300-306,1977. 

This specifies the relative orientation of the target surface and the burner. This is usually the most important consideration for the designer or researcher, when reviewing previous experimental results. The four most common geometric configurations in flame jet experiments have been flames impinging (1) normal to a cylinder in crossflow, (2) normal to a hemi-nosed cylinder. 

Flame impinging normal to a cylinder in crossflow. (From Baukal, C. E., Heat Transfer from Flame Impingement Normal to a Plane Surface, Saarbriicken, Germany VDM Verlag/Dr. Muller, 2009.)... 

Achenbach, E. Distribution of local pressure and skm fiiction around a circular cylinder in crossflow up to Re = 5x 10 . Fluid Mechanics 34, 625-639, 1968. 

For the CHF condition for two-phase crossflow on the shell side of horizontal tube bundles, few investigations have been conducted. Katto et al. (1987) reported CHF data on a uniformly heated cylinder in a crossflow of saturated liquid over a wide range of vapor-to-liquid density ratios. Recently, Dykas and Jensen (1992) and Leroux and Jensen (1992) obtained the CHF condition on individual tubes in a 5 X 27 bundle with known mass flux and quality. At qualities greater than zero, they found that the CHF data are a complex function of mass flux, local quality, pressure level, and bundle geometry. 

Katto, Y., S. Yokoya, S. Miake, and M. Taniguchi, 1987, CHF on a Uniformly Heated Cylinder in a Crossflow of Saturated Liquid over a Very Wide Range of Vapor-to-Liquid Density Ratio, Int. J. Heat Mass Transfer 30.1971-1977. (5)... 

Figure 6.12 shows a curve fitted by Pruppacher et al. (P8) to the many determinations of for steady crossflow past long cylinders in the Re range applicable to free motion. We have approximated this curve by the following expressions ... 

Fand, R. M. Heat Transfer by Forced Convection from a Cylinder to Water in Crossflow, Int. J. Heat Mass Transfer, vol. 8, p. 995, 1965. 

The flow around and therefore the heat transfer around an individual tube within the bundle is influenced by the detachment of the boundary layer and the vortices from the previous tubes. The heat transfer on a tube in the first row is roughly the same as that on a single cylinder with a fluid in crossflow, provided the transverse pitch between the tubes is not too narrow. Further downstream the heat transfer coefficient increases because the previous tubes act as turbulence generators for those which follow. From the fourth or fifth row onwards the flow pattern hardly changes and the mean heat transfer coefficient of the tubes approach a constant end value. As a result of this the mean heat transfer coefficient over all the tubes reaches for an end value independent of the row number. It is roughly constant from about the tenth row onwards. This is illustrated in Fig. 3.26, in which the ratio F of the mean heat transfer coefficient Oim(zR) up to row zR with the end value am (zR —> oo) = amoo is plotted against the row number zR. 

Fand, R.M. and Keswani, K.K. (1972) A continuous correlation equation for heat transfer from cylinders to air in crossflow for Reynolds numbers from 10 to 2x10. Int. I. Heat Mass Transfer, 15, 559-562. 

The application of very high-permeability dryer fabrics in the paper industry made it possible to introduce air through the fabrics. Therefore, the above-mentioned blowing rolls and the hot air ducts below (or above) the felt rolls between the cylinders became very popular. These systems provide better crossflow ventilation, which in turn results in more uniform and higher mass-transfer rates. 

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