ESG-5 The Effect of Tube Pitch on Pressure Drop and Heat Transfer for Large Diameter Air Cooler Tubes

W. J. Marner

Tests have been conducted to determine the effect of tube pitch on the performance of large diameter air cooler tubes. The finned tubes tested had the following dimensions: root diameter of 2.134 in. (54.2 mm); fin spacing of 8.89 fins/in. (350 fins/m); fin height of 0.939 in. (23.9 mm); and fin thickness of 0.023 in. (0.58 mm). These dimensions produced a high outside-to-root area ratio of 25.2. The tubes were made of 304 Stainless Steel with overlapped L-foot, tension wound aluminum fins. The tube bundle had four rows and a transverse pitch of 4.25 in. (0.108 m) on a staggered, equilateral layout.

Isothermal pressure drop and nonisothermal pressure drop and heat transfer data were obtained over Reynolds number ranges of 1 310 to 44 300 and 3 340 to 41 100, respectively. The present experimental results are compared with: (1) appropriate HTRI correlations, and (2) earlier data for ""S-shaped"" and ""slit"" finned tubes which had the same nominal dimensions, but a transverse pitch of 4.50 in. (0.114 m).

The results show that a reduction in transverse pitch from 4.50 in. (0.114 m) to 4.25 in. (0.108 m) increases the pressure drop slightly, but has no perceptible effect on the heat transfer. The present pressure drop and heat transfer data are predicted reasonably well by the present HTRI correlations; however, the data indicate that improvements are possible in both the j-factor correlation and in the temperature correction term in the nonisothermal pressure drop correlation.