Heat Transfer in Air Flow Across a Single-Row Bundle of Tubes With Spiral Grooves

An experimental study has been made of the heat transfer and hydraulic resistance in air flow across a single-row bundle of tubes with spiral grooves on the exterior surface and of a bundle of smooth tubes of the same diameter. Cutting a spiral groove of width 3 mm and depth 2 mm with a pitch of 20 mm on a tube with an outside diameter of 22 mm increased the heat-transfer coefficient in the range of Reynolds numbers 6200–16,000 by 40–53% compared to the smooth-tube bundle. The hydraulic resistance of the tube bundle decreased by 22%. The Reynolds analogy factor increased, on the average, by 41%. Tubes with spiral grooves, in the investigated range of the velocities of flow, have shown a certain increase in the Strouhal number to values of 0.24–0.36. Computer simulation has been carried out of the hydrodynamics of the single-row bundle of smooth-wall tubes and the tubes with spiral grooves. It has been shown that the enhancement of heat transfer and the decrease in the hydraulic resistance alike are attributable to the appearance of nonsymmetric vortex structures induced by the flow across the spiral grooves.