Heat transfer and pressure drop results for one- and two-row arrays of finned tubes

Experiments were performed to measure Nusselt numbers and pressure loss coefficients for annular-finned tubes deployed in either a one-row array or in an in-line or a staggered two-row array. The apparatus was electrically heated and air was the convective heat transfer medium. The transverse and longitudinal pitches were varied parametrically and, for each configuration, the freestream Reynolds number ranged from 7500 to 32,000. For the one-row arrays, both the Nusselt number and the pressure loss coefficient were highly sensitive to the transverse pitch. The Nusselt numbers for the first row of a two-row array did not deviate appreciably from those of the corresponding one-row array, with the greatest deviations occurring for staggered arrays having intermediate values of the longitudinal pitch. For the tubes of the second row, the Nusselt numbers for the staggered arrays generally exceeded those for the in-line arrays and were also less sensitive to the longitudinal pitch. The overall pressure drops for the two-row, staggered arrays were also quite insensitive to the pitch, with values that were about twice those for the corresponding one-row array. On the other hand, the pressure drops for the in-line arrays were always less than twice the one-row values, with a tendency to increase with increasing longitudinal pitch.