STG-3 Heat Transfer and Pressure Drop Performance of Integral Low-Finned Tube Bundles; Effect of Fin Spacing
Heat transfer rates and pressure drops were compared for air flowing across four different ideal tube banks with 3/4-in. (19.1-mm) diameter integral low-finned tubes. The study included new data for 30.7 fins/in. (1201 fins/m) tubes obtained in HTRI Wind Tunnel and results for tubes with 11.33 (446), 19.5 (768), and 27.0 (1063) fins/in. (fins/m) taken from the literature. The tubes were all arranged on a 30-degree staggered layout with a pitch ratio of 1.25.
The experimental data show that there is a decrease in the heat transfer j-factor as the number of fins per unit length increases and that this effect becomes more pronounced as the Reynolds number decreases. The pressure drop results also show some dependency on the fin density.
The previous HTRI method predicted pressure drop data of these four integral low-finned tube banks reasonably well with most of the data falling within -10 to +20 percent. However, previous methods failed to predict heat transfer data satisfactorily. New pressure drop and heat transfer correlations have been developed based on the present data. The new correlations predicted most of the pressure drop and heat transfer data within -10 to +20 percent. However, previous methods failed to predict heat transfer data satisfactorily. New pressure drop and heat transfer correlations have been developed based on the present data. The new correlations predicted most of the pressure drop and heat transfer data within ± 10 percent. It is also found that the new correlations, although derived from one tube diameter and one tube pitch, may be adequately used for the other low-finned tubes subject to some restrictions.