Measurements of the overall heat transfer from combustion gases confined within elliptical tube heat exchangers

Measurements of the overall heat transfer for elliptical cylinders in cross-flow are presented for various flatness ratios and incidence angles. The measurements included the internal convective transfer of confined flowing (hot) gases combined with the external convective transfer. The internal hot gases were created using natural gas flames whereby combustion was completed prior to entering the elliptical test section. Results are reported for three flatness ratios, 0.20, 0.3 1, and 0.52, in addition to three incidence angles, 0, 45, and 90 degrees. The measurements are compared to round tube measurements and previous studies on elliptical cylinders in cross-flow. Results indicate that a significant flatness (0.30 or less) must be achieved to realize any appreciable (greater than 10 percent) change in the overall heat transfer coefficient. The effect of flattening heat exchanger tubes is presented in terms of the heat transfer enhancement gained without any consideration of the increase in the internal pressure losses. (C) 2002 Elsevier Science Inc. All rights reserved.