Effects of Gull-Wing Baffles on the Performance of a Single-Row, Annularly Finned Tube Heat Exchanger

The effect of gull-wing baffling on the performance of a single-row, annularly finned tube heat exchanger is quantified for Reynolds numbers from 5,000 to 13,000. A novel adaptation of the naphthalene sublimation technique provides optically measured sublimation depths that are used to determine local mass-transfer coefficients with a spatial resolution superior to previously reported data. Local and average heat-transfer data for baffled and unbaffled finned tubes are inferred through the analogy between heat and mass transfer. Local data are used to explain the flow and heat-transfer interactions and their impact on overall heat-transfer performance. Pressure drop data are presented for a complete measure of heat-transfer and pumping power performance, and a performance evaluation criterion is used to compare the heat exchangers. The data indicate that the unbaffled geometry provides nearly the same heat transfer as the baffled arrangement, but the unbaffled geometry incurs only 20 to 25% of the baffled pressure drop in the Reynolds number range studied. The use of baffles as a heat-transfer enhancement method should be restricted to very low Reynolds numbers or to applications where pressure drop is not a factor.