Numerical Analyses of Effects of Tube Shape on Performance of a Finned Tube Heat Exchanger

Abstract

Th is article discusses the eff ects of tube geometry on the performance of a multi-row fi nned tube heat exchanger having herringbone wavy fi ns. Th e air-side heat transfer and pressure drop characteristics of the heat exchanger were predicted numerically and the tube-side heat transfer coeffi cient and pressure drop were calculated using commonly adopted equations for turbulent fl ow in a smooth tube. Th e numerical calculations were performed in three dimensions for three frontal air velocities of 1.0, 2.0, and 3.0 m/s, yielding hydraulic diameter Reynolds numbers from 297 to 999. Investigated were fi ve tube geometries, including a round tube, three elliptical oval tubes, and a fl at oval tube. Th e round tube has a 15.875 mm (⅝ ) outside diameter and serves as the baseline tube. Th e four oval tubes were made by reforming the baseline round tube and have the same perimeter as that of the round tube. Th e aspect ratios of the three elliptical tubes are 2.00, 3.00, and 4.29, respectively, and the aspect ratio of the fl at oval tube is 3.00. As the tube aspect ratio is increased, the air-side heat transfer coeffi cient and pressure drop decrease, but the water-side heat transfer coeffi cient and pressure drop increase. At 2.0 m/s frontal velocity, the 3.00 aspect ratio elliptical tube yields a 6.9% lower air-side heat transfer coeffi cient and a 45.9% lower air pressure drop than the round tube. As compared to the 3.00 aspect ratio elliptical tube, the same aspect ratio fl at tube has a 0.6% higher air-side heat transfer coeffi cient and a 2.5% higher air pressure drop.