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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Heat Transfer and Pressure Drop of Serrated Finned Tube Banks in Forced Convection

Get access (open in a dialog) DOI: 10.1615/IHTC15.cnv.008698
pages 1611-1625

摘要

Finned tubes are widely used to enhance heat transfer. To improve efficiency of power generation systems, performance optimization of finned tube heat exchangers is necessary by minimizing the pumping power. Heat transfer and pressure drop characteristics of serrated finned tube banks are investigated experimentally and numerically in this paper. The open-loop wind tunnel was used and fully developed turbulent flow was intruded to the test section. A blower includes an electric heater for air was used to produce air flow and control air temperature. Dummy tube banks were installed upstream and downstream of the test section to ensure the actual installation conditions. Tests were carried out in the range of Reynolds numbers between Re=5000 and 20000. The bare tube with the outside diameter of 38mm was used. Five configurations of resin finned tubes changing the fin height (h=11, 16, 21mm), serrate width (w=2.2, 2.4mm) and twist angle (0, 25degrees) were fabricated by a three-dimensional printer to exclude uncertainties in fin dimensions and shape. The test section consisted of 22 serrated finned tubes in the staggered arrangement with the tube pitch of 65 to 90mm in the flow direction. Pressure drop in the test section and time mean velocity were measured by a differential pressure gauge and non-directional hot-wire anemometer, respectively. Velocity fluctuations were also measured at distances of z=5, 8, 13mm from the tube outside surface. The velocity measurement results showed that measured turbulent intensities decreased with approaching the bare tube (fin inside direction). The visual observation of detaching shear layer and wake area was conducted by the oil film method with silicon oil and titanium powder mixture. The fin surface temperature distribution was measured by a high speed infrared camera of the sampling rate is 0.01 second. Heat transfer rate of the fin surface were measured by the transient temperature change generated by a sharp temperature rise of the air. Numerical investigations were also carried out with CFD code to clarify and support the experimental observations. Low Reynolds number k-E turbulent model was applied. Numerical results for the pressure drop, time mean velocity and wake area were relatively in good agreement with the experimental observations. It is concluded that the heat transfer and pressure drop characteristics of serrated finned tube banks obtained in this paper would lead to the optimization of finned tube heat exchangers.