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An Experimental Study of Heat Transfer and Pressure Drop on the Bend Surface of a U-Duct

[+] Author Affiliations
Tareq Salameh, Bengt Sunden

Lund University, Lund, Sweden

Paper No. GT2010-22139, pp. 13-21; 9 pages
doi:10.1115/GT2010-22139
From:
  • ASME Turbo Expo 2010: Power for Land, Sea, and Air
  • Volume 4: Heat Transfer, Parts A and B
  • Glasgow, UK, June 14–18, 2010
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-4399-4 | eISBN: 978-0-7918-3872-3
  • Copyright © 2010 by ASME

abstract

This work concerns an experimental study of pressure drop and heat transfer for turbulent flow inside a U-duct. Such duct geometries can be found in many engineering applications where cooling air extracts heat from hot internal walls of the duct, e.g., passage cooling inside gas turbine blades. Both friction factors and convective heat transfer coefficients were measured inside a U-duct for three different cases, namely (a) the smooth straight part, (b) the smooth bend (turn) part, and (c) a rough (ribbed) bend (turn) part. The details of the duct geometry were as follows: the cross section area of the straight part was 50×50 mm2 , the inside length of the bend part 240 mm, the cross section area of the rib was 5×5 mm2 and the rib height-to-hydraulic diameter ratio, e/Dh , was 0.1. The Reynolds number was varied from 8,000 to 20,000. The test rig has been built in such a way that various experimental setups can be handled as the bend (turn) part of the U-duct can easily be removed and the rib configuration can be changed. Both the U-duct and the rib were made from plexiglass material to allow optical access for measuring the surface temperature by using a high-resolution measurement technique based on narrow band thermochromic liquid crystals (TLC R35C5W) and a CCD camera placed facing the bend (turn) part of the U-duct. The calibration of the TLC is based on the hue-based color decomposition system using an in-house designed calibration box. The rib was placed transversely to the direction of the main flow at the outer wall of the bend (turn) part where the wall was heated by an electrical heater. The friction factor ratio and the heat transfer enhancement ratio for case (c) at a Reynolds number of 20,000 were 48.75 and 2.66, respectively. It is found that the presence of the rib increases the heat transfer coefficient on the outer wall of the bend part (tip of side U-duct). The uncertainties were 3% and 6% for the Nusselt number and friction factor, respectively.

Copyright © 2010 by ASME

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