Effects of surface roughness on forced convection and friction in an air-cooled equilateral triangular duct

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Effects of surface roughness on forced convection and friction in an air-cooled equilateral triangular duct

 

Author: Lo, Ching-yuen Alex
Title: Effects of surface roughness on forced convection and friction in an air-cooled equilateral triangular duct
Year: 1999
Subject: Heat exchangers
Heat -- Transmission
Surfaces (Technology)
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Mechanical Engineering
Pages: ix, 96 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1479240
URI: http://theses.lib.polyu.edu.hk/handle/200/459
Abstract: This dissertation describes the investigation results of the effect of different surface finishes of an air-cooled equilateral triangular duct at steady state. Experimental investigations had been conducted to study the forced convective heat transfer and pressure drop characteristic of fully-developed turbulent flow in horizontal equilateral triangular ducts which were geometrically identical and with the same hydraulic diameter, but having different surface roughness of 1.2um, 2.0um, 3.0um, 7.5um and 11.5um. In order to achieve fully-developed turbulent flow condition when performing the experiments, hydraulic diameter should be determined by Reynolds number ranging from 7000 to 20000. The entire inner duct walls were heated uniformly, while the outer surfaces were thermally insulated. It was found that the variation of Stanton number (St) with friction coefficient (f) can be expressed by the relationship of St = C*f, where the constant (C) increases from 0.41 to 0.50 when the surface roughness is increased from of 1.2um to 11.5um. It was also concluded that the duct with higher surface roughness tends to have a better heat transfer performance. Non-dimensional expressions for the determination of the heat transfer coefficient and friction factor of the equilateral triangular ducts with different surface roughness were also developed.

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