Browsing by Author "Lo, Yuan-Hsiang"

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Heat Transfer and Friction in a Square Channel with Ribs and Grooves
(2016-01)
Liu, Yao-Hsien
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Lo, Yuan-Hsiang
;
Li, Xin-Xian
;
Huh, Michael
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機械工程學系
Turbulence promoters have been widely applied to enhance heat transfer in internal flow channels, although they cause pressure loss. This study employed the transient liquid-crystal technique to measure the heat transfer distribution in a square channel with compound turbulence promoters with orthogonal (90deg), continuous angled (45deg), discrete angled (45deg), V-shaped, and inverted-V-shaped rib configurations. The rib height-to-hydraulic diameter ratio (e/Dh) and the rib pitch-to-height ratio (P/e) were 0.1 and 8, respectively. Variations in the Nusselt number were observed after adding grooves between the ribs. The Reynolds number tested in this study ranged from 15,000 to 35,000. Adding grooves between the ribs enhanced the heat transfer. The convective heat transfer coefficient increased by up to 40%, whereas the friction factor ratio increased by less than 30%. The discrete angled configuration of grooved ribs exhibited the maximal heat transfer enhancement and thermal performance, whereas the orthogonal configuration attained the minimal heat transfer enhancement and thermal performance. The frictional loss of the V-shaped and inverted-V-shaped configurations was higher than that of the continuous or discrete arrangements for both ribs-only and ribbed-grooved configurations.
Heat transfer of impinging jet arrays onto half-smooth, half-rough target surfaces
(2018-01-05)
Lo, Yuan-Hsiang
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Liu, Yao-Hsien
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機械工程學系
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Department of Mechanical Engineering
Detailed heat transfer distributions from arrays of impinging jets on a half-smooth, half-rough target surface were experimentally investigated using a transient liquid crystal technique. The target surface was roughened through the creation of rectangular grooves aligned with the jet holes. The grooved regions were designed either parallel (longitudinal grooves) or orthogonal (transverse grooves) to the exit flow direction. let-to-jet spacing and jet-to-surface spacing (Z/d) were 4 and 3, respectively. In this experimental test, the effect of crossflow was investigated for three exit flow directions, each with a jet Reynolds number ranging from 2500 to 7700. Heat transfer was enhanced near the edge of grooves, whereas the heat transfer was degraded inside grooves. For the half-smooth, half-rough surface, the sudden change in surface geometry broke the flow development and caused intensified flow mixing in the impingement flow channel. Compared with traditional fully roughened surfaces, the half-rough surface is more effective for heat transfer, and an enhancement of more than 50% was achieved for the longitudinal grooves. The idea of partially roughened surfaces may be further extended to the other internal flow channels with different roughness elements. (C) 2017 Elsevier Ltd. All rights reserved.
Jet impingement heat transfer on target surfaces with longitudinal and transverse grooves
(2013-03-01)
Liu, Yao-Hsien
;
Song, Siao-Jhe
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Lo, Yuan-Hsiang
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機械工程學系
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Department of Mechanical Engineering
This work reports detailed impingement heat transfer measurements on grooved surfaces using transient liquid crystal method. These grooves are machined on the target surfaces with either parallel or orthogonal to the exit flow direction, and are aligned either with the jet holes (inline pattern) or between the jet holes (staggered pattern). The jet-to-target plate spacing (Z/d) is 3 and the average jet Reynolds numbers are from 2500 to 7700. Results show that heat transfer is enhanced near grooves. However, the grooves underneath the jet holes hinder the impingement flow and the jet impingement heat transfer is reduced. Although local heat transfer shows distinct distributions, there is no significant difference in overall/averaged Nusselt numbers on the grooved surfaces and the highest heat transfer enhancement by grooved surfaces is 15%. (C) 2012 Elsevier Ltd. All rights reserved.