碩士 / 國立高雄海洋科技大學 / 輪機工程研究所 / 96 / This research involves the experimental and numerical studis with the objectives to study the endwall heat transfer rates; pressure drops coefficients and thermal performance factors for a narrow channel with attached and detached pin fins. The experimental and numerical works are respectively summarized as follows:
Experimental work
Endwall heat transfer and pressure drop characteristics in four rectangular channels with a channel aspect ratio of 4 and the staggered arrays of circular pin-fins with four clearances (C) between pin-tips and the measured endwall of 0, 1/4, 1/2 and 3/4 pin-diameter (d) are examined comparatively at Reynolds numbers (Re) of 10000, 15000, 20000, 25000 and 30000 to determine the effects of pin-tip leakages on the endwall heat transfer and on channel inlet-to-exit pressure drops. The accelerated flows through pin-to-endwall clearances modify the protrusion-endwall interactions that affect the horseshoe vortices as well as the downstream wakes and shear-layer separations. By way of increasing C/d ratio from 0 to 3/4, the area averaged endwall Nusselt numbers decrease with substantial reductions in channel inlet-to-exit pressure drops. The endwall heat transfer level with detached pin-fins at C/d =1/4 is somewhat less than that with attached pin-fins but the pressure drop coefficient of the former is much lower than that of the later, which leads to the highest thermal performance factor among the four comparative cases in the Re range examined by this study. A set of correlations that evaluate the area averaged endwall Nusselt number and the pressure drop coefficient with Re and C/d as the controlling parameters are derived.
Numerical work
This numerical study comparatively examines the flow and heat transfer characteristics in two rectangular channels with attached and detached pin-fin arrays at Reynolds numbers (Re) of 10000, 15000, 20000, 25000 and 30000 using the commercial code Star CD. Clearances (C) between pin-tips and endwall for the present detached pin-fin array are fixed at 1/4 pin-diameter (d). The presence of pin-to-endwall clearances modifies the endwall flow structures by way of generating the accelerating flows over the pin-tips and results in the large-scale three dimensional vortical flows along two side walls of the detached pin-fin channel that leads to regional heat transfer enhancements. The lack of vortices and flow separations tripped by the attached pin-fins considerably reduces the inlet-to-exit pressure drops in the detached pin-fin channel. But the absence of horseshoe vortices and the downstream wakes as well as the shear-layer separations over the endwall in the detached pin-fin channel moderates the gradients of endwall Nusselt number (Nu) distributions and reduces the area averaged endwall Nu ( ). Boundary-layer type accelerating flows in the clearances between pin-tips and the endwall agitate turbulent activities which consequently augments the endwall Nu over the top surfaces and the projected endwall areas of these detached pins. As the endwall Nu with detached pin-fins is somewhat less than that with attached pin-fins but the channel pressure drop is much lower than that of the later, the thermal performance factors for the detached pin-fin channel are improved from those of the attached pin-fin channel. Flows physics in association with the pressure drop and heat transfer performances reported in our previous experimental study are identified through this numerical study.
| Identifer | oai:union.ndltd.org:TW/096NKIM8484009 |
| Date | January 2007 |
| Creators | Huang, Chuan-chin, 黃傳秦 |
| Contributors | Chiou, Shyr-Fuu, Chang, Shyy-Woei, 邱時甫, 張始偉 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 92 |
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