碩士 / 國立臺南大學 / 材料科學系碩士班 / 96 / The finite difference method in conjunction with the least-squares scheme and the experimental temperature data is proposed to predict the average heat transfer coefficient, heat rate, and the fin efficiency on the circular vertical fin of annular-finned tube heat exchangers in natural convection for various fin spacings. Time dependent terms in the governing equation are removed by using the Laplace transform technique and then the resulting differential equation is solved by using the finite-difference method. The heat transfer coefficient on this annular circular fin is assumed to be non-uniform. Thus the whole plate fin is divided into several sub-fin regions in order to predict the average heat transfer coefficient and the fin efficiency from the knowledge of the ambient temperature and fin temperature recordings at several selected measurement locations. Then the unknown heat transfer coefficient on each sub-fin region can be assumed to be constant. The results show that the average heat transfer coefficient increases with the fin spacing and the fin efficiency decreases with increasing the fin spacing in natural convection. The average heat transfer coefficient and fin efficiency can approach their corresponding asymptotical value obtained from a single annular circular fin for the fin spacing above a certain value. The optimum value of the fin spacing is approximately 0.015m. The tendency of the heat rate seems to increase with the fin spacing. The present estimates of the average heat transfer coefficient under the condition of the ideal isothermal situation are slightly higher than those obtained from the correlation recommended by current textbooks for various fin spacing. This phenomenon can result from the simultaneous consideration of the convection and radiation heat transfer coefficients in the present study. The effect of the fin spacing on the efficiency is very small. The heat rate increases with air speed for fixing the fin spacing. However, the variation of the heat rate with increasing the fin spacing is only slight increment for fixing the air speed. In order to evidence the reliability of the present inverse scheme The present estimated results of the average heat transfer coefficient in natural and forced convection lie in the reasonable range of heat transfer textbook. Thus the reliability of the present inverse scheme is expected.
| Identifer | oai:union.ndltd.org:TW/096NTNT5159006 |
| Date | January 2008 |
| Creators | Chui-thuing Chen, 陳志忠 |
| Contributors | none, none, 陳寒濤, 尤孝雯 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 67 |
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