碩士 / 國立海洋大學 / 機械與輪機工程學系 / 87 / Heat exchanger equipped with staggered fins is a common engineering practice in order to improve its heat transfer efficiency. It has been applied in many cooling systems in electronic equipments and almost all kinds of heat engines and refrigeration systems, such as HVAC (Heating, Venting, & Air- Conditioning), internal combustion engine, gas turbine, etc. The objectives of staggered fins placed inside heat transfer devices are; interruption of pressure field and thermal boundary layer periodically, accelerating flow to take heat away, providing additional heat transfer area, and improving the mixing of fluid. This thesis is an attempt to provide some valuable and practical information for heat exchanger designers in the field of laminar forced convection with staggered fins. Finite-volume numerical method with Patankar''s[23] SIMPLER algorithm are used in the code written in FORTRAN to solve the laminar thermal and flow field in a parallel plate with and without fins.
In order to validate the availability of the program, it was used to analyze the thermal entry length (The Graetz problem) in a parallel plate with constant wall temperature and combined thermal and hydrodynamic entry length with constant wall temperature or constant wall heat flux. Both the local Nusselt number (Nux) and mean Nusselt number (Num) were calculated and compared with those of Kays & Crawford''s [28] analytical solution and other related correlations [30,31] respectively. Numerical results with a single fin were also compared with the finite- element solution of Wong & Chen [29]. The availability of the program for the analysis of forced convection inside a channel with fins was confirmed through these comparisons.
It is found, from the numerical studies for different heights and thickness of fins, that the effects of fin''s height to the heat transfer coefficient is much larger than those of fin''s thickness. The increase in fin''s height acceleretes flow velocity close to the wall boundary outside the recirculation zone and the Nux becomes much larger in that area, hence Num is increased with fin''s height. A height ratio (tH) of about 0.8 and neglect in thickness effects are suggested in the design of fins in heat exchanger. From the numerical results of different interval ratios (LB/L) of staggered fins with tH=0.7, it is suggested that a interval ratio (LB/L) of 1 or smaller could be a better choice. This conclusion is based on the facts that, this kind of arrangement could reduce the effects of flow recirculations at the back side of fin and increase the flow averaged velocity between fins so that higher heat transfer rate can be achieved.
The numerical approaches (Finite-Volume Method with SIMPLER algorithm) and the FORTRAN program developed in this study provide a solid foundation for other types of forced convection in internal flow system with fins. Inclined staggered fins, 3-D laminar forced convection in a parallel plate, laminar flow and thermal analysis in a circular pipe, and 2-D or 3-D turbulent forced convection are suggested in the future study so that more realistic staggered fin arrangements in heat exchanger design and practical applications can be expected.
| Identifer | oai:union.ndltd.org:TW/087NTOU0491004 |
| Date | January 1999 |
| Creators | Ming Chuang Yang, 楊閔雄 |
| Contributors | Hsien Yu Lei, 雷顯宇 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 105 |
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