碩士 / 國立成功大學 / 機械工程學系碩博士班 / 100 / A series of 3-D computational fluid dynamics analyses were carried out to study the thermal-hydraulic characteristics for the in-lined and staggered fin-tube heat exchangers with block type vortex generators mounted behind the tubes. Two types of heat exchangers were investigated in the study: (1) plate fin and tube heat exchangers and (2) rectangular fin and tube heat exchangers.
Firstly, the effects of vortex generator span angles (θ) and transverse locations (Ly) on the heat transfer performance and pressure loss (in terms of j and f factors) at various frontal velocities, ranging from 1 to 4 m/s, were evaluated in detail. Furthermore, optimization was investigated respect to the span angle and transverse location of vortex generators by use of a simplified conjugate-gradient method (SCGM). A search for the optimum span angle (θ) and transverse distance (Ly), ranging from 30°〈 θ 〈 60° and 2 mm 〈 Ly 〈 20 mm, respectively, is performed. The area reduction ratio of mounting vortex generators relative to the plate fin without vortex generators is the objective function to be maximized.
The numerical results showed that the values of j and f factors were increased with increase of vortex generators’ span angle and transverse location. The influences on the plate-fin heat exchanger were more significant for the in-lined arrangement than the staggered arrangement. Optimization analyses provided the following conclusions: (1) For the in-lined plate-fin heat exchanger, the optimal θ and Ly are in the range of 48.8°~53.8° and 7.5~8.5 mm. The increases of j and f factors are 16.8~30.9% and 12.7~24.6%, respectively. The area reduction ratio could reach up to 15~26%. (2) For the staggered plate-fin heat exchanger, the optimal θ and Ly are in the range of 41.9°~52.6° and 5.5~7.5 mm. The increases of j and f factors are 8.0~12.8% and 6.0~10.1%, respectively. The optimum values of area reduction ratio are achieved at 8~14%. (3) For the in-lined rectangular-fin heat exchanger, the optimal θ and Ly are in the range of 34.9°~42.2° and 15.9~19.0 mm. The increases of j and f factors are about 9.8% and 3.9%, respectively. The area reduction ratio is about 15% at the optimum condition.
| Identifer | oai:union.ndltd.org:TW/100NCKU5490077 |
| Date | January 2012 |
| Creators | Ling-FangHsu, 許玲芳 |
| Contributors | Jiin-Yuh Jang, 張錦裕 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 130 |
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