科研之友
微信
新浪微博
Facebook
分享链接
摘要
The feasibility of achieving microscale heat transfer effects in macro geometries using conventional fabrication methods has recently been demonstrated. This paper looks at passive techniques, using nature-inspired Inverted Fish Scale geometrical design, to improve the heat transfer performance of the newly proposed system. In this study, an annular microchannel, with gap size of 300 gm, is formed by securing a cylindrical insert of mean diameter 19.4 mm within a cylindrical pipe of internal diameter 20 mm. The Inverted Fish Scale profile is introduced on the insert surface, so as to improve heat transfer through increasing the convective heat transfer coefficient of the flow, for a constant heat transfer area. Both experimental and numerical investigations are carried out to study the effect of the Inverted Fish Scale enhancement profile on the heat transfer and flow characteristics of the microscale flow. Single-phase liquid flow using distilled water is examined, with Reynolds number ranging from 1300 to 4600. The microchannel is considered hydraulically smooth, with length of 30 mm and hydraulic diameter of 600 gm. Results show that the Inverted Fish Scale (IFS) profile indeed has positive effect in enhancing heat transfer. The maximum convective heat transfer coefficient achieved in the whole study is 52.8 kW/m(2).K, using IFS insert with scale height of 0.21 mm and pitch length of 2.1 mm, at Reynolds number of 4300. This is more than twice the value using Plain insert at the same flow condition. The possible enhancement mechanisms include re-initialization of velocity and thermal boundary layers, flow recirculation and higher turbulence intensity. In addition, the thermo-hydraulic performance factor, which incorporates the undesirable increment in friction factor, is examined. The thermo-hydraulic enhancement of the IFS profile is generally found to be more effective for 1300 less than or similar to Re less than or similar to 3250. In particular, the IFS insert with scale height of 0.21 mm and pitch length of 2.1 mm performs 43% better than the Plain insert, at Reynolds number of 1700. New correlations for the average Nusselt number and friction factor are proposed for the IFS microchannel, to be used in the design of compact heat exchangers. Based on calculations, the present system is able to remove heat flux of up to 375 W/cm(2). The pressure drop values of the system are all less than 3.3 bars, which may be overcome by a commercially available pump. The present study reiterates the feasibility of achieving microscale heat transfer effects in macro geometry systems, and demonstrates the effectiveness of the Inverted Fish Scale profile in enhancing heat transfer performance.
- 出版日期2016-8
