以電液動技術增強垂直放置鰭片空氣對流熱傳性能研究; An experimental investigation of convective heat transfer enhanced by electrohydrodynamics in vertical fin

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题名:	以電液動技術增強垂直放置鰭片空氣對流熱傳性能研究;An experimental investigation of convective heat transfer enhanced by electrohydrodynamics in vertical fin
作者:	盧泰昌;Tai-chang Lu
贡献者:	機械工程研究所
关键词:	垂直平板;EHD熱傳增強;垂直鰭片;斷續型鰭片;flat plate;EHD enhancement;offset strip fin;vertical fin
日期:	2011-01-27
上传时间:	2011-06-04 15:01:44 (UTC+8)
出版者:	國立中央大學
摘要:	本研究利用電液動技術(EHD)增強垂直放置的垂直平板與垂直鰭片，在固定相同正向面積條件下，改變鰭片的高度以及型式，比較四種不同型式鰭片：垂直平板、高度15 mm垂直鰭片、高度29 mm垂直鰭片，單一長度125 mm斷續型鰭片，在自然對流與EHD熱傳增強情況下各參數對熱傳性能的影響。　垂直平板在自然對流與EHD熱傳增強下因為可以直接跟四周冷空氣做熱交換所以有最高的熱傳係數，但因為熱傳面積最小，總熱傳量最低。　影響垂直鰭片的熱傳性能主要來自鰭片間的邊界層發展，在自然對流情形下，兩種高度的垂直鰭片因為邊界層過早形成完全發展，熱傳性能沒有太大差異；在EHD熱傳增強下，邊界層受到離子風影響較晚形成完全發展，高度較低的鰭片外界冷空氣較容易進到流道裡增加熱傳性能，高度15 mm垂直鰭片比高度29 mm垂直鰭片熱傳系數高10 ~ 15 %。斷續型鰭片因為流動阻力與邊界層形成完全發展的關係，熱傳係數與高度29 mm垂直鰭片相似，沒有增強的效果。　Heat transfer of vertical oriented flat plate and straight fin enhanced by electrohydrodynamics (EHD) is experimental investigated in this work. Heat transfer of four types of fin having the same frontal area are discussed under natural convection and EHD enhancement, including flat plate, straight fin with different height, and offset strip fin. 　Heat transfer coefficient of flat plate is the highest among other fins under both natural convection and EHD enhancement, but the heat transfer rate of flat plate is the lowest due to the smallest heat transfer area.　The major reason affecting heat transfer of straight fin is the boundary layer development between fins. Under natural convection, heat transfer coefficient of straight fin - H29 and straight fin - H15 are almost the same due to boundary layer between fins becomes fully development early. Under EHD enhancement, heat transfer coefficient of straight fin - H15 is higher than straight fin - H29 by 10 ~ 15 %. Boundary layer is thinner under corona wind and becoming fully development at late of the fin length. Cold air can enter the channel of straight fin with lower fin height easier than higher fin height. Thus the heat transfer is higher with straight fin - H15 than straight fin - H29. Heat transfer of offset strip fin has no improvement due to the effect of increased flow resistant and boundary layer fully developed.
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