A heat transfer correlation of flow boiling in micro-finned helically coiled tube
- Authors: Cui, Wenzhi , Li, Longjian , Xin, Ming-dao , Jen, Tien-Chien , Chen, Qinghua , Liao, Quan
- Date: 2006
- Subjects: Convective boiling , Heat transfer , Helically coiled tubes , Nucleate boiling
- Type: Article
- Identifier: uj:5275 , http://hdl.handle.net/10210/14944
- Description: Two main mechanisms, nucleate boiling and convective boiling, are widely accepted for in-tube flow boiling. Since the active nuclei on the heated wall are dominant for nucleate boiling and flow pattern governs the convective boiling, the heat transfer coefficient is strongly influenced by the wall heat flux, mass flux and vapor quality, respectively. In practical industrial applications, for example, the evaporators in refrigeration, forced convective evaporation is the dominant process and high heat transfer efficiency can be obtained under smaller temperature difference between wall and liquid. Therefore, it is of importance to develop a correlation of convective boiling heat transfer with a good accuracy. In this paper, a new kind of micro-finned helically coiled tube was developed and the flow boiling heat transfer characteristics were experimentally studied with R134a. Based on the analysis of the mechanisms of flow boiling, heat transfer correlations of the specific micro-finned helically coiled tubes are obtained.
- Full Text:
Heat transfer and bubbles movement of two-side and one-side heating subcooled flow boiling in vertical narrow channels
- Authors: Pan, Liang-Ming , Jen, Tien-Chien , He, Chuan , Xin, Ming-dao , Chen, Qing-hua
- Date: 2006
- Subjects: Subcooled flow boiling , Bubble behaviour , Heat transfer
- Type: Article
- Identifier: uj:5267 , http://hdl.handle.net/10210/14936
- Description: The channels employing hydraulic diameters between 200 m and 3 mm are referred to as minichannels 1 . Compared with conventional channels from the view of the heat transfer, narrow and microchannels have significant heat transfer enhancement characteristics 2,3 . With a smooth internal surface and scouring by flowing fluid, the dirt formed on the surface of the channel wall can be easily removed and the fouling problem is not as serious as the deformed channels. Moreover, heat transfer elements can be easily assembled to compact devices. Since the innovative work of Ishibashi et al. 2 , narrow channels have been adopted extensively in engineering applications, e.g., microelectronic cooling 4,5 , advanced nuclear reactor 6,7 , cryogenic, aviation, and space technology. Because the bubble size has approached the dimension of the channel, the size of the flow channel plays a critical role on the flow boiling heat transfer. This results in that the bubble in the narrow channel acts very differently from those in the non-narrow channel.
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