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Title: Surface effects in flow boiling of R134a in microtubes
Authors: Mahmoud, MM
Karayiannis, TG
Kenning, DBR
Keywords: Flow boiling;R134a;Sruface effects;Microtubes
Issue Date: 2011
Publisher: Elsevier
Citation: International Journal of Heat and Mass Transfer, 54(15-16): 3334 - 3346, Jul 2011
Abstract: The inner surfaces of microtubes may be influenced strongly by the process of making them due to manufacturing difficulties at these scales compared to larger ones, e.g. the surface characteristics of a seamless cold drawn tube may differ from those of a welded tube. Accordingly, flow boiling heat transfer characteristics may vary. In addition, there is no common agreement between researchers on the criteria of selecting tubes for flow boiling experiments. Instead, tubes are usually ordered from commercial suppliers, in many cases without taking into consideration the manufacturing method and its effect on the heat transfer process. This may explain some of the discrepancies in heat transfer characteristics which are found in the open literature. This paper presents a comparison between experimental flow boiling heat transfer results obtained using two different metallic tubes. The first one is a seamless cold drawn stainless steel tube of 1.1 mm inner diameter while the second is a welded stainless steel tube of 1.16 mm inner diameter. Both tubes have a heated length of 150 mm and the flow direction is vertically upwards. The tubes were heated using DC current. Other experimental conditions include: 8 bar system pressure, 300 kg/m2 s mass flux, about 5K inlet sub-cooling and up to 0.9 exit quality. The results are presented in the form of local heat transfer coefficient versus local quality and axial distance. Also, the boiling curves of the two tubes are discussed. The results show a significant effect of tube inner surface morphology on the heat transfer characteristics.
Description: This is the post-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2011 Elsevier
ISSN: 0017-9310
Appears in Collections:Publications
Mechanical and Aerospace Engineering
Dept of Mechanical Aerospace and Civil Engineering Research Papers

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