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Title :Study on Heat Transfer and Fluid Flow Characteristics of Rectangular Finned Surface in Duct
Authors :Didarul, Islam Md.
Issue Date :Sep-2007
Abstract :学位の種類(博士(工学)),学位授与機関(琉球大学),授与年月日(平成19年9月14日),学位記番号(理工研第120号),報告番号(甲理工研第120号)
A detailed experimental investigation of the heat transfer and fluid flow characteristics of rectangular finned surfaces of four different fin patterns, co-angular, zigzag, co-rotating and co-counter rotating was conducted for an airflow (Re = 15700 - 104500) in a duct. Short rectangular fins of either aluminum or resin material were attached in 7 x 7 arrays to a heating surface (base plate) of constant heat flux by double sided thin tape. T-type thermocouples and an infrared camera (TVS 8000) with a 160 x 120 point In-Sb sensor were used to capture the infrared images as well as to measure the temperature and the detailed heat transfer at the endwall along with fin base. Different flow visualization technique, fluorescence dye flow in water channel, smoke flow visualization and oil titanium oxide film flow visualization were used to analysis the flow behavior and its effect on heat transfer. In this study we have first investigated the heat transfer and fluid flow characteristics of co-angular and zigzag fin pattern at a flat plate (200 mm duct height) boundary layer and narrow duct of 20 mm height. Zigzag pattern were found to be more effective in heat transfer at both flat plate and narrow duct case. In case of co-angular pattern dye flow stagnated in front of the fin and formed a strong horseshoe vortex around the fin while the longitudinal vortexes generated by the side top edges touched the fin surface and the endwall. On the other hand in case of zigzag pattern a weak horseshoe vortex appeared and longitudinal vortex struck the endwall mainly and a sinusoidal wavy flow behavior was observed. We have then further investigated heat transfer and flow characteristics of co-rotating pattern and co-counter rotating pattern along with other two pattern at a duct of 50 mm height. The heat transfer result shows that the co-rotating pattern has the highest Nusselt number and the co-angular pattern has the least Nusselt number. Considering the thermal performance, co-rotating pattern with smaller pitch ratio was found to be the most recommended pattern as the heat transfer augmentation with co-rotating pattern is more than three times the fin-less duct. Horseshoe vortex, main longitudinal vortex and rolled up vortex were again confirmed by smoke flow and oil titanium flow visualization. Among the four patterns largest friction factor occurred for the co-rotating pattern at smaller pitch ratio owing to the strong flow interactions and combined vortex attack on the endwall and fin surface whereas the least friction developed for co-angular pattern. Finally the effects of duct height on heat transfer and flow characteristics were investigated and the most important information about vortex structures at several streamwise positions was obtained which shows the reasons of heat transfer enhancement. Vortex structures for co-angular and co-rotating pattern were found different and the reattachment positions were obtained. Comparatively large scale vortex rotation was observed in co-rotating case which is obviously responsible for heat transfer enhancement.
Type Local :学位論文
Publisher :Didarul, Islam Md.
URI :http://hdl.handle.net/20.500.12000/5748
Citation : p.1 -100
Appears in Collections:Doctoral Dissertation (Graduate School of Engineering and Science)

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Islam Md. Didarul_1.pdfAbstract, Chapter 1-43563KbAdobe PDFView/Open
Islam Md. Didarul_2.pdfChapter 52256KbAdobe PDFView/Open
Islam Md. Didarul_3.pdfChapter 6-7, References, Acknowledgements3751KbAdobe PDFView/Open