الفهرس 
Chapter 5: Conclusions and RecommendationsOnly 14 pages are availabe for public view
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Abstract
Convection heat transfer and friction for water flows inside circular microtubes was experimentally investigated. Water flows inside these tubes in steady flow and pulsating flow. The ranges tested for pulsation frequency is of 0.5 Hz to 5 Hz and Reynolds number is of 200 to 5000 during the experimental work the inner diameter of circular microtube was varied. Four values of inner tube diameters was tested in this study as; 0.25, 0.35, 0.52 and 0.7 mm. The experimental results show that, the friction factor in the studied operating ranges decreases as Reynolds number increases but its values are deviated from the conventional tubes due to the small dimensions of the microtube. The friction factor decreases with decreasing microtube diameter. Also, it is observed that, for the different diameters of microtubes the transition from laminar to turbulent flow occurs at Reynolds number in the range of 15002000. Nusselt number increases with increasing Reynolds number for both pulsating flow and steady flow. Nusselt number decreases with decresing microtube diameter. For pulsating flow, Nusselt number takes lower values than steady flow under the same conditions in the studied operating ranges. Comparison between the obtained experimental results with the previous data and the classical correlations for conventional tube was done and the disagreement among the researchers was still. Two empirical correlations for Nusselt number and friction factor were obtained for the range of the studied operating parameters. Key word: Microchannels Heat exchanger <U+2013> Pulsation