Scope and Method of Study. Rapid advances in technology with innovative applications for the downscaled devices have witnessed characteristics of flow contrary to macro-scale behavior. Flow characteristics are found to greatly differ in the transition region, with its capture and location with respect to varying roughness and tube diameter a challenge at these small scales. A careful, systematic and methodological investigation is launched to effectively predict the flow characteristics at these small scales, along with proper representation of the transition region with respect to roughness and diameter. The importance of measurements and instrumentation used has been delved in detail, effectively bringing out their influence.;Findings and Conclusions. The systematic investigation has revealed the importance of precise measurements and sensitive instrumentation in capturing and reporting the location of the transition region with respect to the tube roughness and diameter. The experimental friction factor values obtained showed that the decrease in tube diameter actually delayed the transition region, with the profile not varying greatly for diameters 1374 mum and 2083 mum. Further decrease in diameter up to 732 mum has observed deeper troughs in the transition regions, with no particular shift in the friction factor profile. Further decrease from 732 mum has shifted the entire friction factor profile higher, suggesting the effect of roughness, with the smallest tubes showing the greatest shift and the earliest transition. It can be concluded that the effect of tube diameter and roughness on mini/micro channels is present and has been successfully captured by the systematic experimental investigation carried out.
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