Contents I. INTRODUCTION
Due to rapid advancement in fabrication techniques, the miniaturization of devices and components is ever increasing in many applications. Whether it is in the application of miniature heat exchangers, fuel cells, pumps, compressors, turbines, sensors, or artificial blood vessels, a sound understanding of fluid flow in microscale channels and tubes is required. Indeed, within this last decade, countless researchers have been investigating the phenomenon of fluid flow in mini-, micro-, and even nanochannels. One major area of research in the phenomenon of fluid flow in mini- and microchannels is the friction factor. However, amid all the investigations in mini- and microchannel flow, there seems to be a lack in the study of the flow in the transition region. One obvious question is the location of the transition region with respect to the hydraulic diameter of the channel and the roughness of the channel. To successfully understand friction factor and the location of the transition region, a systematic experimental investigation on various roughness values of micro-tubes is necessary. However, the science behind these advanced technologies seems to be controversial, especially fueled by the experimental results of the fluid flow and heat transfer at these small scales.
