Experimental investigation of friction factor in microtubes and development of correlations for prediction of critical Reynolds number

摘要

Scope and Method of Study. Pressure driven flows through the micro tubes have flow characteristics of their own, which is not supported by any established macro flow theories. It was observed that, surface roughness plays major role in this variation from established theories. In this research, prime objective is to study the friction factor behavior for low relative roughness (0.005-0.013%) nickel tubes. Friction factor behavior was studied for laminar, transition and turbulent regions. Particularly the study concentrated in the start and end of the transition region and change of transition friction factor with diameter for low relative roughness tubes. Additionally the laminar region friction factor which has been conceded as no roughness area was investigated using constricted parameters. Furthermore correlations for prediction of critical Reynolds number were proposed for micro tubes with relative roughness range of 0 to 4%.;Findings and Conclusions. From this work it was established that sensitivity of instrumentation plays significant role in obtaining correct results. It was observed that there is no roughness effect in friction factor for low relative roughness nickel tubes. But for any rational conclusion in transition region behavior for low relative roughness tubes more work is required. It can be established from current work that constricted parameters are promising for improvement of laminar region friction factor. But it requires to be investigated with more data sets with varied shape and size to develop it. Correlations proposed for prediction of critical Reynolds number in microtubes worked very well with cumulative absolute average error of 6%. To verify and generalize the correlations for fluid flow through all micro shapes more data with varied relative roughness is required.