Experimental investigation of pressure drop and friction factor for water flow in microtubes

The pressure drop and friction factor for the flow distilled water in microtubes with the diameters ranging from 0.20 mm to 0.589 mm were investigated experimentally. The experiments were carried out in the Reynolds number range of approximately 100–10000 and the length-to-diameter ratios (L/d) in the range of 16–265. It was observed that two different mechanisms of transition from laminar to turbulent flow occurred as smooth and abrupt. The pressure drop and friction factor values agreed with the values of classical channel flow theory. The L/d ratio had an important effect on the apparent friction factor in case of L/d < 100. It was found that the critical Reynolds number for the transition was between 2000 and 2500.