Experimental study of liquid flow and heat transfer in microtubes

Experiment was conducted to reveal the flow and heat transfer characteristics with deionized water flowing through microtube (1Cr18Ni9Ti) in laminar state. The inner diameter of the test tube is from 300 to 1570 μm. The friction factor obtained from the experiments increases with the surface roughness increase when the relative roughness is greater 1%. For the given heat flux at the outside surface, if the Reynolds number is less than 100, the effect of heat conduction in the tube wall increases with the ratio of wall thickness to the inside diameter; if the Reynolds number is greater than 100, the heat conduction in the tube wall becomes weaker, and the Nusselt number in the fully-developed region approaches the conventional value 4.36.