The flow characteristics of deionized water in stainless steel microtubes were experimentally investigated in this study.The influences of relative surface roughness and inner diameter of tube on pressure drop were discussed.The inner diameters of microtubes were 543.3,654.4 and 737.2 μm,with the relative surface roughness 0.31%,0.16% and 0.1%,respectively.In experiments,long tube and short tube were used and compared to eliminate the effect of inlet and outlet.The relationships between pressure drop and Re...