The effects of viscous heating and the pressure-dependent viscosity on liquid flow in microtubes

The flow characteristics of isopropanol. in microtubes driven by a high pressure ranging from 1 MPa to 30 MPa are studied in this paper. The diameters of the microtubes are from 3 mu m to 100 mu n. The Reynolds number ranges from 0.1 to 1000 approximately. From the present experimental results, two reverse trends of the normalized friction coefficient C* are found for the various diameters. From the analysis of several possible factors, it may be seen that the pressure-dependence viscosity and viscous heating play the leading role. The relationship of viscosity versus pressure pointed out that the viscosity of most liquids, except the water, augmented with the increase of pressure. The analysis based on the energy equation turns out that pressure drop, specific heat, density, flow rate and heat resistance decide the average temperature rise due to viscous dissipation. Therefore, above two factors are treated as the function of pressure. An exponential function with the dependence of pressure is introduced into Hagen-Poiseuille (HP) equation to counteract the difference between experimental and theoretical values. Consequently, C* exhibits different trends which is decided by the relative importance of viscous heating and the pressure-dependent viscosity