THE MEASUREMENT OF VELOCITY PROFILES - AN APPLICATION OF NMR MICROSCOPY

NMR microscopy can be effectively used to measure the velocity field in flowing fluids and at the same time measure molecular properties such as the diffusion coefficient. To demonstrate the capabilities of dynamic NMR microscopy, the laminar flow of water through cylindrical tubes has been studied. Radial profiles of the velocity have been obtained at a spatial resolution of about 20 mum in the axial and transverse directions, both at the junction and for axial displacements on either side of the junction. Experimental data show excellent agreement with numerical solutions of the Navier-Stokes equations. To illustrate the use of NMR microscopy for the study of nonNewtonian fluids, velocity and self-diffusion coefficient maps have been obtained for a high molecular weight polyethylene/water solution flowing through a capillary. A nonparabolic velocity profile and enhanced diffusion in the regions of high shear are observed.