Conceptualization, development, and verification of a bubble void fraction instrument

A December 2002 experimental investigation (coined "HIPLATE") was initiated by the University of Michigan on ONR/DARPA funding. The HIPLATE program investigated the physics of drag reduction by microbubble injection at high Reynolds Number and large scale. An Impedance Void Fraction Meter (IVFM) was developed to surmount the shortcomings of the optical techniques. IVFM detects impedance changes and used Maxwell's equation to relate to void fraction by measuring the voltage difference across two electrodes mounted flush to the solid/fluid interface. The IVFM impedance of the bubble-water mixture along with the optical measurements during the HIPLATE help determine void fraction and interface locations.; An uncertainty analysis was performed with known resistors. It is observed that total error decreased almost linearly across the low resistance range until around 15 kO and increased mildly above 15 kO.; Simulation model of the IVFM using Maxwell's equation could predict the void fraction of water-glass sphere mixture with about 2.4% error, where the diameter of sphere was distributed from 10 to 20% of the electrode size. Simulation model could predict the impedance of the IVFM placed in the prescribed water layer thickness condition within nearly the uncertainty ranges of the experimental setup. A small scale bubble injection test was performed to test the applicability of simulations to dynamic situations. Estimated impedance by simulation using area ratio was than those by experiment about 12% on average. Using the void fraction with the bubbles assumed perfect spheres, the simulation predicted 28.6% smaller impedance change than did the experiments on average. However, the uncertainty intervals of the experimental impedance changes were so large (about 50%) that the applicability of the simulation to the dynamic situation could not be determined from this experiment.; Finally, different configurations of the IVFM with multiple pairs of electrodes are shown to have the ability to improve void fraction measurement in the future.; The relative motion of the friction and separator plates in wet clutches during the disengaged mode causes viscous shear stresses in the fluid passing through the small gap. This results in a drag torque on both the disks that wastes energy and decreases fuel economy. To understand the effect of number of grooves and groove depth on the drag torque reduction, five different plates were manufactured for experiments with various parameters. The mathematical model enabled us to calculate the drag torque on the disks and an axisymmetry solver verified the solution. 3D models of one grooved and one flat disk are simulated using CFD and the drag torque results matched well with experiment within 20%. Flow visualization images showed when the fully flooded plate started to aerate and how it evolved.