Fringe probing of liquid film thickness of a plug bubble in a micropipe

The liquid film thickness of a plug bubble in a micropipe is of interest in micro heat pipe, microfluidics and two-phase flows. A novel technique was developed to measure the liquid film thickness of a plug-like bubble in a capillary pipe utilizing a spatial fringe scattering method. The scattered fringes were measured by CCD camera and the calculated spatial frequencies were used to determine the film thickness between the plug and the wall. To demonstrate the capability of the newly developed technique, a validation experiment was conducted with water/air and water–honey-mixture/gas-plug flows. The velocity-dependent film thickness can also be observed using this measurement technique. This newly developed method is easy to implement and it will be a very useful technique for micro heat pipe research.