Journal of Non-Newtonian Fluid Mechanics, Vol.112, No.2-3, 115-128, 2003
Squeeze flow of a dry foam
Squeeze flow of a dry compressible foam between two circular disks is studied by means of a lubrication analysis. Two simple cases are considered. If the foam behaves as a compressible Newtonian fluid, the approach of the plates can be accommodated by compression of the foam as well as by extrusion. Pressure is governed by a non-linear diffusion-like equation, and at high Peclet number (Pe) the effect of an outer boundary at which pressure remains at ambient does not diffuse far into the test sample. At low Pe pressures remain low and results differ little from those for an incompressible fluid, until the gap between the plates becomes very small. The second analysis concerns a perfectly plastic material, with a yield stress which is inversely proportional to bubble size and which therefore increases at high pressure. An analytic solution is found for this case. Close to the axis of the disks, where pressures are high, the yield stress is large and the foam is compressed rather than extruded. Close to the edge of the plates the foam is extruded. As the gap between the discs is reduced, the central region of stationary foam becomes larger and eventually the test measures elastic compression of the portion of the test sample remaining between the plates. (C) 2003 Elsevier Science B.V. All rights reserved.