Enhanced boiling heat transfer from microconfigured silicon surfaces and entrainment flow adjacent to an isothermal vertical surface

Measurements of pooling boiling from vertical, smooth and regularly-microconfigured etched silicon surfaces, in saturated water at 1 atm, are presented. All specimens were 1.27cm square. The etched microstructures were hexagonal dimples and rectangular trenches. The dimples were 4.1;A model is presented which accounts for the boiling heat transfer enhancement, on microconfigured surfaces. The heat transfer associated with the visible bubbles does not account for the measured boiling heat transfer enhancement. An additional population of very high frequency microbubbles appears to account for the increased heat transfer. These microbubbles apparently grow from the very high density of identical microconfigurations on the surface. Microbubble frequencies of O(10;A separate study examines the steady entrainment flow due to the motion pressure deficit induced by a buoyancy driven flow adjacent to an isothermal vertical surface. Prandtl numbers of 0.72 and 6.7 are considered. The Navier-Stokes equations, with the Boussinesq approximations, are written in streamfunction-vorticity variables and integrated using finite differences. A Poisson equation for the motion-pressure is solved numerically. Coordinate transformations allow the boundary conditions to be applied accurately far from the surface. The numerical results show the extent of the temperature excess upstream of the leading edge. An increase in the mass flow rate results, compared with boundary layer theory, from the upstream entrainment flow included in the calculations. The largest gradients of motion pressure are near the leading edge. These gradients cause the leading edge entrainment flow to resemble a potential flow sink, into the leading edge of the surface.