Discussion Forum

Hi all,


I am currently modelling 2D two phase flow in a microfluidic device, using the laminar two-phase flow physics in the microfluidics module. There is air and water initially in a central filling chamber (with an air inlet and outlet for atmospheric pressure) and air in an adjacent chamber, with all domains initially set at atmospheric pressure. A centrifugal force is applied as 2 volume forces on all domains, and set so that a larger force acts on the water than the fluid using the volume fractions.

Experimentally, the water is pushed into the adjacent chamber and the gas compresses to a steady volume. However, when I have run simulations with COMSOL the initial pressure in the adjacent chamber is very high initially, and over time there is an inversion in pressure so that a negative (gauge) pressure is present at the air inlets and outlets. This results in COMSOL unable to arrive at a converged solution.

I have tried modifying the domains so at all air is continuous intially and even disabling the volume forces altogether, which failed to rectify the high pressure. I can't use pressure point constraints as the pressure needs to vary over time in the compression chamber.

I haven't had experience with COMSOL prior to this project, and am perplexed as to why this high pressure occurs in the first place, which I believe could be causing the convergence issues.

I would greatly appreciate if anyone is able to shine a light on what could be causing such an issue.


Regards,
Niall