Investigation on permeability of ultra-thin screen wick with free surface using gravity flow and numerical simulation methods

The permeability of porous media is an important parameter in designing ultra-thin vapor chambers, while there was a little researched on the ultra-thin mesh wick with a free liquid-gas interface. In the paper, the permeability of single layer mesh screen with different mesh numbers and diameters was investigated using experimental and numerical simulation methods. Experimentally, according to the Bernoulli equation with the resistance term, the flow resistance could be balanced by gravity in a sloping placed wick. And when the flow reaches the equilibrium state, the permeability can be obtained through the flow rate and the incline angle based on Darcy's law. In order to further explore the relationship between permeability and mesh structure, scanning electron microscope (SEM) and optical microscope were used to observe the microstructure. Based on the scanning picture, numerical simulation was carried out to study the source of flow resistance. And then the relationship between permeability and structure parameters was obtained. The result shows that there is an approximately linear relationship between fRe (the product of loss coefficient and Reynolds number) and the hydraulic diameter in the position where the longitudinal and horizontal wires intersect. The work can support the calculation of the capillary limit in design of ultra-thin vapor chamber.