Experimental Study on Capillary Microflows in High Porosity Open-Cell Metal Foams

Area of Science:

• Materials Science
• Surface Chemistry
• Heat Transfer

Background:

• Metal foams are crucial wicking materials in heat pipes.
• Surface properties of metal foams present a capillary limit challenge.
• Improving wicking performance is essential for heat pipe efficiency.

Purpose of the Study:

• To investigate a chemical blackening process for creating superhydrophilic copper foam surfaces.
• To analyze the effect of varying NaOH and NaClO2 concentrations on surface morphology and wicking characteristics.
• To understand the flow transport mechanisms and capillary performance degradation in treated copper foams.

Main Methods:

• Copper foam surface treatment using a chemical blackening process with varying NaOH and NaClO2 concentrations (1.5–4.5 mol/L).
• Microscopic morphology analysis of treated copper foam surfaces using scanning electron microscopy (SEM).
• Capillary experiments to quantify wicking characteristics and flow stratification using microscopy.

Main Results:

• The optimal wicking ability was achieved using a 3.5 mol/L NaOH and NaClO2 solution.
• Scanning electron microscopy revealed changes in microscopic morphology after treatment.
• Gravity significantly influences permeability and effective pore radius, while evaporation effects are negligible.
• Fluid stratified interface formation leads to capillary performance degradation.

Conclusions:

• The optimized chemical blackening process significantly enhances copper foam wicking performance.
• Understanding surface morphology and fluid dynamics is key to overcoming capillary limits in porous wicking materials.
• This research provides insights into flow transport in porous media for improved heat pipe design.