Meaning
Continuum transport phenomena govern the simultaneous movement of immiscible liquid, gas, and dissolved chemical species through complex porous matrices. Analyzing multi phase fluid transport describes gas bubble displacement of liquid electrolyte in gas-evolving electrochemistry and gas diffusion layers of fuel cells. Interfacial drag and surface tension forces dictate velocity fields across distinct fluid phases.
Boundary conditions stop applying when single-phase liquid or gas flow conditions dominate the pore volume completely.
Relative Permeability
Presence of trapped gas bubbles reduces effective cross-sectional areas available for liquid flow. Saturation levels modulate fluid conductivity across porous substrates. Saturation curves plot relative phase mobilities as functions of volumetric liquid fraction.
Saturation hysteresis creates dynamic transport variations between drainage and imbibition cycles.
Capillary Pressure
Pressure differences across curved liquid-gas interfaces force fluids through narrow pore throats. Pore throat size distributions dictate displacement pressures required to clear liquid water from gas diffusion channels. Microscopic contact angles control whether capillary forces pull or repel liquid phases.
Channel Flooding
Liquid condensation in porous transport layers blocks reactant gas transport to active catalyst sites. Excessive liquid buildup starves catalytic reactions, causing voltage drops under high-current operation. Gas velocity must overcome capillary forces to purge liquid water from flow channels.
