Interactions between contact angle hysteresis and pore-scale geometry during flow boiling in ordered porous structure

In flow boiling within porous structures, surface contact angle hysteresis affects bubble dynamics and heat transfer behaviors. In this work, an improved contact angle hysteresis model is incorporated into the lattice Boltzmann method (LBM) to explore the interaction between contact angle hysteresis and pore-scale geometric confinement during flow boiling in ordered porous structures. It is found that contact angle hysteresis considerably increases the number of bubble inception events and bubble generation frequency within porous structures, forming an extended thermal influence region that effectively restrains the propagation of local dryout regions. As the wall superheat increases, heat transfer in porous structures shifts from bubble-dominated regimes to dryout-dominated regimes. At high wall superheat, contact angle hysteresis has a detrimental effect on flow boiling in ordered porous structures. A negative porosity gradient design is demonstrated to enhance flow boiling heat transfer in ordered porous structures with contact angle hysteresis surfaces at high wall superheat, via increasing local velocity, thinning boundary layer, and strengthening bubble-induced flow disturbances.