Lattice Boltzmann modeling of evaporation of porous media considering conjugate heat transfer

Evaporation of liquids from porous media plays a significant role in both natural and industrial applications. Evaporation is influenced by various factors, including porous structure, wettability, and thermal gradients, making it difficult to understand the underlying mechanisms and therefore manipulate the evaporation process. In the present study, a hybrid model combing the pseudopotential multiphase lattice Boltzmann method for the fluid field and a finite-difference solver for the energy equation is used to study the evaporation of porous media considering conjugate heat transfer. The flow field and temperature field are coupled via the Peng-Robinson equation of state, while the cascaded lattice Boltzmannn collision operator is employed to enhance the numerical stability. To account for contact angle effects, a validated geometric formulation scheme is applied. The model is utilized to investigate fluid flow and phase distribution in a porous material during evaporation occurring from the top boundary open to the environment and a constant heat flux (q) imposed at the bottom to provide energy input. In the absence of applied heat flux, the evaporation patterns with and without considering conjugate heat transfer are similar, though the latter yields a higher evaporation rate. The underlying mechanism is elucidated by analyzing the temperature field and energy budget. In contrast, thermal input (q ≠ 0) affects the evaporation rate when the heat-affected region reaches the evaporation front. Moreover, high heat input eventually dries out the bottom of the porous media, altering the evaporation dynamics. Regarding contact angle, a smaller contact angle strengthens capillary pumping from large pores to small pores, causing the evaporation front to extend into the small-pore region after the large-pore region is completely dried out. Due to the Kelvin effect, a larger contact angle results in higher vapor pressure near the liquid-vapor interface, promoting evaporation. This study explores the characteristics of the evaporation process in porous media and provides insights into the underlying mechanisms.