Pseudopotential Lattice Boltzmann (LB) model is an effective mesoscopic method for liquid-vapor phase change simulations. In LB methods, calculations are often carried out in lattice units. Thus, a correct mapping from the lattice unit system to the physical unit system is crucial for accurate simulations of practical problems. The unit conversion for liquid-vapor phase change problems is more complicated than single-phase problems, because an equation of state (EOS) for a non-ideal fluid is introduced in the pseudopotential two-phase model. In the present work, a novel unit conversion method for the pseudopotential LB model is proposed. The basic strategy is to obtain the conversion relations of fundamental units by mapping the surface tension and EOS parameters related to fluid properties, and thus the unit conversion relations of other quantities are deduced. Numerical simulations of benchmark problems including the film evaporation and the bubble heterogeneous nucleation from a V-shaped cavity are carried out, and the simulation results are converted to the physical unit system by the proposed method. The numerical results demonstrate that the proposed method is able to recover the physical-unit latent heat of the fluid in the film evaporation problem. In the bubble nucleation from a V-shaped cavity problem, the conventional unit conversion method cannot derive the correct superheat temperature in physical unit, while the proposed method based on fundamental units recovers the critical superheat temperature which is consistent with the analytical result.

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During the operation of alkaline direct liquid fuel cells, the alkaline electrolyte is usually needed in the anode electrode to accelerate the electrochemical reaction kinetics of the liquid fuel. However, the crossover of the alkaline solution in the anode through the anion exchange membrane to the cathode can increase the transfer resistance of the oxygen in the cathode. In order to reduce the crossover of the alkaline solution, the diffusion process of the alkaline solution in the anion exchange membrane needs to be fully understood. In this work, interface models of anion exchange membrane-alkaline electrolytes are established based on the cell structure of the quaternary ammonium polysulfone (QAPS) membrane to simulate the dynamic process of the alkaline solution in the membrane. The effect of the type and the concentration of the alkaline solution on the transportation of the metal ions and OH − in the membrane are studied. The results show that the agglomeration of Na + is formed more easily than K + in the interface model. Because of the strong interaction of Na + on OH − , OH − ions appear to be concentrated, resulting in that the diffusion coefficients of the metal ion and OH − in the in Na + solution are lower than those in the K + solution. In addition, with the raised concentration of electrolyte solution, the aggregation degrees of the metal ions and OH − can be increased, which means an enlarged mass transfer resistance of the components. Furthermore, by adding a polytetrafluoroethylene (PTFE) layer on the QAPS membrane, the distribution of metal ions tends to be concentrated, and the number of hydrophilic channels in the QAPS membrane is reduced, which significantly increases the alkali resistance of the anion exchange membrane.direct liquid fuel cells, anion exchange membrane, alkali crossover, QAPS membrane