Water concentration profile, vapor phase

Figure 7. Vapor phase water concentration profile ((O) conventional technology (A) wet hydrocarbon flash (VJ wet methanol hydrocarbon flash)...

Takashi discussed the relation of a water-alcohol separation membrane on the basis of a dissolution-diffusion model (Takashi 1999). Their model provides several guiding principles for designing PV membranes. Tyagi et al. developed the transport model for PV. The transport model assumes the presence of an imaginary phase (liquid or vapor), which is in thermodynamic equilibrium with the manbrane phase. Theoretical profiles were compared with experimental concentration profiles. Their work was the first theoretical work that could reconstruct penetrant profiles inside the membrane showing concentration polarization (Tyagi et al. 1995). 

Temperature and concentration profiles at interface. In Fig. 10.5-1 the temperature profile and the concentration profile in terms of humidity are shown at the water-gas interface. Water vapor diffuses from the interface to the bulk gas phase with a driving force in the gas phase of (H. — Hq) kg HjO/kg dry air. There is no driving force for mass transfer in the liquid phase, since water is a pure liquid. The temperature driving force is Tj - Tl in the liquid phase and 7] — Tg K or °C in the gas phase. Sensible heat flows from the bulk liquid to the interface in the liquid. Sensible heat also flows from the interface to the gas phase. Latent heat also leaves the interface in the water vapor, diffusing to the gas phase. The sensible heat flow from the liquid to the interface equals the sensible heat flow in the gas plus the latent heat flow in the gas. 

The binary mixture profile consists of two parabolas thus, the evaporation of each component is unaffected by the vapor concentration of the other. That is, each component has an independent evaporation singularity. If the water-rich phase is denoted phase 1, and the ethanol phase 2, then the independent profiles are additive ... 

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