Film theory mass transfer ppt

Also includes interphase mass transfer and various theories related to it. The film theory has been extensively applied to describe the mass transfer in systems in which fluid phases are present. Diffusion is the flow of molecules between two regions, one of high concentration to one of low concentration. Mass transfer basic theories for mass transfer coefficients 921 these simple models for fluidfluid interfacespretend that fluid motion is incorporated in diffusion and everything is treated as a thin film or semiinfinite slab problem. This is the oldest theory for gasliquid mass transfer developed by lewis and whitman in 1924 3. Film theory stated that the resistance in mass transfer between fluids phase in turbulent flow is present in a thin layer adjacent to the interface called film. Mass transfer basic theories for mass transfer coefficients921. In principle, these two extreme cases should bracket all possible geometries. As previously noted, gas absorption operation involves mass transfer from the gas. According to this theory, mass transfer is directly proportional to molecular diffusivity of. Of mass transfer basics required gasliquid interaction in the molecular level, the twofilm theory absorption theory.

That means the gas molecules must diffuse from the main body of the gas phase to the gasliquid interface, then cross this interface into the liquid side, and finally diffuses from the interface into the main body of the liquid. Instead, we will use a simplified twofilm theory as a basis for analysis. Theory of the twofilm model of the volatilization of organic compounds from water 3. Ammonia highly soluble transfer is usually controlled by gas phase film. H is very large then and process becomes liquid phase controlled. Explains two film theory and how that relates to equimolar counter diffusion, mass transfer coefficients, stefan diffusion, diffusivity and. For example, oxygen slightly soluble transfer is usually controlled by liquid film. In the absorption of gases from bubbles or absorption by wettedwall columns, the mass. As previously noted, gas absorption operation involves mass transfer from the gas phase to the liquid phase. Mass transfer theories for mass transfer coefficients.

Postulates that two nonturbulent fictitious films are present on either side of the interface between thw film mass transfer across these films purely occurs molecular diffusion. So far, we have dealt basically with pure component systems. These simple models for fluidfluid interfacespretend that fluid motion is incorporated in diffusion and everything is treated as a thin film or semiinfinite slab problem. Binary mass transfer in stagnant systems and in laminar flow 5. Film concepts in mass transfer separation processes. That means the gas molecules must diffuse from the main body of the gas phase to the gasliquid interface, then cross this interfaceinto the liquid side, and finally diffuses from the interface into the main body of the liquid. Two film theory theory has been developed by nernst, lewis and whitman.

When we have more than one species present, and composition gradients occur, individual species will move from one location. We can derive the three theories, but the overall difference and conclusions will relate to the impact of d. Helps disperse one fluid in another and create more interfacial area. Department of chemical and biomolecular engineering. That means the gas molecules must diffuse from the main body of the gas phase to the gasliquid interface, then cross this interfaceinto the liquid side, and f. In the film theory, the mass transfer coefficient ko. Mass transfer of solute from one phase to another involves transport from the bulk of one phase to the phase boundary or interface, then movement from the interface into the bulk of the second phase. Diffusion and mass transfer coefficients demonstration. Gasfilm coefficients, overall masstransfer coefficients, and predicted. Learn more about using mass transfer coefficients to quantify the boundary layer. Interphase mass transfer two film theory penetration theory. In gasliquid and liquidliquid separation processes, the mass transfer resistance in. The rate of mass transfer per unit area in terms of the twofilm theory for equimolecular.

L is directly proportional to the diffusion coefficient dal and. The theory considers that the resistance to mass transfer in a given turbulent fluid phase is present in a thin layer adjacent to the interface that is called a film seader et al. If either phase concentration can not be predicted by henrys law then there will be a transfer of mass across the interface until equilibrium is. Most of the industrial processes of mass transfer are unsteady state processes where the gasliquid contact time is too short to achieve steady state condition. Gas absorption operation involves mass transfer from the gas phase to the liquid phase. Gas transfer rates if either phase concentration can not be predicted by henrys law then there will be a transfer of mass across the interface until equilibrium is reached. Ppt mass transfer powerpoint presentation free to view. Transfer of gas across a gasliquid interface can be accomplished by bubbles or by creating large surfaces interfaces. Total resistance for mass transfer is summation of resistance of two films 182018 15 mrs. By considering individual film transfer equations and overall mass transfer equations, equilibrium equations can be developed between overall and individual phase mass transfer coefficients if a is less soluble in liquid i. Mass transfer to a fluid interface is an inherently unsteadystate process. The mechanisms and rate expressions for this transfer.