AECH 4210 Mass Transfer Fundamentals

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Questions and Answers

What does interphase mass transfer depend on?

Molecules' interaction with light

Differences in physico-chemical properties (correct)

Mechanical agitation of the phases

Temperature variations between phases

Which of the following is an example of interphase mass transfer?

Evaporation of water in air

Mixing solid particles in water

Absorption of ammonia by liquid water (correct)

Heating of a metal in oil

What is typically assumed at the interface during steady-state conditions?

Equilibrium is achieved (correct)

Heat transfer is maximized

No concentration gradient exists

Mass is not conserved

What does the Lewis-Whitman two-film model describe?

Gas transfer across the gas-liquid interface Signup and view all the answers

In the context of interphase mass transfer, what happens to gas molecules at the interface?

They are transported to the bulk of the liquid Signup and view all the answers

Which process illustrates how language barriers can resemble gas-liquid transfer?

Slow communication across different languages Signup and view all the answers

Which scenario best depicts the concentration gradient concept in mass transfer?

High concentration of a solute in one phase and low in another Signup and view all the answers

During the mass transfer process, what is mainly transported through the two layers in the Lewis-Whitman model?

Gas molecules Signup and view all the answers

What primarily drives mass transfer through diffusion?

Concentration difference Signup and view all the answers

Which of the following is an example of eddy diffusion?

Smoke dispersing from a smoke stack Signup and view all the answers

What distinguishes convection mass transfer from diffusion mass transfer?

Convection involves bulk fluid movement Signup and view all the answers

What is a key characteristic of forced convective mass transfer?

It is induced by external means, like fans or pumps Signup and view all the answers

How does the rate of diffusion mass transfer compare to convection mass transfer?

Diffusion is slower and limits mass transfer scale Signup and view all the answers

Which scenario best exemplifies free convective mass transfer?

Evaporation of ether due to buoyancy forces Signup and view all the answers

What analogy is used to describe the relationship between diffusion and convection mass transfer processes?

A high-speed train compared to a crawling turtle Signup and view all the answers

What role does turbulence play in mass transfer processes?

It enhances mixing and mass transfer rates Signup and view all the answers

Study Notes

Modes of Mass Transfer

Mass transfer occurs through diffusion, which can be molecular or eddy-based, driven by concentration differences.
Molecular diffusion involves the transfer of substances through a stagnant layer of fluid, whereas eddy diffusion happens in a turbulent flow.
Eddy diffusion is generally more efficient than molecular diffusion, as seen in example scenarios like the dispersion of purple dye in water or smoke from a stack.

Mass Transfer by Convection

Convection refers to large-scale mass transfer resulting from the bulk movement of fluids, influenced by transport properties and flow dynamics.
Free convective mass transfer occurs due to buoyancy, such as ether evaporation.
Forced convective mass transfer is enhanced by external forces (e.g., fans or pumps), exemplified by wind rapidly transporting water particles on a lake's surface.

Comparisons of Mass Transfer Processes

Diffusion mass transfer operates slowly, limiting its effectiveness for large-scale processes.
In contrast, convection mass transfer is much faster and suitable for significant transfers, akin to a train's speed compared to a turtle's.
Both convection and diffusion processes coexist, with convection overshadowing diffusion.

Interphase Mass Transfer

Interphase transfer relies on molecules migrating between distinct phases, influenced by disparities in physical and chemical properties like vapor pressure or solubility.
A concentration gradient exists between the bulk fluid and the interface, with equilibrium often assumed at steady states.
Examples include the absorption of ammonia by water, CO2 from flue gas by amine solvents, and H2S from natural gas.

Two-Film Theory

The Lewis-Whitman two-film model describes mass transfer with gas-liquid interfaces, highlighting double layers through which diffusion occurs.
This model illustrates the complexities of communication between two languages, where barriers slow down interaction, analogous to gas transferring through molecular layers at an interface.

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Description

Explore the principles of mass transfer and separation processes in this quiz based on AECH 4210. Topics include modes of mass transfer such as molecular and eddy diffusion, as well as the significance of concentration differences. Test your understanding of how these processes operate at both microscopic and macroscopic levels.