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# important Questions and Answers: Mass Transfer

Mechanical - Heat and Mass Transfer - Mass Transfer

MASS TRANSFER

1. WHAT IS MASS TRANSFER?

The process of transfer of mass as a result of the species concentration difference in a mixture is known as mass transfer

2. GIVE THE EXAMPLES OF MASS TRANSFER.

1. Humidification of air in cooling tower.

2. The transfer of water vapor into dry air.

3.WHAT ARE THE MODES OF MASS TRANSFER?

There are basically two modes of mass transfer.

1. Diffusion mass transfer.

2.Convective mass transfer.

4. WHAT IS MOLECULAR DIFFUSION?

The transport of water on a microscopic level as a result of diffusion from a region of higher concentration to a region of lower concentration in a mixture of liquids or gases is known as molecular diffusion.

5.STATE FICK S LAW OF DIFFUSION?

The diffusion rate is given by the Fickslaw , which states that molar flux of an element per unit area is directly proportional to concentration gradient.

JA = –DAB (d CA/dx)

6.DEFINE SCHMIDT NUMBER.

It is defined as the ratio of the molecular diffusivity of momentum to the molecular diffusivity of mass.

Sc = Molecular diffusivity of momentum / Molecular diffusivity of mass.

7.DEFINE SCHERWOOD NUMBER.

It is defined as the ratio of concentration gradients at the boundary.

S h = h MX /Dab.

8. DEFINE MOLARCONCENTRATION:

Numberof moleculesof a component per unit volume of the mixture. It is expressed in kg – mole/m3.

MOLAR CONCENTRATION = Number of moles of component /Unit Volume of mixture.

9.DEFINE MASS FRACTION.

Themass fraction is defined as the ratio of mass concentration species to the total mass density of the mixture.

10. DEFINE MOLE FRACTION.

The mole fraction is defined as the ratio of mole concentration of a species to the total molar concentration.

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