This
post covers the unit wise 2 marks questions with answers of Unit V Mass Transfer,
repeatedly asking from Anna University, Chennai, for the subject ME6502- Heat
and Mass Transfer which is the one of the important subjects of Mechanical
Engineering students whom were studying V semester.
Unit
V Mass Transfer
Part- A (2 Marks with Answers)
1. What is meant by mass transfer?
Give examples.
The
process of transfer of mass as a result of the species concentration difference
in a mixture is known as mass transfer.
Ex:
(i)
Humidification o air in a cooling tower
(ii) Evaporation of petrol in the
carburetor of an IC engine.
(iii) The transfer of water vapor into dry
air.
2. What are the modes of mass
transfer?
(i) Diffusion mass transfer
(ii) Convective mass transfer
3. Differentiate molecular
diffusion and eddy diffusion.
Molecular diffusion:
The transport of water on a microscopic
level as a result of diffusion from a region of higher concentration to the
region of lower concentration in a mixture of liquids or gases is known as
molecular diffusion.
Eddy diffusion:
When one of the diffusion fluids is in
turbulent motion, eddy diffusion will takes place.
4. What is convective mass
transfer?
It is the process of mass transfer that
will occur between a surface and a fluid medium when they are at different
concentrations.
5. State Flick’s law of diffusion.
It states that molar flux of an element
per unit area is directly proportional to concentration gradient.
Ma/A = -Dab (dcc/dx)
Where
Ma/A = Molar flux – Kg-mole/sm2
Dab = Diffusion coefficient of
species a and b in m2/s
dcc/dx = Concentration gradient
in kg/m3
6. What is free convective mass
transfer?
If the fluid motion is produced due to
change in density resulting from concentration gradients, the mode of mass
transfer is said to be free or natural convective mass transfer.
Ex:
Evaporation of alcohol.
7. What is forced convective mass
transfer?
If the fluid motion is artificially
created by means of an external force like a blower or fan, that type of mass
transfer is known as forced convective mass transfer.
Ex: The
evaporation of water from an ocean when air blows over it.
8. Define Schmidt number and
Scherwood number.
Schmidt number:
It is defined as the ratio of the
molecular diffusivity of momentum to the molecular diffusivity of mass.
Scherwood number:
It
is defined as the ratio of concentrations gradients at the boundary.
9. Define mass concentration.
Mass concentration or mass density
is defined as the mass of a component per unit volume of the mixture.
It is expressed in terms of kg/m3
10. Define molar concentration.
Molar
concentration or molar density is defined as the number of molecules of a
component per unit volume of the mixture.
It is expressed in terms of kg-mole/m3
11. Define mass fraction.
The
mass fraction is defined as the ratio of the mass concentration of species to
the total mass density of the mixture.
12. Define mole fraction.
The
mole fraction is defined as the ratio of mole concentration of a species to the
total molar concentration.
