PPT - Introduction to Mass Transfer and Diffusion | Mass Transfer - Chemical Engineering PDF Download

 Page 1


Introduction to Mass
Transfer
Page 2


Introduction to Mass
Transfer
Introduction
n Three fundamental transfer processes:
i) Momentum transfer
ii) Heat transfer
iii) Mass transfer
Page 3


Introduction to Mass
Transfer
Introduction
n Three fundamental transfer processes:
i) Momentum transfer
ii) Heat transfer
iii) Mass transfer
n Mass transfer may occur in a gas
mixture, a liquid solution or solid.
n Mass transfer occurs whenever there is
a gradient in the concentration of a
species.
n The basic mechanisms are the same
whether the phase is a gas, liquid, or
solid.
Page 4


Introduction to Mass
Transfer
Introduction
n Three fundamental transfer processes:
i) Momentum transfer
ii) Heat transfer
iii) Mass transfer
n Mass transfer may occur in a gas
mixture, a liquid solution or solid.
n Mass transfer occurs whenever there is
a gradient in the concentration of a
species.
n The basic mechanisms are the same
whether the phase is a gas, liquid, or
solid.
Definition of Concentration
i)  Number of molecules of each species
present per unit volume
(molecules/m
3
)
ii) Molar concentration  of species i =
Number of moles of i per unit volume
(kmol/m
3
)
iii) Mass concentration = Mass of i per
unit volume (kg/m
3
)
Page 5


Introduction to Mass
Transfer
Introduction
n Three fundamental transfer processes:
i) Momentum transfer
ii) Heat transfer
iii) Mass transfer
n Mass transfer may occur in a gas
mixture, a liquid solution or solid.
n Mass transfer occurs whenever there is
a gradient in the concentration of a
species.
n The basic mechanisms are the same
whether the phase is a gas, liquid, or
solid.
Definition of Concentration
i)  Number of molecules of each species
present per unit volume
(molecules/m
3
)
ii) Molar concentration  of species i =
Number of moles of i per unit volume
(kmol/m
3
)
iii) Mass concentration = Mass of i per
unit volume (kg/m
3
)
Diffusion phenomena
n Fick’s law: linear relation between the rate of
diffusion of chemical species and the
concentration gradient of that species.
n Thermal diffusion: Diffusion due to a
temperature gradient. Usually negligible unless
the temperature gradient is very large.
n Pressure diffusion: Diffusion due to a pressure
gradient. Usually negligible unless the pressure
gradient is very large.