14-07-2012, 12:52 PM
MASS TRANSFER
mass transfer.ppt (Size: 3.42 MB / Downloads: 39)
INTRODUCTION
Mass transfer refers to the transfer of a species in the presence of a
concentration gradient of the species.
CLASSIFICATION
Under a concentration gradient mass transfer can occur by either diffusion or convection.
DIFFERENCE
Convective mass transfer occurs on a macroscopic level, whereas diffusive mass transfer occurs on a microscopic level.
Diffusion refers to the mass transfer that occurs a stationary solid or
fluid in which a concentration gradient exists, there will be mass transfer on a microscopic level. This is due to the diffusion from regions of higher concentration to regions of lower concentration.
In contrast, convection refers to mass transfer that occurs across a moving fluid in which a concentration gradient exists. The convective mass
transfer is normally associated with fluid mechanics.
THERMAL DIFFUSION
Mass transfer may also result from a temperature gradient in a system, which is called thermal diffusion.
Similarly, a concentration gradient can give rise to a temperature gradient that results in heat transfer.
These two effects are termed coupled phenomena.