Page 693 - Bird R.B. Transport phenomena

§22.1 Definition of Transfer Coefficients in One Phase 673

Representative Membrane Processes

Dialysis Microfiltration
Blood oxygenation Ultrafiltration
Nanofiltration
Reverse osmosis

Membrane
T
Fig. 22.1-2. Two rather typical kinds of membrane separators,
classified here according to a Peclet number, Pe = 8v/4b , for
e{t
the flow through the membrane. Here 8 is the membrane
thickness, v is the velocity at which solvent passes through
the membrane, and 2) is the effective solute diffusivity
eff
through the membrane. The heavy line represents the mem-
brane, and the arrows represent the flow along or through the
membrane.

Stream of hot gas A
Injected gas A moving
/ away from wall
Interface H M И t H H t t f
Porous wall Fig. 22.1-3. Example of
1 1 1 1 1 1 1 1 1 1 1 1 1 1 mass transfer through a
Cold gas A pumped porous wall: transpira-
through wall tion cooling.

Tube wall

Fig. 22.1-4. Example of a gas-liquid con-
tacting device: the wetted-wall column.
Two chemical species A and В are mov-
ing from the downward-flowing liquid
stream into the upward-flowing gas
stream in a cylindrical tube.