Page 88 - Adsorption Technology & Design, Elsevier (1998)

Rates of adsorption of gases and vapours by porous media 85

1.0

6 = 0.5 It" 6 = 0.2

0.4

7=0.3

1,=0.3
0.1
!
".o

0.04

".o
i .., \~
.o i- i-._ \eo

0.001
1 2 3 0 1 2 3
Dclr~

Figure 4. 7 Effect of heat transfer resistance on uptake of adsorbates. The figures on
the curves represent the parameter 7. The left-hand diagram is for ~ = 0.5
and the right-hand diagram is for & = 0.2 (see text) (source: Ruthven et al.
1980).

represents the heat capacity of the solid adsorbent. When 7 is sufficiently
small, the rate of uptake is controlled by heat transfer, but when 7 ~ oo the
system behaves isothermally (large heat transfer coefficient) and conforms
to the equation (4.22) corresponding to adsorption by crystals at isothermal
conditions. For small values of ?, when heat transfer is the controlling factor
the solution for the uptake curve yields
mt _1_( t$ ){ hat } (4.39)
m---~ - 1 +~ exp -- Cs(1 + ~)
Equation (4.39) may also be obtained from a heat balance on the crystal