Slide 1

Jangam, Mujumdar - Basic Concepts and Definition

in the moisture binding ability of the solid. Table 1.4 summarizes some of the common-

ly used models for sorption isotherms.

Table 1.4. Various sorption models

Type of Model Equation Details

Langmuir equa-
tion 푎푤�

1

푋−

1

푋푚�=^

1

퐶푋푚^

Brunauer-Emmett-
Teller (BET) equa-
tion

푋

푋푚

=

퐶푎푤

( 1 −푎푤)[ 1 +(퐶− 1 )푎푤]^

C is a dimension-

less parameter de-

pending on heat of

sorption for mono-

layer region

Oswin equation (^) 푋=퐾� 푎푤
1 −푎푤
�
푁
Kdependent^ is temperature
Halsey equation
푎푤=exp�−
퐴푋−퐶
푅푇 �^
A is temperature
dependent
Chung-Pfost equa-
tion 푎푤=exp�
−퐴
푇+퐶
exp(−퐵푀)�
Modified Hender-
son equation
푎푤= 1 −exp(−퐴(푇+퐵) 푋퐶) A, B^ and C^ are con-
stants
Chung-Pfost equa-
tion 푎푤=exp �

• 퐴
  푇+퐶

exp(−퐵푀)�

Guggenheim-
Anderson-Boer
(GAB) equation;
modification of
BET equation

푋

푋푚

=

퐶퐾푎푤

( 1 −퐾푎푤)( 1 −퐾푎푤+퐾퐶푎푤)^

C and K are dimen-
sionless parame-
ters depending on
heat of sorption for
mono and multi-
layer region
Lewicki model
푋=퐴�

1

푎푤

− 1 �

푏− 1

A and b are con-

stants

Peleg model
푋=푋푖�

푡

푘 1 +푘 2 푡

�

1.3.2. Drying Kinetics

Consider the drying of a wet solid under fixed drying conditions. In the most general
cases, after an initial period of adjustment, the dry-basis moisture content, X, decreases
linearly with time, t, following the start of the evaporation. This is followed by a non-
linear decrease in X with t until, after a very long time, the solid reaches its equilibrium
moisture content, X* and drying stops. In terms of free moisture content, defined as: