Page 18 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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1.2.1.2.1. Heat conduction
Usually, the rate of the processes in the field of chemical engineering is
presented as a product of two important parts, kinetic constant and driving
force. In the case of heat conduction these values are the thermal conductivity
and the temperature gradient correlated by Fourier's law:

(25,
dFdt dn

where dQ is the quantity of heat transferred through the surface dF for time dr,

— is the temperature gradient and X - the thermal conductivity. It is easy to
dn
Q
see from equation (25) that the dimension of X is J/(m.s. C). The minus on the
right hand side of the equation is for taking into account that the heat is
transferred in direction of decreasing of the temperature gradient.
The value of X for the liquid phase is a function of its specific heat,
density and mol mass, depending also on temperature. It can be taken from
different reference books.
The value of X for gases can be calculated using the equation:

(26)

Q
where A is the value of X at zero C and C* -experimental constant. In Table 1
the values of Xg and C* for different gases are presented.

Table 1. Values of Xg and Q for different gases [33, p. 284]
Gas Xg W/(m.K) C k Gas Xg W/(rn.K) c*
Nitrogen 0.0243 102 Oxygen 0.0234 156
Ammonia 0,0200 626 Carbon oxide 0.0215 144
Hydrogen 0.1590 94 Sulfur dioxide 0.0076 396
Air 0.0234 122 Chlorine 0.0072 351