Page 23 - Packed bed columns for absorption, desorption, rectification and direct heat transfer

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system state of aggregation and the value of the specific heat C p is constant. Let
the components of the fluid velocity in direction of the coordinate axes be w*, w y
and w z and the fluid density and temperature - p and t respectively. The heat
balance for the parallelepiped is composed below. Because the heat transfer
takes place in a moving medium, the heat is passing in and leaving out by
means of the fluid flow.
The quantity of heat passing for unit of time in x direction trough wall
efy ck of the parallelepiped is

(47)

The quantity of heat going out through the opposite wall is

8(w x.pl
d
= Qx + Qx = C pJ.p.W xJy.dz + C. dxjiy.dz =
dx
(48)
dt
= c £.p.w x.dyjk + c dx.dy.dz
&

From Eqs. (47) and (48) the difference between entering and outgoing
heat is

(w x.p dt
+ w x.p— .dx.dy,dz. (49)
dx dx
For the other two axes:

.dx.dy.dz (50)
dy By

and
dt
.dx.dy.dz. (51)
dz dz