Page 467 - Elements of Chemical Reaction Engineering Ebook

438 Steady-State Nonisothermal Reactor Design Chap. 8

I The heat of reaction based on the moles of H2 reacted is

AHR,(423 K) =
3 g mol H,
kJ
= -32.51 - K
at423
mol H,

8.2.8 Heat Added to the Reactor, d

The heat Aow to the reactor, Q , is given in many instances in terms of
the overall heat-transfer coefficient, U, the heat-exchange area, A, and the dif-
ference between the ambient temperature, Tu, and the reaction temperature, T.

CSTRs. Figure 8-2 shows schematics of a CSTR with a heat exchanger. The
coolant enters the exchanger at a mass flow rate mc at a temperature Tal and
leaves at a temperature Tu2. The rate of heat transfer from the exchanger to the
reactor is4

(8-34)

For exothermic
reactions

FAo-=il
I
J"

Holf -pipe Fin-type
jacket baffle

Conventional
jacket
Figure 8-2 CSTR tank reactor with heat exchanger. [(b) Courtesy of Pfaudler, Inc.]

As a first approximation, we aspme a quasi-steady state for the coolant flow
and neglect the accumulation term (i.e., dT,/dt = 0). An energy balance on the
coolant fluid entering and leaving the exchanger is

Information on the overall heat-transfer coefficient may be found in C. 0. Bennett
qnd J. E. Myers, Momentum, Heat, and Mass Transfer, 2nd ed. (New York
Mc-Graw-Hill, .1974), p. 3 16.