Biomedical Engineering Reference
In-Depth Information
Carbon dioxide released:
m
CO
2
¼
44:01
m
EtOH
¼
44:01
46:07
0:1914
kg
¼ 0:1828
kg
46:07
Thus:
m
mix
¼
m
0
m
CO
2
¼ 4:01 0:1828
kg
¼ 3:8272
kg
3.13. REACTION ENERGY BALANCES
We will write all reactor energy balances as
¼
(3.120)
energy accumulation
energy flow in
energy flow out
which is the first law of thermodynamics.
Like the mass balance equation in the previous section, the equation is very simple math-
ematically and in words as it appears. However, due to the difficulty in defining energy, or
rather relating energy to easily measurable quantities in a system, the situation is more
complicated than the mass balance. As such, this equation is also only valid if no nuclear
reaction occurs. The first law of thermodynamics states that energy cannot be created or
destroyed (even chemical and/or biological reactions occur).
We must formulate and solve many energy balance equations in reactor analyses (simul-
taneously with mass balance equations). Therefore, it would be more convenient if we can
translate this literal expression into a mathematical equation.
Figure 3.8
shows a schematic of a system in general where flow streams in and out exist,
there is heat exchange between the surroundings occurring at a known rate and there is work
Flow in
Heat transfer in
Q
W
s
Flow out
FIGURE 3.8
Schematic of a control volume or system of interest for performing energy balances.
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