Interpretation:
To find final temperature, T
To find work required, W
To find entropy change of ammonia gas
Concept Introduction:
Ammonia:
Tc= 405.7.K
PC= 112.8.bar
For isenthalpic process,
For the heat/capacity of ammonia
Use generalized second-virial correlation:
The entropy change is given by
We know that
Where,
Cp = Molar heat capacity
R = Universal Gas Constant
T0= Initial given temperature = 21oC = 294.15K
P0 = Initial given Pressure = 200 kPa
P2 = Final Given Pressure = 1000 kPa
A, B, C, D = Constants for heat capacity of air
A = 3.578
B = 3.020 x 10-3 K-1
C = 0
D = -0.186 x 105K2
W = Power required of the compressor
Tc= Critical Temperature = 405.7 K
Pc = Critical Pressure = 112.8 bar = 112800 kPa
Assume m = 1000 mol/sec
Answer to Problem 7.33P
T = 447.47K
W = 5673.2 kW
Explanation of Solution
Use generalized second-virial correlation:
The entropy change is given by
Let us assume
Given
Where
Substitute all the values to satisfy the following equation by trial and error,
Solving we get,
Where
The actual enthalpy change from
Work required, W = m
The actual final temperature is now found from
Combined with
Now Guess
Substitute all the values to satisfy the following equation by trial and error
Where
By trial and error we get
T= 447.47 K
Substituting the values in the above equation
T = 447.47K
W = 5673.2 kW
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Chapter 7 Solutions
Introduction to Chemical Engineering Thermodynamics
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