(a)
Interpretation:
To find the downstream temperature and the rate of entropy generation.
Concept Introduction:
The properties for ethylene are
Cp = Molar heat capacity
R = Universal Gas Constant
T1= Initial given temperature = 375 K
P1 = Initial given Pressure = 18 bar
P2 = Final Given Pressure = 1.2 bar
A, B, C, D = Constants for heat capacity of air
A = 1.424
B = 14.394 x 10-3 K-1
C = -4.392 x 10-6 K-2
D = 0
W = Power required of the compressor
Tc= Critical Temperature = 282.3 K
Pc = Critical Pressure = 50.4 bar
(a)
Answer to Problem 7.56P
Explanation of Solution
For throttling process,
Assume that
Given
Where
Assuming and substituting variables find T2(=T in the above equation)
We get T2= 365.45 K
Entropy is given as
Where
Substituting all the values into the above equations,
We get S = 22.13 J/(mol.K)
(b)
Interpretation
To find the downstream temperature, the rate of entropy generation and power output in kJ/mol.
Pros and cons of throttling valve and adiabatic expander
Concept Introduction:
The properties for ethylene are
Cp = Molar heat capacity
R = Universal Gas Constant
T1= Initial given temperature = 375 K
P1 = Initial given Pressure = 18 bar
P2 = Final Given Pressure = 1.2 bar
A, B, C, D = Constants for heat capacity of air
A = 1.424
B = 14.394 x 10-3 K-1
C = -4.392 x 10-6 K-2
D = 0
W = Power required of the compressor
Tc= Critical Temperature = 282.3 K
Pc = Critical Pressure = 50.4 bar
(b)
Answer to Problem 7.56P
Pros of expander − Can be used to generate power
Cons of expander − High cost and maintenance
Pros of throttling valve − Temperature of outlet gas is high and can be used for various purposes
Cons of throttling valve − Consumes power
Explanation of Solution
With
Guess:
Given
Now calculate the isentropic enthalpy change,
Calculate actual enthalpy change using the expander efficiency.
Assume T2to satisfy the above value of
Given
We get T2= 270 K
Substituting the values in the above equation, we get
Power is given as,
Pros of expander − Can be used to generate power
Cons of expander − High cost and maintenance
Pros of throttling valve − Temperature of outlet gas is high and can be used for various purposes
Cons of throttling valve − Consumes power
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Chapter 7 Solutions
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