This is a problem from Thermodynamics by Faires and Simmang:

There are 2.27 kg/min of steam undergoing an isothermal process from 27.6 bar tp

Find:

a. ΔS,

b. Q,

c. W(nf), and

d. W(sf) with ΔP=0 and ΔK=+42 kJ/min.

Here are the answers it has given:

a. 1.6 kJ/(K min)

b. 942 kJ/min

c. 846 kJ/min

d. 798 kJ/min

I suspect that it used 1.6 kJ/(K min) and multiplied it by 589K to get 942.4 kJ/min.

Here's my solution:

Given

m=2.27 kg/min

T=316C=589.15K

p1=27.6 bar

p2=6.8 bar

p1/p2=4

a.

ΔS=mR[ln(p1/p2)]

=(2.27kg/min)(0.5 kJ/(kg K))(ln4)

=1.573 kJ/(k min)

b.

Q=TΔS

=589.15K(1.573 kJ/(K min))

=926.99 kJ/min

c. W(nf)

W=Q=926.99 kJ/min

d. W(sf, ΔP=0 and ΔK=+42 kJ/min)

W=Q-ΔK

=926.99-42

=884.99 kJ/min

Can someone tell me where I got wrong? Or is it possible that the book was wrong?

Any help is very much appreciated.

Edit: It's

There are 2.27 kg/min of steam undergoing an isothermal process from 27.6 bar tp

**6.9**bar at 316C.Find:

a. ΔS,

b. Q,

c. W(nf), and

d. W(sf) with ΔP=0 and ΔK=+42 kJ/min.

Here are the answers it has given:

a. 1.6 kJ/(K min)

b. 942 kJ/min

c. 846 kJ/min

d. 798 kJ/min

I suspect that it used 1.6 kJ/(K min) and multiplied it by 589K to get 942.4 kJ/min.

Here's my solution:

Given

m=2.27 kg/min

T=316C=589.15K

p1=27.6 bar

p2=6.8 bar

p1/p2=4

a.

ΔS=mR[ln(p1/p2)]

=(2.27kg/min)(0.5 kJ/(kg K))(ln4)

=1.573 kJ/(k min)

b.

Q=TΔS

=589.15K(1.573 kJ/(K min))

=926.99 kJ/min

c. W(nf)

W=Q=926.99 kJ/min

d. W(sf, ΔP=0 and ΔK=+42 kJ/min)

W=Q-ΔK

=926.99-42

=884.99 kJ/min

Can someone tell me where I got wrong? Or is it possible that the book was wrong?

Any help is very much appreciated.

Edit: It's

**6.9 bar**, not 3.9.
Last edited: