Other
Thermodynamics answers
- Course
- Thermodynamics 2
- Institution
- Vaal University Of Technology (VUT)
Thermo2
[Show more]
Connected book
Book Title:
Author(s):
- Edition:
- ISBN:
- Edition:
Seller
Follow
Content preview
lOMoARcPSD|5769186Solutions - Copy - answers
Thermodynamics 2 (Vaal University of Technology)
Studocu is not sponsored or endorsed by any college or university
Downloaded by MOTHIBELI MAKOANYANA (218110626@edu.vut.ac.za)
, lOMoARcPSD|5769186
THERMODYNAMICS II: TUTORIAL PROBLEMS
THE WORKING FLUID:
1.1 A certain fluid at 10 bar is contained in a cylinder behind a piston, the initial volume
being 0.05 m3. Calculate the work done by the fluid when it expands reversibly:
(i) at constant pressure to a final volume of 0.2 m3;
(ii) according to a linear law to a final volume of 0.2 m3 and final pressure of 2 bar;
(iii) according to a law pV = constant to a final volume of 0.1 m3;
(iv) according to a law p3 = constant to a final volume of 0.06 m3;
(v) according to a law, p = (A/V2) – (B/V), to a final volume of 0.1 m3 and a final
pressure of 1 bar, where A and B are constants.
Sketch all processes on a p- diagram.
Solution:
(i) Consider the constant pressure process:
The work done during this process is the area under the curve:
Work = area of the rectangle
= p x (v2 – v1)
= 10 x 105 x (0.2 – 0.05)
= 150000 N m
(ii) Consider linear law:
1
Downloaded by MOTHIBELI MAKOANYANA (218110626@edu.vut.ac.za)
, lOMoARcPSD|5769186
The work done is the sum of the two areas, the area of the triangle and the area of
the rectangle:
Consider the triangle, Work = 0.5 x base x height
= 0.5 x (v2 – v1) x (p1 – p2)
= 0.5 x (0.2 – 0.05) x (10 bar – 2 bar)
= 60000 N m
Consider the rectangle, Work = p2. (v2 – v1)
= 2 bar x (0.2 – 0.05)
= 30000 N m
The total work done = 60000 + 30000
= 90000 N m
(iii) pV = constant, where v2 = 0.1 m3 and v1 = 0.05 m3
W mp dv
pV = c
p = c/V c = 10 x 105 x 0.05
= 50000 bar (m3)
c
V
W dV
v2 dV
W c
v1 V
W cln v2 ln v1
W 50000xln 0.1 ln 0.05
W 34657Nm
2
Downloaded by MOTHIBELI MAKOANYANA (218110626@edu.vut.ac.za)
, lOMoARcPSD|5769186
(iv) pv3 = constant
p = c/v3 c = 10 x 105 x 0.05(3)
= 125 bar (m3)
W mp dv
c
v3
W dv
dv
W c
v3
1 1
W 0.5c 2 2
v 2 v1
1 1
W 0.5 x125
0.06
2
0.052
W 7639Nm
1.2 1 kg of fluid is compressed reversibly according to a law pv = 0.25, where p is in bar
and v is in m3/kg. The final volume is ¼ of the initial volume. Calculate the work done by
the gas on the fluid and sketch the processes on a p-v diagram.
c = 0.25 x105 bar (m3/kg)
c
p
V
c
V
W dV
v2 dV
c
v1 V
cln v2 ln v1
0.25x105 ln1 ln 0.25
W 34657Nm
3
Downloaded by MOTHIBELI MAKOANYANA (218110626@edu.vut.ac.za)
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through EFT, credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying this summary from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller mothibelimakoanyana1. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy this summary for R288,00. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
73216 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy summaries for 14 years now