Register to reply

Work & Final Temperature in Piston Cylinder (Check my work)

by texas_better
Tags: check, cylinder, final, piston, temperature, work
Share this thread:
Oct13-12, 09:05 AM
P: 1
If someone or a few people, just look this over and tell me if I'm right or if I did something wrong I'd be so grateful. I think it's all there but I'm not sure, there might be something off.

1. The problem statement, all variables and given/known data

Air (which behaves like an ideal gas) undergoes adiabatic expansion in piston cylinder.
T1 = 2000 K
p1 = 4 MPa

Undergoes adiabatic expansion to a volume that is v2 = 10v1. (v = specific vol)

Find T2 (temperature of gas after expansion) and calculate adiabatic work, W, done.

2. Relevant equations

3. The attempt at a solution

I found W = 863 kJ and I know this correct.

The way I did it was by solving for v, specific volume, in pv = RT, and then putting V, volume, in terms of v and m, mass, like [itex]V = vm[/itex]. I then used the polytropic process and the V1's cancel when you sub V2=10V1. I end up w/ 863m (kJ).

Then used Q - W = E2-E1.
Q is 0 (adiabatic)
-W = E2-E1
-W = U2-U1 only internal energy
-W = m(u2-u1) where u = specific enthalpy
-W = mcv(u2-u1) where cv=0.718 kJ/kg*k for air
-W = mcv(T2-T1)

In the final step I substituted W = 863m (kJ), the cv value, T1 = 2000 K, and solved for T2 to get 797k.

Is this legit? Thanks for any help.
Phys.Org News Partner Science news on
Wildfires and other burns play bigger role in climate change, professor finds
SR Labs research to expose BadUSB next week in Vegas
New study advances 'DNA revolution,' tells butterflies' evolutionary history

Register to reply

Related Discussions
Thermodynamics; Finding Work of a Piston cylinder Device Engineering, Comp Sci, & Technology Homework 20
Electrical work in a piston-cylinder filled with refrigerant Engineering, Comp Sci, & Technology Homework 2
Work done by air in piston with temperature change Introductory Physics Homework 4
Work done and total heat transfer for piston-cylinder device Engineering, Comp Sci, & Technology Homework 1
Thermodynamics- work in a cylinder piston device with spring Engineering, Comp Sci, & Technology Homework 4