Steam Engine work application problem

  • Thread starter 8point1
  • Start date
  • #1
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Homework Statement


In a steam engine the pressure and volume of steam satisfy the equation PV1.4=k, where k is a constant. Calculate the work done by the engine (in ft/lbs) during a cycle when the steam starts at a pressure of 100 lb/in2 and a volume of 400in3 and expands to a volume of 1100in3.

Homework Equations


Use the fact that the work done by the gas when the volume expands from volume v1 to volume v2 is:

W=∫V2v1 P dV



The Attempt at a Solution



As usual, getting hung up on where to start. So I tried to find k. Solving for k at the starting pressure of 100lb/in2 and volume of 400in3 I get a k=439,424.2

That # seems way high. Is the problem assuming the pressure is starting at these values (100lb/in2 and 400in3)??

Thanks
 

Answers and Replies

  • #3
26
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interesting.... now I'm even more confused!
 
  • #4
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Our professor didn't say we needed any special formulas or anything - that we should know how to do this from our previous section's lessons. Where do I start? That link shows more variables than I have (I think) like lambda values, etc.
 
  • #5
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Please, any help would be appreciated. I'm not looking for an answer, just a push in the right direction. Here's what I've tried to do to start out:

-put integral in terms of V
-break down Volume values and try to solve for r and h
-ratio between starting values: 100lb/in^2 and 400in^3

?
 
  • #6
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
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The attached article shows how to integrate P dV when PV^gamma = k (Note: there are no lambdas present.) Work is explicitly given in terms of initial pressure and initial and final volumes. (See section "Derivation of discrete formula")
 

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