Solving Unusual Problems: Using the Polytropic Ideal Gas Equation

[mulgerizze]

Homework Statement

Exhaling air through a mask means the lungs needs to be pressurized to 1.1 atm instead of the normal 1atm. To exhale through the mask the lungs are depressurized to 0.9 atm. In either case the temp of the lungs wont be the normal 98.7 degrees Fahrenheit. What is the temperature swing of the lungs in this case?

Relevant Equations

Entropy, polytropic equation for an ideal gas

My teacher likes to make really weird problems. How can I start this problem? The only thing I thought of doing is using the polytropic ideal gas equation when cp= constant. (p2/p1)^k-1/k = T2/T1 and making p1 and t1 in each case the normal state of the lungs

 

[BvU]

Hello (again),

And what do you get when you follow your thought ?

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[mulgerizze]

Hello (again),

And what do you get when you follow your thought ?

$\$

I got that the temperature from 1 atm to 1.1 atm was 114 and the temperature from 1 atm to 0.9 atm was 82

 

[BvU]

I suppose you used (p2/p1)^(k-1)/k = T2/T1 and not (p2/p1)^k-1/k = T2/T1
And k = 7/5 ?

I have trouble dealing with units like Fahrenheit and psi, but I suppose your math is ok.

So if your asumptions (did you list them ?) are correct, this is what omes out. Seems a bit hefty to me, but who knows ...

https://www.physicsforums.com/threads/homework-help-guidelines-for-students-and-helpers.686781/
(don't just dump a number, show your steps)

$\$

 

[mulgerizze]

I suppose you used (p2/p1)^(k-1)/k = T2/T1 and not (p2/p1)^k-1/k = T2/T1
And k = 7/5 ?

I have trouble dealing with units like Fahrenheit and psi, but I suppose your math is ok.

So if your asumptions (did you list them ?) are correct, this is what omes out. Seems a bit hefty to me, but who knows ...

https://www.physicsforums.com/threads/homework-help-guidelines-for-students-and-helpers.686781/
(don't just dump a number, show your steps)

$\$

I assumed cp = constant and that the breathable air is an ideal gas.

My steps for for p=1.1 to p=1 k=1.4 were 98.7+460(1.1atm/1atm)^(1.4-1)/1.4

For p=0.9 to p=1 k=1.4 . 98.7+460(.9atm/1atm)^(1.4-1)/1.4

 

[berkeman]

Homework Statement:: To exhale inhale through the mask the lungs are depressurized to 0.9 atm.

Fixed typo for you in your problem statement.