Register to reply

First law of thermodynamics applied to a submarine

by Carbon884
Tags: thermodynamics
Share this thread:
Jun13-11, 12:49 PM
P: 5

I hope someone can help me with the following question:

A submarine conatins 1000m^3 of air and has a temperature and pressure of 15C and 0.1MPa respectively. Due to the cold seawater a heatflow of 60 MJ/h occurs. The machines on the otherhand adds disspiative Work of 21 kW to the system. The specific heat capacity of air is c(p,air) = 1.005 kJ/Kg*K.

what average Temperature will the air have after one hour of diving?

T1=288.15K => T2=?

Firstly i found the density and mass of the gas:

R(air)= 286.9 J/K*Kg => density= P/T*R(air)=1.209 Kg/m^3 => m= V*density= 1209.63 Kg

Secondly i found the total Energy:

Q/h=Wdiss - Q/h = 15600 KJ/h

Then i used the first law:

dW=0 because V=constant


Q=mcp(T2-T1)= m(R(air)-cv)*(T2-T1)= 288.19K .... which can't possibly be right because that is essentially my T1 temerature. So what did I do wrong?

Thanks for your help in advance ^^.
Phys.Org News Partner Physics news on
Three's a charm: NIST detectors reveal entangled photon triplets
How did evolution optimize circadian clocks?
New webcast series brings cutting-edge physics talks to the world
Jun13-11, 02:14 PM
P: 4
R(air) = Cp - Cv
=> Cp=R(air)+Cv

so, Q=m(R(air)+Cv)(T2-T1)
Jun13-11, 08:55 PM
P: 1,985
The specific heat at constant pressure is given in the problem.
If you assume a constant-volume process, you can calculate cv=cp-R.
Either way the temperature increase is of the order of 10K (around 14K if you consider constant volume).
Review your last step.

Register to reply

Related Discussions
Total pressure of water against submarine Introductory Physics Homework 7
Applied heat and thermodynamics. Classical Physics 3
Good book for applied thermodynamics Mechanical Engineering 2
Submarine Fires Torpedo, Submarine's Recoil? Introductory Physics Homework 16
Explain the first law of thermodynamics as applied to a diagram for me? Introductory Physics Homework 0