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EastWindBreaks
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Homework Statement
Homework Equations
unreliable source of solution:
The Attempt at a Solution
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I came across this problem while practicing for the final exam in thermodynamic,my attempt: i recall this type of problems are not steady-flow system. Since the change in kinetic and potential energy is neglected, and the system does not produce work, therefore, the energy balance equation should becomes:
dE/dt= Q_dot+ m_dot(h_inlet)
h=u+Pv
since the question asks for Q instead of Q_dot: ( m_dot can not be found from given information alone either)
ΔE=ΔU=m(U2-U1)
therefore, m(U2-U1) = Q+ m* (H_inlet)
at this point, I see I can find final mass from ideal gas equation PV=mRT,
i can also find H and U2 from the given temperature and pressure from ideal gas property table of air. (T1=T2, P1=P2)
and U1 of the evacuated bottle is just 0, Q can be finally solved.
what I do not understand is that the solution assuming it's a steady-flow system, even if it is, dE/dt should be 0, so i guess they made a typo there. also, steady or not, it does not seem to alter the solution because dE/dt is 0 under steady-flow, but ΔE is not 0, correct?
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