Thermodynamics - Control Volumes find final temperature

Overall, well done!In summary, the conversation discusses a problem involving balancing equations and using the ideal gas equation to solve for specific enthalpy and temperature. The speaker's approach is to factor out mass and use the equation h = Pv + u to arrive at the final equation, with the suggestion to double check calculations and provide a step-by-step explanation for clarity.
  • #1
WateryFungi
1
0
Homework Statement
Air with a volume of 1.59 m^3 at 2.06267 atm and 298.7 K is compressed by a compressor, which applies 260 kJ/kg of flow work to increase the pressure to 2,094 kPa. Find the final temperature in Kelvin.
Relevant Equations
First Law of Thermodynamics
Energy Balance Equation for Open Systems
Ideal Gas Equation
h = Pv + u
Hi
I'd like to know if my current approach to the problem has any issues.
My attempt:
Balancing the equation:
Qin + Win +mΘout = Qout + Wout + mΘout
Qin+m(hin + v2in/2 + gzin) = m(hout + v2out/2 + gzout)
Wflow + ΔU + m(hin) = m(hout)


I factored out the mass:
wflow + Δu + hin = hout
And I used h = Pv +u where h = specific enthalpy, P=pressure, v=specific volume, u=specific internal energy, to get:
wflow = P2v2 - P1v1

I then used the ideal gas equation Pv = RT, with R = 0.287 kJ/kg*K and P = 2.06267 atm = 209 kPa to get v1
v1 = (0.287 kJ/kg*K)(298.7 K) / (209 kPa) = 0.4102 m3/kg
And plugged it in the previous equation for v2
v2 = (wflow + P1v1) / P2
v2 = [260 kJ/kg + (209 kPa)(0.4102)]/(2,094 kPa) = 0.1651 m3/kg

I then used the ideal gas equation again to solve for T2.

Any insight would be greatly appreciated.
 
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  • #2
Your approach looks correct. The only thing I would suggest is to double check all of your calculations to make sure you haven't made a mistake. Additionally, it might be helpful to include a step-by-step explanation of how you arrived at the final equation to help others understand the problem.
 

FAQ: Thermodynamics - Control Volumes find final temperature

1. What is the definition of a control volume in thermodynamics?

A control volume is a specific region in space that is chosen to study the flow of mass, energy, and momentum in a thermodynamic system. It can be an open or closed system, and is often represented by a physical boundary such as a pipe or a container.

2. How is the final temperature calculated in a control volume analysis?

The final temperature in a control volume analysis is calculated using the First Law of Thermodynamics, which states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. This equation can be rearranged to solve for the final temperature.

3. What are the key assumptions made in a control volume analysis?

The key assumptions made in a control volume analysis include steady-state conditions, which means that the system is not changing with time, and no heat or mass transfer across the boundaries of the control volume. Additionally, the analysis assumes that there are no significant changes in kinetic or potential energy within the control volume.

4. How does the type of fluid affect the final temperature in a control volume analysis?

The type of fluid can greatly affect the final temperature in a control volume analysis. For example, an ideal gas will experience a change in temperature due to changes in pressure and volume, while an incompressible fluid will not experience a change in temperature. Additionally, the specific heat capacity of the fluid will also impact the final temperature.

5. What are some real-world applications of control volume analysis in thermodynamics?

Control volume analysis is commonly used in engineering and physics to analyze and design various systems, such as heat exchangers, turbines, and compressors. It is also used in the study of fluid dynamics, combustion processes, and refrigeration systems. Additionally, control volume analysis is used in the design and optimization of energy systems, such as power plants and renewable energy systems.

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