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Thermodynamics Practice Test: First Law Applied to Flow Processes
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First Law Applied to Flow Processes topics include: Steady and variable flow processes, polytropic process. The first law of thermodynamics, also known as the law of energy conservation, states that energy can't be created or destroyed, but it can be converted from one form to another. In mechanical engineering, this law is applied to flow processes to analyze the energy transfer and transformation within a system.  The first law of thermodynamics for a flow process states that the increase in the internal energy of a system is equal to the amount of energy added to the system by matter... Show more
Thermodynamics Practice Test: First Law Applied to Flow Processes
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25 Questions

1. A gas initially at 500°C, 1 MPa is contained in a piston-cylinder arrangement with an initial volume of 0.1 m^3. It is then slowly expanded according to the relation PV = constant until a final pressure of 100 kPa is attained. Determine the work for this process.
2. A polytropic process(n = − 1) starts with P = 0, V = 0 and ends with P= 600 kPa, V = 0.01 m3. Find the boundary work done.
3. A cylinder/piston contains carbon dioxide at 300°C, 1 MPa with a volume of 200L. The total external force acting on the piston is proportional to V3. This system is allowed to cool to room temperature, 20°C. Find the work.
4. A piston-cylinder contains carbon dioxide at 2MPa with V=50 L. The device has a mass of 4 kg. Everything is initially at 200°C. By heat transfer the whole system cools to 25°C, at which point the gas pressure is 1.5 MPa. Find the work done.
5. In a throttling device, what do we get as SFEE when changes in PE and KE are taken zero?
6. For a turbine, it is seen that work is done by the fluid at the expense of its enthalpy.
7. Fluid flow through which of the following throttles the flow?
8. A cylinder/piston contains saturated vapour R-22 at 10°C; the volume is 10 L. The R-22 is compressed to 60°C, 2 MPa in a reversible polytropic process. If all the heat transfer during the process is with the ambient at 10°C, calculate the work done.
9. Which of the following is true for steady flow?
10. Variable flow processes can be analysed by
11. A balloon behaves such that pressure inside it is proportional to the diameter squared. It contains 2kg of ammonia at 0°C, 60% quality. They are now heated so that the final pressure is 600 kPa. Find the work done in the process.
12. Air goes through a polytropic process from 325 K, 125 kPa to 500 K, 300 kPa. Find the specific work in the process.
13. Helium in a piston/cylinder at 20°C, 100 kPa is brought to 400 K in a reversible polytropic process with exponent n = 1.25. Helium can be assumed to be an ideal gas with constant specific heat. Find the specific work.
14. Rate of energy increase within the control volume is given by
15. What does a diffuser do?
16. A piston-cylinder contains water at 3 MPa, 500°C. It is cooled in a polytropic process to 1 MPa, 200°C. Find the specific work in the process.
17. A cylinder/piston contains air at 100 kPa and 20°C with a V=0.3 m^3. The air is compressed to 800 kPa in a reversible polytropic process with n = 1.2, after which it is expanded back to 100 kPa in a reversible adiabatic process. Find the net work.
18. A heat exchanger is a device in which heat is transferred from one fluid to another.
19. A mass of 2 kg ethane gas at 100°C, 500 kPa, undergoes a reversible polytropic expansion with n = 1.3, to a final temperature of 20°C. Find the work done.
20. In ____ filling a bottle with air at 300K, the gas temperature rises to 420K due to flow work being converted to ____ increase.
21. R-12 in a piston-cylinder arrangement is initially at 50°C, x = 1. It is then expanded in a process so that P = Cv^(−1) to a pressure of 100 kPa. Find the work.
22. Consider air in a cylinder volume of 0.2 L at 7 MPa, 1800K. It now expands in a reversible polytropic process with exponent, n = 1.5, through a volume ratio of 8:1. Calculate the work for the process.
23. A balloon behaves according to the equation P = (C2)V^(1/3), C2 = 100 kPa/m. The balloon is blown up with air from a volume of 1 m^3 to a volume of 3 m^3. Find the work done by the air assuming it is at 25°C.
24. Turbines and engines ____ positive power output, and compressors and pumps ____ power input.
25. A piston-cylinder contains 0.1 kg air at 400 K, 100 kPa which goes through a polytropic compression process (n = 1.3) to a pressure of 300 kPa. How much work has been done by air in the process?

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