# Thermo Cycles and Systems 2

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 Author: RJVan ID: 307164 Filename: Thermo Cycles and Systems 2 Updated: 2016-03-13 19:32:07 Tags: thermodynamics otto carnot rankine refrigeration Folders: Mechanical Engineering Description: Mechanical Professional Engineering Exam Review Show Answers:

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1. Processes involving solids and liquids are always considered to be:
A. Constant Volume processes
B. Constant Temperature processes
D. Constant Pressure processes
A. Constant Volume processes
(this multiple choice question has been scrambled)
2. What is Mean Effective Pressure (MEP) and what is the equation that defines it?

The MEP is the theoretical average pressure to produce an equivalent amount of work during one stroke of a cycle.
3. What is the equation for the horsepower of an Otto cycle, in terms of MEP (p, psig)?
where

• L (feet)
• A (sq.in.)
• N (strokes / minute)
4. What is the equation for the efficiency of an Otto Cycle?
5. What is the difference between these two definitions of efficiency for a Carnot cycle?

is the thermal efficiency where rv,s is the ratio of volumes (isentropic compression ratio).

is the thermal efficiency where rp,s is the ratio of pressures (isentropic pressure ratio).
6. In terms of heat and work, what is the Coefficient of Performance for a refrigeration cycle?

7. In terms of heat and work, what is the Coefficient of Performance for a heat pump?

8. In terms of temperatures, what is the difference between the COP's for a Carnot heat pump and a Carnot refrigerator?
• Carnot:
9. What equation relates condenser horsepower to refrigeration COP?
10. What equation describes the First Law of thermodynamics for closed systems, and what does the equation mean?
Qin = ΔU+W

Any heat entering a closed system can either increase the energy of the system (U) or be used to perform work on the surroundings.
11. What is the equation for thermal efficiency in terms of heat and work?
12. Identify each of these cycles and their processes.
13. What is the equation of a Carnot cycle in terms of enthalpy? What is the equation in terms of high and low temperatures?

14. What is the equation for the efficiency of a Rankine cycle in therms of enthalpy?

15. What can be said of the kinetic and potential energies of a closed system?
The kinetic and potential energies of a closed system are negligible.
16. What is the difference between the Carnot cycle and the basic Rankine cycle?
In the Carnot cycle, the fluid is compressed as a mixture of liquid and vapor. In the Rankine cycle, the fluid is compressed in the liquid state.
17. Identify the processes occurring on paths DA, AB, etc. for these refrigeration cycles.
• A-B = Expansion
• B-C = Vaporization
• C-D = Compression
• D-A = Condensation
18. What is the main difference between an absorption and a vapor compression refrigeration system?
The absorption system does not have a compressor. Instead it uses two working fluids: a refrigerant and an absorbent.
19. Identify this cycle and the processes that comprise it.
Brayton Turbine

• A-B: Isentropic compression
• B-C: Constant pressure heat addition
• C-D: Isentropic expansion
• D-A: Constant pressure cooling
20. Identify this cycle and the processes that comprise it.
Brayton Cooling (or Air Refrigeration)

• A-B: Isentropic cooling
• B-C: Constant pressure heat addition
• C-D: Isentropic compression
• D-A: Constant pressure cooling
21. Is the work done by a compressor in a refrigeration system considered positive or negative?
Because the work is being done on the gas (Win) it is considered negative.
22. What is the difference between an air conditioner and a chiller?
Both are refrigeration systems. An air conditioner produces cold air; a chiller produces cold water.

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