Thermo Cycles and Systems 2

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  1. Processes involving solids and liquids are always considered to be:
    A. Constant Volume processes 
    B. Constant Temperature processes
    C. Constant Cooling Load 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?
    chart?chf=bg,s,00000000&cht=tx&chl=MEP%3D%5Cfrac%7BW_%7Bnet%7D%7D%7BV_A-V_B%7D&chs=256x76

    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)?
    chart?chf=bg,s,00000000&cht=tx&chl=HP%3D%5Cfrac%7BpLAN%7D%7B33%2C000%7D&chs=202x80       where

    • L (feet)
    • A (sq.in.)
    • N (strokes / minute)
  4. What is the equation for the efficiency of an Otto Cycle?
    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Botto%7D%3D1-r_v%5E%7B(1-k)%7D&chs=236x46
  5. What is the difference between these two definitions of efficiency for a Carnot cycle?
    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Bth%7D%3D1-r_%7Bv%2Cs%7D%5E%7B(1-k)%7D&chs=218x50
    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Bth%7D%3D1-r_%7Bp%2Cs%7D%5E%5E%7B%5Cfrac%7B(1-k)%7D%7Bk%7D%7D&chs=246x76
    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Bth%7D%3D1-r_%7Bv%2Cs%7D%5E%5E%7B(1-k)%7D&chs=248x52 is the thermal efficiency where rv,s is the ratio of volumes (isentropic compression ratio).

    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Bth%7D%3D1-r_%7Bp%2Cs%7D%5E%5E%7B%5Cfrac%7B1-k%7D%7Bk%7D&chs=232x70 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?
    chart?chf=bg,s,00000000&cht=tx&chl=COP_%7Bref%7D%3D%5Cfrac%20%7BQ_%7Bin%7D%7D%7BW_%7Bin%7D%7D&chs=228x82 chart?chf=bg,s,00000000&cht=tx&chl=%3D%5Cfrac%7BQ_%7Bin%7D%7D%7BQ_%7Bout%7D-Q_%7Bin%7D%7D&chs=174x90
  7. In terms of heat and work, what is the Coefficient of Performance for a heat pump?
    chart?chf=bg,s,00000000&cht=tx&chl=COP_%7B_%7Bheat%20pump%7D%7D%3D%5Cfrac%7BQ_%7Bin%7D%2BW_%7Bin%7D%7D%7BW_%7Bin%7D%7D&chs=368x82

    chart?chf=bg,s,00000000&cht=tx&chl=COP_%7B_%7Bheat%20pump%7D%7D%3DCOP_%7B_%7Bref%7D%7D%2B1&chs=404x36
  8. In terms of temperatures, what is the difference between the COP's for a Carnot heat pump and a Carnot refrigerator?
    • Carnot:
    • chart?chf=bg,s,00000000&cht=tx&chl=COP_%7Bref%7D%3D%5Cfrac%7BT_%7Blow%7D%7D%7BT_%7Bhigh%7D-T_%7Blow%7D%7D&chs=338x76
    • chart?chf=bg,s,00000000&cht=tx&chl=COP_%7Bht%20%5C%20pump%7D%3D%5Cfrac%7BT_%7Bhigh%7D%7D%7BT_%7Bhigh%7D-T_%7Blow%7D%7D&chs=400x76
  9. What equation relates condenser horsepower to refrigeration COP?
    chart?chf=bg,s,00000000&cht=tx&chl=HP_%7Bcond%7D%3D%5Cfrac%7B4.715%20%5Cdot%20Q_%7Bton%7D%7D%7BCOP%7D&chs=296x84
  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?
    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Bth%7D%3D%20%5Cfrac%7BW_%7Bnet%7D%7D%7BQ_%7Bin%7D&chs=160x82
  12. Identify each of these cycles and their processes.
    Image Upload
    Image Upload
  13. What is the equation of a Carnot cycle in terms of enthalpy? What is the equation in terms of high and low temperatures?
    Image Upload
    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Bth%7D%3D&chs=82x34chart?chf=bg,s,00000000&cht=tx&chl=%5Cfrac%7B(h_B-h_C)-(h_A-h_D)%7D%7B(h_B-h_A)&chs=272x86chart?chf=bg,s,00000000&cht=tx&chl=%3D%5Cfrac%7BT_%7Bhigh%7D-T_%7Blow%7D%7D%7BT_%7Bhigh%7D&chs=204x76

    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Bth%7D%3D%5Cfrac%7BW_%7Bs%2Cturb%7D-W_%7Bs%2Cpump%7D%7D%7BQ_%7Bin%7D%7D&chs=326x82
  14. What is the equation for the efficiency of a Rankine cycle in therms of enthalpy?
    Image Upload
    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Bth%7D%3D&chs=82x34chart?chf=bg,s,00000000&cht=tx&chl=%5Cfrac%7B(h_B-h_C)-(h_E-h_D)%7D%7B(h_B-h_E)&chs=274x86

    chart?chf=bg,s,00000000&cht=tx&chl=%5Ceta_%7Bth%7D%3D%5Cfrac%7B%7BW_%7Bturbine%7D-W_%7Bpump%7D%7D%7D%7BQ_%7Bin%7D%7D&chs=328x82
  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.
    Image Upload
    • 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.
    Image Upload
    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.
    Image Upload
    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.

Card Set Information

Author:
RJVan
ID:
307164
Filename:
Thermo Cycles and Systems 2
Updated:
2016-03-13 23:32:07
Tags:
thermodynamics otto carnot rankine refrigeration
Folders:
Mechanical Engineering
Description:
Mechanical Professional Engineering Exam Review
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