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UNIT 19 REVIEW QUESTIONS ANSWER KEY GO BACK TO INDEX
19-1) List the refrigerant characteristics that are shown on a pressure-enthalpy
diagram (PH).
19-2) What is the saturation curve?
19-3) Where are the pressure lines and how are they marked?
19-4) Define enthalpy.
19-5) Explain the difference between enthalpy and specific enthalpy.
19-6) Where are the specific enthalpy lines and how are they marked?
The specific enthalpy lines are vertical lines going from top to bottom; the
19-7) Why are the temperature lines horizontal inside the saturated curve?
19-8) What are the constant quality lines?
19-9) As you move to the right or left along a constant pressure line in the saturated
liquid area, what happens to the temperature?
19-10) As you move to the right or left along a constant pressure line, what happens
to the specific enthalpy?
19-11) As you move up or down along a constant enthalpy line, what happens to the
pressure?
19-12) As you move up along a constant enthalpy line, in the constant-quality area,
what happens to the temperature?
19-13) In refrigeration, how do we define entropy?
19-14) Why does some of the refrigerant liquid flash-vaporize in the metering
device?
19-15) At what point in the refrigeration cycle does the last of the liquid vaporize?
19-16) What happens to the refrigerant pressure during desuperheating?
19-17) When does liquid refrigerant first begin forming in the condenser?
19-18) What is subcooling?
19-19) How much heat enters the refrigerant in the metering device when some of it
flashes to a vapor cooling the remaining liquid to the evaporator temperature?
19-20) What can bubbles of refrigerant vapor do to the metering device’s operating
efficiency?
19-21) When does a refrigerant pick up most of the heat as it circulates through a
system?
19-22) Define adiabatic.
19-23) Define isothermal.
19-24) Explain how a system’s refrigeration effect can be determined.
19-25) Determine the refrigeration effect of the following system. The liquid
entering the evaporator has an enthalpy of 64 Btu/lb and the vapor leaving the
evaporator has an enthalpy of 121 Btu/lb.
19-26) What is the net refrigeration effect for the system in question 25 if the system
is circulating 4 pounds of refrigerant a minute?
19-27) When drawing a PH diagram of an operating system, how is placement of the
condenser and evaporator lines determined?
19-28) When drawing a PH diagram of an operating system, how is placement of the
compressor line determined?
19-29) When drawing a PH diagram of an operating system, how is placement of the
metering device line determined?
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19-30) Why is the condenser line wider than the evaporator line in a PH diagram of a
refrigeration cycle?
19-31) How can a PH diagram be used to select the system compressor?
19-32) How can a PH diagram be used to determine the heat of compression?
19-33) How can a PH diagram be used to determine the RCOP for a particular
system?
19-34) How many pounds of refrigerant must flow through a 4-ton evaporator each
minute if each pound has an enthalpy of 50.0 Btu/lb?
19-35) What will happen in the evaporator if the compressor capacity is not large
enough to remove all of the vapor?
19-36) On a blank sheet of paper sketch a typical PH diagram for a refrigeration
system. You do not need to duplicate all the scales on the PH diagram. Just show
the saturation curve and the four cycle lines.
