Evaporator Questions

1.   The evaporator absorbs heat from the air or brine because the liquid refrigerant entering the evaporator   Ans

            (A)    Has a lower temperature than the air or brine.

                   (B)    Has a higher temperature than the air or brine.

                   (C)   Boils to a low-pressure gas. 

                   (D)   Boils to a high-pressure gas.      

2. The evaporator     Ans             

        (A) Removes heat from the refrigerant.

        (B) Absorbs heat into the refrigerant.    

        (C) Stores liquid refrigerant.

        (D) Keeps the compressor busy.

  3. As the load on an evaporator decreases, the    Ans

        (A)    Discharge pressure increases.

        (B)    Oil pressure increases.

        (C)    Suction pressure increases.

        (D)    Suction pressure decreases.

  4. The heat picked up in the evaporator must equal the heat    Ans

        (A)  Gained by the condenser

        (B)  Lost by the condenser

        (C)  Of compression.

        (D)  Lost by the medium being cooled.

  5. The disadvantage of a flooded system is that it       Ans

        (A) Cannot be used on multiple systems.

        (B) Needs a large charge of refrigerant.

        (C) Cannot be used with a low-pressure motor Control.

        (D)    Can be used only with ammonia.

  6. Flooded feeds are different from direct expansion feeds because they     Ans

        (A)   Allow for regurgitation of liquid refrigerant.

        (B)    Use bigger and better evaporators for this purpose.

        (C)    Are not as effective in operation.

        (D)    Allow for recirculation of liquid refrigerant.

  7.   The suction pressure of any refrigeration system is adjusted        Ans

(A)  To a corresponding evaporator temperature below the material being cooled.

(B)  To a corresponding evaporator temperature equal to the material being cooled.

(C)  To a pressure above atmospheric at all times.

(D)  None of the above.

8.A direct expansion evaporator has frost on the up­per and lower coils but not on center coils. This indicates:      Ans

               (A)     the evaporator is flooded.

(B)     the evaporator is starved.

(C)     the evaporator is short of refrigerant.

(D)     there is oil logging in the evaporator

  9.  When the evaporator load increases, what happens to the suction pressure?    Ans

                  (A)     It decreases.

(B)     It increases.

(C)     It stays the same.

(D)     None of the above

  10.     Baffles in a gravity coil evaporator are used       Ans

                  (A)     for condensation.

(B)     for proper air flow.

(C)     to prevent moisture carry-over

(D)     all of the above.

  11.     The temperature of the medium being cooled must be     Ans

                  (A)     below the freezing point of the area to be cooled.

(B)     above the evaporator temperature.

(C)     equal to the evaporator temperature.

(D)     below the evaporator temperature.

  12.     Assuming all other conditions are constant,      Ans

                  (A)     as low-side pressure falls, compressor capacity increases.

(B)     as load decreases, the low-side pressure de­creases.

(C)     as head pressure increases, plant capacity in­creases.

(D)     as low-side pressure decreases, there is no change.

  13.     The two basic types of evaporators are      Ans

                  (A)     prime surface and finned.

(B)     finned and plate.

(C)     direct expansion feed and plate.

(D)     flooded and direct expansion feed.

  14.     A decrease in load on an evaporator causes       Ans

                  (A)     more refrigerant to be required.

(B)     pressure drop in the evaporator

(C)     increase in evaporator capacity.

(D)     more heat to be absorbed.

15.   which of the following statements is most nearly correct?       Ans

                    (A)          The efficiency of an evaporator coil decreases as the frost thickness increases.

              (B)          The efficiency of an absorber depends on and varies directly with the compressor speed.

              (C)          To lubricate the inside surfaces of an evaporator coil, 10 drops of machine oil per minute should                

                                  be pumped into the coil.

              (D)          To lubricate the cylinder walls of an ammo­nia compressor, 10 drops of machine oil per minute should be drawn into the                                    cylinder.

16. Prime surface evaporators operating below 32 deg  must frequently be     Ans 

                                                   (A)                   purged.

                                                    (B)                  cleared.

                                                    (C)                 defrosted.

17. Which of the following would not cause a starved evaporator?      Ans

                                (A)  Improper bulb location

                               (B) Clogged distributor line

                               (C) Shortage of refrigerant     

                                (D) Metering device stuck in open position

18.  A Freon-12 refrigerating system in an air condi­tioning plant is equipped with a finned-tube

            evaporation In operation, the outer surface of this evaporator is wet. Thus, the evaporator is      Ans

                                 (A)          not operating at highest efficiency.

                                 ( B)          not receiving enough refrigerant.

                                  (C)          operating efficiently.

                                  (D)          operating with an oversized expansion valve

19.    The fastest way to remove frost from a direct ex­pansion finned-tube evaporator is to      Ans

            (A)          shut it down and let the frost melt.

            (B)          run a hot gas line to the coil.

            (C)          wash frost off with warm water.

            (D)          scrape frost off.

20.    A predetermined amount of refrigerant is used in what type of evaporator?      Ans

                (A)          Flooded evaporator

           (B)          Direct-expansion evaporator

           (C)          Indirect-type chiller

21.The selection of the proper evaporator depends mainly on      Ans

              (A)   price.

              (B)   size.

              (C)   color.

              (D)   application.

  22. What happens in an evaporator?       Ans

                (A)   High-pressure liquid converts to low-pressure liquid.

               (B)   Refrigerant in the gas state is saturated

               (C)   Low-pressure liquid converts to low-pressure gas.

               (D)   High-pressure gas converts to low-pre liquid.

  23. Is the temperature outside the evaporator  lower than the inside temperature?      Ans

                 (A)   Higher

                (B)   Stays the same

                (C)   Lower

                (D)   100 lower

  24.  Secondary refrigerants are usually      Ans

                 (A)   azeotrope.

                (B)   halocarbons.

                (C)   water or brine.

                (D)   trifluoromethane.

  25.  In a refrigeration system, where would you superheat?      Ans

              (A)   After the metering device as refrigerant enters the evaporator

              (B)   In the middle of the evaporator coil,' saturation

              (C)   After the evaporator so that no saturated vapor enters the compressor

              (D)   Superheat is a metering device c

  26. The disadvantage of the direct expansion syste compared to the flooded system, is that it        Ans

              (A)   requires a large refrigerant charge.

              (B)   frosts up much more quickly.

              (C)   passes flash gas through the evaporator.

              (D)   requires a larger compressor.

27. The refrigerant leaving a flooded evaporator is        Ans

               (A)      just like that leaving a D-X evaporator, slightly superheated.

              (B)      just like that leaving a D-X evaporator, satu­rated.

              (C)      saturated, while that leaving a D-X evapora­tor is slightly superheated.

              (D)      slightly superheated, and leaving a D-X evaporator saturated.

  28. The flow of refrigerant into a flooded evaporator is controlled so it has      Ans

                (A)      mostly liquid refrigerant at the inlet but gas near the outlet.

               (B)      all its tubes wetted by liquid refrigerant from beginning to end.

               (C)      mostly liquid refrigerant at its outlet but gas at its inlet.

               (D)      a mixture of liquid and vapor refrigerant in its tubes from beginning to end.

  29. As flash gas increases, evaporator capacity      Ans

                (A)      Increases.

               (B)      Decreases.

               (C)       stays the same.

               (D)      increases or decreases depending on the evaporator pressure.

  30. Superheat is wanted at the outlet of a D-X evapo­rator mainly to       Ans  

                (A)   improve evaporator efficiency

               (B) . Increase evaporator capacity

               (C) . Protect the compressor

               (D)  increase system capacity.

27. The refrigerant leaving a flooded evaporator is      Ans

               (A)      just like that leaving a D-X evaporator, slightly superheated.

               (B)      just like that leaving a D-X evaporator, satu­rated.

              (C)      saturated, while that leaving a D-X evapora­tor is slightly superheated.

              (D)      slightly superheated, and leaving a D-X evaporator saturated.

  28. The flow of refrigerant into a flooded evaporator is controlled so it has        Ans

               (A)      mostly liquid refrigerant at the inlet but gas near the outlet.

              (B)      all its tubes wetted by liquid refrigerant from beginning to end.

              (C)      mostly liquid refrigerant at its outlet but gas at its inlet.

              (D)      a mixture of liquid and vapor refrigerant in its tubes from beginning to end.

  29. As flash gas increases, evaporator capacity        Ans

              (A)      Increases.

             (B)      Decreases.

             (C)       stays the same.

             (D)      increases or decreases depending on the evaporator pressure

30. Superheat is wanted at the outlet of a D-X evapo­rator mainly to       Ans

              (A)   improve evaporator efficiency

             (B) . Increase evaporator capacity

             (C) . Protect the compressor

             (D)  increase system capacity.