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MCQ's On FRESH WATER GENERATOR | Marine Engineering
MAMQ & A
Marine Geek
5 min read
FRESH WATER GENERATOR
1. Because of the reduced ____ in the distillation system, some of the seawater boils through passing the evaporator
pressure
temperature
density
volume
2. Which of the following statements is true concerning low-pressure distilling units?
High conductivity of the distillate indicates distillate salinity is excessive.
Increasing the absolute pressure of the shell will increase the distiller's capacity.
Mesh separators are used in evaporators to filter the distillate.
Reducing the brine density will reduce the heat lost overboard.
3. Which of the listed conditions will cause the feed water, that has not flashed to vapour in the first stage of a flash evaporator, to flow into the second stage?
Gravity siphon effect
Higher vacuum in the second-stage
Difference in brine density between first and second stages
Lower pressure in first- stage
4. The purpose of a three-way, solenoid, dump valve on an evaporator is to
prevent excessive saline distillate from entering the freshwater system
drain the evaporator first- effect only
drain the evaporator second-effect only
allow the evaporator's first- and second effects to be drained with one valve
5. Vacuum evaporators onboard are tested for max vacuum by
Pressure testing of evaporator shell
Carry out leak test for distillate pp
Carry out leak test for vacuum pp and fittings
None of the above
6. Scale formation in freshwater generators leads to
Impaired heat transfer
Reduced capacity
Increase in shell temperature
All of above
7. Excessive scale formation in a distilling plant may result from
poor distillate quality
reduced evaporator capacity
low brine concentration
improper vacuum regulation
8. When a flash evaporator is being operated in extremely cold water, you may need to throttle the seawater supply to
prevent cold shocking the evaporator
maintain the feed water temperature above the required minimum input temperature
avoid flooding the evaporator shell
increase the evaporator distilling rate
9. If a flash-type evaporator is operating in extremely cold seawater temperatures, the engineer may expect that
the evaporator feed heater will require less steam
the capacity will remain the same regardless of the evaporator shell temperature
the average salinity of the distillate may increase due to excessive vacuum
the average salinity of the distillate may decrease due to excessive vacuum
10. When any low-pressure distilling plant is operated with less than the designed vacuum, the
heat level rises
heat level drops
capacity increases
scale formation decreases
11. Which of the following statements is true concerning low-pressure distilling units?
High conductivity of the distillate indicates distillate salinity is excessive.
Increasing the absolute pressure of the shell will increase the distiller's capacity.
Mesh separators are used in evaporators to filter the distillate.
Reducing the brine density will reduce the heat lost overboard.
12. When a flash evaporator is being operated in extremely cold water, you may need to throttle the seawater supply to
prevent cold shocking the evaporator
maintain the feed water temperature above the required minimum input temperature
avoid flooding the evaporator shell
increase the evaporator distilling rate
13. A salinity-indicating system functions on the basic principle of measuring the
electrical inductance of water
electrical conductivity of water
specific gravity of water
hydrogen ion concentration of water
14. In reverse osmosis-type freshwater generator plants, pretreatment of the feed water is done to:
Soften the feed water
Sterilize the feed water
To facilitate wash through of salt deposits on elements
Add necessary minerals to the water
15. Salinity of distilled water produced from fresh water generator onboard depends on
Amount of feed set in freshwater production
Amount of salt water leaking from condenser if any
Efficiency of brine ejector from the evaporator shell
All of above
16. The purpose of a three-way, solenoid, dump valve on an evaporator is to
prevent excessive saline distillate from entering the freshwater system
drain the evaporator first- effect only
drain the evaporator second-effect only
allow the evaporator's first- and second effects to be drained with one valve
17. A vacuum is created in an evaporator-type distilling plant by
the flashing of the feed water
the condensation of the saltwater feed
air ejectors, eductors, or a separate vacuum pump
condensation of the distillate
18. When any low-pressure distilling plant is operated at less than the designed vacuum (higher absolute pressure), what happens?
the corresponding saturation temperature drops
the distillate production capacity increases
the rate of scale formation increases
the distillate purity increases
19. When a flash evaporator is being operated in extremely cold water, you may need to throttle the seawater supply to
prevent cold shocking the evaporator
maintain the feed water temperature above the required minimum input temperature
avoid flooding the evaporator shell
increase the evaporator distilling rate
20. The purpose of a three-way, solenoid, dump valve on an evaporator is to
prevent excessively saline distillate from entering the freshwater system
drain the evaporator first- effect only
drain the evaporator second-effect only
allow the evaporator's first- and second effects to be drained with one valve
21. A constant pressure range is maintained in the potable water system of many vessels by using
constant speed supply pumps
variable speed supply pumps
an air cushion in a hydrophore vessel
a pressure regulator in the pump suction piping
22. A salinity-indicating system functions on the basic principle of measuring the
electrical inductance of water
electrical conductivity of water
specific gravity of water
hydrogen ion concentration of water
23. The process during which liquid containing a reasonable amount of sensible heat at a particular pressure immediately changes into steam after being admitted to a chamber at a lower pressure is called
boiling off
flash evaporation
condensation
none of the above
24. In a flash-type evaporator, all saltwater headers are vented through individual vent cocks to the
saltwater heater shell
second-stage condenser
atmosphere
second-stage flash Chamber
25. Why would a flash-type distilling unit be more efficient when operated in cooler seawater temperatures?
Steam carryover between stages is reduced.
Evaporator vacuum is increased.
The amount of available flash steam is decreased.
Feed water flow from the feed water heater is increased.
26. When distilling sea water the cooling water discharging from the distiller is fed back to evaporator as feed water
to decrease scale formation
for better cooling effect
more economical purpose
to raise vacuum
27. Under normal operating conditions, the highest temperature and pressure conditions existing in a flash-type evaporator will occur in the
first stage
second stage
distillate cooler
saltwater feed heater
28. Under normal operating conditions, the highest temperature and pressure conditions existing in a flash-type evaporator will occur in the
first stage
second stage
distillate cooler
saltwater feed heater
29. In ____, hot diesel engine jacket water passes over the heat exchanger stack and heats the seawater passing through the tubes
a flash generator
a flash evaporator
a vacuum boiling evaporator
a boiler
30. Scale accumulation on evaporator heat exchange surfaces
increases brine density
increases distillate salinity
reduces metal corrosion
reduces heat transfer
31. When a flash-type evaporator is to be secured for an extended period of time, the entire unit should be drained, cleaned, and
completely filled with salt water
filled with descaling compound
tightly closed to exclude air
vented to the atmosphere
32. When a flash-type evaporator is to be secured for an extended period of time, the entire unit should be drained, cleaned, and
completely filled with salt water
filled with descaling compound
tightly closed to exclude air
vented to the atmosphere
33. Which of the listed conditions will cause the feed water, that has not flashed first-stage of a flash evaporator, to flow into the second-stage
Gravity siphon effect
Higher vacuum in the second-stage
Difference in brine density between first and second stages
Lower pressure in first-stage
34. In a two-stage flash-type evaporator, excess brine in the first stage automatically passes
directly to the second-stage feed heater
directly overboard through the brine cooler
into the second stage flash chamber
into the second stage vapour condenser
35. Why would an evaporator-type distilling unit be more efficient when operated in a cooler seawater temperature?
Steam carryover between stages is reduced.
Evaporator vacuum is increased.
The amount of available flash steam is decreased.
Feed water flow from the feed water heater is increased.
36. The primary reason low-pressure evaporators produce distillate more efficiently, and with less scale formation, than high pressure evaporators is
evaporation is accomplished in a vacuum
due to the higher temperature of the incoming feed
due to the latent heat of evaporation principle
evaporation in a submerged medium produces more distillate
37. Scale accumulation on evaporator heating surfaces will cause
immediate loss of vacuum
increased distillate quality
immediate tube failure
reduced evaporator capacity
38. Why would a flash-type distilling unit be more efficient when operated in cooler seawater temperatures?
Steam carryover between stages is reduced.
Evaporator vacuum is increased.
The amount of available flash steam is decreased.
Feed water flow from the feed water heater is increased.