In a flash evaporator, scale as a result of higher than normal temperatures in most likely to occur in the （）

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• In the operation of a flash type evaporator equipped with air ejectors,the air and non- condensable gases are evacuated directly from the （）.

  A . first stage flash chamber B . second stage flash chamber C . first stage after condenser D . second stage distilling condenser

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• The heated feed-water entering any flash chamber of a flash-type evaporator will（）

  A . vaporize, with the un-flashed water remaining at the temperature at which it entered the flash chamber B . vaporize, with the un-flashed eater equalizing to the saturation conditions existing in the f lash chamber C . vaporize, with the remaining water a t a temperature greater than it entered the flash chamber D . boil, allowing steam bubbles to rise through the brine at the bottom of the flash chamber

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• The demisters installed in a flash-type evaporator serve to （）

  A . deaerate the first effect distillate B . filter the condensed flash vapors C . deaerate the first and second effect distillate D . remove small water droplets entrained in the flashed vapor

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• One distinct advantage of flash type evaporators, as compared to most other evaporators, is that in a flash evaporator （）.

  A . high temperature distillate can be re- circulated to induce additional flashing B . scale formation is not a severe problem C . cold shocking is more effective in removing scale D . water purity is greatly increased at high capacity

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• The efficiency of a flash type evaporator can be increased by（）

  A . lowering brine discharge density B . decreasing the absolute pressure of each stage C . increasing the saltwater feed heater temperature D . increasing the pressure at the spray pipe

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• On a multistage flash-type evaporator, the flash chamber is （）

  A . combined as part of the salt water feed heater B . the open area above the brine levels in the first and second stages C . combined as part of the distillate cooler D . another term used to describe the vapor feed heater

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• For a flash type evaporator, the seawater heater will have to maintain a enough temperature to minimize scale formation（）

  A . lower B . higher C . low D . high

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• The vacuum maintained in the salt water feed heater shell of a flash-type evaporator is generally accomplished by （）.

  A . a separate air ejector unit B . a direct unimpeded connection between second stage and salt water feed heater C . either by vacuum drag or an external line from the first stage via a fixed orifice D . the fixed orifice provided in the steam supply line

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• Which of the following descriptions best identifies the operating principal of a flash-type evaporator?（）

  A . Sea water is heated to boiling temperature while under a vacuum B . Sea water is passed over heated plates in a thin film C . Heated sea water is injected into a vacuum chamber D . Sea water is forced through a heated eductor

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• The flash-evaporator is different with the submerged-tube evaporator in that for the former（）

  A . Water is heated into vapor on heating surfaces B . Water is vaporized by pressure difference C . There are no heating-transfer surfaces D . There are more heating-transfer surface

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• When a flash-type evaporator is to be secured for an extended period of time, the entire unit should be drained, cleaned, and （）.

  A . completely filled with saltwater B . filled with de-scaling compound C . tightly closed to exclude air D . vented to the atmosphere

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• A vacuum is initially established in the first and second stages of a low pressure evaporator by the use of （）

  A . vacuum drag from the auxiliary condensate system B . individual vacuum pumps C . a single non-condensing air ejector D . a two stage air ejector

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• Small droplets of water entrained in the flashed vapor produced in a flash-type evaporator, are removed by the （）

  A . spray pipes B . demisters C . condensers D . splash baffle

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• The design of for a flash type evaporator is of critical importance because it must provide an optimum feedwater spray pattern that facilitates the flashing process, and it must also maintain a pressure differential between successive stages（）

  A . condenser B . flashing device C . lashing device D . vacuum pum

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• Early models of the flash-type evaporators used a separate shell-and-tube heat exchanger as the air ejector condenser.More recent models use a combined air ejector condenser with the（）

  A . distilling condenser B . salt water feed heater C . distillate cooler D . flash chamber

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• The heated feedwater entering any flash chamber of a flash-type evaporator will（）

  A . vaporize, with the unflashed water remaining at the temperature at which it entered the flash chamber B . vaporize, with the unflashed water equalizing to the saturation conditions existing in the flash chamber C . vaporize, with the remaining water at the temperature greater than it entered the flash chamber D . boil, allowing steam bubbles to rise through the brine at the bottom of the flash chamber

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• What is the operating principal of a flash type evaporator?（）

  A . Sea water is heated to boiling temperature under a vacuum B . Sea water is passed over heated plates in a thin film C . Heated sea water is injected into a vacuum chamber D . Sea water is forced through a heated eductor

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• Under normal operating conditions, the highest temperature and pressure conditions existing in a flash-type evaporator will occur in the （）.

  A . first stage B . second stage C . distillate cooler D . salt water feed heater

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• In a vacuum boiling evaporator, the fresh water generated is pumped out by （）.

  A . a brine pump B . an air ejector C . a feed water pump D . a condensate pum

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• In which of the areas listed would you expect to find the highest salt concentration in a flash evaporator?（）

  A . Distiller air ejector cooling medium B . Saltwater heater discharge C . First-stage internal feed box D . Second-stage internal feed box

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• On which of the following heated surfaces of a flash type evaporator would you be more likely to find soft scale formation?（）

  A . Feed-water heater internal tube surfaces B . Internal distillate cooler tubes C . Flash chamber vertical surfaces D . Distilling condenser tube

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• Which of the listed problems could produce a high absolute pressure within a flash type evaporator?（）

  A . Production of high salinity distillate B . Seawater feed temperature below 165℃ C . A leak in the first stage demister D . A cracked distillate pump vent line

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• The latent heat of evaporation is dissipated in the （） in a compression refrigeration system.

  A . evaporator B . condenser C . expansion valve D . compressor

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• In a flash type evaporator, all saltwater heaters are vented through individual vent cocks to the ______.

  A.saltwater heater shell B.second-stage condenser C.atmosphere D.second-stage flash chamber

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