单选题The vacuum maintained in the salt water feed heater shell of a flash-type evaporator is generally accomplished by （）.Aa separate air ejector unitBa direct unimpeded connection between second stage and salt water feed heaterCeither by vacuum drag or an external line from the first stage via a fixed orificeDthe fixed orifice provided in the steam supply line
单选题
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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