🔍 Key Concepts

• Flash evaporator operation in multiple-effect systems (how each chamber’s pressure and temperature relate) • Role of identical centrifugal pumps when used as a brine recirculating / transfer pump versus a feed pump • Effect of discharge valve position on NPSH, flow rate, and pressure differential across pump "N" in relation to the vapor pressure in chamber "II"

💭 Think About

• Compare what happens to flow and pressure when a centrifugal pump like pump "N" is run with its discharge wide open versus throttled—how does that affect the pressure in chamber "II" and the boiling/flash conditions? • Look at the piping: where does pump "N" take suction from and where does it discharge to? If the vapor pressure in chamber "II" is 2.1 psia at 170°F, what happens if the pump cannot develop enough differential pressure above that vapor pressure? • Think about which choice would change the pressure balance between chambers II and III, and which ones would more likely affect production rate, distillate purity, or brine concentration—which of these is most sensitive to an over‑pumped recirculation line?

✅ Before You Answer

• Confirm from the diagram exactly what pump "N" is connected to (suction and discharge points) and whether it is moving brine, distillate, or feed seawater. • Compare vapor pressure at 170°F with the suction pressure available to pump "N"—would running wide open lead to flashing/cavitation or to a strong pressure increase? • Decide which options would require a change in evaporation/condensation conditions versus a simple change in flow or mixing, and eliminate the ones that don’t logically follow from opening pump "N"’s discharge.