🔍 Key Concepts

• double-effect distilling unit heat flow path between first and second effect • role of vapor from the first effect in multi-stage evaporation systems • difference between auxiliary steam heating and inter-effect heating

💭 Think About

• Trace how energy is reused from the first effect to the second effect in order to improve efficiency. What physically moves from the first effect to the second effect? • Ask yourself: is the second effect normally supplied with fresh steam again, or is it designed to use something that would otherwise be wasted from the first effect? • Consider which option represents a logical source of heat transfer that minimizes fuel/steam consumption in a multi‑effect evaporator.

✅ Before You Answer

• Verify which stream from the first effect is normally sent to the second effect in a double‑effect plant (brine, distillate, or vapor). • Check whether auxiliary steam is typically used once at the first effect or repeatedly at each effect in an efficient system. • Confirm which of the choices is actually hot enough and in the correct phase to provide significant heating to the brine in the second effect.