Question 119General Subjects - Assistant Engineer

The correct answer is D) evaporation is accomplished in a vacuum. Low-pressure evaporators operate in a vacuum, which lowers the boiling point of the feed water. This allows the water to evaporate at a lower temperature compared to high-pressure evaporators. Evaporating at a lower temperature results in less scale formation, as the solubility of dissolved salts is higher at lower temperatures. Additionally, the vacuum reduces the energy required for evaporation, making the process more efficient. The other options are incorrect because they do not directly address the key reason for the improved efficiency and reduced scale formation in low-pressure evaporators. The temperature of the incoming feed (A) and the latent heat of evaporation (B) are not the primary factors, and evaporation in a submerged medium (C) is not a characteristic of low-pressure evaporators.