Evaporator Operation Under Vacuum Conditions

What would be the temperature of the product inside the evaporator?

An evaporator is operated at 15 in. Hg vacuum. What would be the temperature of the product inside the evaporator? Assume the product has the same boiling point as water. a. 100°C b. 50°C c. 25°C d. 0°C

Final answer:

The boiling point of water decreases under vacuum conditions. At 15 in. Hg vacuum, water's boiling point is lower than the standard 100°C, and the closest option provided is 50°C.

Explanation:

The boiling point of water varies with changes in pressure. At standard atmospheric pressure of 1 atm or 760 mmHg, the boiling point of water is 100°C. When an evaporator is operated under a vacuum, the pressure decreases. At 15 in. Hg vacuum, the pressure is significantly lower than 1 atm. To find the corresponding temperature for this reduced pressure, one can refer to a water vapor pressure chart.

Generally, water boils at lower temperatures under a vacuum because the vapor pressure needed for boiling is reached at a lower temperature. Given that 15 in. Hg vacuum is about a 50% reduction in atmospheric pressure (roughly equal to 0.5 atm), it is reasonable to expect the boiling point to be significantly lower than 100°C.

While an exact temperature is not given in the reference information provided, the choices tell us that the correct answer must be significantly lower than 100°C, but not at freezing temperature. Therefore, considering the options and the principles discussed, the most plausible temperature of the product inside the evaporator would likely be around option (b) 50°C.