Question

In the drying process, which of the following parameters is the same as the adiabatic saturation temperature:

• A. Absolute humidity
• B. Dew point
• C. Relative humidity
• D. Wet bulb temperature

Hint:

The wet bulb temperature represents the adiabatic saturation temperature, as both involve cooling due to evaporation without external heat exchange.

Answer 1

The Correct Option is D

Step 1: Understanding adiabatic saturation temperature. The adiabatic saturation temperature is the temperature at which air becomes saturated with water vapor through the evaporation process under adiabatic conditions (without heat exchange with the surroundings). 

Step 2: Relation to wet bulb temperature. The wet bulb temperature is the temperature measured by a thermometer covered with a wet cloth, where the evaporation of water cools the thermometer. Under adiabatic conditions, the wet bulb temperature equals the adiabatic saturation temperature. 

Step 3: Why other options are incorrect. 
- (A) Absolute humidity: Refers to the mass of water vapor in a given volume of air, unrelated to temperature. 
- (B) Dew point: The temperature at which air becomes saturated and condensation begins, different from the wet bulb temperature. 
- (C) Relative humidity: The ratio of the actual water vapor content to the maximum possible water vapor content at a specific temperature, not the same as the adiabatic saturation temperature.

Answer 2

The question asks which drying parameter is numerically the same as the adiabatic saturation temperature, the temperature air reaches when water evaporates into it with no outside heat added or removed. Let's check each parameter against that condition.

1. Absolute humidity: This measures the mass of water vapor present in a given volume or mass of air. It is a moisture content value, not a temperature at all, so it cannot equal a temperature reading.
2. Dew point: This is the temperature at which air becomes saturated purely by cooling it at constant moisture content, with no evaporation adding new water vapor. It is generally lower than the adiabatic saturation temperature except for air that is already saturated.
3. Relative humidity: This is a ratio, comparing the actual water vapor in air to the maximum it could hold at that temperature. Being a percentage rather than a temperature, it cannot be numerically equal to the adiabatic saturation temperature.
4. Wet bulb temperature: This is measured with a thermometer whose bulb is covered by a wet wick, so evaporating water cools the bulb until it reaches equilibrium. Under adiabatic conditions, this equilibrium temperature works out to be numerically the same as the adiabatic saturation temperature, because both describe air cooling purely through evaporation with no external heat exchange.

Since both the wet bulb reading and the adiabatic saturation temperature come from the same evaporative cooling process under adiabatic conditions, they end up numerically equal, unlike the moisture-content or ratio-based parameters in the other options.

So the correct answer is Wet bulb temperature.