Question

Arrange the following temperature terms with reference to water/water vapor:
A. Dry-bulb temperature $(T_{D})$
B. Boiling temperature $(T_{B})$
C. Dew temperature $(T_{DW})$
D. Wet bulb temperature ($T_W$)
Choose the correct answer from the options given below:

• A. B, D, C, A
• B. A, B, C, D
• C. B, A, D, C
• D. A, B, D, C

Hint:

For any air that isn't raining (not 100% relative humidity), remember the "Descending Alphabet" of air: Dry-bulb $>$ Wet-bulb $>$ Dew-point ($T_D > T_W > T_{DW}$). Boiling is always the "hot" outlier at the top!

Answer 1

The Correct Option is C

Concept: Psychrometrics defines several temperatures related to the air-water vapor mixture. Their relative values depend on the saturation state of the air.

Step 1: Rank the temperatures for a standard unsaturated air-water system.

• B (Boiling temperature): $100^{\circ}C$ at 1 atm. This is the highest as it represents phase change of pure water.
• A (Dry-bulb temperature): The actual ambient air temperature measured by a standard thermometer.
• D (Wet-bulb temperature): The temperature reached by evaporating water into the air; it is lower than $T_D$ due to evaporative cooling.
• C (Dew temperature): The temperature at which the air becomes fully saturated and water begins to condense; it is the lowest of the three air temperatures unless the air is 100% saturated.

Step 2: Ordering.
The descending order is $T_B > T_D > T_W > T_{DW}$ (B, A, D, C).