Question

At 65% relative humidity, dry bulb temperature will be

• A. Equal to dew point temperature
• B. Less than wet bulb temperature
• C. Greater than wet bulb temperature
• D. Equal to wet bulb temperature

Hint:

Always remember the inequality for unsaturated air ($\%\text{RH} < 100$): $\text{DBT} > \text{WBT} > \text{DPT}$. They only become equal at 100% saturation.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Psychrometrics describes the thermodynamic properties of moist air. For any unsaturated air condition (relative humidity \(< 100\%\)), evaporative cooling depresses the wet bulb temperature below the dry bulb temperature.
Key Formula or Approach:
\[ \text{For } \text{RH} \text{WBT} > \text{DPT} \]
\[ \text{For } \text{RH} = 100\%: \quad \text{DBT} = \text{WBT} = \text{DPT} \]

Step 2: Detailed Explanation:
For air at 65% relative humidity (unsaturated air):
- Dry Bulb Temperature (DBT) is the true sensible ambient temperature.
- Wet Bulb Temperature (WBT) is lowered below DBT due to evaporative cooling of water from the wetted wick.
- Dew Point Temperature (DPT) is the lowest temperature at which condensation begins.
Therefore, at 65% RH, the dry bulb temperature is strictly greater than the wet bulb temperature.

Step 3: Final Answer:
Hence, dry bulb temperature will be Greater than wet bulb temperature, corresponding to option (C).