ANS:C - Wet bulb temperature

The wet bulb temperature is a thermodynamic property of moist air that represents the lowest temperature that can be reached by evaporative cooling of the air at constant pressure and with the addition of water vapor. It is one of the key parameters used in psychrometrics, the study of the physical and thermal properties of moist air. Here's how the wet bulb temperature is determined and its significance:

1. Measurement Method: The wet bulb temperature is typically measured using a thermometer with its bulb covered by a wetted wick or cloth. The thermometer is exposed to the moving air, and the moisture on the wetted surface evaporates, cooling the thermometer bulb. The temperature reading obtained under these conditions is the wet bulb temperature.
2. Evaporative Cooling: The wet bulb temperature represents the temperature to which the air can be cooled by evaporation alone, under adiabatic conditions (no heat exchange with the surroundings). As water evaporates from the wetted surface, it absorbs heat from the air, reducing its temperature. The rate of evaporation depends on factors such as air velocity, humidity, and the temperature difference between the wet bulb and dry bulb temperatures.
3. Indication of Moisture Content: The wet bulb temperature provides information about the moisture content of the air. If the wet bulb temperature is close to the dry bulb temperature, it indicates that the air is close to being saturated with moisture and has a high relative humidity. Conversely, if there is a significant difference between the wet bulb and dry bulb temperatures, it suggests that the air is relatively dry.
4. Psychrometric Charts: Wet bulb temperature readings are often used in conjunction with dry bulb temperature readings to plot points on psychrometric charts, which provide a graphical representation of the thermodynamic properties of moist air. These charts are valuable tools for engineers and HVAC professionals to analyze and design air conditioning and refrigeration systems, as well as to assess the comfort conditions in indoor environments.