What are wet bulb and dry bulb temperatures?

Q: What are wet bulb and dry bulb temperatures?

Krishna: Dry bulb temperature is the temperature of the air as measured by a standard thermometer, while wet bulb temperature is the temperature measured by a thermometer with its bulb covered in a wet cloth. The wet bulb temperature indicates how much the air can be cooled by evaporating water into it, and it's always lower than the dry bulb temperature unless the air is fully saturated (100% humidity).

Dry Bulb Temperature: This is the temperature that is commonly referred to as the air temperature.
It's measured by a standard thermometer, where the bulb is exposed to the air without any special covering. It reflects the actual heat content of the air.

The Dry Bulb Temperature refers basically to the ambient air temperature. It is called "Dry Bulb" because the air temperature is indicated by a thermometer not affected by the moisture of the air.

Dry-bulb temperature  can be measured using a normal thermometer freely exposed to the air but shielded from radiation and moisture. The temperature is usually given in degrees Celsius (^oC) or degrees Fahrenheit (^oF). The SI unit is Kelvin (K). Zero Kelvin equals to -273^oC.

Wet Bulb Temperature: The Wet Bulb temperature is the temperature of adiabatic saturation. This is the temperature indicated by a moistened thermometer bulb exposed to the air flow.This temperature is measured by a thermometer with its bulb covered by a wet wick or cloth. As water evaporates from the wet cloth, it cools the thermometer bulb, resulting in a lower temperature reading.
The wet bulb temperature indicates the lowest temperature achievable through evaporative cooling, which is affected by the humidity of the air. When the air is dry, evaporation happens quickly, and the wet bulb temperature is significantly lower than the dry bulb temperature.
When the air is humid, evaporation is slower, and the wet bulb temperature will be closer to the dry bulb temperature. In saturated air (100% humidity), no evaporation occurs, and the wet bulb and dry bulb temperatures are the same.

The Wet Bulb temperature is the temperature of adiabatic saturation. This is the temperature indicated by a moistened thermometer bulb exposed to the air flow.

And there is also another one: The dew point temperature.

Dew Point temperature: The Dew Point is the temperature at which water vapor starts to condense out of the air, the temperature at which air becomes completely saturated. Above this temperature the moisture will stay in the air.

If the dew-point temperature is close to the air temperature, the relative humidity is high, and if the dew point is well below the air temperature, the relative humidity is low.

If moisture condensates on a cold bottle from the refrigerator, the dew-point temperature of the air is above the temperature in the refrigerator.

The Dew Point temperature can be measured by filling a metal can with water and ice cubes. Stir by a thermometer and watch the outside of the can. When the vapor in the air starts to condensate on the outside of the can, the temperature on the thermometer is pretty close to the dew point of the actual air.

The Dew Point is given by the saturation line in the psychrometric chart.