Wet bulb temperature is the temperature recorded by a thermometer covered with a wet cloth, indicating the ease of water evaporation. It is crucial for understanding humidity levels and human comfort, as high wet bulb temperatures can impede the body's ability to cool itself. The measurement is typically done using a sling psychrometer, which compares wet and dry bulb temperatures.

1. Wet Bulb Temperature
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 Definition
 Why the term- “Wet Bulb” (WB)
 Define a Bulb
 Define a Wick
 Applications
 How it is measured
 WBT in a Psychrometric Chart

2. What is Wet Bulb Temperature
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 Wet Bulb Temperature is defined as the temperature
measured by the Thermometer whose Bulb is covered
by a wet cloth or wick.
 Lowest Temperature that can be reached by the
evaporation of water only.
 Wet Bulb Temperature tells you how easy it is for water
to evaporate.

3. Why the term- Wet Bulb
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 Originates from a device called “Sling Psychrometer”,
consisting of two thermometers usually mercury or alcohol
types, secured on a common base with a swivel handle at one
end.
 The thermometers are identical except that one has a gauze
sock on the bulb that is saturated with clear, clean, often
distilled water. Hence, the term, “Wet Bulb” or “WB”.
 The other thermometer, appropriately called the dry bulb
(“DB”) thermometer, simply registers the air temperature
without any humidity effects.(Dry bulb is the temperature
measured by ordinary thermometer)
 A low Wet Bulb and high Dry Bulb means low humidity levels.

4. What is a Bulb
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 The bulb is the lowest part of the thermometer,
which has a spherical shape. This section of the
thermometer acts as a reservoir to hold mercury -
- a silvery colored, heavy metal on the periodic
table of elements.
 Mercury stays in liquid form when it is in an
enclosed container, and maintained at room
temperature. Like other liquids, metallic mercury
expands in response to heat. If the temperature
is sufficiently high, mercury in the bulb moves up
the capillary.

5. Why a Wick
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 Wick is used to reduce the temperature recorded
by evaporation of water. It indicates the amount of
evaporative cooling.
 Material of Wick is an absorbent mainly a Cotton.

6. Applications
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 Humans sweat by means of evaporation normally, when you want to know how well water will
evaporate, you need to know the difference between the wet bulb and dry bulb temperatures , if the
difference is 0 there will be no evaporation and no heat transfer could occur between skin and
ambient
 Humans have an internal body temperature of approximately 98.6 degrees Fahrenheit and cannot
tolerate a wet-bulb temperature above 95 degrees for longer than six hours. Humans cool
themselves through the skin. Internal heat can dissipate when the external temperature is cooler
than internal body temperature. But when the external wet-bulb temperature is 95 degrees or
above, the body can't cool itself.
 Wet bulb temperature is used to measure the temperature of air in saturated state.
 If the relative humidity is low the water on the wet bulb will evaporate rapidly and the wet bulb
temperature will drop.

7. How it is Measured
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 Device for measuring WBT is Sling Psychrometer,
which consists of a pair of mercury bulb thermometers,
one with a wet "sock" to measure the wet-bulb
temperature and the other with the bulb exposed and
dry for the dry-bulb temperature.
 Wet Bulb temperature is expressed in Degree Celsius
or Degree Fahrenheit. (deg C or deg F)

8. WBT in Psychrometric Chart
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9. Solve the quiz
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Use Standard Pyschrometric Chart to solve.

10. Thank You
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