Humidity & Types

Humidity Types

There are four types of humidity that are important to understand:

• Humidity (General)
• Absolute Humidity
• Relative Humidity
• Body Humidity
• Humidity Deficit

Humidity

• The amount of water vapor in the atmosphere, involving the kinetic energy of molecules in the air.

Absolute Humidity

• The actual weight or amount of water vapor in the air, representing the actual water vapor content.
• Essential for solving problems related to humidity.
• Measured by weighing the water vapor extracted from air.
• Can be fully saturated or partially saturated.
• Air is fully saturated with water vapor at 37 degrees Celsius and 760 millimeters of mercury, which is equivalent to 43.8 milligrams per liter.
• Commonly measured in milligrams of water vapor per liter (mg/L).
• When temperature increases, the water vapor content also increases.

Saturated vs. Unsaturated Air

• A gas doesn't have to be fully saturated with water vapor.
• If air is 50% saturated, its water vapor pressure and absolute humidity are half of the fully saturated state.
• Air is fully saturated at 37°C and 760 mmHg, with:
  • Water vapor pressure: 47
  • Absolute humidity: 43.8 mg/L (the maximum value on the reference chart)
• Example: If air is 50% saturated, then
  • Water vapor pressure: 0.50 \times 47 = 23.5 (units not specified in transcript)
  • Absolute humidity: 0.50 \times 43.8 = 21.9 mg/L

Calculating Absolute Humidity

• Absolute\ Humidity = (%\ Saturated) \times (Water\ Vapor\ Content)
• Where the Water Vapor Content for 100% saturation is 43.8 \frac{mg}{L}.
• Example:
  • If saturation is 50%:
    0.50 \times 43.8 \frac{mg}{L} = 21.9 \frac{mg}{L}

Temperature and Water Vapor Content

• As temperature goes up, well, your water vapor content is also gonna go up. Because of the video that we just see, the pressure above, you know, the you have the the the liquid, and then you have the pressure above it, and that should increase the heat, and that's just gonna get more and more in there. It's gonna continue to go up.
• When the temperature increases, all the air molecules expand. As they expand, more space is created within this area. So we can store more water vapor in this area.
• If you had a tent at 27 degrees Celsius, well, you'd go over here, and you would use 25.75 milligrams per liter as your value.

Relative Humidity

• Expressed when a gas is not fully saturated; it uses relative terms.
• It is the ratio of the actual water vapor content to its saturated capacity at a given temperature.

Formula:

• Relative\ Humidity\ (%) = \frac{Content}{Capacity} \times 100
• To determine capacity, refer to a chart based on temperature.
• Example: At 20°C, capacity is 17.3 mg/L.
  • If absolute humidity (content) is 12 mg/L, then:
    Relative\ Humidity = \frac{12}{17.3} \times 100 = 69\%

Body Humidity

• The ratio of actual water vapor content to the water vapor capacity in a saturated gas at body temperature.
• If a question mentions body temperature, it relates to body humidity.
• When trying to work out body humidity, well, the capacity is always gonna be fixed at 43.8. Why is it gonna be fixed at 43.8? Because if you go to that chart, Go over that chart there. See again, 43.8 is maxed water vapor content.

Body Humidity Calculation

• Body \ Humidity = \frac{Actual \ Water \ Vapor \ Content}{43.8}
• Capacity is fixed at 43.8, which is the maximum water vapor content at body temperature.

Humidity Deficit

• Involves a fixed capacity of 43.8.

Key Points for Calculations:

• For body humidity and humidity deficit problems, use the fixed value of 43.8.
• For relative and absolute humidity, you may need to refer to a chart to find values based on temperature.

Additional Concepts

Content vs. Capacity

• Capacity: How much water vapor it can hold. A 100% saturated where it's it's at its max capacity.

Relative Humidity at 100%

• When relative humidity is 100%, the gas is fully saturated with water vapor.
• The water vapor content of a volume of gas equals its capacity.
• Example: If 20 degrees Celsius has a capacity of 17.3 milligrams per liter. If your relative humidity is a 100%, well, what if it's what if 20 degrees Celsius has a capacity, you know, of 17.3 milligrams per liter?

Absolute Humidity

• Measured in grams, represents the actual amount of water vapor in a given volume.
• Example: 10 grams of water vapor in one cubic meter means absolute humidity is 10 grams per cubic meter.

Relative Humidity

• Expressed as a percentage, indicating the degree of saturation.
• Example: If one cubic meter can hold up to 20 grams of water vapor, but only has 10 grams, the relative humidity is 50%.
• Heating air increases its capacity to hold water vapor, decreasing relative humidity.
• Cooling air decreases its capacity, increasing relative humidity.