12 Questions
What does the temperature represent on a psychrometric chart?
Horizontal axis
What does the CDE curve on a psychrometric chart represent?
Saturation humidity
At what point on a psychrometric chart is the air completely saturated with moisture?
Dew point C
What does point A (81°F) on a psychrometric chart represent?
Air not completely saturated used for drying purposes
What does the FCA dotted line on a psychrometric chart represent?
Absolute humidity relationship between T and P.
What does the dew point represent on a psychrometric chart?
Temperature of air-water vapor mixture cooled to saturation
What does the relative saturation (percent relative humidity) represent?
The ratio of the partial pressure of water vapor in the air to the vapor pressure of free water at the same temperature
Which of the following is true about the GK curve with 50% relative humidity?
It represents the relationship between temperature and relative humidity
What happens when air at point A (81°F) is used to dry a wet material?
The difference in vapor pressure between the surface water and the air leads to the liquid evaporating, which may cool the surface below the air temperature
What is the definition of wet-bulb temperature?
The equilibrium of heat transfer between air and liquid
How is the wet-bulb temperature measured?
By a thermometer with the bulb covered by a wick saturated with water
What is the purpose of measuring the dry-bulb temperature?
To measure the actual air temperature
Study Notes
Psychrometric Chart
- Represents the relationship between temperature and humidity of air-water vapor system at constant pressure
- Temperature is on the horizontal axis, and absolute humidity (weight of water vapor per unit weight of dry air) is on the vertical axis
Saturation Humidity (CDE Curve)
- Represents the saturation humidity at which partial pressure of water vapor = vapor pressure of free water at the same temperature
- Air is completely saturated with moisture (100% relative humidity) and humidity doesn't change when in contact with liquid water at the same temperature
Dew Point
- Temperature at which air-water vapor mixture becomes saturated (maximum amount of moisture without condensation)
- Cooling below dew point causes water vapor to condense into a two-phase system of saturated air and droplets of free water
Relative Saturation (RH)
- Represents the ratio of partial pressure of water vapor in air to vapor pressure of free water at the same temperature
- Can be calculated by dividing absolute humidity (FCA) by saturation humidity (CDE) at the same temperature
Wet-Bulb Temperature
- Occurs when air is used to dry a wet material, leading to evaporation of liquid and cooling of the surface
- Measured by a thermometer with a bulb covered by a wick saturated with water
- Represents the equilibrium of heat transfer between air and liquid, with heat transferred from air to liquid at a rate proportional to the temperature difference
Test your knowledge on the psychrometric chart which shows the relationship between temperature and humidity in an air-water vapor system at constant pressure. Learn about the CDE curve representing saturation humidity and its significance in determining air conditions.
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