Question

What is the enthalpy of moist air at 70°F (20°C) and 75 percent relative humidity for an elevation of (a) sea level and (b) 5000 ft (1525 m).

Answer 1

The enthalpy of moist air is the sum of the enthalpy of dry air and the enthalpy of water vapor. Vapor pressure of water at 20.0°C is about 2.34 kPa, which corresponds to approximately 2.31% of atmospheric pressure. At 100% relative humidity, 20.0°C air contains approximately 17.3 g of water vapor per kg of dry air.

Step-by-step explanation:

The enthalpy of moist air is the sum of the enthalpy of dry air and the enthalpy of water vapor.

To calculate the enthalpy of moist air, we can use the psychrometric chart or equations.

However, the given question does not provide sufficient information to calculate the enthalpy directly.

Instead, it asks about the vapor pressure of water at 20.0°C, the percentage of atmospheric pressure it corresponds to, and the percentage of 20.0°C air that is water vapor at 100% relative humidity.

These concepts are related to understanding the properties of moist air.

1. Vapor Pressure of Water at 20.0°C: The vapor pressure of water at 20.0°C is 2.34 kPa.
2. Percentage of Atmospheric Pressure: At 20.0°C, the atmospheric pressure is approximately 101.3 kPa. So, the vapor pressure of water at 20.0°C corresponds to about 2.31% of the atmospheric pressure.
3. Percentage of 20.0°C Air that is Water Vapor at 100% Relative Humidity: If the air has 100% relative humidity at 20.0°C, it means the air is saturated with water vapor.
4. At saturation, the air contains the maximum amount of water vapor it can hold at that temperature.
5. By looking at humidity tables or psychrometric charts, we can determine that 20.0°C air with 100% relative humidity contains approximately 17.3 g of water vapor per kg of dry air.