E3.11 Moist Air Properties

Example 3.11: Calculate moist air properties given dry-bulb temperature (t) 100 °F, wet-bulb temperature (t*) 80 °F, and pressure 29.921 in Hg. Use Mollier Diagram.

Solution: Dry-bulb temperature, t = 100 °F, Wet-bulb temperature, t^* = 80 °F.

Humidity ratio at saturation, W_s^* :

Draw a vertical line from wet bulb temperature, 80 °F till it intersects the saturation line.

Draw a horizontal line and extend it to read humidity ratio, W_s^* = 0.022 pound of water per pound of dry air.

Absolute humidity ratio, W:

Locate the point that describes the actual condition of air (100 °F dry-bulb, and 80 °F wet-bulb temperature).

Draw a horizontal line to read, W = 0.0175 pound of water per pound of dry air.

Humidity ratio at saturation W_s:

Draw a vertical line from a point representing the dry-bulb temperature.

Extend this line till it intersects the saturation line.

Draw a horizontal line to read the humidity ratio, W_s = 0.043 pound of water per pound of dry air.

Relative humidity, φ = 42%.

Volume of humid air, υ: = 14.5 ft³/lb.

Enthalpy of the humid air, h:

Read the enthalpy of saturated air at wet-bulb temperature = 43.6 Btu/lb

Read the residual enthalpy of actual air = -.024

h = 43.6 - 0.24 = 43.36 Btu/lb

Dew point can be found by drawing a horizontal line from a point representing the humid air and reading the saturation temperature, t_d.

t_d.=