Computes the water vapor volume fraction at equilibrium, i.e., when the rate of condensation of water vapor equals the rate of evaporation of liquid water or ice, depending on the temperature.

The water vapor volume fraction $$x_w$$ is computed with:

$x_w(p,T) = \frac{p_w(T)}{p}$

where

• $$p$$ is the pressure,

• $$T$$ is the temperature and

• $$p_w$$ is the water vapor saturation pressure at the given temperature.

This water vapor volume fraction corresponds to a relative humidity of 100%.

Parameters
Returns

quantity – Water vapor volume fraction.

Raises

ValueError – If equilibrium cannot be reached in the pressure and temperature conditions.

Notes

For some values of the pressure and temperature, the equilibrium does not exist. An exception is raised in those cases.