Question

Specific humidity (ω) is represented by: (where, p = p_a + p_v : p_a is pressure of dry air and p_v is pressure of water vapour)
1. \(\omega = 0.622 \frac{p_a}{p}\)
2. \(\omega = 0.622 \frac{p_v}{p-p_v}\)
3. \(\omega = 0.622 \frac{p_v}{p}\)
4. \(\omega = 0.622 \frac{p_a}{p-p_a}\)

Answer 1

Correct Answer - Option 2 : \(\omega = 0.622 \frac{p_v}{p-p_v}\)

Concept:

 

Humidity ratio/Specific humidity (ω ) (kg/kg) of a given moist air sample is defined as the ratio of the mass of water vapour (mw) to the mass of dry air (ma) contained in the sample.

\(w = \frac{{{m_w}}}{{{m_a}}} = 0.622\frac{{{P_v}}}{{P - {P_v }}} \)

where p = pa + pv ,  pa is the pressure of dry air and pv is the pressure of water vapour/

Relative humidity (ϕ):

It is defined as the ratio of the partial pressure of water vapour (pv)in a mixture to the saturation pressure (ps) of pure water at the same temperature of the mixture.

\(\phi = \frac{{{p_v}}}{{{p_{vs}}}}\)