Question

The pressure, dry bulb temperature and relative humidity of air in a room are 1 bar, ${30}^{\circ }C$ and 70%, respectively. If the saturated steam pressure at ${30}^{\circ }C$ is 4.25 kPa, the specific humidity of the room air in kg of water vapour/kg dry air is

• A. 0.0083
• B. 0.0101
• C. 0.0191
• D. 0.0232

Answer 1

The correct option is C 0.0191

$p_{\text{atm}}=1\text{bar}=100\text{kPa}$

$DBT={30}^{\circ }C$

Relative humidity,
$\varphi =70\%=0.7$

$p_{vs}=4.25\text{kPa}$

Specific humidity : $\omega =?$

$\varphi =\frac{p_v}{p_{vs}}$

$0.7=\frac{p_v}{4.25}$

$p_v=2.975\text{kPa}$

Specific humidity,
$\omega =0.622\times \frac{p_v}{p-p_v}$

$=0.622\times \frac{2.975}{100-2.975}$

$=0.0191\text{kg w.v./kg d.a}.$