Question

6. Moist air with a dbt of 40c has a relative humidity of 50%. Atmospheric pressure is 1.01bar. The saturation pressure of vapour at 40c is 7.38kpa & saturation pressure of vapour at 150c is 4.578bar. Find (i) specific humidity. (ii) moist air as stated above is compressed to 5.05 bar & its corresponding dbt is 150c, then find the relative humidity of compressed air.

Answer 1

Answer:

Patm = 101 kPa

Tsat = 400C

Psat = 7.384 kPa

\(\phi_1\) = 0.5 = \(\frac{P_v}{P_{sat}}=\frac{P_v}{7.384}\)

\(P_{v_1}\) = 3.692

\(\omega\) = 0.622\(\frac{P_v}{P_{atm}-P_v}\)

   = 0.622\(\times \frac{3.692}{101-3.692}\)

\(\omega_1\)= 0.0236\(\frac{kg \ Vap}{kg \ da}\)

As the moist air is compressed, the specific humidity is unaffected.

i.e., \(\omega_1=\omega_2\)

0.0236 = 0.622\(\frac{P_{V_2}}{505-P_{V_2}}\)

\(P_{V_2}\) = 18.46 kPa

\(\phi_2\) = \(\frac{P_{V_2}}{P_{sat}}\) = \(\frac{18.46}{475.8}\times\)100 = 3.9%.

Explanation: