Question

Q5 A mixture of air and water vapour at 1.013 bar and 16 degree C has a dew
point of 5degree C. Calculate the relative and specific humidity’s?

Answer 1

Question #78813

A mixture of air and water vapour at 1.013 bar and 16 degree C has a dew point of 5 degree C. Calculate the relative and specific humidity’s?

Answer:

Define the saturation pressure from the saturated steam table:

$$P _ {s} (5 ^ {\circ} \mathrm {C}) = 872.6 \mathrm {Pa},$$ $$P _ {s} (16 ^ {\circ} \mathrm {C}) = 1818.8 \mathrm {Pa}.$$

The relative humidity is defined as:

$$\varphi = \frac {P _ {s} (5 ^ {\circ} \mathrm {C})}{P _ {s} (16 ^ {\circ} \mathrm {C})} = \frac {872.6}{1818.8} = 0.480 = 48\%.$$

The specific humidity is defined as:

$$x = \frac {P _ {s} (5 ^ {\circ} \mathrm {C})}{P - P _ {s} (5 ^ {\circ} \mathrm {C})} = \frac {872.6}{1.013 \cdot 10 ^ {5} - 872.6} = 0.00540 \mathrm {kg/kg}.$$

NOTE: you can find a saturation steam table at

https://www.nist.gov/sites/default/files/documents/srd/NISTIR5078-Tab1.pdf

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