Partial pressure of water vapour at dew point temperature of moist air is 1.5 × 10^-3 MPa. The barometric pressure is 0.1 MPa. The specific humidity of air is

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Question

This question was previously asked in

UPPSC AE Mechanical 2019 Official Paper II (Held on 13 Dec 2020)

Answer 1

Concept:

Specific humidity (ω) or Absolute humidity or humidity ratio:

Mass of water vapor in a unit mass of dry air usually expressed as grams of vapor (v) per kilogram of dry air (d.a).

It is also given by:

Pt = Pv + Pa

where, P_t= total pressure, P_v= partial pressure of vapour, P_a = partial pressure of air.

Calculation:

Given:

Pt = 0.1 MPa, Pv = 1.5 × 10-3 MPa.

ω = 9.47 gm/kg-da.