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The equation of state for moist unsaturated air. The state of a sample of moist air is characterized by its: Pressure, p. Absolute temperature, T. Density, ρ (or specific volume α = 1/ρ), and. Some measure of its moisture content, e.g. The water vapour mixing ratio, r, defined as the mass of water vapour in the sample per unit mass of dry air.
The density of moist air is evaluated using an equation of state ρ a = pM a ZRT 1 −x ν 1 − M ν M a, (1) where the quantities and units are p/Pa: pressure, t/ C: air temperature, T/K: thermodynamic temperature = 273.15 + t/ C, x v: mole fraction of water vapour, M a/(gmol −1): molar mass of dry air, M v/(gmol−1): molar mass of
26 Μαρ 2019 · Chapter 7 – Moist Air • Equivalent and Wet-Bulb Temperatures • Consider a closed system of dry air, water vapor (moist air), and water (or ice). • The enthalpy of the system can be written as • where we have made use of lv(T) = hv – hwand mt = mv + mw.
Equation of state for moist (or total) air pa = ρ a Rm T = ρ aR T′ v (2.30) Gas constant for moist air (2.31) R m = R ′ 1 + ω v ε 1 + ω v = R ′ 1 + 1 − ε ε q v = R ′ (1 + 0.608q v ) Virtual temperature (2.32) Temperature of dry air having the same density as a sample
When vapor content increases in moist air the amount of Oxygen and Nitrogen are decreased per unit volume and the density of the mix decreases since the mass is decreasing. dry air is more dense that humid air! Based on specific volume of moist air the moist air density can be calculated. ρ = 1 / v.
5 Ιουν 2012 · We will call the system consisting of dry air and water vapor “moist air” and it can be unsaturated or saturated with water vapor. Since liquid water is absent, moist air is a two-component system with one phase present. As such, according to equation (6.1) we need three state variables to specify the system's state.
Equation of state for moist air • commonly used in atmospheric thermodynamics: – water vapor pressure (e) : the partial pressure due to water vapor molecules. (How could this be measured? We will see later that it can be determined theoretically/analytically with the Clausius-Clapeyron equation.) – mixing ratio : rv = mv/m d