Dalton’s Law of partial pressures considers a mixture of two or more gases, and states that the total pressure of the mixture is equal to the sum of the individual pressures, if each gas separately occupied the space.
A cubic metre of air contains 0.906 kg of nitrogen of specific gas constant 297 J/(kg K),
0. 278 kg of oxygen of specific gas constant 260 J/(kg K) and 0.015 kg of argon of specific gas constant 208 J/(kg K). What will be the total pressure at 20°C?
PV = mRT
V = 1 m3 so p = mRT
For the nitrogen pn = 0.906 x 297 x 293.15 = 78 881 Pa
For the oxygen pO = 0.278 x 260 x 293.15 = 21 189 Pa
For the argon pA = 0.015 x 208 x 293.15 = 915 Pa
Total pressure = 100 985 Pa
(1.009 85 bar)
The properties of refrigerant fluids at the pressures and temperatures of interest to refrigeration engineers exhibit considerable deviation from the ideal gas laws. It is therefore necessary to use tabulated or computer-based information for thermodynamic calculations.
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