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Thermodynamics Interaction Studies Solids, Liquids and Gases Part 2

Tham khảo tài liệu 'thermodynamics interaction studies solids, liquids and gases part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 50 Thermodynamics - Interaction Studies - Solids Liquids and Gases wide range of conditions in the so called perfect gas approximation are connected by an equation of the form pV mRT 1 where p is pressure Pa V is volume m3 m is mass kg T is temperature K and R is the specific gas constant whose value depends on the gas. If we express the amount of substance in terms of number of moles n m M where M is the gas molecular weight we can rewrite 1 as pV nR T 2 where R is the universal gas costant whose value is 8.3143 J mol-1 K-1. In the kinetic theory of gases the perfect gas is modelled as a collection of rigid spheres randomly moving and bouncing between each other with no common interaction apart from these mutual shocks. This lack of reciprocal interaction leads to derive the internal energy of the gas that is the sum of all the kinetic energies of the rigid spheres as proportional to its temperature. A second consequence is that for a mixture of different gases we can define for each component i a partial pressure pi as the pressure that it would have if it was alone at the same temperature and occupying the same volume. Similarly we can define the partial volume Vi as that occupied by the same mass at the same pressure and temperature holding Dalton s law for a mixture of gases i p ỵ pi 3 Where for each gas it holds piV niR T 4 We can still make use of 1 for a mixture of gases provided we compute a specific gas constant R as fl s i 5 m K 7 The atmosphere is composed by a mixture of gases water substance in any of its three physical states and solid or liquid suspended particles aerosol . The main components of dry atmospheric air are listed in Table 1. Gas Molar fraction Mass fraction Specific gas constant J Kg-1 K-1 Nitrogen N2 0.7809 0.7552 296.80 Oxygen O2 0.2095 0.2315 259.83 Argon Ar 0.0093 0.0128 208.13 Carbon dioxide CO2 0.0003 0.0005 188.92 Table 1. Main component of dry atmospheric air. The composition of air is constant up to about 100 km while higher .