A
AAAS AASE Ablation ABSOLUTE EFFICIENCY ABSOLUTE PRESSURE ABSOLUTE TEMPERATURE ABSORPTIVITY ACCELERATION PRESSURE GRADIENT ACCIDENTS TO CHEMICAL PLANT Accommodation coefficient Acentric factor ACETIC ACID ACETONE ACETYLENE COMBUSTION ACHE'S ACID RAIN ACID VIOLET 19, MONOMETHYL ACKERMANN CORRECTION FACTOR ACOUSTIC CAVITATION ACOUSTIC FIELDS ACOUSTIC FLOWMETERS ACOUSTIC INSTABILITIES ACOUSTIC VIBRATION ACOUSTIC WAVES ACOUSTICS OF BONE ACRYLIC CATION RESINS, ACRS Activity coefficient ADAPTIVE GRIDS ADAPTIVE TWO-DIMENSIONAL MESH REFINEMENT METHOD Added mass ADDITIVES ADENOSINE TRIPHOSPHATE, ATP ADHESION BETWEEN LIQUIDS Adiabatic conditions ADIABATIC DISC TEMPERATURE ADIABATIC EXPONENT ADIABATIC PROCESSES ADIABATIC SATURATION TEMPERATURE ADIABATIC SHEAR BAND ADIABATIC THROTTLING Adiabatic wall temperature ADSORBATE ADSORBENT ADSORBERS Adsorption ADSORPTION OF GASES ADSORPTIVE BUBBLE TECHNIQUES ADSUBBLE TECHNIQUES ADVANCED BOILING WATER REACTOR, ABWR Advanced gas-cooled reactor AEA TECHNOLOGY AELOPILE OF HERO AERATION AERODYNAMIC COEFFICIENTS AERODYNAMIC EFFICIENCY AERODYNAMIC FLOW SPECTRUM AERODYNAMIC RESISTANCE OF ATMOSPHERE Aerodynamics AEROGELS AEROGENERATORS AEROSOL FILTRATION Aerosols AEROSOLS, CLIMATIC EFFECTS AFTERBURNING AGGLOMERATES Agglomerates and complex shape particles AGGLOMERATION OF PARTICLES AGITATED VESSEL HEAT TRANSFER AGITATED VESSEL MASS TRANSFER AGITATED VESSELS AGITATION CAVITATION NUMBER AGITATION DEVICES AGR AICHE AIR (PROPERTIES OF) AIR CARRYUNDER AIR CONDITIONING AIR COOLED CONDENSERS AIR COOLED HEAT EXCHANGERS AIR COOLERS AIR CUSHIONS AIR CYCLE HEAT PUMPS AIR CYCLE REFRIGERATION AIR EJECTOR AIR JET ENGINES AIR POLLUTANTS AIR POLLUTION AIR SPRAYS AIR-TO-AIR HEAT PUMPS AIR-TO-WATER HEAT PUMP AIR-WATER SYSTEM AIRCRAFT, AERODYNAMICS OF AIRCRAFT, PARABOLIC FLIGHTS AIRLESS DRYING AISI AL-SI PHASES FORMED FROM COMBUSTIBLE SOLID RESIDUES Albedo ALBEDO, OF EARTH ALCOHOL ALDEHYDES ALFVEN NUMBER ALFVEN WAVES ALGEBRA, FUNDAMENTAL THEOREM OF ALIGNED MAGNETIC FIELD ALIPHATIC HYDROCARBONS ALKANES ALLEN FLOW ALLOY SOLIDIFICATION ALLOY STEELS ALLOYS ALPHA PARTICLES ALTERNATIVE ENERGY SOURCES Alternative formulations ALUMINA ALUMINOSILICATE ZEOLITES ALUMINUM ALUMINUM COMBUSTION ALUMINUM OXIDE AMAGAT'S LAW AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE, AAAS AMERICAN INSTITUTE FOR CHEMICAL ENGINEERS, AICheE AMERICAN IRON AND STEEL INSTITUTE, AISI AMERICAN PETROLEUM INSTITUTE, API AMERICAN SOCIETY OF HEATING, REFRIGERATION AND AIR-CONDITIONING ENGINEERS, ASHRAE, INC AMERICAN SOCIETY OF MECHANICAL ENGINEERS, ASME AMMONIA COMBUSTION AMMONIUM NITRATE FERTILIZER AMMONIUM PERCHLORATE AMORPHOUS AND NANOSTRUCTURED SILICON FILMS AMPLIFIED SPECTRUM ANABOLISM ANALOGY BETWEEN HEAT AND MASS TRANSFER ANALYTICAL TREATMENT OF FINS WITH TEMPERATURE-DEPENDENT SURFACE HEAT FLUX ANEMOMETERS (LASER DOPPLER) ANEMOMETERS (PULSED THERMAL) ANEMOMETERS (VANE) ANEROID BAROMETER ANGLED TURBULATORS Angular discretization methods ANL ANNEALING ANNULAR DISPERSED FLOW ANNULAR FIXED BEDS Annular flow ANNULAR FLOW SYSTEM ANNULAR FLOW, IN LIQUID-METAL BOILING ANNULAR PIPES ANNULAR POROUS MEDIUM ANODE Anomalous diffraction ANTI-FREEZE ANTI-NEUTRINO ANTIDERIVATIVE FUNCTION ANTIGRAVITY ANZAAS API API GRAVITY Application to nongray media Application to rough surfaces Applications of inverse radiation analysis APPLICATORS Applied problems AQUEOUS SOLUTIONS WITH NONLINEAR SURFACE ENERGY AQUIFER ARC DYNAMIC ARCHIMEDES FORCE ARCHIMEDES NUMBER ARCHIMEDES PRINCIPLE ARGON ARGON-ION LASER ARGONNE NATIONAL LABORATORY, ANL ARMAND CORRELATIONS, FOR VOID FRACTION IN ANNULAR FLOW ARMORED VEHICLE CABIN AROMATIC CHEMICALS, OR AROMATICS AROMATIC HYDROCARBONS ARRHENIUS EQUATION ASCENDING SLUG FLOW IN A VERTICAL PIPE ASH FORMATION ASH LAYER MODEL ASHRAE ASME ASPECT RATIO ASSOCIATE CATALYSIS Association for Applied Solar Energy, AASE ASYMMETRIC HEATING ASYMPTOTE ASYMPTOTIC EXPANSION ASYMPTOTIC METHODS ATMOSPHERE ATMOSPHERE (PHYSICAL PROPERTIES OF) ATMOSPHERIC PRESSURE GLOW DISCHARGE ATOM ATOMIC ENERGY AUTHORITY ATOMIC HYDROGEN BEAM ATOMIC MEDIA ATOMIC NUMBER ATOMIC PORES ATOMIC SPECTROSCOPY ATOMIC SURFACE DIFFUSION ATOMIC WEIGHT ATOMISTIC DEFORMATION ATOMISTIC-CONTINUUM ADAPTIVITY ATOMISTIC-TO-CONTINUUM COUPLING ATOMIZATION ATOMIZATION TURBULENT ATOMIZERS ATOMIZING LIQUIDS ATOMIZING SPRAY ATTENUATION COEFFICIENT, PHOTON TRANSMISSION ATTENUATION, OPTICAL ATTRACTORS AUGMENTATION OF HEAT TRANSFER, SINGLE PHASE AUGMENTATION OF HEAT TRANSFER, TWO-PHASE AUSTENITE-MARTENSITE TRANSFORMATION Australian and New Zealand Association for the Advancement of Science, ANZAAS AUTO CORRELATION AUTO-IGNITION AUTOMATIC SAMPLING AUTOMOTIVE GAS TURBINES Available data for molecules of practical interest AVERAGE FILM FLOW RATE MEASUREMENT AVERAGE PHASE VELOCITY AVERAGE VOID FRACTION MEASUREMENT AVIATION FUEL-AIR REACTION AVOGADRO NUMBER AVOGADRO'S LAW AXIAL FLOW COMPRESSOR AXIAL FLOW FANS AXIAL TURBINE AXISYMMETRIC JET AXISYMMETRIC NARROWING AZEOTROPES D'ALEMBERT PARADOX
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AIR (PROPERTIES OF)

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Atmospheric air is a mixture of nitrogen and oxygen being the earth atmosphere. Main components of air which are practically the same throughout the globe are nitrogen (78.08 volume per cent) and oxygen (20.95 v.%). Along with them air contains 0.94 v.% of inert gases and 0.03 v.% of carbon dioxide. The air of such a composition is named dry. Its molecular mass is regarded to be M = 28.96 g/mole.

In the lower atmosphere strata the air contains also water vapor, its concentration is substantially variable depending on the partial water vapor pressure at the appropriate temperature and relative humidity. For instance at 20°C and relative humidity 80% air contains about 0.02 v.% of water vapor. In the air layers adjacent to the earth surface other components may be present being in most cases of antropogenic origin.

At ambient pressure and temperature air can be regarded as a perfect gas, its properties may be described by equations:

where v denotes specific volume; u is specific internal energy; R is the gas constant for air.

At low temperatures the air is liquified. The normal (at 0.1013 MPa) boiling (condensation) temperature of the oxygen is equal— 183°C, that of the nitrogen -195.8°C. Liquid air at atmospheric pressure behaves practically as an ideal solution following the Raoult's Law. The normal condensation temperature of air is -191.4°C, the normal boiling temperature -194°C.

At elevated temperatures air undergoes some physicochemical transformations. The nitrogen reacts with oxygen producing various oxides: N2O, NO, NO2, NO3. Their equilibrium concentration can be derived from the isotherm equations of the respective reactions.

At temperatures higher than 2000 K and moderate pressures the nitrogen and oxygen start to dissociate, and at temperatures exceeding 4000 K and atmospheric pressure the ionization of oxygen, nitrogen, and other components becomes evident. This implies the transition of air into the plasma state. The equilibrium dissociation degree can be calculated according to the Saha equation.

The thermodynamic properties of air along the saturation curve are given in Table 1; these properties for the liquid and gaseous air—in Table 2.

Table 1. Thermodynamic properties of air along the saturation curve

Table 2. Thermodynamic properties of liquid and gaseous air

The enthalpy is taken as zero at an arbitrary point. The entropy is taken zero for the solid air at 0K.

Air is a mixture mainly consisting of diatomic gases. Therefore its heat capacity at close to normal temperatures and pressures may with good accuracy be taken equal to

where

With increasing temperature the heat capacity slightly increases due to exciting of the vibrational degrees of freedom in the oxygen and nitrogen molecules. Table 3 gives air heat capacity values for a wide range of temperatures and pressures.

Table 3. Air heat capacity cp, KJ/kg · K

As for all pure substances in the supercritical region, the isobars and isotherms of the heat capacity cp have maximums the steeper the closer to the critical point.

The temperature dependence of the viscosity of air is qualitatively the same as for pure substances: in the liquid phase the viscosity decreases with temperature following an approximately exponential function; in the gas phase at low pressures the viscosity increases according to equation:

with increasing pressure at constant temperature the viscosity increases. This dependence is most strong in the vicinity of the critical point. Air viscosity values at various temperatures and pressures are given in Table 4.

Table 4. Air viscosity η · 107, N · s/m2

The behavior of the thermal conductivity of air is similar to the viscosity: in the liquid phase with growing temperature the heat conductivity decreases whereas in the gas phase-increases. At low pressures the temperature dependence is described by the equation:

Along the isotherm with increasing pressure the thermal conductivity increases. In Table 5 the air thermal conductivity is given at various temperatures and pressures.

Table 5. Air thermal conductivity λ · 103, W/m · K

At low pressures and high temperatures the thermal conductivity sharply increases due to dissociation. With growing temperature the thermal conductivity goes through maximums which are connected with maximum heat transfer by the heats of respective reactions. Thermal conductivities of air at dissociation conditions are given in Table 6.

Table 6. Air thermal conductivity at high temperatures λ · 103, W/m · K

REFERENCES

Additional information about air properties can be found in the following literature: Handbook, edited by V. P. Glushko (1978) "Nauka" Publishing House, Moskow (in Russian).

Wassermann, A. A. and Rabinovitch, V. A. (1968) Thermophysical properties of liquid air and its components. Standarts Publishing House, Moscow (in Russian).

Handbook Thermophysical Properties of Gases and Liquids, edited by N. B. Vargaftic (1972) "Nauka" Publishing House, Moscow (in Russian).

References

  1. Additional information about air properties can be found in the following literature: Handbook, edited by V. P. Glushko (1978) "Nauka" Publishing House, Moskow (in Russian).
  2. Wassermann, A. A. and Rabinovitch, V. A. (1968) Thermophysical properties of liquid air and its components. Standarts Publishing House, Moscow (in Russian).
  3. Handbook Thermophysical Properties of Gases and Liquids, edited by N. B. Vargaftic (1972) "Nauka" Publishing House, Moscow (in Russian).

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