A B C D
DALL TUBE DALTON'S LAW DALTON'S LAW OF PARTIAL PRESSURES DAMAGE INTERFACE DAMPING, OF HEAT EXCHANGER TUBES DARCY EQUATION DARCY FREE CONVECTION DARCY NUMBER DARCY'S LAW DARCY-PRANDTL NUMBER Data for molecules of practical interest DATING OF ARCHAEOLOGICAL SAMPLES DDT, DEFLAGRATION TO DETONATION TRANSITION DE LAVAL NOZZLES DE-ICING DEBORAH NUMBER DEBYE TEMPERATURE DECANTATION DECANTERS DECELERATING DROPS DECONVOLUTION, OPTICS DEEP SHAFT DEFINITE INTEGRALS DEFLAGRATION DEFLAGRATION TO DETONATION TRANSITION, DDT DEGENERACY DEGREES OF FREEDOM DEHYDRATION DELIQUESCENCE DELTA FUNCTION DENDRITE LAYER DENDRITIC CRYSTALS DENSITY GAS MODEL DENSITY MAXIMUM OF WATER DENSITY MEASUREMENT DENSITY OF GASES DENSITY OF LIQUIDS DENSITY, HOMOGENEOUS DENSITY, OF THE ATMOSPHERE DENSITY-WAVE OSCILLATIONS DEPARTMENT OF THE ENVIRONMENT, DoE DEPARTURE FROM FILM BOILING DEPARTURE FROM NUCLEATE BOILING, DNB DEPHLEGMATOR DEPOSITION DEPOSITION OF HOMO- AND HETERO-EPITAXIAL SILICON THICK FILMS BY MESO-PLASMA CVD DEPOSITION OF PARTICLES DEPOSITION RATE OF DROPLETS IN ANNULAR FLOW DERIAZ TURBINES Derivative (derived) unit of measurement DESALINATION DESALINATION OF OIL DESALINATION, FLASH EVAPORATION FOR DESICCANTS DESICCATION DESIGN BASIS ACCIDENT DESTRUCTION OF SURFACES DETECTION OF CHEMICAL AND BIOLOGICAL AEROSOLIZED POLLUTANTS DETERGENTS DETERMINANTS Determination of material properties: optical tomography applications DETERMINISTIC CHAOS DETONATION DETONATION WAVE DEUTERIUM DEUTERIUM OXIDE DEUTSCH-ANDERSON EQUATION DEVIATORIC STRESS DEVOLATIZATION OF COAL PARTICLES DEW POINT DEWAR DEWATERING DIAMETER, HYDRAULIC DIAMOND-SHAPED CYLINDER BUNDLE DIAPHRAGM GAUGE DIE DIE-CASTING DIELECTRIC HEATING DIELECTROPHORETIC FORCES DIESEL CONDITIONS DIESEL ENGINES DIESEL FUEL DIESEL JET DESTRUCTION DIESEL SPRAY DIESEL-EMITTED PARTICLES Differential approximations DIFFERENTIAL CONDENSATION CURVE DIFFERENTIAL EQUATIONS DIFFERENTIAL PRESSURE FLOWMETERS DIFFERENTIAL PRESSURE TRANSDUCERS DIFFRACTION DIFFUSER DIFFUSION DIFFUSION APPROXIMATION IN MULTIDIMENSIONAL RADIATIVE TRANSFER PROBLEMS DIFFUSION COEFFICIENT DIFFUSION COEFFICIENT OF GASES DIFFUSION EQUATIONS DIFFUSION FLAMES DIFFUSION IN ELECTROLYTE SOLUTION DIFFUSION LAW DIFFUSION PUMP DIFFUSIVE CONVECTION DILATANCY DILATANT FLUIDS DILATION OF GRANULAR MATERIAL DILUTANT FLUIDS DILUTE SUSPENSION Dimension (of a secondary quantity with respect to a given primary quantity) Dimensional Analysis Dimensional Analysis and Similarity Dimensional equation DIMENSIONAL MATRIX Dimensional quantity (variable) DIMENSIONAL STABLE ANODES, DSAS DIMENSIONALLY HOMOGENEOUS EQUATIONS DIMENSIONLESS GROUPS Dimensionless Parameters Dimensionless quantity (Dimensionless variable) DIMERS DIOXINS DIPHENYL DIPOLE MOMENT DIRAC DELTA FUNCTION DIRECT CONTACT CONDENSERS DIRECT CONTACT EVAPORATORS DIRECT CONTACT HEAT EXCHANGERS DIRECT CONTACT HEAT TRANSFER DIRECT CONTACT MASS TRANSFER DIRECT INVERSION OPTICAL TECHNIQUE DIRECT NUMERICAL SIMULATIONS, DNS DIRICHLET CONDITIONS DIRICHLET'S PROBLEM DISCHARGE COEFFICIENT DISCRETE ENERGY DISCRETE ORDINATE APPROXIMATION Discrete ordinates and finite volume methods Discrete ordinates method Discrete ordinates method for one-dimensional problems DISK AND DOUGHNUT BAFFLES DISK TYPE CENTRIFUGE DISK TYPE STEAM TURBINE DISORDER Dispersed Flow DISPERSED FLOW, IN NOZZLES DISPERSED LIQUID FLOWS DISPERSION IN POROUS MEDIA DISPERSION OF PARTICLES DISPERSION RELATIONSHIPS, FOR WAVES IN FLUIDS DISPLACEMENT CHROMATOGRAPHY Displacement thickness DISPLACEMENT THICKNESS, OF BOUNDARY LAYER DISSIPATION OF HEAT FROM EARTH'S SURFACE DISSIPATIVE SYSTEMS DISSOLVED AIR FLOTATION, DAF DISSOLVED SOLIDS DISTILLATION DISTILLATION REBOILERS DISTRIBUTIONS DISTURBANCE WAVES, IN ANNULAR FLOW DISYMMETRY OF SCATTERED LIGHT DITTUS-BOELTER CORRELATION DITTUS-BOELTER EQUATION DNB, DEPARTURE FROM NUCLEATE BOILING DOE DOLINSKII, A.A. DOMESTIC WATER HEATER DONNEN EFFECT DOPING DOPPLER ANEMOMETRY DOPPLER BROADENING DOPPLER BURST DOPPLER EFFECT DOPPLER GLOBAL VELOCIMETRY DOPPLER SHIFT DOUBLE DIFFUSIVE CONVECTION IN A ROTATING POROUS LAYER DOUBLE EXPOSURE HOLOGRAPHY DOUBLE FLASH METHODS DOUBLE-DIFFUSIVE MAGNETOCONVECTION DOUBLE-PIPE EXCHANGERS DOUBLING TIME DOUBLY STRATIFIED DARCY POROUS MEDIUM DOWTHERM DRAFT TUBE MIXER DRAG Drag Coefficient DRAG FORCE DRAG FORCE ON PARTICLES DRAG INDUCED FLOW DRAG ON A PARTICLE DRAG ON PARTICLES AND SPHERES DRAG ON REACTOR DRAG ON SOLID SPHERES AND BUBBLES DRAG REDUCTION DRAINING INTENSELY EVAPORATED WAVE FILMS DREITSER, G.A. DRIFT FLUX Drift flux models DRIFT VELOCITY DROP FORMATION DROP SHAPES DROP SPLITTING DROP TOWERS DROPLET COLLISION DROPLET DEPOSITION AND ENTRAINMENT, IN ANNULAR FLOW DROPLET DETECTION DROPLET GENERATION DROPLET MEASUREMENTS DROPLET SIZE DISTRIBUTION DROPLET SPRAYS DROPLET STREAM DROPLET SURFACE TENSION DROPLET/LIQUID SEPARATION DROPLETS Drops DROPS, MASS TRANSFER TO AND FROM Dropsize measurement DROPWISE CONDENSATION DROPWISE PROMOTERS DROWNING OUT DRUM TYPE STEAM TURBINE DRY CONTAINMENTS, FOR NUCLEAR REACTORS DRY-BULB TEMPERATURE DRYERS DRYING DRYING CHAMBERS DRYOUT DUAL-PURPOSE HEAT PUMPS DUBOIS' BODY SURFACE DUCTILE FRACTURE DUCTS, NONCIRCULAR, FLOW IN DUFOUR EFFECT DUNE FLOW DUST, AS AN AIR POLLUTANT DUSTS DUSTY PLASMAS DWARF GALAXIES DYE LASERS DYNAMIC INSTABILITIES IN TWO-PHASE SYSTEMS Dynamic Pressure DYNAMIC WAVES DYNAMICAL SIMILARITY DYNAMICS
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DENSITY OF GASES

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In most treatments of heat and mass transfer in engineering, it is usual to treat fluids as continua. Thus, it becomes possible to introduce the concept of a fluid (liquid or gas) density at a point. On this basis, the mass density of a gas, ρ, is simply the mass of a gas contained in a macroscopic volume whereas the amount-of-substance density, , is the amount (number of moles) of a gas in the same volume. The density of a gas is a strong function of temperature and pressure. For very low pressures, every gas conforms to the Perfect Gas equation

where R is the universal gas constant and T, the absolute temperature. But there are significant deviations from this simple behavior as the pressure is increased.

One of the simplest means of representation of the behavior of real gases qualitatively is the Van der Waals' Equation of State, expressed as:

in which a and b are constant characteristics of a particular substance which account for the attractive forces between molecules and their finite size. Since the van der Waals' equation reveals a critical point, the constants a and b can be related to the critical state parameters

and

These relationships do, in fact, provide a very crude means of estimating the density of a gas from the van der Waals' equation of state if the critical state variables are known for the substance. More accurate equations of state, such as that of Redlich and Kwong or Benedict, Webb and Rubin, have been developed which may be used in a similar manner for the estimation of the density of gases. However, none of these simple equations of state represent the behavior of any real substances over a wide range of conditions so that one must always have recourse to measurements, at least to define the parameters in an equation of state.

For some fluids, very accurate equations of state exist which describe the density, as well as other thermodynamic properties of a gas, over a wide range of conditions. These equations are based on a set of critically-evaluated experimental data. Equations used to describe these data are often quite complicated [e.g., de Reuck and Craven (1993)].

The density of a gas is sometimes expressed in terms of a virial expansion, which emerges from a statistical mechanical treatment of the gas. Here,

where B, C... are known as virial coefficients which have a known relationship to the forces between molecules. For moderately low densities, equations of this form can be used to calculate gas densities if B and C are available, which is sometimes the case [Dymond and Smith (1980)].

Other means of estimating the density of gases are available, such as those based upon Corresponding States procedures (Reid et al.).

REFERENCES

Bett, K. E., Rowlinson, J. S., and Saville, G. (1975) Thermodynamics for Chemical Engineers, Athlone Press, London. DOI: 10.1016/0300-9467(76)80049-4

de Reuck, K. M. and Craven, R. J. B. (1993) International Thermodynamic Tables of the Fluid State—12. Methanol (Blackwell Scientific, London).

Dymond, J. H. and Smith, E. B. (1980) The Virial Coefficients of Pure Gases and Mixtures. A Critical Compilation (Clarendon Press, Oxford).

Reid, R. C., Prausnitz, J. M., and Sherwood, T. K. (1977) The Properties of Gases and Liquids, 3rd ed. (McGraw-Hill, New York).

References

  1. Bett, K. E., Rowlinson, J. S., and Saville, G. (1975) Thermodynamics for Chemical Engineers, Athlone Press, London. DOI: 10.1016/0300-9467(76)80049-4
  2. de Reuck, K. M. and Craven, R. J. B. (1993) International Thermodynamic Tables of the Fluid State—12. Methanol (Blackwell Scientific, London).
  3. Dymond, J. H. and Smith, E. B. (1980) The Virial Coefficients of Pure Gases and Mixtures. A Critical Compilation (Clarendon Press, Oxford).
  4. Reid, R. C., Prausnitz, J. M., and Sherwood, T. K. (1977) The Properties of Gases and Liquids, 3rd ed. (McGraw-Hill, New York).

Following from:

EQUATION OF STATE

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CRITICAL POINT, THERMODYNAMICS
DENSITY MEASUREMENT

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