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Beattie-Bridgeman equation of state  is one of the best known and is a reasonably accurate equation of state. It is given by
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where the constants for various substances are found in Table 2-4.
Benedict-Webb-Rubin equation of state  is one of the more recent and very accurate equations of state. It is given by
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where the constants for various substances are given in Table 2-4.
Boiling  is the phase change process that occurs at the solid-liquid interface when a liquid is brought into contact with a surface maintained at a temperature sufficiently above the saturation temperature of the liquid.
Compressed liquid  has a pressure greater than the saturation pressure corresponding to the temperature.
Compressed liquid region  is all compressed liquid states located in the region to the left of the saturated liquid line and below the critical temperature line. In the absence of compressed liquid data, a general approximation is to treat compressed liquid as saturated liquid at the given temperature.
Compressibility factor Z  is a correction factor to account for deviation from ideal-gas behavior at a given temperature and pressure. Z = Pv/RT.
Critical point  is defined as the point at which the saturated liquid and saturated vapor states are identical.
Critical pressure Pcr  is the pressure of a substance at the critical point.
Critical temperature Tcr  is the temperature of a substance at the critical point.
Critical volume vcr  is the volume of a substance at the critical point.
Dome  is the saturation states located beneath the joined saturated liquid line and saturated vapor line.
Enthalpy H  (from the Greek word enthalpien, which means to heat)is a property and is defined as the sum of the internal energy U and the PV product.
Enthalpy of vaporization  (or latent heat of vaporization) is the quantity hfg listed in the saturation tables.
Equation of state  is any equation that relates the pressure, temperature, and specific volume of a substance. Property relations that involve other properties of a substance at equilibrium states are also referred to as equations of state.
Evaporation  is the phase change from liquid to vapor and occurs at the liquid-vapor interface when the vapor pressure is less than the saturation pressure of the liquid at a given temperature.
Evaporative coolers  cool hot and dry outdoor air by forcing it to flow through a wet cloth or honey-comb structure where some of the water evaporates by absorbing heat from the air, and thus cooling the air. Evaporative coolers are commonly used in dry climates and provide effective cooling.
Gas constant R   is different for each gas and is determined from R =Ru/M.
Gas phase of a substance  has molecules that are far apart from each other, and a molecular order is nonexistent. Gas molecules move about at random, continually colliding with each other and the walls of the container they are in.
Generalized compressibility chart  shows that by curve-fitting all the data, gases seem to obey the principle of corresponding states reasonably well.
Ideal gas  is a gas that obeys the ideal-gas equation of state.
Ideal-gas equation of state  (or ideal-gas relation) predicts the P-v-T behavior of a gas quite accurately within some properly selected region where Pv = RT.
Latent heat  is the amount of energy absorbed or released during a phase-change process.
Latent heat of fusion  is the amount of energy absorbed during melting and is equivalent to the amount of energy released during freezing.
Latent heat of vaporization  is the amount of energy absorbed during vaporization and is equivalent to the energy released during condensation.
Liquid phase  has a molecular spacing not much different from that of the solid phase, except the molecules are no longer at fixed positions relative to each other. In a liquid, chunks of molecules float about each other; however, the molecules maintain an orderly structure within each chunk and retain their original positions with respect to one another. The distances between molecules generally experience a slight increase as a solid turns liquid, with water being a rare exception.
Liquid-vapor saturation curve  is a plot of saturation temperature Tsat versus saturation pressure Psat.
Mass of a system  is equal to the product of its molar mass M and the mole number N.
Melting line  separates the solid and liquid regions on the phase diagram.
Molar mass M   can simply be defined as the mass of one mole (also called a gram-mole, abbreviated gmol) of a substance in grams, or the mass of one kmol (also called a kilogram-mole, abbreviated kgmol) in kilograms. In English units, it is the mass of 1 lbmol in lbm. Notice that the molar mass of a substance has the same numerical value in both unit systems because of the way it is defined.
Package icing  is the practice of using ice in product packages to remove heat and keep the products cool during transit by taking advantage of the large latent heat of fusion of water commonly, but its use is limited to products that are not harmed by contact with ice and the moisture provided by the ice.
Phase diagram  is the P-T diagram of a pure substance and shows all three phases separated from each other by the sublimation line, vaporization line, and melting line.
Phase equilibrium  for liquid water that is open to the atmosphere can be expressed as follows: The vapor pressure of the water in the air must be equal to the saturation pressure of water at the water temperature.
Principle of corresponding states  is the fact that compressibility factor Z for all gases is approximately the same at the same reduced pressure and temperature.
Pseudo-reduced specific volume vR  is used with the generalized compressibility chart to determine the third property when P and v, or T and v, are given instead of P and T.
P-v-T surface  is a three-dimensional surface in space which represents the P-v-T behavior of a substance. All states along the path of a quasi-equilibrium process lie on the P-v-T surface since such a process must pass through equilibrium states. The single-phase regions appear as curved surfaces on the P-v-T surface, and the two-phase regions as surfaces perpendicular to the P-T plane.
Pure substance  is a substance that has a fixed chemical composition throughout.
Quality x  is the ratio of the mass of vapor to the total mass of a saturated mixture. The quality lies in the range 0 ≤ x ≤ 1.
Reduced pressure PR  is the ratio of the pressure to the critical pressure.
Reduced temperature TR  is the ratio of the temperature to the critical temperature.
Reference state  is chosen to assign a value of zero for a convenient property or properties at that state.
Relative humidity  is the ratio of the actual amount of moisture (water) in atmospheric air at a given temperature to the maximum amount air can hold at that temperature.
Saturated air  is air that cannot hold any more moisture at its state.
Saturated liquid  is a liquid that is about to vaporize.
Saturated liquid line  is the saturated liquid states connected by a line that meets the saturated vapor line at the critical point, forming a dome.
Saturated liquid-vapor mixture  is a mixture of the liquid and vapor phases that coexist in equilibrium.
Saturated liquid-vapor mixture (wet region)  is a mixture of the liquid and vapor phases that coexist in equilibrium.
Saturated vapor  is a vapor that is about to condense.
Saturated vapor line  is the saturated vapor states connected by a line that meets the saturated liquid line at the critical point, forming a dome.
Saturation pressure Psat  is called the pressure at which a pure substance changes phase at a given temperature.
Saturation temperature Tsat  is the temperature at which a pure substance changes phase at a given pressure.
Solid phase  has molecules arranged in a three-dimensional pattern (lattice) that is repeated throughout. Because of the small distances between molecules in a solid, the attractive forces of molecules on each other are large and keep the molecules at fixed positions.
Subcooled liquid  has a temperature less than the saturation temperature corresponding to the pressure.
Sublimation  is the process of passing from the solid phase directly into the vapor phase.
Sublimation line  separates the solid and vapor regions on the phase diagram.
Superheated vapor  is a vapor that is not about to condense (not a saturated vapor). A superheated vapor has a temperature greater than the saturation temperature for the pressure.
Superheated vapor region  is all the superheated states located to the right of the saturated vapor line and above the critical temperature line.
Swamp coolers  (see evaporative coolers).
Triple line  is the locus of the conditions where all three phases of a pure substance coexist in equilibrium. The states on the triple line of a substance have the same pressure and temperature but different specific volumes.
Triple point  is a point on the P-T diagram that represents the triple line.
Universal gas constant Ru  is the same for all substances and its value is 8.314 kJ/kmol·K and 1.986 Btu/lbmol·R.
Vacuum cooling  is a way to cool a substance by reducing the pressure of the sealed cooling chamber to the saturation pressure at the desired low temperature and evaporating some water from the products to be cooled. The heat of vaporization during evaporation is absorbed from the products, which lowers the product temperature.
Vacuum freezing  is the application of vacuum cooling when the pressure (actually, the vapor pressure) in the vacuum chamber is dropped below 0.6 kPa, the saturation pressure of water at 0°C.
van der Waals equation of state  is one of the earliest attempts to correct the ideal gas equation for real gas behavior.
Vapor  implies a gas that is not far from a state of condensation.
Vapor pressure  is the pressure of water vapor in a gas mixture.
Vaporization line  separates the liquid and vapor regions on the phase diagram.
Virial equations of state  is an equation of state of a substance expressed in a series form as
P = RT/v + a(T)/v2 + b(T)/v3 + c(T)/v4 + d(T)/v5 +…

where the coefficients a(T ), b(T ), c(T ), and so on, are functions of temperature alone and are called virial coefficients.
Wet region  (see saturated liquid-vapor mixture region).





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