Thermodynamic properties specific volume

Enthalpy. Enthalpy is the thermodynamic property of a substance defined as the sum of its internal energy plus the quantity Pv//, where P = pressure of the substance, v = its specific volume, and J = the mechanical equivalent of heat. Enthalpy is also known as total heat and heat content. 

Available data on the thermodynamic and transport properties of carbon dioxide have been reviewed and tables compiled giving specific volume, enthalpy, and entropy values for carbon dioxide at temperatures from 255 K to 1088 K and at pressures from atmospheric to 27,600 kPa (4,000 psia). Diagrams of compressibiHty factor, specific heat at constant pressure, specific heat at constant volume, specific heat ratio, velocity of sound in carbon dioxide, viscosity, and thermal conductivity have also been prepared (5). 

From Water Density at Atmospheric Pressure and Temperatures from 0 to 100°C, Tables of Standard Handbook Data, Standartov, Moscow, 1978. To conserve space, only a few tables of density values are given. The reader is reminded that density values may he found as the reciprocal of the specific volume values tabulated in the Thermodynamic Properties Tables subsection. 

Temperature, pressure, and composition are thermodynamic coordinates representing conditions imposed upon or exhibited by the system, andtne functional dependence of the thermodynamic properties on these conditions is determined by experiment. This is quite direct for molar or specific volume which can be measured, and leads immediately to the conclusion that there exists an equation of. state relating molar volume to temperature, pressure, and composition for any particular homogeneous PVT system. The equation of state is a primaiy tool in apphcations of thermodyuamics. 

An alternative is to consider the value of the thermodynamic property per unit mass. Such quantities are called specific properties. Thus the specific volume is the volume per unit mass. It is the reciprocal of the density and is an intensive property. 

In this table the parameters are defined as follows Bo is the boiling number, d i is the hydraulic diameter, / is the friction factor, h is the local heat transfer coefficient, k is the thermal conductivity, Nu is the Nusselt number, Pr is the Prandtl number, q is the heat flux, v is the specific volume, X is the Martinelli parameter, Xvt is the Martinelli parameter for laminar liquid-turbulent vapor flow, Xw is the Martinelli parameter for laminar liquid-laminar vapor flow, Xq is thermodynamic equilibrium quality, z is the streamwise coordinate, fi is the viscosity, p is the density, <7 is the surface tension the subscripts are L for saturated fluid, LG for property difference between saturated vapor and saturated liquid, G for saturated vapor, sp for singlephase, and tp for two-phase. 

The thermodynamic properties of a number of compounds are shown in Appendix D as pressure-enthalpy diagrams with lines of constant temperature, entropy, and specific volume. The vapor, liquid, and two-phase regions are clearly evident on these plots. The conditions under which each compound may exhibit ideal gas properties are identified by the region on the plot where the enthalpy is independent of pressure at a given temperature (i.e., the lower the pressure and the higher the temperature relative to the critical conditions, the more nearly the properties can be described by the ideal gas law). 

The view that the clay surface perturbs water molecules at distances well in excess of 10 A has been largely based on measurements of thermodynamic properties of the adsorbed water as a function of the water content of the clay-water mixture. There is an extensive literature on this subject which has been summarized by Low (6.). The properties examined are, among others, the apparent specific heat capacity, the partial specific volume, and the apparent specific expansibility (6.). These measurements were made on samples prepared by mixing predetermined amounts of water and smectite to achieve the desired number of adsorbed water layers. The number of water layers adsorbed on the clay is derived from the amount of water added to the clay and the surface area of the clay. 

Considering other families of similar compounds, the contributions given by Guillermet and Frisk (1992), Guillermet and Grimvall (1991) (cohesive and thermodynamic properties, atomic average volumes, etc. of nitrides, borides, etc. of transition metals) are other examples of systematic descriptions of selected groups of phases and of the use of special interpolation and extrapolation procedures to predict specific properties. 

Table 8 displays the computed internal energy and specific heat at constant volume. The fact that these agree well with each other, and with experiment, despite the differences in local structure of liquids based on the two potentials emphasizes the insensitivity of thermodynamic properties (except pressure) to structural details. 

As there exists a phase equilibrium both phases must have reached in the internal thermodynamic equilibrium with respect to the arrangement and distribution of the molecules the measuring time. Therefore, no time effects or path dependencies of the thermodynamic properties in the liquid crystalline phase should be expected. To check this point for the l.c. polymer, a cut through the measured V(P) curves at 2000 bar has been made (Fig. 6) and the volume values are inserted at different temperatures in Fig. 7, which represents the measured isobaric volume-temperature curve at 2000 bar 38). It can be seen from Fig. 7 that all specific volumes obtained by the cut through the isotherms in Fig. 6 he on the directly measured isobar. No path dependence can be detected in the l.c. phase. From these observations we can conclude that the volume as well as other properties of the polymers depend only on temperature and pressure. The liquid crystalline phase of the polymer is a homogeneous phase, which is in its internal thermodynamic equilibrium within the normal measuring time. 

Finally, the thermodynamic properties of a system considered as variables may be classified as either intensive or extensive variables. The distinction between these two types of variables is best understood in terms of an operation. We consider a system in some fixed state and divide this system into two or more parts without changing any other properties of the system. Those variables whose value remains the same in this operation are called intensive variables. Such variables are the temperature, pressure, concentration variables, and specific and molar quantities. Those variables whose values are changed because of the operation are known as extensive variables. Such variables are the volume and the amount of substance (number of moles) of the components forming the system. 

Surface effects are negligible in many cases. However, when the surface-to-volume ratio of the system is large, surface effects may become appreciable. Moreover, there are phenomena associated with surfaces that are important in themselves. Only an introduction to the thermodynamics of surfaces can be given here, and the discussion is limited to fluid phases and the surfaces between such phases. Thus, consideration of solid-fluid interfaces are omitted, although the basic equations that are developed are applicable to such interfaces provided that the specific face of the crystal is designated. Also, the thermodynamic properties of films are omitted. 

To perform experiments at a constant pressure, a flow-type supercritical biomass conversion system was used. Major sections of the flow-type system consisted of pump stations, preheaters, supercritical treatment tube, cooling system, and separatory tank. The reaction time was calculated by dividing the volume of the treatment tube by the volumetric flow rate at the given conditions. Knowledge of the thermodynamic properties of the solvent, particularly correlation among temperature, pressure, and specific gravity, is important in order to accurately calculate the reaction treatment. Detailed information of the treatment with this equipment can... 

Figure 13.6 shows a schematic for IGC operation. Inverse, in this instance, refers to the observation that the powder is the unknown material, and the vapor that is injected into the column is known, which is inverse to the conditions that exist in traditional gas chromatography. After the initial injection of the known gas probe, the retention time and volume of the probe are measured as it passes through the packed powder bed. The gas probes range from a series of alkanes, which are nonpolar in nature, to polar probes such as chloroform and water. Using these different probes, the acid-base nature of the compound, specific surface energies of adsorption, and other thermodynamic properties are calculated. The governing equations for these calculations are based upon fundamental thermodynamic principles, and reveal a great deal of information about the surface of powder with a relatively simple experimental setup (Fig. 13.6). This technique has been applied to a number of different applications. IGC has been used to detect the following scenarios ...

These results may be tabulated along with the corresponding conditions of T and P existing at section 2 for a large number of runs. In addition, specific-volume measurements may be made for these same conditions, and these may be tabulated. Corresponding values of the internal energy of water may be calculated by Eq. (2.6), U = H - PV, and these numbers too may be tabulated. In this way tables of thermodynamic properties may be compiled over the entire useful range of conditions. The most widely used such tabulation is for H20 and is known as the steam tables, t... 

The EXPL05 code can also be used for the calculation of the thermodynamic properties of propellant gases and shows an error of usually less than 5 % (loading densities ca. 0.2 g cm-3) when the maximum pressure, the specific energy and the co-volume are considered. 

If any thermodynamic property G of a system is a single-valued function of certain variables x, y, z, etc., which again are the properties of the system then G is called a state property of that system. It means that G does not depend upon the path taken to bring the system to that state or condition and depends only on the properties of the system in that state. For example, the state of one mole of an ideal gas is completely defined by defining pressure and temperature, and under these defined conditions, it as a definite specific volume. All the three i.e., pressure, temperature and specific volume of an ideal gas are its state properties. 

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