Vapor pressure specific vaporization enthalpy

II2 = specific enthalpy at the evaporator outlet (saturated vapor enthalpy at the evaporator pressure (J kg-1, kJkg ) H4 = specific enthalpy at the condenser... 

This paper considers systems of lesser dimensionality than the previous study, namely, systems of two compounds, which (ignoring the vapor) can form only one or two phases. Specifically, excess enthalpies and phase compositions have been measured (at ambient pressure) by isoperibol calorimetry for n-butanol/water at 30.0 and 55.0 °C and for n-butoxyethanol/water at 55.0 and 65.0 °C. (Butanol, or C4E0, is C HgOH butoxyethanol, or C4E1, is C HgCX OH.) The miscibility... 

Because ASPEN is to be used with coal conversion processes, its streams can be designated to carry an arbitrary number of solids or solid phases. This is done by specifying any number of substreams. In fact, the conventional vapor/liquid stream is normally assumed as a substream and solids can comprise other substreams. For the conventional vapor/liquid substream, process data is carried on component molar flows, total molar flow, temperature pressure, specific enthalpy, specific entropy, density, molar vapor fraction, molar liquid fraction, and molecular weight. For solid substreams, which are called "non-conventional substreams," the characterizing data is not as deterministic. The information associated with these substreams is called "attributes". Such attributes may be particle size distribution, ultimate and proximate analyses, or other material specific information. Another type of substream is an "informa-... 

Determine the vapor pressure, specific internal energy, and specific enthalpy of saturated steam... 

The specified variables are the final temperature and pressure, T2 and P2- The dependent variables are the vapor fraction, t /, the liquid and vapor compositions, X, and the total enthalpy of the two phases, /Z2 + H, and the heat duty, Q. The term isothermal should not be interpreted to imply that the transition from initial conditions to final conditions is at constant temperature is, in general, different from T. It simply means that within the flash drum the temperature, as well as the pressure, is fixed. The heat duty required to bring about the final conditions is equal to the enthalpy change, Q = (Hj + 2) - i> where is the enthalpy at and P,. Isothermal flash conditions may be represented by a point ( 2, P2) on tbs phase envelope diagram. It is clearly possible that this point may fall either within the phase envelope or outside it, in which case the system would be all vapor or all liquid (or dense phase). A flash drum operating at such conditions would have a single product and no phase separation would take place. In a single-phase situation, the dependent variables are the properties of the vapor or liquid product. The liquid or vapor composition is, of course, identical to the feed or overall composition, Z,. Note that any set of temperature and pressure specifications is feasible. 

Using the data in Illustration 6.4-1, and the same reference state, compute the vapor pressure of oxygen over the temperature range of —200°C to the critical temperature, and also compute the specific volume, enthalpy, and entropy along the vapor-liquid equilibrium phase envelope. Add these results to Figs. 6.4-3, 6.4-4, and 6.4-5. 

W. M. Haynes and R. D. Goodwin, Thermophysical Properties of Normal Butane from 135 to 700 K at Pressures to 70 MPa, U.S. Dept, of Commerce, National Bureau of Standards Monograph 169, 1982, 192 pp. Tabulated data include densities, compressibility factors, internal energies, enthalpies, entropies, heat capacities, fugacities and more. Equations are given for calculating vapor pressures, liquid and vapor densities, ideal gas properties, second virial coefficients, heats of vaporization, liquid specific heats, enthalpies and entropies. 

Solvent volatility is an important factor in electrospinning. Since electrospinning requires a quick evaporation rate and phase separation, vapor pressure of the solvent affects the dr5dng time and evaporation rate. Other parameters affecting evaporation rate are boiling point, specific heat, enthalpy and heat of vaporization, rate of heat supply, interaction between solvent molecules, surface tension of the liquid, and air movement above the liquid surface. 

Temper- ature cn Vapor Pressure (psia) Specific Volume Enthalpy btullbj Entropy (btuHb -°F) ... 

These volumes contain extensive tabulations of physical data relevant to concentrated solutions of binary systems, both organic and inorganic. The properties that are tabulated include dielectric constant, viscosity,. equivalent conductivity, surface tension, diffusion and thermal diffusion coefficients, vapor pressure, specific heat, electrochemical data, enthalpy of combustion, enthalpy of dilution and solution, transition enthalpies, and other properties. These books contain extensive tabulations of data pertinent to water and electrolyte solutions. The data are well organized and there is a general compound index as well as references to the original data sources. 

The accumulation terms on the left-hand side need further specification. The temperatnre and the enthalpy changes have to be transformed into relationships of the independent variables, i.e. pressure and composition. At the right-hand side the vapor enthalpy can be written as the sum of the liquid enthalpy Hi and the heat of evaporation H ap, which results in ... 

In reviewing the data in Table 6.3 it should be kept in mind that the heats of vaporization for a mixture evaluated under constant pressure conditions are considerably different from those for the same mixture determined under constant temperature conditions. For constant-pressure processes, the heat of vaporization of a specific mixture is the difference between the saturated-vapor enthalpy, /Zy, and the saturated-liquid enthalpy, /z, at the specified composition. For constant-temperature processes, the total pressure of the system must be adjusted continuously, resulting in a somewhat different value for the heat of vaporization. This is analogous to the difference in specific heats at constant volume and at constant pressure. Since evaporation is normally performed under constant pressure, the isobaric heat of vaporization is generally implied when the unqualified term heat of vaporization is used. 

For non-polar components like hydrocarbons, the results are very satisfactory for calculations of vapor pressure, density, enthalpy, and specific, heat and reasonably close for viscosity and conductivity provided that is greater than 0.10. 

Cp = specific heat e = specific internal energy h = enthalpy k =therm conductivity p = pressure, s = specific entropy t = temperature T = absolute temperature u = specific internal energy [L = viscosity V = specific volume f = subscript denoting saturated hquid g = subscript denoting saturated vapor... 

Single-Effect Evaporators The heat requirements of a singleeffect continuous evaporator can be calculated by the usual methods of stoichiometry. If enthalpy data or specific heat and heat-of-solution data are not available, the heat requirement can be estimated as the sum of the heat needed to raise the feed from feed to product temperature and the heat required to evaporate the water. The latent heat of water is taken at the vapor-head pressure instead of at the product temperature in order to compensate partiaUv for any heat of solution. If sufficient vapor-pressure data are available for the solution, methods are available to calculate the true latent heat from the slope of the Diihriugliue [Othmer, Ind. Eng. Chem., 32, 841 (1940)]. 

In calculations with humid air, when the pressure is not high (usually the atmosphetic pressure of 1 bar), water vapor and dry air can be handled as an ideal gas, as we have already done in Eqs. (4.76) and (4.78). For ideal gases the specific enthalpy is just a function of tempetatute ... 

Temperature rc) Humidity kg HjO/kg dry air) Water vapor partial pressure (kPa) Water v K>r partial density (kg/m ) Water vaporization heat M/kg) Mixture enthalpy (kj/kg dry air) Dry air partial density (lKinematic viscosity (I0< mJ/s) Specific heat (kJ/K kg) Heat conductivity (W/m K) Diffusion factor water air (1 O mJ/s) Temperature rc)... 

To use a thermodynamic graph, locate the fluid s initial state on the graph. (For a saturated fluid, this point lies either on the saturated liquid or on the saturated vapor curve, at a pressure py) Read the enthalpy hy volume v, and entropy from the graph. If thermodynamic tables are used, interpolate these values from the tables. Calculate the specific internal energy in the initial state , with Eq. (6.3.23). 

When thermodynamic tables are used, read the enthalpy hf, volume Vj, and entropy Sf of the saturated liquid at ambient pressure, po, interpolating if necessary. In the same way, read these values (hg, Vg, Sg) for the saturated vapor state at ambient pressure. Then use the following equation to calculate the specific internal energy... 

To accommodate the step-by-step, recycling and checking for convergences requires input of vapor pressure relationships (such as Wilson s, Renon s, etc.) through the previously determined constants, latent heat of vaporization data (equations) for each component (or enthalpy of liquid and vapor), specific heat data per component, and possibly special solubility or Henry s Law deviations when the system indicates. 

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). 

Selected compound-specific functions, property-temperature-property relationships, or structure-temperature-property relationships are supplied and discussed in this book for density (Section 3.5), refractive index (Section 4.5), surface tension (Section 5.4), viscosity (Section 6.4), vapor pressure (Section 7.4), enthalpy of vaporization (Section 8.5), aqueous solubility (Section 11.8), and air-water partition coefficients (Section 12.5). 

Now for those of you who may say, This table has its place but what about enthalpy values far to the right of this saturated liquid line or far to the left of this saturated vapor line Chap. 2 addresses this question most specifically. Please consider the fact that pressure increase has little effect on liquid enthalpy at constant temperature. Similarly, notice how pressure lines tend to converge on the vapor dew point line of the phase envelope. This indicates that at constant temperature, increasing the pressure of vapor tends to approach the enthalpy value of the saturation vapor dew point line of the phase envelope of a P vs. H enthalpy figure. See Fig. 2.1 in Chap. 2. 

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