Mollier chart

The theoretical steam rate (sometimes referred to as the water rate) for stream turbines can be determined from Keenan and Keyes or Mollier charts following a constant entropy path. The theoretical steam rate is given as Ib/hr/kw which is easily converted to Ib/hr/hp. One word of caution—in using Keenan and Keyes, steam pressures are given in PSIG. Sea level is the basis. For low steam pressures at high altitudes appropriate coirections must be made. See the section on Pressure Drop Air-Cooled Air Side Heat Exchangers, in this handbook, for the equation to correct atmospheric pressure for altitude. 

Molecular weight, effect on centrifugal sizing, 159 Mollier charts, 27 Monitoring system, 356 Motor, 146 enclosure, 260 equations, 267 insulation, 257 locked rotor torque, 270 selection, 270 service factor, 262 starting characteristics, 270 starting time, 273, 274 synchronous vs induction, 265 variable frequency drives, 27/, 280 voltage, 258 Motors... 

Figure 12-12A. Illustration of isentropic path on log pressure-enthalpy diagram, showing Mollier chart method of finding final temperature and calculation of H for reversible and adiabatic compression. (Used by permission Edmister, W. C. Applied Hydrocarbon Thermodynamics, 1961. Gulf Publishing Company, Houston, Texas. All rights reserved.)...

After identifying the initial temperature (T) and pressure (P) values, the final temperature and both enthalpy values (H) can be read on the same entropy line of the appropriate gas Mollier chart. For the adiabatic process, the work done on the gas is equal to AH, see Figures 12-13A-D. The following is reproduced by permission of Edmister, W. C., Applied Hydrocarbon Thermodynamics, Gulf Publishing Company. ... 

When a Mollier chart is available for the gas involved the first method, which is illustrated by Figure 12-12A is the most convenient. On the abscissa of Figure 12-12A four enthalpy differences are illustrated. (Hg — Hj) is the enthalpy difference for the isentropic path. (Hg — Hi°) is the ideal gas state enthalpy difference for the terminal temperatures of the isentropic path. The other AH values are the isothermal pressure corrections to the enthalpy at the terminal temperatures. A generalized chart for evaluating these pressure corrections was presented previously. 

As Mollier charts are available for only a few pure components and practically no mixtures, this calculation method is very limited. For example, it cannot be used for most process calculations because these gases are usually mixtures. Some of the charts available for mixtures are the H-S charts presented by Brown for natural gases of gravities from 0.6 to 1.0. ... 

Figure 12-24A. Mollier chart for properties of ammonia. (Used by permission Dept, of Commerce, U.S. Bureau of Standards.)...

The use of an enthalpy diagram or Mollier chart is perhaps the most accurate and is an easy method for determining horsepower. Figure 12-70 illustrates the compression paths on an ammonia diagram. 

The theoretical values for enthalpy may be read from a Mollier chart, where hj is the enthalpy of the steam at the turbine inlet, and hg is the enthalpy of the steam at the exhaust pressure and at the inlet entropy. The expansion of steam through the turbine is theoretically at constant entropy. These theoretical rates must be corrected for performance inefficiencies of the particular turbine. The calculations presented here are good for the average design, but exact values for a particular make and model turbine must be quoted by... 

Figure 4.2 and also Chapter 2, for theoretical and practical cycles on the Mollier chart and for volumetric efficiency). 

In the case of thick-walled HP vessels, the strain energy in the vessel shell can contribute to the available energy, but for vessels below about 20 MN/m2 (200 barg) it is negligible and can be ignored. If a Mollier chart for the gas is available, the adiabatic energy can be measured directly. This is the preferred method, but in many cases the relevant chart is not available. 

The work of Loh et al. (1983) was done using the same principles as those used to generate Figure 4.7. That is, from the initial temperature and pressure, an isenthalpic cooling curve, and its intersection with the hydrate three-phase locus, was determined. However, the isenthalpic line was determined via the Soave-Redlich-Kwong equation-of-state rather than the Mollier charts of... 

In the corresponding calculation for Hj an alternative way has to be found to calculate the output of the steam circulator, since steam is highly imperfect. The steam is expanded isothermally at 25 °C, from standard pressure, 1 bar, saturated to standard partial pressure 0.0088 bar. A minor extrapolation of the Mollier chart gives G, = H-TS = 2590 - 2555.14 and Gf = 2590 - 2745.96. Hence AG = — 190.82kWskg and AG = 3.435kWsmoP (steam circulator). 

The steam/water enthalpy and entropy values for calculation of AG came from the steam tables and Mollier chart. See also Kotas (1995), p. 239, for moist standard atmosphere analysis. 

The Mollier chart plots humidity (abscissa) against enthalpy (lines sloping diagonally from top left to bottom right). Lines of constant temperature are shallow curves at a small slope to the horizontal. The chart is nonorthogonal (no horizontal lines) and hence a little difficult to plot and interpret initially. However, the area of greatest interest is expanded, and they are therefore easy to read accurately. They tend to cover a wider... 

FIG. 12-5 Mollier chart showing changes in during an adiabatic saturation process for an organic system (nitrogen-toluene). 

Ys = humidity at saturation, from the adiabatic saturation contour on Mollier chart... 

Modern high-pressure boiler practice (where the working temperature exceeds the critical temperature of water) has available tables of steam data3 up to 1000°F. and 3500 lb./in.2, and many older approximations are no longer permissible. A Mollier chart for steam up to 2800° F. is given by Pflaum and Schulz.4... 

To derive the solubility parameter of a gas Cernia and Mancini (1965) used the relation suggested by Hildebrand (1951) that a gas solubility parameter is equal to the square root of the ratio of the internal compression energy and the molar volume. Using the van der Waals equation of state, Cernia and Mancini obtained solubility parameters for ethylene, but they related that calculations carried out along the classical lines of interpolating Mollier chart data were time-consuming. 

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