Enthalpy/entropy diagram

The overall effieieney of a radial-inflow turbine is a funetion of effieieneies from various eomponents sueh as the nozzle and rotor. A typieal turbine expansion enthalpy/entropy diagram is shown in Figure 8-7. The total enthalpy remains eonstant through the nozzle, sinee neither work nor heat is transferred to or from the fluid. Within the rotor, the total enthalpy ehanges. Downstream of the rotor the total enthalpy remains eonstant. 

In their original air standard cycle analysis, using constant specific heats, Hawthorne and Davis 4 considered the dry [CBTIiXr cycle. They assumed a perfect heat exchanger, with the specific heats of gas and air constant and identical, so that Ty becomes equal to Tj in Fig. 6.6. From their examination of the enthalpy-entropy diagram of this... 

Figure 2-38. Mollier (enthalpy-entropy) diagram for steam.

When the gas does not behave as an ideal gas, the change in its condition can be followed on a temperature-entropy or an enthalpy-entropy diagram. The intermediate pressures P,i. P 2,. .., are then selected so that the enthalpy change (A//) is the same in each cylinder. 

Fig. 1.4 Pressure-volume and enthalpy-entropy diagrams for rocket propulsion.

The thermodynamic process can be indicated both on a P-V (pressure-volume) diagram and on a h-S(enthalpy-entropy) diagram as shown in figure n. A. 2. The propellants enter the chamber at point i and are gasified. They react as a constant pressure, pc, and then they are expanded isentropically through the nozzle to the exhaust pressure pe. The throat conditions are noted with the subscript t. 

As was shown by Baehr (3) the available energy or exergy can be represented graphically very easily in an enthalpy, entropy diagram (see Figure 1). 

Knoche 4) plotted the reactants and reaction products in one enthalpy, entropy diagram by superposition, thus he was able to evaluate immediately the irreversible entropy production, respectively the exergy losses of the combustion (see Figure 2). 

Figure 1. Enthalpy, entropy diagram with graphical presentation of exergy (3).

Figure 4. Enthalpy, entropy diagram with exergy for reactants e- and reaction products 2 after an isothermal, isobaric combustion Q4) The change of state from 1 to la is a release of heat at constant temperature, therefore the entropy decreases.

The evaluation of the irreversible entropy production is very easily performed in these enthalpy, entropy diagrams as was shown by Knoche (A). It is simply for one mole methane ... 

The difference to the copper process is, that the reduction of nickel oxide with methane is an endothermic process, thus a heat engine could be employed. Figures 9 and 10 show the enthalpy, entropy diagrams of the reactions outlined in equations (8) and (9). (A metallurgist will not favor the reoxidation of nickel since it is very difficult, but equilibrium thernodynamic considerations do allow it.)... 

Figure 9. Enthalpy, entropy diagram of nickel oxide reduction with methane.

Conditions at key points are indicated on the enthalpy-entropy diagram. The process steam is extracted from the turbine at an intermediate point, while the rest of the stream expands to 1 in. Hg and is condensed (example is corrected from Perry, 6th ed., 9.43, 1984). 

Fig. 7.1. The enthalpy-entropy diagram for sterically stabilized dispersions.

FIG. 2—A Molller (enthalpy-entropy) diagram combining Information on cycle water and ateam properties, chemistry, and corrosion [6,101. 

R. W. Haywood, Thermodynamic Tables in SI (Metric) Units and Enthalpy-Entropy Diagram for Steam. Pressure-Enthalpy Diagram for Refrigerant 12 , Cambridge University Press, Cambridge, 1968. 

The enthalpy-entropy diagram (see Fig. 2.12) visualizes the expansion of gaseous air in an ideal turbine, a real turbine and a throttle. The entropy increase dS during the expansion is accompanied by a loss of technical available work dE = dS. Here T is the ambient temperature introduced in the exergy... 

Figure 4.4 shows the thermodynamic processes in a jet pump in a Mollier enthalpy-entropy diagram. The inlet conditions of motive flow and suction flow are assumed to be saturated steam. This is also a common situation in real processes. Besides this, it is also assumed that the expansion in the motive nozzles ends just with the suction pressure p. In the case of a non-dissipative expansion in the motive nozzle, the change of state would be described by the perpendicular from point 1 to point 2. While a real expansion with losses leads to point 2. ... 

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