Entropy diagram

FIG. 2-5 Temperatnre-entropy diagram for air. [Landshaum, Dadds, Stevens, et at. Am. Inst. Chem. Eng. J., l(S), 303 (1955). Reproduced hif peimission of the authors and of the editor, Ameiican Institute of Chemical Engineers.]... 

FIG. 2-8 Temperatnre-entropy diagram for carbon monoxide. Pressure P, in atmospheres density p, in grams per cubic enthalpy H, in joules per gram. (From Must and Stewart, NBS Tech. Note 202, 1963.)... 

FIG, 2-13 Temperahire-entropy diagram for nitrogen. Seotion of T-S diagram for nitrogen by E. S. Burnett, 1950. (Repainted from U.S. Bur Minos Rop. Invest. 4729.)... 

The Carnot refrigeratiou cycle is reversible and consists of adiabatic (iseutropic due to reversible character) compression (1-2), isothermal rejection of heat (2-3), adiabatic expansion (3-4) and isothermal addition of heat (4-1). The temperature-entropy diagram is shown in Fig. 11-70. The Carnot cycle is an unattainable ideal which serves as a standard of comparison and it provides a convenient guide to the temperatures that should be maintained to achieve maximum effectiveness. 

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. 

Figure 8-9. Enthaipy-entropy diagram for a muitistage turbine.

The Joule-Brayton (JB) constant pressure closed cycle is the basis of the cyclic gas turbine power plant, with steady flow of air (or gas) through a compressor, heater, turbine, cooler within a closed circuit (Fig. 1.4). The turbine drives the compressor and a generator delivering the electrical power, heat is supplied at a constant pressure and is also rejected at constant pressure. The temperature-entropy diagram for this cycle is also... 

Temperature - entropy diagram Fig. 1.4. Joule-Brayton cycle (after Ref. [1]). 

The second law of thermodynamics may be used to show that a cyclic heat power plant (or cyclic heat engine) achieves maximum efficiency by operating on a reversible cycle called the Carnot cycle for a given (maximum) temperature of supply (T ax) and given (minimum) temperature of heat rejection (T jn). Such a Carnot power plant receives all its heat (Qq) at the maximum temperature (i.e. Tq = and rejects all its heat (Q ) at the minimum temperature (i.e. 7 = 7, in) the other processes are reversible and adiabatic and therefore isentropic (see the temperature-entropy diagram of Fig. 1.8). Its thermal efficiency is... 

Fig. 1.8. Temperature-entropy diagram for a Carnot cycle (after Ref. (11).

Fig. 1.10. Temperature-entropy diagram. showing reheat, intercooling and recuperation.

Fig. 4.3. Temperature-entropy diagram for two step cooling, (a) Cooling air taken at appropriate pre.ssures and (b) LP cooling air throttled from compressor exit.

Fig. 4..S. Temperalure-entropy diagram for single-slep cooling—irreversible cycle CHT ici (after Ref. (5 ).

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. 

Figure 1 IB. Temperature-entropy diagram for water and steam 814...

A three-stage compressor is required to compress air from 140 kN/m2 and 283 K to 4000 kN/m2. Calculate fee ideal intermediate pressures, the work required per kilogram of gas, and fee isothermal efficiency of fee process. Assume the compression to be adiabatic and the interstage cooling to cool the air to the initial temperature. Show qualitatively, by means of temperature-entropy diagrams, fee effect of unequal work distribution and imperfect intercooling, on the performance of the compressor. 

Calculate the ideal intermediate pressures and the work required per kilogram of gas. Assume compression to be isentropic and the gas to behave as an ideal gas. Indicate on a temperature-entropy diagram the effect of imperfect imercooling on the work done at each stage. 

Temperature-entropy diagram, water and steam 814 Temperature gradient, flow over plane surface 688... 

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