Efficiency isentropic

The turbine isentropic efficiency tjt measures the ratio of the actual to ideal work obtained ... 

For a single-stage expansion with isentropic efficiency of 85 percent, from Eq. (6.2),... 

Exampie A.3.1 The pressures for three steam mains have been set to the conditions given in Table A.l. Medium- and low-pressure steam are generated by expanding high-pressure steam through a steam turbine with an isentropic efficiency of 80 percent. The cost of fuel is 4.00 GJ and the cost of electricity is 0.07 h. Boiler feedwater is available at 100°C with a heat capacity... 

Polytropic efficiency is the hmited value of the isentropic efficiency as the pressure ratio approaches 1.0, and the value of the polytropic efficiency is higher than the corresponding adiabatic efficiency as seen in Fig. 10-66. 

For the actual systems, compressor work will be higher than for ideal for the isentropic efficiency and other losses. In the case of hermetic or accessible compressors where an elec trical motor is cooled by the refrigerant, condenser capacity should be ... 

Isothermal efficiency heat rejected at 105 F 85% Isentropic efficiency. 

Figure 8-8. Relationship between polytropic and isentropic efficiency during expansion.

The polytropic efficiency in a turbine can be related to the isentropic efficiency and obtained by combining the previous two equations... 

The operating cost for air compression is basically the electric utility needed ftir ihe isentropic compression. Electric energy needed to compress air may be calculated using Eq. (2.29). The isentropic efficiency of the compressor is taken as 60% and the electric energy cost is 0.06/kWhr,... 

As alternatives to the isentropic efficiencies for the turbomachinery components, tjt and Tjc. which relate the overall enthalpy changes, small-stage or poly tropic efficiencies (Tjpj and Tjpc) are often used. The pressure-temperature relationship along an expansion line is then p T = constant, where z = [y y OtJpt]-... 

Compressor Isentropic efficiency T)c = Isentropic enthalpy ri.se/enthalpy rise... 

The analysis of Hawthorne and Davis [1] for irreversible a/s cycles is developed using the criteria of component irreversibility, firstly for the simple cycle and subsequently for the recuperative cycle. In the main analyses, the isentropic efficiencies are used for the turbomachinery components. Following certain significant relationships, alternative expressions, involving polytropic efficiency and. tc and jcj, are given, without a detailed derivation, in equations with p added to the number. 

Thus there are three modifications to the a/s efficiency analysis, involving (i) the specific heats ( and n ), (ii) the fuel-air ratio / and the increased turbine mass flow (I +/), and (iii) the pressure loss term S. The second of these is small for most gas turbines which have large air-fuel ratios and / is of the order of l/IOO. The third, which can be significant, can also be allowed for a modification of the a/s turbine efficiency, as given in Hawthorne and Davis [I]. (However, this is not very convenient as the isentropic efficiency tjt then varies with r and jc, leading to substantial modifications of the Hawthome-Davis chart.)... 

From the study of uncooled cycles in Chapter 3, we next move to consider irreversible cycles with compressor and turbine isentropic efficiencies, tjc and r/p, respectively. 

By introducing isentropic efficiencies of the turbine ni and compressor the turbine work output is given as ... 

Methane is compressed from 1 bar and 290 K to 10 bar. If the isentropic efficiency is 0.85, calculate the energy required to compress 10,000 kg/h. Estimate the exit gas temperature. 

For a single-stage expansion with isentropic efficiency of 80%... 

FiN = inlet volumetric flowrate (m3-s 1) y = ratio of heat capacities Cp/Cy (—) rjis = isentropic efficiency (—)... 

The isentropic efficiency (see Appendix B) is a function of the machine design and pressure ratio (Pout/Pm) A first estimate of the isentropic efficiency of a reciprocating compressor can be obtained from ... 

Equation B.28 is useful to estimate the polytropic coefficient n if the inlet and outlet pressures are known, along with an estimate of the isentropic efficiency. Knowing the polytropic coefficient allows the outlet temperature for a real gas compression to be estimated from Equation B.26. 

Generally, the efficiency of steam turbines decreases with decreasing load. The overall turbine efficiency can be represented by two components the isentropic efficiency and the mechanical efficiency. The mechanical efficiency reflects the efficiency with which the energy that is extracted from steam is transformed into useful power and accounts for mechanical frictional losses, heat losses, and so on. The mechanical efficiency is high (typically 0.95 to 0.99)6. However, the mechanical efficiency does not reflect the efficiency with which energy is extracted from steam. This is characterized by the isentropic efficiency introduced in Figure 2.1 and Equation 2.3, defined as ... 

---