Isentropic compressor

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

Table 23.3 summarizes the conditions at each state point. (Points 2s and 4s represent points the conditions for isentropic processes input properties in the table are underlined.) Point a is at atmospheric conditions (the dead state). Point 1, the compressor inlet, is reached after the atmospheric air undergoes a throttling process (constant enthalpy) and experiences a 0.2 psi pressure drop, and point 2s would be achieved in an isentropic compressor. The ratio of the reduced pressure equals the ratio of the actual pressures for an isentropic process. In point 2, the enthalpy is calculated from the compressor isentropic efficiency. In the combustion chamber, the pressure drops 2 psi and the temperature is increased to 1800°F. Point 4s and 4 are analyzed similarly to 2s and 2. Finally, the pressure drops to point 5 where the air enters the atmosphere. The accompanying h-s (or T-s) diagram shows the cycle and includes all of the pressure drops and turbine and compressor inefficiencies. 

Compressor isentropic efficiency at 75% (commonly called adiabatic)... 

W is gas flow rate, in Ib/min Es is compressor isentropic efficiency, in fraction. 

It should be noted that the inside diameter decreases with increasing pressure since outer diameter was heid constant. This approach maintains consistency of the piping system arrangement but results in increased hydraulic resistance. Turbine and compressor isentropic efficiency were assumed to decrease with increasing pressure as shown in Table 6-4. 

The sensitivity of Brayton turbine and compressor isentropic efficiency to overall plant performance was examined for a range of efficiencies 2% from their baseline values Turbine and compressor efficiencies were assumed to vary simultaneously as listed in Table 6 5. 

The turboalternator has many characteristics that determine the operational efficiency of the Brayton power cycle. Irreversibilities in the component which affect the system efficiency include the turbine and compressor isentropic efficiency, bearing power losses, windage losses, EM PR alternator losses, thermal management power losses (pump), and ambient heat loss to space. These losses will be described in more detail in the sub-component sections below. Reference 9-11 describes the significance of these parasitic losses to the overall power system efficiency. 

Refrigerating capacity is the product of mass flow rate of refrigerant m and refrigerating effect R which is (for isobaric evaporation) R = hevaporator outlet evaporator mJef Powei P required foi the coiTipressiou, necessary for the motor selection, is the product of mass flow rate m and work of compression W. The latter is, for the isentropic compression, W = hjisehatge suction- Both of thoso chai acteristics could be calculated for the ideal (without losses) and for the ac tual compressor. ideaUy, the mass flow rate is equal to the product of the compressor displacement per unit time and the gas density p m = p. 

Similar to volumetric efficiency, isentropic (adiabatic) efficiency T is the ratio of the work required for isentropic compression of the gas to work input to the compressor shaft. The adiabatic efficiency is less than one mainly due to pressure drop through the valve ports and other restricted passages and the heating of the gas during compression. 

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 ... 

The Brayton cycle in its ideal form consists of two isobaric processes and two isentropic processes. The two isobaric processes consist of the combustor system of the gas turbine and the gas side of the HRSG. The two isentropic processes represent the compression (Compressor) and the expansion (Turbine Expander) processes in the gas turbine. Figure 2-1 shows the Ideal Brayton Cycle. 

From this relationship, it is obvious that polytropic efficiency is the limiting value of the isentropic efficiency as the pressure increase approaches zero, and the value of the polytropic efficiency is higher than the corresponding adiabatic efficiency. Figure 3-6 shows the relationship between adiabatic and polytropic efficiency as the pressure ratio across the compressor increases. Figure 3-7 shows the relationship across the turbine. 

It has played a dual role, one in Equation 2.18 on specific heat ratio and the other as an isentropic exponent in Equation 2.53. In the previous calculation of the speed of sound. Equation 2.32, the k assumes the singular specific heat ratio value, such as at compressor suction conditions. When a non-perfect gas is being compressed from point 1 to point 2, as in the head Equation 2.66, k at 2 will not necessarily be the same as k at 1. Fortunately, in many practical conditions, the k doesn t change very... 

Why use an adiabatic relationship with a compressor whose cylinder is almost always cooled An assumption made in Chapter 2 on adiabatic isentropic relationships was that heat transfer was zero. In practical applications, however, the cooling generally offsets the effect of efficiency. As a side note, cylinder cooling is as much cylinder stabilization for the various load points as it is heat removal. 

Qis = last stage inlet volume, cfm Tp = pressure ratio across the compressor k = isentropic compression exponent... 

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,... 

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. 

A reversible adiabatic process is known as isentropic. Thus, the two conditions are directly related. In actual practice compressors generate friction heat, give off heat, have valve leakage and have piston ring leakage. These deviations... 

Adiabatic compression (termed adiabatic isentropic or constant entropy) of a gas in a centrifugal machine has the same characteristics as in any other compressor. That is, no heat is transferred to or from the gas during the compression operation. The characteristic equation... 

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

HA A single-stage double-acting compressor running at 3 Hz is used to compress air from 110 kN/irr and 382 K to 1150 kN/nr. If the internal diameter of the cylinder is 20 cm, the length of stroke 25 cm and the piston clearance 5%, calculate (a) the maximum capacity of the machine, referred to air at the initial temperature and pressure, ami power requirements under isentropic conditions. 

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 ... 

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