Compressors adiabatic compression efficiency

So far, we have limited our discussion to adiabatic compression efficiency. This sort of inefficiency downgrades work to heat. For a given compression ratio, the temperature rise of the gas as it flows through the compressor may be excessive, thus indicating a low adiabatic compression efficiency. Both centrifugal and reciprocating compressors suffer from this common problem, which is the subject of Chap. 30. 

Volumetric efficiency applies only to reciprocating compressors. A reduction in volumetric efficiency reduces the gas flow through the compressor. A reduction in volumetric efficiency need not reduce the adiabatic compression efficiency. 

Which is more efficient—my beat-up, old centrifugal compressor, or my brand-new reciprocating compressor Both machines are working in parallel, but which has a better adiabatic compression efficiency ... 

The adiabatic compression efficiency of the air compressor, running in its normal condition, is only 79.4 percent of its design condition. The manufacturer s design adiabatic compression efficiency is quoted as 81 percent. Therefore, the normal condition adiabatic compression efficiency is approximately... 

Not too good A detergent solution was injected into the air intake of the axial compressor, and the adiabatic compression efficiency recovered to about 80 percent. 

The adiabatic compression efficiency of the air compressor, running in its normal condition, is only 79.4 percent of its... 

Compression efficiency is the ratio of the work required to adiabatically compress a gas to the work actually done within the compressor cylinder as shown by indicator cards. Figures 12-12 and 12-16. The heat generated during compression adds to the work that must be done in the cylinder. Valves may vary from 50-95% efficient depending on cylinder design and the ratio of compression. Compression efficiency (or sometimes termed volumetric efficiency) is affected by several details of the systems ... 

Adiabatic Efficiency. The ratio of theoretical adiabatic horsepower to actual brake horsepower required at the compressor shaft is adiabatic efficiency. It is equal to compression efficiency X mechanical efficiency. ... 

Assume a process for each of the four devices (1) compressor as adiabatic with efficiency of 85%, (2) combustion chamber as isobaric, (3) turbine as adiabatic with efficiency of 89%, and (4) heat exchanger as isobaric on both hot and cold sides. Input the given information (1) working fluid is air, (2) inlet pressure and temperature of the compression device are 14.7 psia and 60°F, (3) inlet pressure and temperature of the turbine are 120 psia and 2000°F, (4) mass flow rate of air is 1 Ibm/sec, (5) exit pressure of the turbine is 14.7 psia, (6) display the exit temperature of the compressor (it is 562.5°F), and (7) input the exit temperature of the exhaust turbine gas... 

Pressure increase in the pump or compressor V is adiabatic with an isentropic compression efficiency factor t],v = 0.9. 

Air entering at 70°F and atmospheric pressure is to be compressed to 4CK10 Iby/in. gauge in a reciprocating compressor at the rate of 125 std ft min. How many stages should be used What is the theoretical shaft work per standard cubic foot for frictionless adiabatic compression What is the brake horsepower if the efficiency of each stage is 85 percent For air y = 1.40. 

Example 9.6. An adiabatic compressor is compressing air from 20°C and 1 to 4 atm. The airflow rate is lOOkg/h, and the power required to drive the compressor is 5.3 kW. What are the efficiency of the compressor and the temperature of the outlet air What would the. outlet air temperature be if the compressor were 100 percent efficient ... 

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. 

The gas compression in practically all commercial machines is polytropic. That is, it is not adiabatic or isothermal, but some form peculiar to the gas properties and the hydraulic design of the compressor. Actual machines may be rated on adiabatic performance and then related to polytropic conditions by the polytropic efficiency. Other performance rating procedures handle the calculations as polytropic. For reference, both methods are presented. 

Calculate the compression ratio, Pd/Ps = P2/P1 = Pc-From Table 12-9B for the compressor frame selected, select polytropic efficiency, Cp, and using Figure 12-65A, determine adiabatic efficiency, e d. 

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. 

Whereas reciprocating compressors are normally designed on the basis of adiabatic work (together with an isentropic efficiency), centrifugal compressors are usually designed on the basis of polytropic work. By analogy with Equation B.15, the work required for a poly tropic compression is given by ... 

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