Adiabatic compressor efficiency

The area enclosed by the solid line is the total or actual compression work. The area enclosed by the dotted line is ideal or useful compression work. The areas between the dotted line and the solid line represent compression work lost to heat. The area inside the dotted line, divided by the area inside the solid line, is called adiabatic compressor efficiency. 

Unfortunately, valve disablers have a detrimental effect on the adiabatic compressor efficiency. This means that, even though no gas may be moving through the crank end of a cylinder, the piston is still doing work on the gas inside the crank end of the cylinder. If you would like proof, place your hand on the valve cap on such a disabled cylinder. The high temperature you will feel is wasted compression work going to useless heat. I have measured in the field that, after a cylinder end is completely disabled, it is still converting 20 percent of the former compression work to heat. 

But we learned to care. You see, rotor fouling is a double-edged sword. It cuts two ways. One aspect of rotor fouling is loss of adiabatic compressor efficiency, which wastes work and reduces flow. The other edge of the blade is vibration. 

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... 

Find the compressor power required, turbine power produced, heating load, and COP for a heat pump that uses R-12 as the working fluid and is designed to operate at an evaporator temperature of 2°C and a condenser temperature of 39°C. The compressor efficiency is 78%. The mass rate flow of R-12 is 0.32 kg/sec. The throttling valve is replaced by an adiabatic turbine with 74% 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. 

A compressor operates adiabatically with air entering at Tt and P, with a molar flow rate The discharge pressure is P2 and the compressor efficiency is 77. Estimate the power requirement the compressor and the temperature of the discharge stream for one of the following sets of opera" conditions. 

Saturated steam at 175 kPa is compressed adiabatically in a centrifugal compressor to 650 kPa at the rate of 1.5 kg s 1. The compressor efficiency is 75 percent What is the power requirement of the compressor and what arc the enthalpy and entropy of the steam in its final state ... 

Solution Saturated steam at 100 kPa is compressed adiabatically to 300 kPa with a compressor efficiency of 0.75. From the results of Example 7.8, we have ... 

Compressor efficiencies are usually expressed as isentropic efficiencies, i.e., on the basis of an adiabatic reversible process. Isothermal efficiencies are sometimes quoted, and design calculations are simplified when isothermal efficiencies are used. In either case, the efficiency is defined as the ratio of the power required for the ideal process to the power actually consumed. 

Figure PI 6.24 shows a process that accomplishes the chilling of O.S kg s of water from 261 4 C. The water acts as its own refrigerant by means of a recycle loop. The compressor (vacuii pump) maintains a suction pressure at point 4 such that the saturation temperature in the sepa is 4°C, and discharges at point 5 to a pressure of 6 kPa. The compressor operates adiabatically an efficiency of 75 percent. The condenser discharges saturated liquid water at 6 kPa. 

A compressor operates adiabatically with air entering at T and Pi witii a molar flow rate A. The discliarge pressure is P2 and tlie compressor efficiency is r]. Estimate tlie power requirement of tlie compressor and tlie temperature of tlie discliarge stream for one of tile following sets of operating conditions. 

Tests on an adiabatic gas compressoryield values for inlet conditions (Ti, Pi) and outlet conditions (T2, P2)- Assuming ideal gases witli constant heat capacities, determine tlie compressor efficiency for one of tlie following ... 

Example 9.4. A 100 percent efficient compressor is required to compress air from 1 to 3 atm. The inlet temperature is 68°F. Calculate the work per pound-mole for an isothermal compressor and an adiabatic compressor. 

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 ... 

See Prob. 9j29. An alternative procedure is to use an inlet or outlet valve which can be stopp ed in the open position by some remote controller. For a 100 percent efficient, adiabatic compressor, what is the effect of a stuck-open inlet valve on the pressure I ratio, flow rate, and power requirement Such devices are normally called valve unloaders. 

Turbomachine adiabatic/isentropic efficiencies CT Compressor Expander ST HP/IP/LP cylinders. 

In order to arrive at numerical results, some further assumptions were made. The compressors have adiabatic stage efficiency. The expanders have 80 efficiency. The liquid pump has 100 efficiency. All heat exchange has a minimum temperature difference of 4°C. 

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