Compressors adiabatic

Since most compressors operate along a polytropic path approaching the adiabatic, compressor calculations are generally based on the adiabatic cui ve. 

A measure of the energy which dissipates in the bubble column can be derived from the adiabatic compressor power ... 

A definite correlation of the results of the measurements can be achieved by using the adiabatic compressor power per unit volume of reactor according to Eq. (10) which is shown in Fig. 15 [27]. The experimentally determined loss factor is required in Eq. (10). The measured data for spargers with holes dL= 0.2 - 2 mm can be correlated with Eq. (24). 

Fig. 15. Reference floe diameter dp for bubble columns versus mass related adiabatic compressor power PJqV...

The theoretical horsepower requirements for an adiabatic compressor (equivalent to LHP) can be obtained from the following equation.33... 

The energy lost due to friction is actually dissipated into thermal energy, which raises the temperature of the gas. This temperature rise is in addition to that due to the isentropic compression, so that the total temperature rise across an adiabatic compressor stage is given by... 

L15 For a two-stage adiabatic compressor where the gas is cooled to the inlet gas temperature between stages, the theoretical work is given by... 

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. 

Liquids are usually moved by pumps, generally rotating equipment The same equations apply to adiabatic pumps as to adiabatic compressors. Thus, Eqs. (7.25) through (7.27) and (7.29) are valid. However, application of Eq. (7.26) for the calculation of = —Aff requires values of the enthalpy of compressed liquids, and these are seldom available. The fundamental property relation, Eq. (6.8), provides an alternative. For an isentropic process,... 

FORMAT (///,26X, ADIABATIC COMPRESSOR CALCULATION, /, 78(1H )) CALL ADIAB... 

Power equation. The power required by an adiabatic compressor is readily calculated from Eq. (8.25). The dimensional formula is... 

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. 

The difference between the two answers is due to the rise in temperature of the gas in the adiabatic compressor. From Eq. D.17 we can calculate that the adiabatic compressor s outlet temperature was 1.369 times its inlet temperature, or 723 R. Thus, by the perfect-gas law we know that its exit volume is 1.369 times thp exit volume for the isothermal compressor, and the integral of V dP must be larger. ... 

In calculating the work recjuirement for adiabatic compressors, we must evaluate the factor - 1 in every problem. To save time, special-... 

This statement can be used for compressors as well. In the case of an adiabatic compressor, the best possible device is a reversible, adiabatic compressor for which the inlet and outlet entropies are the same. It is commonly called an isentropic compressor. Thus, we normally define... 

Consider the steady-flow, adiabatic compressor shown in Fig. 9.11. The energy balance for this process (taking the compressor as the system and... 

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 ... 

Compressors are pumps which pump gases over significant changes in pressure. These are normally practically adiabatic and result in a significant temperature rise for the gas. The work of compression is less for an isothermal than for an adiabatic compressor for this reason many compressors are staged, with intercooling to decrease the work requirement. 

How many horsepower are required to compress 20 Ibmol/h of helium from 1 atm at 70°F to 10 atm in (a) an isothermal compressor, (b) an adiabatic compressor, and (c) a two-stage, adiabatic compressor with optimum interstage pressure and intercooling to 68 F For helium k = 1.666. 

Show that as k approaches 1, Eq. 9.15 (adiabatic compressor) approaches as a limit Eq. 9.13 (isothermal compressor). Hint See Prob. 8.58. 

Most PD compressors are connected to constant-speed motors, because variable-speed motors are much more expensive. This poses a problem in controlling the compressor flow rate. One way to control a compressor with a constant-speed motor is to vary the clearance volume by means of clearance pockets, which are connected to or disconnected from the head of the compressor by remotely operated valves. For a 100 percent effleient, adiabatic compressor, what is the effect of such a pocket on the pressure ratio, flow rate, and power requirement ... 

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