Efficiency adiabatic

Adiabatic efficiency is given by the following relationship Ideal work... 

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. 

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. 

First, the required head is calculated. Either the polytropic or adiabatic head can be used to calculate horsepower so long as the polytropic or adiabatic efficiency is used with the companion head. 

Figure 2 gives the relationship between polytropic and adiabatic efficiencies. 

Figure 2. Uncooled compressor relationship between adiabatic efficiency and polytropic efficiency.

HP = Gas horsepower W = Flow, Ib/min Hpoiy = Polytropic head Had = Adiabatic head Ep = Polytropic efficiency Ea = Adiabatic efficiency... 

If the system differential pressure requirements are low, sometimes a fan can be used. A fan is limited to a maximum of about 65 inches of water (just over 2psi) in vacuum service or 77 inches of water in pressure service (just under 3psi). To estimate fan horsepower use the equations found in Chapter 6 in the section entitled Horsepower Calculation. In lieu of manufacturer s data use an adiabatic efficiency of 50% for initial work. 

Besides affecting the volumetric efficiency, the leakage also has an eltcL t on the adiabatic efficiency. Figure 4-5 is a plot of the tip speed ratio, u/u, (operating to optimum) against the efficiency ratio, off-peak-to-peak effi-... 

The screw compressor can be evaluated using the adiabatic work equation. Discharge temperature can be calculated by taking the adiabatic temperature rise and dividing by the adiabatic efficiency then multiplying by the... 

Figure 4-7. Pressure ratio vs. adiabatic efficiency for an SRM compressor. (Modified from [4].)...

Wa = adiabatic work input P[ = inlet pressure Qi = inlet volume T(a = adiabatic efficiency... 

Step 3. Refer to Figure 4-7 and select an efficiency at a pressure ratio of 3 and a volume ratio, r of 2.44. The adiabatic efficiency is 74%. Now, from Figure 4-5, select a value of efficiency ratio using the tip speed ratio just calculated. Because the value is. 99+, round off to an even 1.0. With a multiplier of 1.0, the final adiabatic efficiency is the value read directly off the curve or T a = 74. The molecular weight correction for efficiency, per rule of thumb, is 0.6 for a final efficiency of 73.4. 

Step 3. Use Figure 4-7 to obtain the adiabatic efficiency for pressure ratio - 3.5 and volume ratio of 2.77. From the curve, adiabatic efficiency = 13%. Next, look up the efficiency ratio on Figure 4-5 for the tip speed ratio just developed and obtain a value of. 98. Use this value as a multiplier to derate the adiabatic efficiency for operation at other than the optimum tip speed. 

Academic des Sciences, 224 Accelerometers, 349 Accumulators, 317 Acoustic Velocity, 26, 39 Adiabatic, 30 Adiabatic efficiency dry, helical, 101 sliding vane, 126 Adiabatic exponent for air-vapor mixtures, 494 Adiabatic head, 32 Adiabatic head... 

Head coefficient, 156 Head equation, adiabatic, 3 t Head equation, poly tropic, I Head, centrifugal, 156 Head, reciprocating, 58 Heat run test (dry), 413 Helical compressor, 5, 7 adiabatic efficiency, Itil applicalion mnge, 7. ly asymmetric profile, 96 bearings, 116 capacity control, 95 casings, 114 circular profile, 95 cooling, I i 1 discharge temperature (dry), I 17... 

The adiabatic efficiency is a function of the pressure ratio, and thus, dependent on the thermodynamic state of the gas undergoing compression. ... 

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. ... 

Figures 12-65 and 12-65A give the relationship between polytropic and adiabatic efficiencies. The adiabatic efficiency can be calculated from operating data, and the polytropic efficiency can be read from the curves. For other cases, ep may be calculated from the preceding relation and the adiabatic efficiency may be determined from the curves. Figure 12-66 illustrates the relationships that may exist while evaluating a particular compressor design.

An important point to remember when calculating is that when you are using adiabatic head, use adiabatic efficiency and when using polytropic head, use polytropic efficiency. ... 

Figure 12-65A. Polytropic to adiabatic efficiency conversion. (Used by permission Bui. P-26 and P-11A, 1966. Elliott Co.)...

At polytropic efficiency from Table 12-9B, using Figure 12-65A, read adiabatic efficiency, e d. 

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. 

Determine Polytropic head, adiabatic head, and adiabatic efficiency. 

Op = polytropic efficiency, fraction Cgj = adiabatic efficiency, fraction... 

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