Compressor adiabatic head

Adiabatic Head. The height in ft of gas supported at the compressor discharge as the gas discharges into a system at the desired pressure level is the adiabatic head. The compression of the gas column is adiabatic. The temperature and pressure of the compression column will be related by the adiabatic expression. 

The computer program PROG61 calculates the polytropic and adiabatic heads of a compressor. Table 6-5 shows the input data and results of the gas mixture. The gas discharge temperature is 310.4°F and the compressor polytropic head is 76874 ft with a total break horsepower = 960 hp. 

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 approximate number of stages for a centrifugal compressor, column (I), is a function of the adiabatic (and actually the polytropic) head and varies with the efficiency and physical properties of the gas. 

Real compression processes operate between adiabatic and isothermal compression. Actual compression processes are polytropic processes. This is because the gas being compressed is not at constant entropy as in the adiabatic process, or at constant temperature as in the isothermal processes. Generally, compressors have performance characteristics that are analogous to those of pumps. Their performance curves relate flow capacity to head. The head developed by a fluid between states 1 and 2 can be derived from the general thermodynamic equation. 

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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