What does Polytropic head mean?
What does Polytropic head mean?
The Polytropic Head is an expression used for dynamic compressors to denote the foot-pounds of work required per pound of gas.
What is compressor work formula?
For compressors work is calculated by dividing the enthalpy difference (Δht), from (8), by a mechanical efficiency ( η m c = 97 % ) . Polytropic head (Δhp) is calculated using the difference in entropy (ΔS) and temperature (ΔT), as shown in (9).
What is adiabatic head?
The adiabatic compression theoretical part of the Compressor Simulation Model calculates the adiabatic head, equal to the difference in enthalpy of the gas between inlet and discharge, at constant entropy. The adiabatic head ‘Had’ is expressed, like enthalpy, in kiloJoule per kilogram of gas.
How do you calculate polytropic head?
Units of Polytropic Head – The polytropic head can be expressed in ‘metres’ or ‘kJ/kg’ or ‘N.m/kg’. The conversion is 1 kJ/kg = 102.04 m. Therefore in this case the compressor head which was calculated as 173.7 kJ/kg is 17,720 m.
How do you calculate Polytropic head?
How do you calculate polytropic efficiency of a compressor?
The n is related to k through polytropic efficiency Ep: (11.67) q1 = gas capacity at the inlet condition, cfm….11.3. 3 Centrifugal Compressors.
| Gas-specific gravity: | 0.68 |
|---|---|
| Inlet temperature: | 100 °F |
| Discharge pressure: | 600 psia |
| Polytropic efficiency: | Ep = 0.61 + 0.03 log (q1) |
What is Polytropic process and derive equation of work done in Polytropic process?
The specific heats will be discussed later. Notice that the results we obtained for an ideal gas undergoing a polytropic process when n = 1, is identical to that for an ideal gas undergoing the isothermal process….The Polytropic Process:
| Process | Exponent n |
|---|---|
| Adiabatic & ideal gas | k = CP/CV |
What is the value of polytropic index?
Most practical thermodynamic processes can be considered polytropic with values ranging between the theoretical limits of 1 and 1.4. The value can also be considered as defining the gradient of the compression and expansion lines on a logarithmic pressure/volume diagram.
How do you calculate the isentropic and polytropic head?
The isentropic head is calculated by equation 3A: Similarly, the polytropic head is calculated by equation 3B: The actual discharge temperature based on the isentropic path is calculated by equation 4A. The actual discharge temperature based on the polytropic is calculated by equation 4B.
What are the units of a polytropic head?
Units of Polytropic Head – The polytropic head can be expressed in ‘metres’ or ‘kJ/kg’ or ‘N.m/kg’. The conversion is 1 kJ/kg = 102.04 m. Therefore in this case the compressor head which was…
How to calculate discharge temperature in polytropic head?
Polytropic Head. However, in short to calculate the discharge temperature T2=T1*r^ ( (n-1)/n) where r is the pressure ratio As you have the mass flow calculate the density at suction conditions from P1/ (Z1*R*T1) where R is the Gas Constant. Volumetric flow at suction conditions is then mass flow divided by suction density.
What is the formula for the polytropic exponent?
The formula is: Critical Pressure (Pc) and Critical Temperature (Tc) – These two values are used to calculate a value called compressibility (Z). The polytropic exponent can be determined when inlet and discharge pressure and temperature is known by the thermodynamic relationship given in equation below.
