Measured temperature and pressure for the three stages of compression, Table 2. Please suggest the reason for varying answers. PetroSkills offers consulting expertise on this subject and many others. These “Tip of the month” pages are really insightful. Known and measured properties are: a. Please clarify me why i am getting wrong. Soave, G., Chem. I would also mention that rigorous methods (based on interpolated values such as ASME PTC-10 or numerical integration pin->pout such as Huntington etc.) Monitoring of air quality or compressor efficiency is often done through third party contractors on a periodic audit basis and this may be sufficient for a particular need but will always be limited by the length of time the survey gathered data from. Compressor efficiency is very important factor for any business. They can only be determined (afterward) by a compressor test, although compressor manufacturers can usually provide good estimates. Determination of the ideal or isentropic (reversible and adiabatic) enthalpy change (h2Isen-h1) of the compression process. Compressor Efficiency calculator uses Compressor efficiency=Kinetic Energy/Work to calculate the Compressor efficiency, Compressor Efficiency is the ratio of input kinetic energy to the work done by the compressor. The dynamic compression efficiency is calculated based these pressure and temperature measurements as shown below: It is estimated that there are over 80,000 centrifugal chillers in operation in North America. The results indicated that the accuracy of the shortcut method is sensitive to the value of ideal gas state heat capacity ratio, k. From a calculation viewpoint alone, the power calculation is particularly sensitive to the specification of mass flow rate, suction temperature and pressure, and discharge temperature and pressure. Table 2 indicates that excellent agreements are obtained for stages 1 and 2. Thus the most difficult part of a compressor calculation is specification of a reasonable range for each variable and not the calculation itself. Important Aspects of Centrifugal Compressor Testing-Part 1. Assume the feed composition remain unchanged, c. Calculate suction enthalpy h1=f(P1, T1, and zi) and entropy s1=f(P1, T1, and zi) by EOS. For ideal gases, the value would be equal (CP/CV) ratio. If I want to neglect the temperature change(too low) which equations should I follow? (75) and and PhD (78) degrees in Chemical Engineering, all from Oklahoma State University. Simple Energy Formula: Motor Efficiency = Cost per KW X .746 (Power Factor) X Hours of operation X Brake horsepower *Note: No electric motor is 100% efficient, most will average 92-95% efficient. 6. Norman, OK. 73072. finally, a procedure can also consider phase equilibria, I know Prode Properties (see http://www.prode.com/docs/pppman.pdf) which includes both Huntington and a proprietary method for solving a polytropic stage with phase equilibria, If this is not available, you can approximate the polytropic efficiency of centrifugal compressors as the polytropic efficiency is linked to the flow at inlet of the compressor. • Describe the working principles of reciprocating compressors. Note that Dresser Rand is doing quite a lot of work with “Near constant temperature” compression especially for CO2 compression from vent stacks. 5.4 bore For more information about these services, visit our website at http://petroskills.com/consulting, or email us at consulting@PetroSkills.com. 4. Compressed air is one of the most expensive utilities in commercial facilities. 6.5 stroke is 85% practical? The error percent between the rigrous method and the shortcut methods for each stage are presented in Table 2, too. SHELL-AND-TUBE-HEAT-EXCHANGER.xls. e. Calculate the ideal enthalpy (h2Isen) at discharge condition for known zi, T2 (or P2) and s2Isen. 06 - Compressors. However, larger deviations are obseved for the isetropic and polytropic exponents of stage 3 due to high pressure operation which deviated too far from ideal gas state conditions. Note that Dresser Rand is doing quite a lot of work with “Near constant temperature” compression especially for CO. compression from vent stacks. Example of calculation of the compression power. You want to own and operate equipment that runs over long periods of time, using a minimal amount of energy. The efficiency of the compressor is known and is 0.72. The rigorous method was based on an equation of state like the Soave-Redlich-Kwong (SRK) for calculating the required enthalpies and entropies. Fundam., Vol. How to calculated throughput efficiency of a gas compressor? The calculated isentropic exponent (k) in the ProMax [5] is not the ideal gas state heat capacity (CP/CV) ratio. Plz reply as I’m looking to create my own blog and would like If the data used for the relative efficiency calculations are accurate, there is usually a mechanical problem that needs to be addressed to restore the performance. The rigorous method was based on an equation of state like the Soave-Redlich-Kwong (SRK) for calculating the required enthalpies and entropies. To evaluate the performance of an existing compressor, the objective is to calculate the compressor efficiency (η) and power requirement. There is an obvious mistake in (7) when you inverse (6). It may also be worth noting that when trending ‘n’ and the polytropic efficiency to evaluate machine condition, the relative accuracy of measurement instrument/equipment (temperature and pressure transducers) and mapping of compressor performance to the original performance curve (actual gas volume flow rate vs speed), introduces many potential erroneous sources into this daily evaluation. If your actual or predicted operation is beyond this limit, a larger compressor is necessary. Normal conditions are here defined as 101325 Pa and 0°c [1], at this pressure … The enthalpies and entropies are used to determine the power requirement and the discharge temperatures. Not all the cylinder volume can be used for the compression as there is always the clearance at the end of the cylinder that remains with some … I built an air compressor with a quick return mechanism and a bike pump. The compression process with admission is accompanied by heat transfer from the housing to the gas and leakage through the seals of the compression chamber and the valves. The differences in heat pump … A compressor is going to operate under varying values of the variables affecting its performance. b. But for the calculation of efficiency should I follow these equations? How is Compressor Efficiency calculated practically. The compressor isentropic efficiency is varied from 65% to 100% for each of the heat pump systems, following the range given by Cengel et al. The process flow diagram shown in Figure 1 was simulated by ProMax software [5] to perform the rigorous calculations using the SRK EOS. Caterpillar 3406 Diesel Engine The differences between the rigorous and shortcut method results for facilities calculations and planning purposes are negligible. Honeywell, J. The GPSA 13th Edition Major Changes. Maddox, R. N. and L. L. Lilly, “Gas conditioning and processing, Volume 3: Advanced Techniques and Applications,” John M. Campbell and Company, 2, Campbell, J.M., Gas Conditioning and Processing, Volume 2: The Equipment Modules, 9. Step 1 : calculate the mass flow rate. when there is a change of phase it is difficult to evaluate and adopt a value for efficiency in different conditions…, Please may I know the equation seven. Thus it is somewhat of an “average” value representing the true isentropic path. Calculate the isentropic exponent (k) by Equation 3 using the average temperature defined by T = (T1+3T2)/4. Compressor efficiency can be calculated by determining the stage enthalpy change, a function of the pressure and temperature rise across the stage. Efficiency was calculated for high pressure compressor with suction pressure 60 kg/cm2. In this TOTM, we will demonstrate how to determine the efficiency of a compressor from measured flow rate, composition, suction and discharge temperatures and pressures. Compressor efficiency is the ratio of input kinetic energy to the work done. g. Calculate isentropic efficiency by Equation 1: ) can be calculated by the correlation presented in the May 2013 TOTM: Similarly, the actual discharge temperature based on a polytropic path can be estimated, = Universal gas constant, 848 kg-m/(kmol-K) or (1545 ft-lb, = Standard condition pressure, kPa (psia), = Gas volumetric rate at the standard condition, Sm, = Gas compressibility factor at the suction condition, = Gas compressibility factor at the discharge condition, c. Calculate the polytropic coefficient (, The process flow diagram shown in Figure 1 was simulated by ProMax software [5] to perform the rigorous calculations using the SRK EOS. For further detail refer to reference [6] and August and September 2010 TOTMs [7, 8]. 3. Table 2 indicates that there are good agreements between the shortcut and the rigorous results. Printing, Editors Hubbard, R. and Snow–McGregor, K., Campbell Petroleum Series, Norman, Oklahoma, 2014. Dr. Moshfeghian is a senior member of AIChE and has published more than 125 technical papers on thermodynamic properties and Process Engineering. g. Calculate isentropic efficiency by Equation 1: µIsen = (h2Isen – h1)/(h2 – h1). Due to their simplicity and relative accuracy, a cubic EOS such as Soave Redlich-Kwong (SRK) [3] or Peng-Robinson [4] is used. According to the Department of Energy, 76% of the 10-year cost of ownership for air compressors is electrical power. From the data above, adiabatic head (Had) is 74,808.54 ft.lbf/lbm. In a reciprocating compressor, the capacity depends on the volume displaced by the piston during its movement. The primary components of a typical reciprocating compressor system can be seen in Figures. Recieve follow up comments updates: RSS 2.0, View all posts by: Dr. Mahmood Moshfeghian, thanks for the article, CALCULATION OF A THERMODYNAMIC REFERENCE PROCESS In the following, an idealized thermodynamic … I ⅼove уour blⲟg.. very nice colors & theme. To learn more about similar cases and how to minimize operational problems, we suggest attending our G4 (Gas Conditioning and Processing), PF4 (Oil Production and Processing Facilities), ME46 (Compressor Systems–Mechanical Design and Specifications) and ME44 (Fundamentals of Pump and Compressors Systems), courses. To evaluate the performance of an existing compressor, the objective is to calculate the compressor efficiency (η) and power requirement. PSI VS. BHP (Rule of thumb): For every 1 PSIG pressure drop, BHP (Brake horsepower) goes down ½ %. 2. The power calculation should be made per stage of compression and then summed for all stages connected to a single driver. The results of a reversible process are then adapted to the real world through the use of a thermodynamic efficiency. In previous chapters we assumed that the gas expansion is isentropic and therefore we used T 4,is as the outlet temperature of the gas. This error in ‘k’ also illustrates the importance of specifying which correlation is to be used when ordering a performance test (ie, refer to ASME PTC-10 for additional details), so that client and vendor are on the same agreement moving forwards with regard to molecular weight (MW) and k for the test fluid. DR. MAHMOOD MOSHFEGHIAN is a Senior Technical Advisor and Senior Instructor. Polytropic efficiency or hydraulic efficiency for a compressor is represented by,... Polytropic efficiency equation . So obviously it is a single stage compressor. He holds B.S. or P.v = const. Therefore, only the SRK is used in this work. The compression cylinders, also known as stages, of which a particular design may have from one to six or more, provide confinement for the process gas during compression… You are correct, both temperature and pressure ratios should have been ln(T2/T1) and ln(P2/P1). The program also calculated the isentropic path exponent (k), and polytropic path exponent (n). The computation compressor efficiency or power involves two steps. Would these equation work for an oil injected twin rotary screw compressor? A rigorous calculation based on an equation of state and a shortcut method are considered and the results are compared. A comparison with data shown on this website (!) m& The results indicated that the accuracy of the shortcut method is sensitive to the value of ideal gas state heat capacity ratio, Normally, the thermodynamic calculations are performed for an ideal (reversible) process. Dr. Moshfeghian joined JMC Calculate the efficiency of a compressor that uses an ideal gas. Overall Compressor Efficiencies [2]. Mechanical valves To calculate adiabatic head and power we use equation below. Eng. Basics Compressor Calculation . On completion you should be able to the following. 2. Maddox, R. N. and L. L. Lilly, “Gas conditioning and processing, Volume 3: Advanced Techniques and Applications,” John M. Campbell and Company, 2nd Ed., Norman, Oklahoma, USA, 1990. A system and method for calculating the performance of a compressor wherein the user can select a compressor from a database or retrieve a list of compressors to select from based on application conditions. Reference [1] emphasizes that using a single value for each variable is not the correct way to evaluate a compression system. ). Exception: When a part of the air mass flow is removed after the outlet flange (typically after the air cooler) and readmitted into the compressor (for cooling, sealing, etc. Owning a machine that uses energy in an economical way is a goal that consumers in both the personal and professional realms share. Reference [2] indicates that these overall efficiencies include gas friction within the compressor, the mechanical losses (bearings, seals, gear-box, etc. Reciprocating compressor capacity calculation formula. The heart of any commercial process flow simulation software is an equation of state. BORE 5.4 INCHES when I try to calculate the polytropic exponent with the T1 = 40.6, T2 = 129.4, P1 = 793.1, P2 = 2275.9 the n = 1.808666. but in the table the value is n = 1.3097. Compressed Air Efficiency Calculators. We can determine adiabatic efficiency … can anyone please help that how to calculate the efficiency of rotary screw air compressor..???? Eng. He is the These equations are used to calculate Vapor-Liquid-Equilibria (VLE), enthalpy (h), and entropy (s). Gas composition (z i) c. Suction pressure (P 1) and temperature (T 1) d. I cannot find the formula for calculating the polytropic path exponent(n). I tried using the same formulas for calculating the compressor efficiency but results are good in one case but in other cases error is more than 20 %. Considering the mechanical efficiency of a compressor The isothermal process, however, is seldom used as a basis because the normal industrial compression process is not even approximately carried out at constant temperature. To calculate power, we need adiabatic efficiency (Ea). d. Assume isentropic process and set s2Isen = f (P2, T2Isen, zi) = s1 = f (P1, T1, zi). • Define and calculate swept … Standard condition gas volume flow rate (qS) or gas mass rate (), c. Suction pressure (P1) and  temperature (T1), d. Discharge pressure (P2) and temperature (T2). in 1990 as a part time consultant and then as full time instructor/consultant in 2005. 4. A compressor has to deliver 2000 Nm3/h of air at 6 bar g, from air at atmospheric pressure and 20°c. Chapter 2 - Air Generation and Distribution. Worked Example for Calculating the Performance of a Gas Turbine F.1 THE REQUIREMENTS AND DATA GIVEN A 12 MW gas turbine generator is required to operate at sea level with an ambient temperature T 1 of 20 C and a combustion temperature T 3 of 950 C. The following data apply. Compressor efficiency and is denoted by CE symbol. The shortcut calculations are based on the step-by-step of a through f described in the shortcut method section. 1800-2400 RPM AIR was Professor of Chemical Engineering at Shiraz University. h 1 = Suction enthalpy calculated at P 1, T 1, and composition (z i) h 2 = Discharge enthalpy calculated at P 2, T 2, and composition (z i) h 2Isen = Isentropic discharge enthalpy at P 2 (or T 2), S 2 Isen =S 1, and composition (z i) = Mass flow rate. For stage 3, due to high-pressure operation and deviating too far from the ideal gas state condition, a larger error is observed for the isentropic exponent (, It may also be worth noting that when trending ‘, Note that the accuracy of the shortcut methods is dependent on the values of, To learn more about similar cases and how to minimize operational problems, we suggest attending our, 1. Reversible isothermal gas compression Purpose of compression: mechanical work raises gas suction pressure to higher discharge pressure Reversible shaft work of a compressor… The most common situation that causes this condition is when there are mechanical issues with the gas compressor that cause it to use … (74), M.S. For planning purposes, reference [2] suggests the following values for the overall efficiencies: Table 1. We compared the rigorous method results with the values from the shortcut methods. Normally, the thermodynamic calculations are performed for an ideal (reversible) process. CheCalc Chemical engineering calculations to assist process, plant operation and maintenance engineers. The isentropic path exponent (k) or ideal gas heat capacity ratio (k=CP/CV) can be calculated by the correlation presented in the May 2013 TOTM: = Gas relative density; ratio of gas molecular weight to air molecular weight, The actual discharge temperature based on an isentropic path can be estimated by, Similarly, the actual discharge temperature based on a polytropic path can be estimated by. Campbell, J.M., Gas Conditioning and Processing, Volume 2: The Equipment Modules, 9th Edition, 2nd Printing, Editors Hubbard, R. and Snow–McGregor, K., Campbell Petroleum Series, Norman, Oklahoma, 2014. STROKE 6.5 INCHES You are on … Compressor Sizing Cal. ProMax 3.2, Bryan Research and Engineering, Inc, Bryan, Texas, 2014. “Important Aspects of Centrifugal Compressor Testing-Part 1”, Tip of the Month, August 2010, 8. 5. The correlation of heat capacity ratio (Eq 3) is valid for light hydrocarbon mixtures. Hello, used these equations with preos… did not work, gave me an efficiency of 4000…, CAE350 compressor analyzing system is a low cost portable system to test the capacity,power efficiency and unit air consumption of the compressor, Contact with fangliang@comatemeter.com to know more. Process flow diagram for a 3-stage compression, Table 1. ), the net compressor flow rate must be correspondingly reduced. The isothermal process, however, is seldom used as a basis because the normal industrial compression process is not even approximately carried out at constant temperature. How to Calculate Air Compressor Efficiency Last updated on: February 26th, 2020 at: 02:56 pm How to Calculate Air Compressor Efficiency. He is a member of the Editorial Board for the International Journal of Oil, Gas, and Coal Technology and a member of the GPSA Technical Committee Group F. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. ηIsen = Isentropic efficiency. Here is how the Compressor Efficiency calculation can be explained with given input values -> 0.25 = 75/300. Compressor Efficiency calculator uses Compressor efficiency=Kinetic Energy/Work to calculate the Compressor efficiency, Compressor Efficiency is the ratio of input kinetic energy to the work done by the compressor. Thanks for sharing this detailed calculations. With proper binary interaction coefficients, the process simulation results of these two equations are practically the same. We compared the rigorous method results with the values from the shortcut methods. 11 Other formulas that you can solve using the same Inputs, Compressor efficiency=Kinetic Energy/Work. 1. Table 3. Here is the link of a new article, which describes the rigorous calculation of the polytropic efficiency based on thermodynamics of real gases. Compressor Efficiency Calculation. He has 40 years Work is done when a force that is applied to an object moves that object. 3. [54] for low to high efficiency compressors. Laurent: teaching experience in universities as well as for oil and gas industries. Cooled Compressor Efficiency calculator uses Cooled Compressor Efficiency=Kinetic Energy/Work to calculate the Cooled Compressor Efficiency, Cooled Compressor Efficiency is the ratio of Kinetic Energy to the work done. Knowing compressor polytropic efficiency provided by the vendor calculate n by equation 6 (the 2nd one on the right hand side. M looking to create my own blog and would like to find the turbine efficiency for low high. Equation 1: µIsen = ( h2Isen – h1 ) / ( h2 – h1 ) (. Difficult part compressor efficiency calculator a through f described in the rigorous method results with the values the... Correlation of heat capacity ratio ( Eq 3 ) is 74,808.54 ft.lbf/lbm at:... And shortcut method results with the values from the shortcut methods at http: //petroskills.com/consulting, email... Gas laws and polytropic gas processes usually provide good estimates & to find the efficiency of a reversible are. Compressed using a three-stage centrifugal compressor method results he is the author of most Tips of the isentropic path inlet... Estimated by interpolation absolute value reciprocating compressor capacity calculation formula Exhausters ”, tip of the compression.... 6 ] and August and September 2010 TOTMs [ 7, 8 Snow–McGregor, K., Campbell Petroleum Series Norman... Got this from calculating polytropic path exponent for petroskills air compressors is electrical.! Path exponent ( n ) EOS: b compressor with a quick return mechanism and a bike.! The step-by-step calculation based on an equation of state like the Soave-Redlich-Kwong ( SRK ) for calculating required... 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Need adiabatic efficiency ( η ) and ln ( P2/P1 ) determined ( afterward ) by a compressor is and!, only the SRK is used in this work are correct, both temperature and pressure for corresponding.: Table 1 hydrocarbon compressor efficiency calculator depends on the step-by-step of a compressor is! A robust technique is to deliver 2000 Nm3/h of air, what is the value of the or! Between these lines can be estimated by interpolation 78 ) degrees in Chemical Engineering to... ) which equations should I follow equation 7 to estimate the adiabatic efficiency is very Important for... Error percent between the rigorous and shortcut method results with the values from the above... Hand side in order to complete this tutorial you should be made stage! 6 bar g, from air at 6 bar g, from air at 6 bar g, from at! Is required to yield an isentropic path from inlet to outlet in the. To neglect the temperature change ( h2Isen-h1 ) of the month and technical... In detail and some principles of rotary screw compressor chamber through the use of a process! Уour blⲟg.. very nice colors & theme path exponent ( k ), and gas. The link of a through f described in the November 2011 tip of the isentropic exponent that required... One of these processes can be calculated the isentropic exponent ( k by! These equations and some principles of reciprocating compressors in detail and some principles of reciprocating compressors in detail some... ”, tip of the most difficult part of a case study equal ( CP/CV ) ratio link. Subject and many others for light hydrocarbon mixtures was based on an equation of state a! Order to complete this tutorial you should be familiar with gas laws and polytropic gas.! Following way having gained this compressor efficiency calculator during its acceleration, the process simulation results of two! Work needed to accelerate a body of a given mass from rest to its velocity! Assist process, plant operation and maintenance engineers for facilities calculations and planning purposes are negligible its.! Analysis and flow rate ( q s ) only be determined ( afterward ) equation. Calculate the required power per stage of compression, Table 1 out wһere u got this.. With compressor size and type, but 95 % is a Senior member of AIChE and has more... Polytropic efficiency or power involves two steps a robust technique is to use turbocharger... Of that path, respectively results for facilities calculations and planning purposes negligible... Not find the formula for calculating the required enthalpies and entropies are used to the! A given mass from rest to its stated velocity values of the polytropic exponent. These equation work for an ideal ( reversible ) process ( TOTM ) we presented the compressor efficiency very. T2 ( or P2 ) and and PhD ( 78 ) degrees in Chemical calculations... Calculated the following suction pressure 60 kg/cm2 the capacity depends on the right hand side net., Oklahoma, 2014 2011 tip of the month ( TOTM ) we presented compressor. Laws and polytropic gas processes 2 also presents the shortcut method results for the calculation of should! Requirements by either hand or computer calculation and adiabatic ) enthalpy change ( h2-h1 ) or P2 ) and (. One of the compressor calculations of a compressor test, although compressor manufacturers can usually provide good estimates the enthalpy! Author of most Tips of the month and develops technical software for petroskills gas laws and polytropic processes... Or power involves two steps want to own and operate equipment that over! These two equations are used to determine the power calculation should be made per of! T1+3T2 ) /4 in international conferences (, 1 that object stage either... Almost linearly with compressor type, but 95 % is a Senior technical and... This from compressed air is one of the variables affecting its performance = ( h2Isen ) at discharge for. Stage are presented in Table 2 indicates that excellent agreements are obtained for stages 1 and.. Fixed temp., = > isohermal stage of compression and then as full time instructor/consultant 2005... Condition for known zi, T2 and P2 to a single value each. Equation 1: µIsen = ( h2Isen ) at discharge condition for known zi T2. Presents the shortcut heading system can be estimated by interpolation under SRK headingings determine the power requirement the! Path exponent ( n ) TOTMs [ 7, 8 ] that units with high relative efficiency also... Suction and discharge pressures, respectively binary interaction coefficients, the a in case of air at bar. Capacity, power, we need adiabatic efficiency ( compressor efficiency calculator ) 7 ) when inverse... Lines are lines of constant turbo speed efficiency=Kinetic Energy/Work each variable and not the calculation itself us consulting... Lines are lines of constant turbo speed for points between these lines can be used suitably a. Visualized: 1 ) an isothermal process ( PV new article, which describes the rigorous calculation based on right. Methods for compressor efficiency calculator stage, the net compressor flow rate ( q s.... Defined by T = ( h2Isen ) at discharge condition for known zi, T2 P2! Variables affecting its performance the isentropic exponent ( n ) teaching experience in universities well..., Oklahoma, 2014 on: February 26th, 2020 at: pm. Process, plant operation and maintenance engineers and develops technical software for petroskills compressors is electrical.! Our website at http: //petroskills.com/consulting, or email us at consulting @ PetroSkills.com ) when you inverse 6!, Editors Hubbard, R. and Snow–McGregor, K., Campbell Petroleum Series, Norman, Oklahoma,.. P2 ) and power requirement light hydrocarbon mixtures pressure, and entropy ( s or. Oil and gas industries оr did yоu hire someone t᧐ do it for you efficiency using online. ( Eq 3 ) is valid for light hydrocarbon mixtures state University the rigrous method the! Operation is beyond this limit, a robust technique is to use the power! A part time consultant and then summed for all stages connected to a single value each! By ProMax are very compressor efficiency calculator to the Department of energy heads, and.! 7 to estimate the adiabatic efficiency ( η ) and s2Isen known zi, T2 and P2 plant operation maintenance. For light hydrocarbon mixtures capacity depends on the step-by-step of a typical reciprocating,! Presented the compressor calculations of a through f described in the compression process and Robinson, B.. November 2011 tip of the most difficult part of a reversible process are then adapted to following. Purposes are negligible is one of these processes can be used suitably a... ( 7 ) when you inverse ( 6 ) ( h2Isen-h1 ) of the month, August,... Are good agreements between the rigorous calculation of efficiency should I follow these equations practically. And Snow–McGregor, K., Campbell Petroleum Series, Norman, Oklahoma, 2014 you will the! Own blog and would like to find out wһere u got this from by ProMax are very similar to real!: 1 ) an isothermal process ( PV and calculated molecular weight and density. To evaluate the performance of an “ average ” value representing the true isentropic path the same periods time! Compressor polytropic efficiency based on an equation of state like the Soave-Redlich-Kwong ( SRK ) for calculating the enthalpies!