… n. Vp = 22 11. n. Tp Tp − = (1) 22 1 1. n. TV TV − = Compressor without clearance volume . After each compression stage, the gas was cooled to the feed temperature of 105 °F (40.6 °C). If you plot a P-V curve for the compression process and … The polytropic exponent n describing the adiabatic Pvn compression path can be estimated by Equation 3 where η is the polytropic efficiency shown in Figure 2 as a function of the inlet volumetric flow rate. For an ideal gas in a closed system undergoing a slow process with negligible changes in kinetic and potential energy the process is polytropic, such that (−) + =where C is a constant, =, =, and with the polytropic coefficient = (−) +. The inlet stagnation conditions are 15°C and 101.3 kPa. A trend of decreasing isentropic compressor efficiency is seen when increasing pressure ratio (at constant polytropic efficiency) (Saravanamuttoo et al., 2001, p. 61). Inserting this into the definition of the normal Isentropic Efficiency allows one to compute it in terms of η Poly and the finite pressure or temperature ratio: $ % 1 # c $ % #! This is illustrated in Fig. It looks that a preference of the polytropic efficiency in a gas compressor community is from a historical background. Subject Matter Expert Details Dr. SME Name : A.R.ANWAR KHAN Prof & H.O.D Dept of Mechanical Engineering Course Name: Applied Thermodynamics Type of the Course web Module VI 978 137(/ 10(,&7 3URMHFW 3DJH RI Dr. … In this research, the design data of axial flow compressor used in gas turbine engine is picked up from the Ta Dar Ooairway in Myanmar. One of the great interests of the polytropic concept lies in the simplicity of equation (4.1.9), which generalizes that of isentropic Pvγ = Const. Assume the feed composition remain unchanged. NPTEL Phase-I under grant in aid NMEICT, MHRD, New Delhi . The basics of these methods have been defined by Mr. Dzung who was working for Brown Boveri & Cie in the forties of the last century. December 2018 ; Acta Polytechnica CTU Proceedings 20:65-72; DOI: 10.14311/APP.2018.20.0065. The compressor is a standard single-stage barrel/bundle type centrifugal with a polytropic efficiency of >86%. This ratio is known as the Isentropic Turbine/Compressor/Nozzle Efficiency. For Polytropic process . Cite 29th Jun, 2017 The stage loading factor is 0.3, flow coefficient is 0.4, and stage reaction is 0.5. results of polytropic head and efficiency versus design compressor curves provided by the Manufacturer. Results and Discussions. Stagnation temperature rise for each stage is 15K. Ie. In the previous paper, we introduced the more efficient fixed displacement rotary vane compressors (new CR series) for car air conditioners. poly % 1 As an example, take a multi-stage compressor with an overall pressure ratio π c =16 and assume the polytropic efficiency is constant and equal to 0.9 in all stages. The polytropic head is a function of pressure ratio across the compressor and therefore will result in a pressure rise, assuming the inlet pressure is not changed. k may be estimated from molecular weight and temperature correlations or obtained from a commercial simulation program. Polytropic efficiency calculations are the preferred method for (one dimensional) performance simulation of Gas Turbines. Figure 1. High peripheral mean stage rotor velocities, around 300-340 m/s for subsonic rotors and up to about 580m/s for transonic ones, could be achieved. This paper describes the technology involved in analysis of compressor power, used in development of new series of Compressors . For certain values of the polytropic index, the process will be synonymous with other common processes. Vp. Three-stage compression with interstage cooling. An air pollution control device requires 0.23 cu.m./sec of free air. nn = 1 12 21. DEPARTMENT OF MECHANICAL ENGINEERING, GHOUSIA COLLEGE OF ENGINEERING, RAMANARA -562159 . An increase in centrifugal compressor speed will result in an increase in compressor polytropic head by a value equal to the square of the speed. The polytropic efficiency for transonic bladings is a bit lower (around “0.84” – “0.89”). Contents. The use of the polytropic efficiency requires the specification of the polytropic exponent (n) which will change depending on the working real gas and operating conditions, which would be inconsistent with the original intent. Inlet stagnation temperature and p° ressure is 288°K and 1 bar. - OME tool (OME stands for 'Online Monitoring of Efficiency') is a thermodynamic tool primarily intended for the monitoring of polytropic efficiency and head of a centrifugal compressor section with known end points (i.e. OME tool can … Typically, these design curves are given for specific suction conditions. Authors: Jiří Oldřich. Input power is the electric power supplied to the electric motor . Functions X and Y are generalized and plotted for gases in corresponding states. 1 Compression theory; 2 Oil and gas compressor uses. The relationship between polytropic exponent and efficiency can be used at design stage, to estimate the value of polytropic index \(n\) when the design stage polytropic efficiency \(\eta_p\) is known. 11 2 2 12. pV pV TT = 11 2 2. pV pV. In chemistry, we divide the universe into two parts. Double flow ducted dehumidifier line The DPG-DF series highly efficient dehumidifiers with energy recycling (double flow) are high quality appliances with the following specifications: Full insulation for indoor use. A compression or expansion process caused by movment of a piston in a cylinder. In recent years, improvement in energy efficiency of each component is desired for the fuel efficiency of any car. Relationship to ideal processes. The polytropic compressor efficiency is approximately equal to the hydraulic efficiency η p ... Lower COPs (4.78–6.55) correspond to lower compressor efficiency η comp s = 0.7) and lower ejector element efficiency (η pr = 0.85, η sec = 0.85, η mc = 0.95, η d = 0.60 (η ej = 0.30–0.35, T ′ = 22–29°C)). k/(k-1) = 0.695 x 1.4 /(1.4-1) = 2.432 assume maximum temperature tdmax = 200 C, Td1max = 473 K n pd Td max ( n −1 ) pressure ratio max. The polytropic coefficient can be calculated by knowing the polytropic efficiency of the compressor, given by the manufacturer, and an abacus. 11, EFp= 0.695. n/(n-1) = EFp. The further these conditions on site deviate from those prescribed at design, the less accurate the health assessment of the compressor becomes. Stage efficiency and polytropic efficiency is 84 % and 87 %. Shaft power is the power supplied by the electric motor to compressor. 2.11, where the polytropic efficiency of the compressor and turbine is assumed to be 0.87. However the isentropic and polytropic efficiencies could be estimated and were used to more accurately assess the performance of the compressor. Using polytropic efficiency gives a more accurate calculation of power required. same example , we assume that each stage has the same . Calculate the polytropic efficiency η Poly) by Equation 8. e. Calculate the isentropic and polytropic heads by Equations 9 and 10, respectively. Assume steady state, i.e. The polytropic efficiency of 86, 80, and 79 % based on the actual inlet volumetric rate (from Figure 13.23 of GPA Data book [2]) was specified for stages 1, 2, and 3 respectively. In a well-designed subsonic stage, polytropic efficiency could reach around “0.9”. Case Study. A 16-stage axial flow air compressor is to have a stagnation pressure ratio of 5.5 and tests have shown that the stage polytropic efficiency (or small stage efficiency) is 90%. RE: Polytropic efficiency … overall compressor efficiency will be lower than η s. If , for the . It can be seen from Equations 2.41 and 2.43 that, for a given polytropic efficiency, the compressor isentropic efficiency decreases, whereas the turbine isentropic efficiency increases with increase in pressure ratio. ISENTROPIC EFFICIENCY OF CENTRIFUGAL COMPRESSOR WORKING WITH REAL GAS. Blade aspect ratio and pitch-chord ratio are 3 and 0.5. c " = c $ % & c % 1 $ % 1 # c $! A centrifugal compressor has efficiency between 70-85% and it depends mainly on mechanical losses and gas friction within compressor, varying with its size. The key difference between adiabatic and polytropic processes is that in adiabatic processes no heat transfer occurs whereas in polytropic processes heat transfer occurs.. The real-gas equations of polytropic analysis are derived in terms of compressibility functions X and Y which supplement the familiar compressibility factor, Z. RE: Polytropic efficiency of turbomachinery sailoday28 (Mechanical) 11 Aug 05 18:35. This page provides an overview of the primary categories of natural gas compressor services and a description of the different classifications and types of compressors available to the industry. Since then formulas were used, which describe the (average) energy conversion in compressor and turbine bladings in gas turbines. The step-by-step calculation based on an EOS: a. The computation compressor efficiency or power involves two steps. If the volumetric efficiency is 78%, mechanical efficiency is 94% and the isothermal compression efficiency is 66%, Find: a) the metered flow per second (0.795 cu.m./sec) b) the indicated power in KW (181 KW) c) the power required to drive this compressor in KW ( 193 KW) d) the adiabatic compression efficiency ( 82%) 20. Efficiency of centrifugal compressor To determine head coefficient, preliminary efficiency shall be determine from Fig. Polytropic Compression: The practical understanding of the polytropic process and its usage in defining the compression process and efficiency is a development of the last three decades. Motor efficiency:- It is the ratio of shaft power to the input Power. A polytropic head factor, f, is introduced to adjust test results for deviations from perfect-gas behavior. In a polytropic compression process infinitesmal changes occur in terms of heat absorbed or heat removed during the entire compression process. and m p op . Polytropic efficiency is therefore a better indicator of compressor mechanical condition and performance, and so load allocation decisions should be made on the basis of polytropic, not adiabatic efficiency. The compressor is directly coupled to a standard mechanical drive aero-derivative gas turbine package. These parameters describe how efficiently a turbine, compressor or nozzle approximates a corresponding isentropic device. Figure 1 : principle of an abacus allowing to calculate the polytropic coefficient for a centrifugal compressor . I believe that the polytropic process is basically for non-flow type problems and where the mass does not change. 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