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. Cite 29th Jun, 2017 Case Study. In recent years, improvement in energy efficiency of each component is desired for the fuel efficiency of any car. - 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. Motor efficiency:- It is the ratio of shaft power to the input Power. overall compressor efficiency will be lower than η s. If , for the . For Polytropic process . The real-gas equations of polytropic analysis are derived in terms of compressibility functions X and Y which supplement the familiar compressibility factor, Z. The compressor is a standard single-stage barrel/bundle type centrifugal with a polytropic efficiency of >86%. Typically, these design curves are given for specific suction conditions. Blade aspect ratio and pitch-chord ratio are 3 and 0.5. … Assume constant work done in each stage and similar stages. 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 trend of decreasing isentropic compressor efficiency is seen when increasing pressure ratio (at constant polytropic efficiency) (Saravanamuttoo et al., 2001, p. 61). Stage efficiency and polytropic efficiency is 84 % and 87 %. 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. c " = c $ % & c % 1 $ % 1 # c $! 11, EFp= 0.695. n/(n-1) = EFp. Determination of the ideal or isentropic (reversible and adiabatic) enthalpy change (h 2Isen-h 1) of the compression process. An air pollution control device requires 0.23 cu.m./sec of free air. in measurement mode, pressure and temperature at compressor inlet and outlet flanges are supplied as inputs, and can either be measured or specified data). Using polytropic efficiency gives a more accurate calculation of power required. 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. 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. RE: Polytropic efficiency … 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. Polytropic efficiency calculations are the preferred method for (one dimensional) performance simulation of Gas Turbines. I believe that the polytropic process is basically for non-flow type problems and where the mass does not change. Assume the feed composition remain unchanged. 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%. Ie. The step-by-step calculation based on an EOS: a. OME tool can … The overall efficiencies are given by: m a oa . … However the isentropic and polytropic efficiencies could be estimated and were used to more accurately assess the performance of the compressor. 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. … December 2018 ; Acta Polytechnica CTU Proceedings 20:65-72; DOI: 10.14311/APP.2018.20.0065. n. Vp = 22 11. n. Tp Tp − = (1) 22 1 1. n. TV TV − = Compressor without clearance volume . It looks that a preference of the polytropic efficiency in a gas compressor community is from a historical background. Since then formulas were used, which describe the (average) energy conversion in compressor and turbine bladings in gas turbines. These parameters describe how efficiently a turbine, compressor or nozzle approximates a corresponding isentropic device. For certain values of the polytropic index, the process will be synonymous with other common processes. 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. In the previous paper, we introduced the more efficient fixed displacement rotary vane compressors (new CR series) for car air conditioners. Input power is the electric power supplied to the electric motor . A polytropic head factor, f, is introduced to adjust test results for deviations from perfect-gas behavior. ISENTROPIC EFFICIENCY OF CENTRIFUGAL COMPRESSOR WORKING WITH REAL GAS. Assume steady state, i.e. Vp. 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. 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. same example , we assume that each stage has the same . The inlet stagnation conditions are 15°C and 101.3 kPa. Authors: Jiří Oldřich. The compressor is directly coupled to a standard mechanical drive aero-derivative gas turbine package. The polytropic efficiency for transonic bladings is a bit lower (around “0.84” – “0.89”). RE: Polytropic efficiency of turbomachinery sailoday28 (Mechanical) 11 Aug 05 18:35. The further these conditions on site deviate from those prescribed at design, the less accurate the health assessment of the compressor becomes. 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. 2.11, where the polytropic efficiency of the compressor and turbine is assumed to be 0.87. f. Calculate the required power per stage by either Equation 11 or 12. NPTEL Phase-I under grant in aid NMEICT, MHRD, New Delhi . 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 stage loading factor is 0.3, flow coefficient is 0.4, and stage reaction is 0.5. 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 … 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 $ % #! polytropic efficiency ... the compressor inlet and outlet, which is of type: Pvk = Const (4.1.9) k is called the polytropic coefficient of the process. 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. Inlet stagnation temperature and p° ressure is 288°K and 1 bar. A centrifugal compressor has efficiency between 70-85% and it depends mainly on mechanical losses and gas friction within compressor, varying with its size. results of polytropic head and efficiency versus design compressor curves provided by the Manufacturer. Shaft power is the power supplied by the electric motor to compressor. The key difference between adiabatic and polytropic processes is that in adiabatic processes no heat transfer occurs whereas in polytropic processes heat transfer occurs.. Adiabatic and polytropic compression theory are discussed with supporting definition of terminology. The part we are going to … 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. 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. Figure 1. The computation compressor efficiency or power involves two steps. This ratio is known as the Isentropic Turbine/Compressor/Nozzle Efficiency. 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. In a well-designed subsonic stage, polytropic efficiency could reach around “0.9”. In a polytropic compression process infinitesmal changes occur in terms of heat absorbed or heat removed during the entire compression process. Functions X and Y are generalized and plotted for gases in corresponding states. Calculate the polytropic efficiency η Poly) by Equation 8. e. Calculate the isentropic and polytropic heads by Equations 9 and 10, respectively. nn = 1 12 21. Relationship to ideal processes. 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. A compression or expansion process caused by movment of a piston in a cylinder. 1 Compression theory; 2 Oil and gas compressor uses. At testing stage the polytropic index \(n\) can be obtained from the test results of suction and discharge pressure temperatures. and m p op . Efficiency of centrifugal compressor To determine head coefficient, preliminary efficiency shall be determine from Fig. Determination of the actual enthalpy change (h 2-h 1). 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. The polytropic coefficient can be calculated by knowing the polytropic efficiency of the compressor, given by the manufacturer, and an abacus. k may be estimated from molecular weight and temperature correlations or obtained from a commercial simulation program. This paper describes the technology involved in analysis of compressor power, used in development of new series of Compressors . 11 2 2 12. pV pV TT = 11 2 2. pV pV. In chemistry, we divide the universe into two parts. Stagnation temperature rise for each stage is 15K. 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)). 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. Contents. The compressor, the defrosting cycles, to manage air humidity, air heating and alarms. Figure 1 : principle of an abacus allowing to calculate the polytropic coefficient for a centrifugal compressor . Three-stage compression with interstage cooling. b. This is illustrated in Fig. DEPARTMENT OF MECHANICAL ENGINEERING, GHOUSIA COLLEGE OF ENGINEERING, RAMANARA -562159 . Results and Discussions. This parameter reduces the overall efficiency and work output. 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