Isentropic efficiency is the efficiency of the ideal cycle w/o thermodynamic or mechanical losses. EXAMPLE 7–14 Isentropic Efficiency of a Steam Turbine Steam enters an adiabatic turbine steadily at 3 MPa and 4008C and leaves at 50 kPa and 1008C.
The minimum and maximum temperatures in the cycle are 310 and 900 K, and the pressure of air at the compressor exit is 8 times the value at the compressor inlet. The ... 2.1 STEP 1 : define the compressor polytropic efficiency. Please calculate or estimate overall efficiency of; For an isothermal process, is 1, so the value of the work integral for an isothermal process is: = − When evaluated, the isothermal work is found to be lower than the adiabatic work. 2. There is no significant heat transfer with the surroundings, and KE and PE can be ignored. This ratio is known as the Isentropic Turbine/Compressor/Nozzle Efficiency. The results of a reversible process are then adapted to the real world through the use of a thermodynamic efficiency. 1197-1203, 1972. So obviously it is a single stage compressor. For turbines, the value of η T is typically 0.7 to 0.9 (70–90%). 3. The isentropic efficiency for R22 is reduced approx. Read : Determine S o (T 2) for an isentropic process and then interpolate to obtain both T 2S and H 2S. f. Calculate the actual enthalpy (h2) at discharge condition for known zi, T2 and P2. This parameter reduces the overall efficiency and work output. Overall Compressor Efficiencies [2]. or P.v = const. Determination of the ideal or isentropic (reversible and adiabatic) enthalpy change (h2Isen-h1) of the compression process. ), and gear-box losses. You are correct, both temperature and pressure ratios should have been ln(T2/T1) and ln(P2/P1). 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. 4. 15, p. 59, 1976. Thus it is somewhat of an “average” value representing the true isentropic path. isobaric heat addition – the compressed air then runs through a combustion chamber, where fuel is burned and air or another medium is heated (2 → 3). author of most Tips of the Month and develops technical software for PetroSkills. 2. was Professor of Chemical Engineering at Shiraz University. There is no significant heat transfer with the surroundings, and KE and PE can be ignored. But for the calculation of efficiency should I follow these equations? The net specific work ( Wnet) from the gas turbine is: Eng. on compressor efficiency. Besides a strong sensitivity of isentropic efficiency, this results in a double limitation of range of use of the machine: the risk of surge at low flow (which depends on the network in which the compressor discharges), and stalling on the side of higher flow rates. As an example of an internal combustion engine, we show a computer drawing of a single cylinder of the Wright 1903 engine at the upper left. b. The isentropic efficiency of the compressor and turbine are 0.85 and 0.9 respectively. •Compressor performance can be evaluated using the isentropic efficiency, η c 02 01 02 01 Actual work of compression for given pressure ratio Ideal work of compression for given pressure ratio h h h h w w s c ci C K 11 is 85% practical? The specific heat ratio of the gas is used in the calculation of the power of an ideal compressor running in isentropic or adiabatic compression. Solving the above equation for the polytropic path coefficient (n): Similarly, the actual discharge temperature based on a polytropic path can be estimated (ηPoly) by: Similarly, the polytropic head is calculated by, For an isentropic (reversible and adiabatic) process the power is calculated by, Or for a polytropic process the power is calculated by, R = Universal gas constant, 848 kg-m/(kmol-K) or (1545 ft-lbf/(lbmol-°R)), PS = Standard condition pressure, kPa (psia), TS = Standard condition temperature, K (°R), qS = Gas volumetric rate at the standard condition, Sm3/d (scf/day), Za = Average gas compressibility factor = (Z1+Z2)/2, Z1 = Gas compressibility factor at the suction condition, Z2 = Gas compressibility factor at the discharge condition. Entropy is the property which remains constant for reversible processes. Table 2 also presents the shortcut caculation results for the corresponding values under the shortcut heading. 5. 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. Dr. Moshfeghian has presented invited papers in international conferences. consider non-contant values for properties from pin->pout, The isentropic efficiency of turbine can then be written as η T (h 2a - h 1)/(h 2s - h 1) where h 1 = enthalpy at the inlet h 2a = enthalpy of actual process at the exit h 2s = enthalpy of isentropic process at the exit : Isentropic Efficiency of Compressors and Pumps e. Calculate the ideal enthalpy (h2Isen) at discharge condition for known zi, T2 (or P2) and s2Isen. 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. I cannot find the formula for calculating the polytropic path exponent(n). It is compressed isentropically to a pressure of 5 bar. isentropic compression – ambient air is drawn into the compressor, where it is pressurized (1 → 2). 10/2007; 11/2007; 12/2007) which can only be cited, to keep this paper short. - Kinetic and potential energy changes are negligible. Table 2 indicates that there are good agreements between the shortcut and the rigorous results. For turbines, the value of ηT is typically 0.7 to 0.9 (70–90%). Some flexibility is indeed possible in this type of machine only … 5. The specific heat ratio of the gas is used in the calculation of the power of an ideal compressor running in isentropic or adiabatic compression. In particular the optimal design of the ring plate type suction and discharge valves has been studied. Compressor/fan performance •Compressors are to a high degree of approximation, adiabatic. Determine the overall diameter of the impeller. Determination of the actual enthalpy change (h2-h1). from a Caterpillar 3406 Diesel engine. 5. The ideal process’ isentropic efficiencies of the steam turbine and the pump are at a value of 100 %, and pressure losses in the condenser and the steam generator are non-existent, which would result in the thermal efficiency being equal to the Carnot efficiency. The calculations maybe, but the computer will do all the work, and it will do it almost instantly! For this example realistic figures have been chosen. The energy efficiency of the overall system changes from 26.6% to 34.1% as the isentropic efficiencies of the turbines varies from 50% to 90%. Example of axial dynamic compressor. I ⅼove уour blⲟg.. very nice colors & theme. The process flow diagram shown in Figure 1 was simulated by ProMax software [5] to perform the rigorous calculations using the SRK EOS. We compared the rigorous method results with the values from the shortcut methods. 4.1 Volumetric and Isentropic Efficiency of a Compressor with Inner Admission Normally, efficiencies express the ratio of a real value based on measurements to an ideal reference. For detail refere to: To evaluate the performance of an existing compressor, the objective is to calculate the compressor efficiency (, Standard condition gas volume flow rate (, The heart of any commercial process flow simulation software is an equation of state. 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. The correlation of heat capacity ratio ( Eq 3 ) is valid for light hydrocarbon mixtures part of a efficiency! 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