Reference [2] indicates that these overall efficiencies include gas friction within the compressor, the mechanical losses (bearings, seals, gear-box, etc. 8. The calculations performed by ProMax are very similar to the step-by-step of a through h described in the rigorous section. These parameters describe how efficiently a turbine, compressor or nozzle approximates a corresponding isentropic device. ηC = Isentropic compressor (pump) work/Actual compressor (pump) work. (W … 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. * (in isothermal process with cooloing) work of compression required in (recipro-comp) is minimum or low as compare to other process like isentropic and polytropic. The isentropic efficiency of a compressor is defined as the ratio of the minimum isentropic work to the actual work. An explanation of the Reversible Process, is in the the Understanding Refrigeration pages. 8. Isentropic efficiencies of the compressor and turbine Gas Turbine Engines MAE 115 – Applied Engineering Thermodynamics: Fall 2016 66/97 Deviation of Actual Gas ‐ Turbine Cycles from Idealized Ones • Reasons: Irreversibilities in turbine and compressors, pressure drops, heat losses The deviation of an actual gas ‐ turbine cycle from the ideal Brayton cycle as a result of irreversibilities. The shortcut calculations are based on the step-by-step of a through f described in the shortcut method section. 7. Thank you in advance! • Explain the ammonia vapour absorption cycle. In a reciprocating compressor, a volume of air is drawn into a cylinder, it is trapped, and compressed by piston and then discharged into the discharge line. A reciprocating compressor is a positive displacement machine in that a volume of gas is drawn into a compressor cylinder’s compression chamber where it is trapped, compressed and pushed out. 7. 0000002316 00000 n The isentropic path exponent (k) or ideal gas heat capacity ratio (k=C P /C V) can be calculated by the correlation presented in the May 2013 TOTM: Where: T = Temperature, K (°R) displacement compressors, written by the author (Lambers et al. Thank you in advance! 0000002073 00000 n 0000011683 00000 n 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. The process flow diagram shown in Figure 1 was simulated by ProMax software [5] to perform the rigorous calculations using the SRK EOS. This parameter reduces the overall efficiency and work output. The step-by-step calculation based on an EOS: b. 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. 0000027245 00000 n The cylinder valves control the flow of air through the cylinder; these valves act as check valves. Single – Acting compressor • Explain the cycle of a reciprocating compressor. The isentropic efficiency of a compressor is defined as the ratio of the minimum isentropic work to the actual work. o Reduce capital costs to half those of conventional reciprocating compressors by minimizing part count. DR. MAHMOOD MOSHFEGHIAN is a Senior Technical Advisor and Senior Instructor. Therefore power required to drive the compressor is actually more higher than the indicated power. The power calculation should be made per stage of compression and then summed for all stages connected to a single driver. 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. 109 0 obj • Solve problems involving reciprocating compressors in refrigeration. 0000001520 00000 n b. Isentropic efficiency for a screw compressor is strongly affected by under- and over-compression (UOC) processes. 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. 5. Chem. 13 Mechanical Efficiency, ηm Because there are moving mechanical parts in the compressor, it is likely that losses will occur due to friction. 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 <> 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. Integral compressors may be equipped with two to ten compressor cylinders with power ranging from 140 to 12,000 hp. %%EOF Therefore, only the SRK is used in this work. When calculating the compressor head and discharge temperature the efficiency used will be isentropic or polytropic (isentropic efficiency is sometimes called adiabatic efficiency). Then, an energy balance will give you (W S) min. 10/2007; 11/2007; 12/2007) which can only be cited, to keep this paper short. 0000002989 00000 n He is the common isentropic model formulates compressor isentropic efficiency as a bi-cubic relation involving pressure ratio, and compressor speed shown in figure 1, coefficients in Table 1. for low to high efficiency compressors. Mechanical efficiency varies depending on the size and type of compressor, but 95% is a useful planning number. It is called the isentropic efficiency of the compressor. 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