1/17/2023 0 Comments Turbine thermodynamics calculator![]() ![]() The mechanical efficiency varies with compressor size and type, but 95% is a useful planning number. Reference indicates that these overall efficiencies include gas friction within the compressor, the mechanical losses (bearings, seals, gear-box, etc.), and gear-box losses. For planning purposes, reference suggests the following values for the overall efficiencies: They can only be determined (afterward) by a compressor test, although compressor manufacturers can usually provide good estimates. A rigorous calculation based on an equation of state and a shortcut method are considered and the results are compared.Ĭompressor efficiencies vary with compressor type, size, and throughput. 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. Note that Dresser Rand is doing quite a lot of work with “Near constant temperature” compression especially for CO 2 compression from vent stacks. 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. Any one of these processes can be used suitably as a basis for evaluating compression power requirements by either hand or computer calculation. In the compression process there are three ideal processes that can be visualized: 1) an isothermal process (PV 1 =C 1 ), 2) an isentropic process (PV k =C 2 ) and 3) a polytropic process (PV n =C 3 ). The results of a reversible process are then adapted to the real world through the use of a thermodynamic efficiency. Normally, the thermodynamic calculations are performed for an ideal (reversible) process. ![]() Reference emphasizes that using a single value for each variable is not the correct way to evaluate a compression system. Thus the most difficult part of a compressor calculation is specification of a reasonable range for each variable and not the calculation itself. A compressor is going to operate under varying values of the variables affecting its performance. The results indicated that the accuracy of the shortcut method is sensitive to the value of ideal gas state heat capacity ratio, k.įrom 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. The enthalpies and entropies are used to determine the power requirement and the discharge temperatures. The rigorous method was based on an equation of state like the Soave-Redlich-Kwong (SRK) for calculating the required enthalpies and entropies. We compared the rigorous method results with the values from the shortcut methods. In the November 2011 tip of the month (TOTM) we presented the compressor calculations of a case study. ![]()
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