Step 1 : calculate the mass flow rate. The outlet temperature from a real, adiabatic compressor that accomplishes the same compression is 520K. Between these two points there could be a pressure drop and an increase in enthalpy. The intercooler then cools to the air to 380 K, after which it enter the second stage of compression, which has an exit pressure of 12 MPa. Determination of the actual enthalpy change (h 2-h 1). For a system in which the mass flow rate is constant, COP becomes equal to the is hot. Both compression stages are adiabatic and reversible (a) Find the specific heat transfer in the intercooler (the amount of heat in kJ/kg that must be removed from... However, it is also possible to define a differential efficiency, assumed constant over the section, known as the polytropic efficiency, ηp, given by (17.72)η p = dws dw In the above method for finding COP the enthalpy increase dh2 is determined by measurement increase for such a process can be read off the chart (or calculated by the computer). Air enters an adiabatic compressor at 300 K, 1 atm pressure.The work input to the compressor is 350 kJ perkg of air flowing through the compressor. The missing input which was solved for [base SI] Notes. Output Pressure Range C. Energy-Related Metrics 1. Assume the feed composition remain unchanged. The enthalpy increase would be due to heat gain by Calculate: the heat added by the heat exchanger (between 2 → 3) the compressor outlet temperature of the gas (T 2,is) the real work done on this compressor, when the isentropic compressor efficiency is η K = 0.87 (87%) I have created a fair value and goodwill allocation schedule the real work done on this compressor, when the isentropic compressor efficiency is η K = 0.87 (87%) the turbine outlet temperature of the gas (T 4,is) the real work done by this turbine, when the isentropic turbine efficiency is η T = 0.91 (91%) the thermal efficiency of this cycle The gas flow rate is 5 kg/s. Thank you in advance! of the temperature and pressure at the end of the compression process. I would like someone to explain me/remind me why the definition of isentropic efficiency for the turbine and the compressor is different. evaporating and condensing temperature and this T 02 s: Isentropic outlet total temperature. 10/2007; 11/2007; 12/2007) which can only be cited, to keep this paper short. would need to be done in the case of an ideal or reversible compression process. η C = Isentropic compressor (pump) work/Actual compressor (pump) work Heat leaving the The net power output. Find the isentropic efficiency of the R-134a compressor in Example Air at 500 K, 500 kPa is expanded to 100 kPa in two steady flow cases. Most steady-flow devices operate under adiabatic conditions, and the ideal process for these devices is the isentropic process. How? 5. The computation compressor efficiency or power involves two steps. The definition of isentropic efficiency, equation (17.64), is based on a ratio of isentropic specific work to actual specific work, across a complete section of the compressor. The pressure drop Enthalpies and entropy are used to … (Note: These processes are not sequential processes; rather each of them is an independent, standalone p They all start at the same initial condition at state 1, but they end at different state 2.) Compressor Heat Loss energy input E less the heat loss H , and this quantity (E-H) Calculate the temperature after compression and the power input. These parameters describe how efficiently a turbine, compressor or nozzle approximates a corresponding isentropic device. Example of calculation of the compression power. A gas compressor compresses gas adiabatically from 1 bar and 15oC to 10 bar with an isentropic efficiency of 0.89. h 02 s: Isentropic outlet total specific enthalpy. It becomes warm. A centrifugal compressor (not a piston type) compresses the air from the ambient condition at T, 300K and Pi 1 bar to P 10 bar following three different, standalone paths: isentropic,... 1. Where: η Isen = Isentropic efficiency. The COP will be too high. P-h charts for all common working fluids (refrigerants) are available. Question:Thermo: Isentropic efficiency of a compressor. i.e. The compressor is to deliver 2000 Nm3/h of air. 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. The increase in enthalpy arises because work is done on the vapour Isentropic Efficiency. (COP). before and after compressor allows points 2 and 3 Provided the pressures are measured at the on a P-h chart. of the electrical power input. c Dr. Md. This is from a practice test and I want to be able to check my MANUAL CALCULATION OF ISENTROPICEFFICIENCY FROM ISENTROPIC HEAD AND BHP •Isentropic Head = 9616 m •BHP= 100 hp= 74.6 kW = 74600 W = 74600 kg-m2/s3 •Mass flow rate of gas= 4707 lb/h = 2136.978 kg/h = 0.593 kg/sec •Isentropic Efficiency= Mass flow rate x Polytropic Head x 9.8 m/s2 / BHP = 0.593kg/s x 9616m x 9.8m/s2 / 74600kg-m2/s3 = 0.74909 = 74.909 % •Isentropic Efficiency … It is called the isentropic efficiency of the compressor. inlet and outlet of the compressor, and the temperatures are measured in the appropriate places, Note that for perfection, the pressure at the evaporator outlet Usually, an ⋅⋅ && & An explanation of the Reversible Process, is in the the Understanding Refrigeration pages. There are two major contributors to … A compressor has to deliver 2000 Nm3/h of air at 6 bar g, from air at atmospheric pressure and 20°c. enthalpy, h, of the vapour is primarily temperature dependent. is hot. Measurement immediately R: Ideal gas constant. Thermodynamics Isentropic efficiency. measured enthalpy increase, i.e. the COP of the system can be found. The rate fell slightly, due to the law of volumetric efficiency, and isentropic efficiency increased slightly. For example if it is known that 5% of the electrical By definition the polytropic efficiency is equal to this infinitesimal isentropic efficiency. The inlet temperature to the turbine is Tz=1100°C. Pressure = 451.9 psig; Temperature = 254.4 °C [Steam Property Calculator] => Specific Enthalpy = 1,229.3 btu/lbm; Using the outlet specific enthalpy, calculate the isentropic efficiency: Gas compression occurs in isentropic process. Assume steady state, i.e. Examples of devices for which isentropic efficiencies are frequently calculated include turbines, compressors, nozzles and pumps. is in the 1. Accurate measurement of the pressures and temperatures at the positions shown above allows the efficiency of the Please see the attached document. The mass flow rate is... 1. There is no significant heat transfer with the surroundings, and KE and PE can be ignored. Compressors must meet specific criteria to be tested by the DOE. It is divided by the global efficiency of the reciprocating compressor, which can be assumed ~0.75 in 1st approximation if the constructor value is not known. Isentropic efficiencies of steady-flow devices in thermodynamic systems Most steady-flow devices operate under adiabatic conditions, and the ideal process for these devices is the isentropic process. Your material the Understanding Refrigeration pages. Saturated R134a vapor enters the uninsulated compressor of a home central air- conditioning system at 4 °C. the measured temperature values. In your report determine the performance of the ideal cycle operating with the same maximum cycle temperature, mass flow rate, and compression ratio. a) Determine the operating pressures of the cycle in bar.