In thermodynamics, an isentropic process is an idealized thermodynamic process that is both adiabatic and reversible. The work transfers of the system are frictionless, and there is no net transfer of heat or matter. Such an idealized process is useful in engineering as a model of and basis of comparison for real processes. This is idealized as reversible processes do not occur in reality; thinking of a process as both adiabatic and reversible would show that the initial and final entropies are the same, thus, the reason it is called isentropic (entropy does not change). Thermodynamic processes are named based on the effect they would have on the system (ex. isovolumetric: constant volume, isenthalpic: constant enthalpy). Even though in reality it is not necessarily possible to carry out an isentropic process, some may be approximated as such.
The word "isentropic" can be interpreted in another way, since its meaning is deducible from its etymology. It means a process in which the entropy of the system remains unchanged, as mentioned this requires the process to be both adiabatic and reversible. However, this could also occur in a system where the work done on the system includes friction internal to the system, and heat is withdrawn from the system in just the right amount to compensate for the internal friction, so as to leave the entropy unchanged. However, in relation to the universe, the entropy of the universe would increase as a result.
In a certain thermodynamics textbook, specific work done by an isentropic compressor/pump in an ideal rankine cycles, is given by the following;
Wpump = h2 - h1
Wpump = v(P2 - P1), where v = v1
When I carry out these two calculations between any two states, I get vastly different answers...
In the book for our thermodynamics, it states that a process that is internally reversible and adiabatic, has to be isentropic, but an isentropic process doesn't have to be reversible and adiabatic. I don't really understand this. I always thought isentropic and reversible mean the same thing...
We know that if potential and kinetic energy our negligible, the isentropic efficiency of a compressor is isentropic enthalpy change divided by actual enthalpy change: n=(h2s-h1)/(h2a-h1)
So I already answered this question and here is the answer: n1 is the isentropic efficiency of the...
h and s can be obtained from "Saturated refrigerant-134a—Pressure table"
however, how to get h2? it is not on the curve, and neither p or dV is given in the question. Thank you
A short background: My question focuses solely on the part of the refrigeration cycle to do with the compressor, where the cycle begins. The first state is before the refrigerant enters the compressor, and the second state is after the refrigerant leaves the compressor. My goal is to obtain...
Hello forumites,
I've been working with the following expression for the change in internal energy in an isentropic scenario.
$$dU = n*c_v *dT = -pdV$$
However, I'm a bit stumped here, the left hand side of the expression (or middle rather), states the change in internal energy is the...
Homework Statement
Consider the isentropic expansion of air from a fixed given reservoir (i.e. total pressure and temperature). Investigate the behaviour of the value of the Reynolds number of the flow, as a function of the Mach Number M of the expanded flow.
For small values of M, the...
Homework Statement
Steam is expanded from 90 bar, 412°C to 4.0 bar saturation in a high pressure turbine, after-which a certain percentage of the steam is bled off to a feed heater. The remaining steam is then expanded through a low pressure turbine to 1.0 bar and dryness fraction of 0.93. All...
Homework Statement
for isentropic process, which of the following is true about the relationship of temperature and pressure?
(1): P2/P1=(T2/T1)^[γ/(γ-1)]
(2): P2/P1=(T2/T1)^[(γ-1)/γ]
where γ = 1.4 for air
Homework Equations
stated above
The Attempt at a Solution
I have found equation (1)...
Homework Statement
Water vapor at 6 MPa, 600C enters a turbine operating at steady state and expands to 10 kPa. The mass flow rate is 2 kg/s, and the power developed is 2626 kW. Stray heat transfer and kinetic and potential energy effects are negligible. Determine (a) the isentropic turbine...
Several questions:
What does compression actually means? In the case of isentropic calculations a changed in density (or specific volume) is included in the calculations (isentropic.jpg) so isentropic means that compressibility is included in those calculations or what?In a previous thread, a...
Homework Statement
Ive looked through several published journals online trying to find an experiment that I can use as background research for my report, something I can compare my findings to but I am just wasting lots of time that I could be doing the rest of my report so what I am trying to...
Homework Statement
We did an experiment which included having an electric motor provide power to drive the compressor and we had instrumentation available to measure the compressor shaft torque and shaft rotational speed and 6 water filled manometer tubes were used as measurements of the...
Homework Statement
We did a lab experiment for isentropic efficiency of a compressor and was asked to plot the following graphs, change in stagnation pressure across the compressor (∆p0) vs air mass flow rate, and isentropic efficiency vs air mass flow rate. I have plotted the graphs but not...
I have trouble understanding why we classify an inviscid adiabatic incompressible flow along a streamline as isentropic
I understand this from a Thermodynamic definition/explanation
$$dS = dQ/T$$
Adiabatic Invsicid
$$dQ =0= dS$$
So no heat added or lost no change in entropy I'm fine with that...
Halfway through my thesis on a mach 2 ramjet, and I unfortunately realize that I need 50-72 CFM to test it. The only ACs I have are 2 CFM portable pancakes. Is it possible to run say a 25 CFM AC at 50 CFM for a short period of 10-60 seconds? Is there a quantitative way to find how long the AC...
Homework Statement
Find the isentropic efficiency of the pump: effpump=(h4s-h3)/(h4-h3)
state 3: p3=1.5 bar, h3=467.11, x3=0, v3=1.0528/1000 m3/kg ,s3=1.4336 kJ/kg*K, T3=111.4 deg C
state 4: p4=60 bar, h4=474.14, compressed liquid
state 4s: p4=60 bar, s3=s4s
The values in red are the ones I...
Hi
can anyone help me about the following ?
if I have the experimental data of inlet and outlet of expander (temperature and pressure) working in ORC.
Now if I want to find the Isentropic efficiencie :
the Isentropic expansion can be found by (entropy in = entropy out)
but how to find the...
Hi,
I'm doing a high school physics project and am trying to figure out if a certain setup that I'm using is adiabatic or isothermal, in order to determine what equation I can use to calculate the work that my setup does-- the threads I've come across so far only explain the difference, but not...
Why do we always see the claim that an isentropic process for a system is adiabatic and reversible? The change in entropy for a process is the sum of the entropy transfer accompanying heat and the entropy production. The entropy production term is always at least zero, and the transfer term...
if a gas expands isentropically (consider the process reversible adiabatic), from point 1 in a nozzle to point 2 downstream of the nozzle. If you know the pressure and temperature at point 1, can you use the relationship pv=1/M RT to work out the specific volume at point 1? And similarly if you...
Homework Statement
Nitrogen enters an insulated compressor operating at steady state at 1 bar, 310 K with a mass flow rate of 1000 kg/h and exits at 10 bar. Change in KE and PE is zero. Heat transfer is zero. Assume ideal gas with k=1.391.
Find minimum theoretical power input required and the...
Homework Statement
\rho_0, c_0 is the mean density, the mean speed of sound in the ideal gas.
Is the following correct?
c(\rho)=c_0\left(\frac{\rho}{\rho_0}\right)^{\frac{\kappa-1}{2}}
Homework Equations
p = const * \rho^\kappa, c=\sqrt{\frac{\partial p}{\partial \rho}}
The Attempt at...
Isentropic means a process where entropy remains constant. Now formula for entropy is
ΔS = ΔQ/T
now in an isentropic process, ΔS=0...so that means ΔQ = 0 ...right?
but if ΔQ = 0, that is an adiabatic process.
so are isentropic and adiabatic processes are...
Homework Statement
A spherical air bubble in a lake expands as it rises slowly to the surface. At the point it starts to rise, the pressure is 2.00 atm, the temperature of the water is 10.0 ∘C, and the radius of the bubble is 5.00 × 10^−3 m. At the surface, the pressure is 1.00 atm and the...
Workdone= integral Pdv
a kg of saturated water was compressed isentropically from 1 bar to 10 bar.
I solved it in the following logic: Since water is incompressible dv=0 , work =0
But my answers was wrong.
The solution was integral Vdp where V is Vf at 1 bar
My doubt is , is workdone...
I am trying to understand my superchargers isentropic chart.
For an example case where a supercharger outputs 10m3/hr but the engine only takes 6.57m3/hr in capacity, I get a volume ratio (VR) of 1.52 - easy...
I can then work out a pressure ratio by VR^k = 2.0^1.4 = 1.8
The theoretical...
My classmates and I are working on a senior design project where we optimize a baseline turbofan for supersonic cruise. We are a little confused about when to use polytropic vs isentropic efficiencies. I have read to begin with isentropic, however is there anyone who could explain a little more...
I have been given a fundamental equation of a system as
u = \frac{s^4}{v^2}
After writing down the 3 equations of state, namely:
T = 4\frac{S^3}{VN}
P = \frac{1}{2}\frac{S^4}{V^{3}N}
\mu = -\frac{S^4}{VN^{2}}
I need to determine the equation of isentropic (dS = 0) processes on the P-V...
Hello all,
Its review time again for another Thermodynamics midterm. As such, I have a practice exam to try for optional extra review work. I've come across a problem that I'm somewhat stumped on. I've tried the problem, but I feel as though I've made too many assumptions in trying to solve...
Hello. I was working on a sample problem on my thermodynamics book about isentropic nozzles. Pressures, velocities, and temperatures of steam entering to a non isentropic nozzle and exiting it are known. The question asks me to find the velocity of the steam exiting, if the nozzle were...
Homework Statement
The power output of an adiabatic steam turbine is 5 MW. If the device can be assumed
to operate as a steady flow device with isentropic expansion, determine the
following:
i) The dryness fraction, x, at the exit from the turbine;
ii) The work output per unit mass of steam...
Hello,
I am looking at a problem concerning flow through a converging-diverging nozzle. The governing equations are relatively straight-forward for gasses that closely follow the ideal gas law. However I am looking at an unusual gas which is certainly not represented by the ideal gas...
Homework Statement
An amount of saturated steam at a pressure of 10 Bar, undergoes an isentropic (constant entropy) expansion. The final temperature is 30C.
Find the final specific enthalpy and specific volume.
Homework Equations
Saturated Steam tables, Linear Interpolation methods?
No...
i was reading an example of area calculation of a nozzle,in which mass flow rate was and coeff. of discharge (ratio of actual mass flow rate to isentropic mass flowrate) was given.
i though the mass flow rate given in example is isentropic and we will first calculate actual mass flowrate from...
Homework Statement
Saturated steam with a pressure of 30 bars is isentropically expanded to a pressure of 1 bar. What is the quality (x) of the steam after expansion?
Homework Equations
No clue. I do have a table containing all necessary data such as temperature, specific volume...
Homework Statement
An engine operates on an air cycle consisting of the following non-flow
processes in succession:
1-2 isentropic compression from an initial state of 80 kPa, 27°C and the
volume of 0.071 m
3
through the volume compression ratio of 17.75;
2-3 reversible heat...
I am a bit confused by the definition of an isentropic process in the flow of an ideal gas.
isentropic implies reversible & adiabatic.
for a process to be reversible, there are no losses to friction (viscosity in this case),
for a process to be adiabatic, there is no heat transfer with...
Hi,
I'm have big problems calculating the Isentropic Effeciencies of steam turbines. There is a HP, IP and LP turbine in the system. I know the calculation is (h1 - h2)/(h1 - h2'), i have the temperatures and pressures in and out for the first two turbines so i can easily get h1 and h2 from the...
Air at 1175 K, 8 bar enters a turbine operating at steady state and expands adiabatically to 1 bar. The isentropic turbine efficiency is 92%. Employing the ideal gas model with k=1.4 for the air, determine (a) the work developed by the turbine, in kJ per kg of air flowing, and (b) the...
Hi guys,
I'm struggling with some equations regarding the enthalpy change over a compressor in a vcc system.
I'm currently working on a model for the whole system and I think I've got all equations except the one describing the enthalpy difference betweeen the inlet and outlet of the...
I came up with my own design problem, after completing a refrigeration design problem on the completion of my thermo I class. My design problem is this: I want to accelerate air to 56m/s via a compressor and then a nozzle. I'm trying to do a cost analysis of how much power I would save if the...
I know the answer is 6328kW, I just not sure on how the book came up with that answer. Can anyone help?
An isentropic steam turbine processes 5 kg/s of steam at 4MPa,which is exhausted at 50 kPa and 100oC. 5% of this flow is diverted for feed water heating at 700kPa. Determine the power...
Hi everyone!
I have a question and I would be so thankful if you could help me!
For a Centrifugal Gas Compressor, if I have the flow rate, the input and output temperatures and pressures in specified rpm, then could I calculate its needed work, isentropic head and efficiency? how?
Thanks!
Sara
If I have a container containing a liquid mixed with some other substance that has much a higher boiling point (i.e. water and salt). This liquid will be in equilibrium with its vapor (the salt vapor pressure is negligible).
Now I quasi-statically adiabatically expand this vapor. Isentropic...
Hello.
I am writing a Matlab program for calculating properties and processes of dry air using real gas tables. The only tables I could find were from Perry's Chemical Engineer's Handbook (7th edition, 1999).
Mostly I make use of cubic interpolation and in some critical cases numerical...
Hi all,
Will like to check if my below thoughts are right:
1) For a totally reversible process, it has to be both internally and externally reversible. And the definition of externally reversible means heat transfer between a system and reservoir where the temperature are the same.
2)...
definition wise i got the difference between these two efficiencies.
but in practice how does these two differ?
i was referring to this book:
Jet propulsion: a simple guide to the aerodynamics and thermodynamic design ... By N. A. Cumpsty
he has mentioned this:
"using polytropic...
Homework Statement
I have a system u =Av-2exp(s/R)
N moles of this substance initially at T0 and P0 are expanded isentropically until the pressure is halved. What is the final temperature?
Homework Equations
du = \partialu\partials ds + \partialu\partialv dv
du = Tds - Pdv...
Homework Statement
Neon gas at the rate of 100kg/min enters an adiabatic turbine at a temperature and pressure of 1073K and 1.5 MPa. The gas leaves the turbine at a pressure of 200kPa. If the real(actual) power output of the turbine is 370 kW, determine the isentropic efficiency of the...