Calculating (Seiliger) Cyclic Process - beginner question

[Gracy123]

Hi to all,

I am new here and hope that you would help me figure out a few things, that don't let me sleep lately

first one:

I'm given a Seiliger CP (Engine). Given is:

T1 = 300K
p1 = 2,25 bar
E = V1/V2 = 17
V(h) = V1-V2 = 0,003 m^3
R = Rair = 287,1 Nm/Kg*K (for the whole problem)
etc.
(* some of the letters might not be those you are used to see (like Vh for sure) as the data is given in German, sorry. I think Vh is translated Cubic Capacity in English, not sure...)

What I first did is I calculated V1 using the ideal gas low:

p*V1 = R*T1 ===> V1 = 0,3828 m^3

as V2 = V1/E = 0,0225 m^3

obviously something here is wrong, as Vh which is V1-V2 is no longer = 0,003m^3

I can also go ahead and use E and Vh and calculate as follows:

E = V1/V2 = 17 ==> V1 = 17*V2
Vh = V1 - V2 = 17*V2 - V2 = 0,003 m^3
==> V2 = 0,0001875 m^3 and V1 = 17*V2 = 0,0031875

This also looks more right, but why is the Ideal Gas low no longer valid here?? For the other steps (2,3,4,5) it is used again to find various unknows parameters...

I'm confused!?

Thank you in advance guys!!!

 

[CH5OH]

this seems like school stuff,
ideal gas law not pv=mrt?
E=compression ratio
V(h)=swept volume

 

[Latexman]

Homework is not allowed here.

Check your units on p*V1 = R*T1. V1 should be volume/moles.

Good luck,
Latexman

 

[Gracy123]

Nope... not school stuff )))

and R is R specific (Nm/Kg*K) - that's why no m or n.

 

[Latexman]

Sorry - didn't catch that first time through.

Good luck,
Latexman

 

[CH5OH]

R=Nm * K-1 * mol-1
P V = m R T
N * m-2 * m3 = mol * Nm * K-1 * mol-1 * K
Nm=Nm

or
R=Nm * K-1 * kg-1
P V = m R T
N * m-2 * m3 = kg * Nm * K-1 * kg-1 * K
Nm=Nm

you left out the amount of gas (mol or kg)

 

[Gracy123]

you are right! I was sleeping I guess

I am also trying to calcucalte the efficiency of the turbo compressor attached to the engine....

As far as I remember this should be possible based on the input and output temp and pressure...

I have:

Tin (atmospheric) - 273,15K
Pin (atmospheric) - 1 bar

Tout - 360K
Pout - 2,25 bar

Could anyone please remind me how this is calculated... the expected result should be about 0,82 ...

 

[CH5OH]

efficiency=work compressor * work turbo-1

 

[dcasto]

calculate the temperature of the discharge at a constant entropy (s) sin = sout. Look at change in enthalpy (H) for 100% eff work. Then iterate where delta entropy is greater than zero until discharge temp is equal to what you see. Look at delta H which will be greater than when delta s was 0. Compare the two delta H's