# I Question about Jet engines (thermodynamics)

1. Nov 21, 2016

### Maximilian Popelier

Hi, I need help
I got a project for school about jet engines. They say bysubstitution of equations 5.1, 5.2, 5.5 and 5.6
butI don't know the steps how i get t0 the last formule.

Thank you
Maximilian Popelier

2. Nov 21, 2016

### Staff: Mentor

Take eq. (5.7) and replace $w_a$ and $q_a$ by the right-hand side of (5.5) and (5.6), and then further simplify using (5.1) and (5.2).

3. Nov 21, 2016

### Maximilian Popelier

Tank you very much i will try it tomorrow

4. Nov 22, 2016

### Maximilian Popelier

hi thank you..
but now i'm stuck here....

5. Nov 22, 2016

### Staff: Mentor

You made a mistake in the numerator. After having corrected that mistake, before you use equations (5.1) and (5.2), notice that η is 1 - something, so try to get that 1.

6. Nov 23, 2016

### Maximilian Popelier

Im sorry I tried it but im again stuck at the next step...

7. Nov 23, 2016

### Staff: Mentor

8. Nov 23, 2016

### Maximilian Popelier

My whole Project or just the formule?
Here is the formule:

#### Attached Files:

• ###### furmule gip.PNG
File size:
4.8 KB
Views:
42
9. Nov 23, 2016

### Staff: Mentor

You made a mistake in the last equality
$$1 + \frac{-a}{b} = 1 - \frac{a}{b}$$
$$1 + \frac{-a}{b} \neq 1 - \frac{a}{-b}$$

10. Nov 23, 2016

### Maximilian Popelier

owww... sorry but im still stuck

#### Attached Files:

• ###### fysica.PNG
File size:
3 KB
Views:
46
11. Nov 23, 2016

### Staff: Mentor

You can now take out a factor in front of the fraction.

12. Nov 23, 2016

### Maximilian Popelier

How if i do it i have do divise the T1 by the Factor

13. Nov 23, 2016

### Maximilian Popelier

i forgot the 1 -

14. Nov 23, 2016

### Staff: Mentor

Take a factor out of the numerator only.

15. Nov 23, 2016

### Maximilian Popelier

oke and then?

16. Nov 23, 2016

### Staff: Mentor

Then you should get eq. (5.8). You can write what you got in post #13 such that you get the same term in $T_1$ and $T_3$ in the numerator and the denominator.

17. Nov 23, 2016

### Maximilian Popelier

sorry i don't get it but i got this

18. Nov 23, 2016

### Staff: Mentor

Compare what is in the parenthesis with the denominator.

I now see you also made a mistake when changing $T_4$ to $T_3$ in the numerator.

19. Nov 24, 2016

### Maximilian Popelier

Nice i got it!!
Ty very much

20. Nov 24, 2016

### Maximilian Popelier

Oh i didn't get it i got a "-" wrong i will take a picture