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# HGL and EGL at nozzle watch

1. in the two notes , the shape of graph at the gradual contraction region is are different , which is correct ? the first one ? or the second one ?
in the first picture , we can see that the gradient of graph of HGL is increasing downwards , whereas in the second photo , the gradient of HGL is decreasing downwards? in the second picture , the shape of EGL at gradual contaction region is also different with the first one ? which is correct ?

Attached Images

3. I don't think I really understand what you are asking, but in the second picture there's a head or pressure loss as the fluid enters the expansion, whereas the nozzle in the first picture appears to be joined straight onto the pipe, with no expansion, and hence no hear or pressure loss due to an expansion.
4. (Original post by Smack)
I don't think I really understand what you are asking, but in the second picture there's a head or pressure loss as the fluid enters the expansion, whereas the nozzle in the first picture appears to be joined straight onto the pipe, with no expansion, and hence no hear or pressure loss due to an expansion.
no , i am asking about the region where the nozzle ' contract gradually ' , i dont understand why the shape of graph for HGL is different .... can you explain ?

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5. I'm still not entirely sure what it is you're asking. Both graphs show the HGL decrease through the nozzle. The second one looks fine to me, although I am not sure why the first one, assuming it's the red line, goes down vertically at the end.
6. (Original post by Smack)
I'm still not entirely sure what it is you're asking. Both graphs show the HGL decrease through the nozzle. The second one looks fine to me, although I am not sure why the first one, assuming it's the red line, goes down vertically at the end.
concentrate on the HGL line , we can discover that the shape of 2 graph at the nozzle is different , why are they different ? can you explain , both are decreasing at the nozzle , but the gradient is different , the gradient of the first one is increasing downwards , while the second one is decreasing downwards... which one is correct?
7. (Original post by wilson dang)
concentrate on the HGL line , we can discover that the shape of 2 graph at the nozzle is different , why are they different ? can you explain , both are decreasing at the nozzle , but the gradient is different , the gradient of the first one is increasing downwards , while the second one is decreasing downwards... which one is correct?
OK, I think I see now.

According to this:

http://www.engineeringtoolbox.com/en...ine-d_613.html

the HGL curve looks similar to the first image you have posted. But I also think this could be an issue of trying to look too closely at a small section of a graph that is meant to represent the entire system. I would clarify with your lecturer next time you see him/her.

Or, you could even plot your own HGL going through a nozzle to see what happens, making up your own numbers, using something like Excel.
8. (Original post by Smack)
OK, I think I see now.

According to this:

http://www.engineeringtoolbox.com/en...ine-d_613.html

the HGL curve looks similar to the first image you have posted. But I also think this could be an issue of trying to look too closely at a small section of a graph that is meant to represent the entire system. I would clarify with your lecturer next time you see him/her.

Or, you could even plot your own HGL going through a nozzle to see what happens, making up your own numbers, using something like Excel.
No, I just wanna know which one is correct, I am just first year uni students, haven't do into so deep. I just wanna the rough idea only

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9. (Original post by wilson dang)
No, I just wanna know which one is correct, I am just first year uni students, haven't do into so deep. I just wanna the rough idea only

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If you could plot your own HGL line you would see which one is correct. It has been five years since I have covered material like this so I am quite rusty. It shouldn't take too long to plot a quite graph using Excel, if you make up your own parameters. Say, water going into a 20 cm long nozzle that goes from a diameter of 10 cm to 5 cm, with 10 m of head going into it.
10. But the problem is I dunno know to carry out the experiment and I dont have the devices, I hope someone can clarify for me

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11. Just out of curiosity, what brand of engineering is it that you study? HGL appears to be more relevant to open-channel flow or flow where the pipe is not full. Hence, I don't think that some of the assumptions I was going to use hold correct, and I'm not sure what's going on.
12. I plotted the HGL for the nozzle I described above, with an inlet velocity of 2 m/s and it looked pretty much like the first image, except the line did not go vertical. Playing around with the numbers produces the same shape of graph (although sometimes the HGL goes negative towards the end of the nozzle).
13. (Original post by Smack)
I plotted the HGL for the nozzle I described above, with an inlet velocity of 2 m/s and it looked pretty much like the first image, except the line did not go vertical. Playing around with the numbers produces the same shape of graph (although sometimes the HGL goes negative towards the end of the nozzle).
what do you mean by the line didnt go vertical ? which line are you referring to ?
do you also mean the graph of HGL in the second picture is wrong ?
14. (Original post by wilson dang)
what do you mean by the line didnt go vertical ? which line are you referring to ?
do you also mean the graph of HGL in the second picture is wrong ?
In your first graph, the HGL appears to go vertical at the outlet of the nozzle. I didn't get that.
15. (Original post by Smack)
In your first graph, the HGL appears to go vertical at the outlet of the nozzle. I didn't get that.
Then, what do you get, can you show your graph??

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16. (Original post by wilson dang)
Then, what do you get, can you show your graph??

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Sure.
Attached Images

17. (Original post by Smack)
Sure.
So, the second figure in post 1 is wrong???

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18. I don't know really.
19. Actually looking at the first graph, it kinda looks like the red line representing the HGL is drawn on and not part of the notes. Is this correct?

Also, as I said in post 7, I think this could be an issue of trying to look too closely at a small section of a graph that is meant to represent the entire system. I would clarify with your lecturer next time you see him/her.
20. (Original post by Smack)
Actually looking at the first graph, it kinda looks like the red line representing the HGL is drawn on and not part of the notes. Is this correct?

Also, as I said in post 7, I think this could be an issue of trying to look too closely at a small section of a graph that is meant to represent the entire system. I would clarify with your lecturer next time you see him/her.
do you have any idea now ?

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