# Homework Help: Friction loss is significant in short pipe

1. Apr 8, 2016

### foo9008

1. The problem statement, all variables and given/known data
i was told that the friction loss is significant in short pipe , but not so significant in long pipe . However , the friction formula is given by formula f(L/D)(V^2)/2g , as L is big , friction loss is big . so the friction loss is big , right ?

2. Relevant equations

3. The attempt at a solution

2. Apr 8, 2016

### SteamKing

Staff Emeritus
I wouldn't always be so credulous of what "somebody" tells you. Friction loss depends not only on L/D, but also V.

3. Apr 8, 2016

### foo9008

it was written in a book .... why the friction loss due to entrance effect is significant in short pipe , but not so significant in long pipe ????

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4. Apr 8, 2016

### SteamKing

Staff Emeritus
Well, why do you think this situation would be so?

What is the relative loss due to entrance effect compared with the loss in a section of straight pipe?

Note: Your original post mentioned only friction losses. Now, you are talking about losses due to entrance effects. It's important to disclose all information at the start of a discussion to prevent misunderstandings.

5. Apr 8, 2016

### foo9008

sorry , i mean friction due to entrance effect . why it is negligible in long pipe ? the friction formula is given by formula f(L/D)(V^2)/2g , as L is big , friction loss is big . so the friction loss is big , right ?

6. Apr 8, 2016

### SteamKing

Staff Emeritus
So, if the friction loss in a long pipe is relatively large, what about the ratio of the entrance loss to the friction loss in the long pipe? Is it a large ratio or a small ratio?
Is the entrance loss affected by the length of the pipe to which it is applied?

7. Apr 8, 2016

### foo9008

if the friction loss in a long pipe is relatively large, the ratio of the entrance loss to the friction loss in the long pipe woul be small , ?
due to this reason , the friction loss due to entrance effect is negligible ?

8. Apr 9, 2016

### SteamKing

Staff Emeritus
In a long pipe.

How would the friction loss due to the entrance effect compare to the friction loss in a short pipe?

9. Apr 9, 2016

### foo9008

the friction loss in short pipe is small , so the friction due to entrance effect is significant in short pipe compared to the friction loss in short pipe??????

10. Apr 9, 2016

### SteamKing

Staff Emeritus
Yes.

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