Calculating Major Head Loss Due to Pipe Friction

In summary: L(expansion) , we should also have also head loss due...You should have head loss for fittings beside the pump as well.
  • #1
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1. The problem statement, all variables and given/known
i am having problem of finding the major loss caused by pipe friction in this question. the formula of major loss is given by fL(V^2) / 2gD , how to get the total length of pipe so that i can gt the major head loss?
. Relevant equations

The Attempt at a Solution

 

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  • #2
foo9008 said:
1. The problem statement, all variables and given/known
i am having problem of finding the major loss caused by pipe friction in this question. the formula of major loss is given by fL(V^2) / 2gD , how to get the total length of pipe so that i can gt the major head loss?
. Relevant equations

The Attempt at a Solution

The length of pipe is shown at the bottom of the figure, to wit: 120 m of pipe, d = 50 mm
 
  • #3
SteamKing said:
The length of pipe is shown at the bottom of the figure, to wit: 120 m of pipe, d = 50 mm
But, that's part of the pipe, right? Not the total length? How to find the total length??
 
  • #4
foo9008 said:
But, that's part of the pipe, right? Not the total length? How to find the total length??
No, it's the total length. The diagram just may not be clear on that point.
 
  • #5
SteamKing said:
No, it's the total length. The diagram just may not be clear on that point.
Why are you sure it's total length?
 
  • #6
foo9008 said:
Why are you sure it's total length?
Well, if it isn't, you've got a problem, since you don't have a scaled drawing from which you can estimate total length of pipe.
 
  • #7
SteamKing said:
Well, if it isn't, you've got a problem, since you don't have a scaled drawing from which you can estimate total length of pipe.
Ok, thanks
 
  • #8
SteamKing said:
Well, if it isn't, you've got a problem, since you don't have a scaled drawing from which you can estimate total length of pipe.
my working is
P1 / ρg +z1 + (v^2) /2g -hL(entrance) -hL(open valve) +hL(pump) -hL (expansion) -hL(elbow) -hL(half open-valve)-hL(exit) - 32 μL(kinematic viscocity) / ρg(D^2) = P2/ ρg + (v2^2) / 2g + z2
do i have left out anything ?
so the power required = ρgQ(hL pump)
32 μL(kinematic viscocity) / ρg(D^2) = major loss due to friction in pipe
 
  • #9
foo9008 said:
my working is
P1 / ρg +z1 + (v^2) /2g -hL(entrance) -hL(open valve) +hL(pump) -hL (expansion) -hL(elbow) -hL(half open-valve)-hL(exit) - 32 μL(kinematic viscocity) / ρg(D^2) = P2/ ρg + (v2^2) / 2g + z2
do i have left out anything ?
It's not clear that the flow for this system is laminar, which is what the formula 32 μLν / ρg(D2) is for.

You also have a centrifugal pump in the system, which must be treated separately from the rest of the piping and fittings. The pump is not a point of head loss, for example, but it provides a certain amount of head at its outlet to discharge fluid into the remainder of the piping system.

You have hL (expansion) - hL(elbow) immediately after the pump. The hL (elbow) should be the loss for a screwed 90° fitting, but the hL (expansion) should be the hL for an elbow which has an inside diameter of 50 mm (to match the connecting piping) and a bend radius of 300 mm. There should be a formula or table in your text so that you can determine the head loss for this fitting.
so the power required = ρgQ(hL pump)
32 μL(kinematic viscocity) / ρg(D^2) = major loss due to friction in pipe
It's not clear that the flow for this system is laminar, which is what the formula above is for.
 
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  • #10
SteamKing said:
It's not clear that the flow for this system is laminar, which is what the formula 32 μLν / ρg(D2) is for.

You also have a centrifugal pump in the system, which must be treated separately from the rest of the piping and fittings. The pump is not a point of head loss, for example, but it provides a certain amount of head at its outlet to discharge fluid into the remainder of the piping system.

You have hL (expansion) - hL(elbow) immediately after the pump. The hL (elbow) should be the loss for a screwed 90° fitting, but the hL (expansion) should be the hL for an elbow which has an inside diameter of 50 mm (to match the connecting piping) and a bend radius of 300 mm. There should be a formula or table in your text so that you can determine the head loss for this fitting.

It's not clear that the flow for this system is laminar, which is what the formula above is for.
that's why i have positive hL(pump)

my hL(expansion ) comes from this part (refer to the picture uploaded) , yes , my hL(elbow ) refers to the head loss due to 90 degree elbow

do you mean beside the hL(expansion) , we should also have also head loss due to the 300mm bend , so we have to find the Kl(coefficient ) from the specific table ? ?
 

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  • #11
one more question , is roughness ratio = e / D ? or e only ? P/s : in this question , i was given that the roughness ratio = 0.008 , i am not sure this refer to e or e / D , can someone clarify ?
kXY54ho.png

i need e / D to find the friction factor
8igH5U8.png


P /s : this is turbulent flow , pls ignore my 32 μL(kinematic viscocity) / ρg(D^2) earlier .
 
  • #12
foo9008 said:
that's why i have positive hL(pump)

my hL(expansion ) comes from this part (refer to the picture uploaded) , yes , my hL(elbow ) refers to the head loss due to 90 degree elbow

do you mean beside the hL(expansion) , we should also have also head loss due to the 300mm bend , so we have to find the Kl(coefficient ) from the specific table ? ?
It's not clear from the diagram what the hL(expansion) is referring to. AFAIK, the piping is the same diameter before and after the pump.

And

Yes, any fitting or bend which is not straight pipe will have a different head loss which needs to be accounted for. This includes the bend with 300 mm radius.
 
  • #13
SteamKing said:
It's not clear from the diagram what the hL(expansion) is referring to. AFAIK, the piping is the same diameter before and after the pump.

And

Yes, any fitting or bend which is not straight pipe will have a different head loss which needs to be accounted for. This includes the bend with 300 mm radius.
but , the text stated that the diameter are different , namely 300mm and 50mm . But , the picture show the same diameter . Ok , if we follow the text , the hL (expansion) = [(1.53- 0.011)^2 ] / (2x 9.81) ,
0.003 = π[(25x10^-3 ) ^2 ] v1 ( before expansion), 0.003= π[(300x10^-3 ) ^2 ] v2 (after expansion), v1 = 1.53m/s , v2 = 0.011m/s

is it correct ?
 
  • #14
foo9008 said:
one more question , is roughness ratio = e / D ? or e only ? P/s : in this question , i was given that the roughness ratio = 0.008 , i am not sure this refer to e or e / D , can someone clarify ?
kXY54ho.png

i need e / D to find the friction factor
8igH5U8.png


P /s : this is turbulent flow , pls ignore my 32 μL(kinematic viscocity) / ρg(D^2) earlier .
The absolute roughness ε is usually measured in mm. The relative roughness (ε/D) is non-dimensional.

I think in the table above, the absolute roughness coefficient k should just be the absolute roughness.

The roughness ratio of 0.008 you were given for this pipe suggests that the absolute roughness was taken from the middle of the "new cast iron" range of the table above, which is conservative.

EDIT: Corrected comment about the roughness ratio of the pipe.
 
  • #15
foo9008 said:
but , the text stated that the diameter are different , namely 300mm and 50mm . But , the picture show the same diameter . Ok , if we follow the text , the hL (expansion) = [(1.53- 0.011)^2 ] / (2x 9.81) ,
0.003 = π[(25x10^-3 ) ^2 ] v1 ( before expansion), 0.003= π[(300x10^-3 ) ^2 ] v2 (after expansion), v1 = 1.53m/s , v2 = 0.011m/s

is it correct ?
No, it is not.
You haven't provided any text, except what's on the diagram.
The diagram clearly states "300 mm bend radius". The pipe being bent is still d = 50 mm.

There is little point to putting a larger size fitting in the middle of smaller pipe size before and after the fitting.

The headaches of fabrication alone would not recommend this.
 
  • #16
SteamKing said:
The absolute roughness ε is usually measured in mm. The relative roughness (ε/D) is non-dimensional.

I think in the table above, the absolute roughness coefficient k should just be the absolute roughness.

The roughness ratio of 0.008 you were given for this pipe suggests that the absolute roughness was taken from the middle of the "new cast iron" range of the table above, which is conservative.

EDIT: Corrected comment about the roughness ratio of the pipe.
so , it should be / (surd f ) = 2log ( 3.7 / 0.008 ) ?
 
  • #17
foo9008 said:
so , it should be / (surd f ) = 2log ( 3.7 / 0.008 ) ?
Yes.
 
  • #18
SteamKing said:
No, it is not.
You haven't provided any text, except what's on the diagram.
The diagram clearly states "300 mm bend radius". The pipe being bent is still d = 50 mm.

There is little point to putting a larger size fitting in the middle of smaller pipe size before and after the fitting.

The headaches of fabrication alone would not recommend this.
the full text is two reservoirs are connected by pipe of 50mm diameter .The water with dynamic viscosity = 10^-7 (m^20 /s is pumped from 1 to 2 at 0.006(m^3) /s . Compute the pump power required with roughness ration = 0.008 .
 
  • #19
foo9008 said:
the full text is two reservoirs are connected by pipe of 50mm diameter .The water with dynamic viscosity = 10^-7 (m^20 /s is pumped from 1 to 2 at 0.006(m^3) /s . Compute the pump power required with roughness ration = 0.008 .
See. There's nothing in this text about any 300 mm diameter pipe. It's the bend radius which is 300 mm, as shown on the diagram. :smile:
 

1. What is major head loss due to pipe friction?

Major head loss due to pipe friction is the decrease in the total energy of a fluid that occurs as it flows through a pipe. This loss of energy is caused by the friction between the fluid and the walls of the pipe.

2. How is major head loss calculated?

Major head loss is typically calculated using the Darcy-Weisbach equation, which takes into account factors such as the fluid velocity, pipe diameter, and roughness of the pipe walls. The equation can be solved using a variety of methods, including hand calculations or computer software.

3. What are the units for major head loss?

Major head loss is typically measured in units of length, such as feet or meters. This is because it represents the height of a column of fluid that would have the same amount of energy as the lost energy due to friction.

4. How does pipe material affect major head loss?

The material of the pipe can have a significant impact on the amount of major head loss that occurs. Pipes with rougher surfaces, such as cast iron, will have higher friction and therefore higher major head loss compared to smoother pipes, such as PVC.

5. Can minor head loss be ignored when calculating major head loss?

No, minor head loss should not be ignored as it can also contribute to the overall head loss in a pipe system. Minor head loss is caused by factors such as bends, valves, and fittings, and can be calculated separately and added to the total head loss to get a more accurate result.

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