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Apparently, n is the exponent of the flow velocity V as shown on the diagram.foo9008 said:Homework Statement
what is the meaning of n here ? i only know the formula of head loss is f(L/ D ) (V^2) / (2g)
Homework Equations
The Attempt at a Solution
so , the formula of head loss still f (L)(v^n) / (2gD ) ? at turbulent region ?SteamKing said:Apparently, n is the exponent of the flow velocity V as shown on the diagram.
For laminar flow, the friction factor f is directly proportional to V.
For the transition zone, the friction factor is proportional to a certain power of V, which is expressed as f ∝ Vn, where n = 1.75 - 2.0.
For fully turbulent flow, f ∝ V2.
Yes, if you make n = 2.foo9008 said:so , the formula of head loss still f (L)(v^n) / (2gD ) ? at turbulent region ?
the book gave that for fully turbulent flow , n = 1.75-2.0 , THE CORRECT SHOULD BE for transition zone flow , n = 1.75-2.0 ?SteamKing said:Apparently, n is the exponent of the flow velocity V as shown on the diagram.
For laminar flow, the friction factor f is directly proportional to V.
For the transition zone, the friction factor is proportional to a certain power of V, which is expressed as f ∝ Vn, where n = 1.75 - 2.0.
For fully turbulent flow, f ∝ V2.
The roughness of the pipe wall also has an influence.foo9008 said:the book gave that for fully turbulent flow , n = 1.75-2.0 , THE CORRECT SHOULD BE for transition zone flow , n = 1.75-2.0 ?
for transition region , the relationship between the velocity and friction factor is not constant , it may vary ... so there's is discontinuous line on the graph , am i right ?SteamKing said:The roughness of the pipe wall also has an influence.
Look, the book is trying to establish an approximate relationship between the velocity of the flow and the friction factor, as illustrated by the diagram. For whatever reason, they would like this relationship to be a smooth curve throughout the flow regimes from purely laminar flow to purely turbulent flow.
The dashed line in the transition region appears to be an extrapolation of what happens after fully laminar flow has stopped and when fully turbulent flow is established.foo9008 said:for transition region , the relationship between the velocity and friction factor is not constant , it may vary ... so there's is discontinuous line on the graph , am i right ?
SteamKing said:The dashed line in the transition region appears to be an extrapolation of what happens after fully laminar flow has stopped and when fully turbulent flow is established.
When flow is laminar, the friction factor is directly proportional to flow velocity; when flow is fully turbulent, friction factor is proportional to flow velocity raised to the power indicated by the exponent on the graph. In the transition zone, there is some non-linear relationship between friction factor and flow velocity; it's not entirely linear, but it's not fully quadratic, either.
Darcy -weisbech equationgave that hf = fL(v^2) / 2gD , and Darcy -weisbech equation is for both laminar and turbulent , am i right ? why according to the graph , the friction factor is directly proportional to hf / shouldn't it be n= 2 ?SteamKing said:The dashed line in the transition region appears to be an extrapolation of what happens after fully laminar flow has stopped and when fully turbulent flow is established.
When flow is laminar, the friction factor is directly proportional to flow velocity; when flow is fully turbulent, friction factor is proportional to flow velocity raised to the power indicated by the exponent on the graph. In the transition zone, there is some non-linear relationship between friction factor and flow velocity; it's not entirely linear, but it's not fully quadratic, either.
If you look at the formulations of the D-W friction factor, you'll see that f for laminar flow is very different for f for fully turbulent flow.foo9008 said:Darcy -weisbech equationgave that hf = fL(v^2) / 2gD , and Darcy -weisbech equation is for both laminar and turbulent , am i right ? why according to the graph , the friction factor is directly proportional to hf / shouldn't it be n= 2 ?
i know that , when the flow is fully turbulent , the friction factor is independent of velocity , but for both laminar and fully turbulent flow , the head loss has the formula of fL(v^2) / 2gD , so for both flow , the hf is directly proportional to v^2 , am i right ? but the diagram for v and hf is proportional, is the diagram wrong ?SteamKing said:If you look at the formulations of the D-W friction factor, you'll see that f for laminar flow is very different for f for fully turbulent flow.
https://en.wikipedia.org/wiki/Darcy–Weisbach_equation
You also shouldn't confuse how f behaves with flow velocity with how head loss behaves with flow velocity. The Moody diagram, for example, establishes that for turbulent flow, f is independent of flow velocity.
The diagram in the OP documents Reynold's measurements of friction versus pipe length. It's not clear how well Reynold's measurements correlate with the work of others based on this one diagram.
There's only one diagram: a plot of head loss versus flow velocity made using data recorded by Reynolds.foo9008 said:i know that , when the flow is fully turbulent , the friction factor is independent of velocity , but for both laminar and fully turbulent flow , the head loss has the formula of fL(v^2) / 2gD , so for both flow , the hf is directly proportional to v^2 , am i right ? but the diagram for v and hf is proportional, is the diagram wrong ?
P/s: in the first diagram , it's a graph if hf vs velocity , not friction factor vs velocity
So, this is for to show expermintal data only? In real life, we wouldq use the formula hf = f(L/D)(V^2)/2g ?SteamKing said:There's only one diagram: a plot of head loss versus flow velocity made using data recorded by Reynolds.
Apparently, Reynolds chose not to use the modern formula, HL = f (L/D) v2 / 2g to plot his results. That's why there's a range of exponents. IDK why Reynolds chose this method; if you want to know, you'll have to research Reynolds work on the matter.
The N value in the Head Loss Formula is a dimensionless constant that represents the roughness of the pipe's interior surface. It takes into account factors such as the material of the pipe and any buildup of sediment or corrosion on the inside walls.
Friction in pipes causes resistance to the flow of fluid, resulting in a decrease in flow rate. This is due to the energy required to overcome the frictional forces and maintain the flow.
Friction in pipes is caused by the interaction between the fluid and the interior walls of the pipe. This can be due to factors such as the roughness of the pipe, sediment buildup, or changes in the fluid's velocity.
The N value for a specific pipe is determined experimentally through tests using a known flow rate and measuring the resulting head loss. The N value can also be estimated based on the material of the pipe and its surface roughness.
Understanding the N value in the Head Loss Formula is important for accurately predicting and calculating the head loss in a pipe due to friction. This information is crucial in designing and maintaining efficient piping systems.