### Discussion :: Chemical Engineering Basics - Section 1 (Q.No.4)

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Priti Singh said: (Mar 15, 2013) | |

Friction factor f is entirely dependent on the nature of the material so roughness is a measure so as density and viscosity of the fluid passing through the pipe. |

Giri said: (May 31, 2013) | |

dp=4flv2(density)/2g. So it should depend upon length. |

Abhilash said: (Jul 29, 2013) | |

We can calculate it by equation 16/Re. where Re is the Reynolds no. and as we know that Re = density*vel*dia/viscocity. |

Thabasum said: (Jul 31, 2013) | |

hfs = (4flv^2)/2d it's simplifies. f = (hfs*2d)/(lv^2). f is doesn't depends on l and v. |

Anjali said: (Oct 9, 2013) | |

But one Formula says that it depends on length. dh = (4*f)* (l/d)* (u2/density*g) Than...? |

Sachin said: (Oct 24, 2013) | |

As F= 16/Nre. And Nre= density*v*l/viscosity. So it depend on length and not depend upon mass flow rate. |

Hardik said: (Dec 3, 2013) | |

As for Calculating the Fanning Factor density and viscosity required. and then friction factor is 2*fanning factor*length*square of velocity/Dia of Pipe. SO ITS DEPEND ON LENGTH. |

Hardik Sharma said: (Dec 3, 2013) | |

To calculate the velocity (if it is not given) by continuity Eqn. Mass flow is required so I think it does not depend on roughness. |

Subhra Kanti Dhar said: (Jan 23, 2014) | |

For laminar flow in pipe f=16/Re. & for turbulent flow in pipe f=0.0791*Re^-0.25. And Re depends upon fluid density, dynamic viscosity, dia of the pipe, fluid velocity. So Re does not depend upon length. That is why f is independent of length. |

S.K. said: (Jun 7, 2014) | |

Can someone please explain how friction factor depends on mass flow rate of the fluid? |

Narendra said: (Jun 7, 2014) | |

F depends upon Re and Re doesn't depend upon length and roughness depend upon dia only so A. |

Vishal said: (Jul 17, 2014) | |

But as we know h = 4flv2/2gd. |

Mohammad said: (Jul 27, 2014) | |

Hi Guys. Greetings. As far as the friction factor is concerned it is true that the friction factor is independent of length, why ? The answer is f is a dimensionless number and is a ratio of the shear stress at the wall of a conduit to the kinetic energy or velocity head of the flow, and thus you will not find any dependence of f(friction factor) on length. Hope this answers your question. |

A.K said: (Aug 2, 2014) | |

If we keep eyes on formula there is length in it. So how can you say that it does not depend on length. |

Mohammad said: (Sep 20, 2014) | |

@A.K. The formula is hf = 4fLv2/2gD. Which is made to find out the friction loss in the pipe, so the friction loss hf (frictional head) is dependent on length (how long we want to pump a fluid). To find out friction factor value we prefer Analogies (Reynold or Colburn Analogy etc) which are fully based on dimensionless numbers(Prandtl and Stanton number) in those numbers you will never find any length factor. On this basis I'm claiming the friction factor is independent of length. Hope this answers your question. |

Zakawat said: (Mar 13, 2015) | |

Re = flv2/2gD. From above relation we can conclude that friction factor depend upon length of pipe. But f is independent of mass flow rate a/c to me. |

Aka said: (Jan 12, 2016) | |

Pressure drop due to frictional loss is (4fLv^2)/(2gD). Where f is the fanning friction factor. And that is dependent on Reynolds number which is Dv*rho/mu. Question asked is related to frictional factor and not pressure drop die to frictional losses. |

Aka said: (Jan 12, 2016) | |

Due* Frictional* Hence frictional factor is not dependent on length. |

Nain said: (Jul 13, 2016) | |

@Muhammad. Very well done, Thanks. |

Saswata said: (Jul 19, 2016) | |

f = 16\ Re. -> Re = Dvd\vicosity. |

Raghu said: (Sep 4, 2016) | |

For laminar flow friction factor doesn't depend on length & diameter of the pipe. But in the turbulent flow, it definitely depends on length and diameter because friction factor is a relative shear stress between fluid layers. |

Suraj Singh said: (Oct 1, 2016) | |

When the flow of liquid then in pipe flow work below the ATM pressure hence friction formula says depend on length but not a roughness because roughness is different for different material. |

Prem said: (Feb 13, 2017) | |

They asked f for the pipe. f equals 16/re. for a pipe Reynolds no. diameter is considered. re for a flat plate length is considered. So for a pipe, since diameter is considered to calculate Reynolds no. Pipe length is not required. Friction factor is independent of pipe length. |

Sushil said: (Jun 20, 2017) | |

@ALL. Here the length given may refers to the (entrance length) afterwards the flow becames fully developed and hence friction factor start existing. |

Laxman said: (Mar 9, 2018) | |

Pipe roughness; fluid density & viscosity and mass flow rate of fluid if these parameters u alter, frictional losses of particular will change. Isn't it? What is going to do by increasing or decreasing length. |

Ivana said: (Oct 14, 2018) | |

@Laxman. When the length increases friction losses increase. But f is independent of length. |

Ritik Gupta said: (Oct 23, 2018) | |

It does not depend upon length but its depend upon flow rate because if the flow rate is high then friction is less. So, A is the right answer. |

Ajama said: (Apr 10, 2019) | |

Thanks all for explaining. |

M. Aaisha Banu said: (May 7, 2019) | |

In turbulent flow the friction formula also based length of the pipe. Then how should it be independent on the length? Please explain. |

N.D.Madhani said: (Oct 14, 2019) | |

Friction factor does not depends on pipe length. |

Dhanaji said: (Dec 20, 2019) | |

Oh really. It should depend on length by looking at the formula we can say this. Also by logic, more the length more will be the friction. Please correct me if I am wrong. Thanks. |

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