FLUID MECHANIC

Laminar Flow :Laminar flow is a flow regime characterized by high

momentum diffusion and low momentum convection. When a fluid is

flowing through a closed channel such as a pipe or between two flat

plates, either of two types of flow may occur depending on the velocity

of the fluid: laminar flow or turbulent flow.

 

Turbulent Flow: In fluid dynamics, turbulence or turbulent flow is a flow

regime characterized by chaotic property changes. This includes low

momentum diffusion, high momentum convection, and rapid variation

of pressure and flow velocity in space and time.

 

Most flows encountered in practice are turbulent.

 

DIFFERENCES between Laminar Flow AND Turbulent flow

Laminar Flow     -Path line for each particles are parallel.

                          -Low velocity

                          -Viscosity plays a significant part in laminar

                          -Velocity profile shown as parabolic curve.

 

Turbulent Flow    -Particles are in irregular path line

                            -High velocity

                            -Inertia plays a significant part in turbulent

                            -Velocity profile shown as logarithm curve

 

Reynolds number(Re)-Inertial forces

                                   Viscous forces

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reynolds number is used to determine the regime flow.

 

For flow in circular pipe:

Re<2300                                  Laminar Flow

2300<Re<4000                       Transitional flow

Re>4000                                  Turbulent flow

 

 

HERE IS THE VIDEO TO SHOW THE VARIOUS TYPES OF FLOW IN PIPE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FRICTION FACTOR,f

By estimating the friction factor, itis used in computing the loss of head in clean new pipes and in closed conduits running full with steady flow

-Reynolds number(Re) and relative roughness( e/D) WHERE e is pipe roughness and D is diameter of pipe when clculating the friction factor in pipe

-Relative roughness is not significant part in laminar flow but it solely depends on the viscosity.

  By calcuting the friction factor,(a) Find the Reynolds number

                                                       (b) Find the relative roughness

                                                       (c) Find the friction factor from moody chart or using formula below

                                      Friction factor(f)=64v/DV=64/R

 

Pipe roughness table:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MOODY CHART:Used to find friction factor

There are four zones in moody chart: Laminar flow,transition region,turbulent flow and critical region

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

HERE IS THE VIDEO TO SHOW HOW TO USE MODDY CHART TO FIND FRICTION FACTOR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In turbulent flow,relative roughness is significant when calculating the friction factor.

 

Friction Loss in pipe

-It means the loss of energy or head that occurs in pipe flow due to the viscous effects generated by the surface of pipe.

-It is divided into two ,wich are major loss and minor loss

When fluids flow in pipe, shear stress will occur.

This is due to the energy loss that can be measured by pressure differences.

Major loss-it occurs throughout the pipe flow

Minor loss-it is defined as the losses due to the local disturbances such as changes in cross section with elbows,valves,pumps and many others.

                    -it also can be divided into many types such as (a) loss of head at entrance

                                                                                             (b) loss of head at submerged discharge

                                                                                             (c) loss due to contraction

                                                                                             (d)loss due to expansion

                                                                                             (e)loss in elbows and bends

 

By calculating the friction loss in most of the time, we can use this formula:

 

 

                                                                                                                                                                    

                                                                               DARCY-WEISBACH EQUATION

 

 

 

 

 

 

                                               f:friction factor

                               L:length

                               D:diameter

                               V:velocity

                               g:gravity

 

Friction in noncircular conduits means friction caused when water flow through the noncircular pipe such as rectangular duct

Friction in circular conduits means friction caused when water flow through the circular pipe

 

 

In nonideal fluid dynamics, the Hagen–Poiseuille equation, also known as the Hagen–Poiseuille law, Poiseuille law or Poiseuille equation, is a physical law that gives the pressure drop in an incompressible and Newtonian fluid in laminar flow flowing through a long cylindrical pipe of constant cross section.It is used in laminar flow.