Civil - Mechanics Of Fluids - Flow Through Pipes
FLOW THROUGH PIPES
1. What is meant by energy loss in a pipe?
When the fluid flows through a pipe, it loses some energy or head due to frictional resistance and other reasons. It is called energy loss. The losses are classified as; Majorlosses and Minor losses
2. Explain the major losses in a pipe.
The major energy losses in a pipe is mainly due to the frictional resistance caused by the shear force between the fluid particles and boundary walls of the pipe and also due to viscosity of the fluid.
3. Explain minor losses in a pipe.
The loss of energy or head due to change of velocity of the flowing fluid in magnitude or direction is called minor losses. It includes: sudden expansion of the pipe, sudden contraction of the pipe, bend in a pipe, pipe fittings and obstruction in the pipe, etc.
4. State Darcy-Weisbach equation OR What is the expression for head loss due to friction?
hf = 4flv2 / 2gd
where, h f = Head loss due to friction (m), L = Length of the pipe (m),
d = Diameter of the pipe (m), V = Velocity of flow (m/sec)
f = Coefficient of friction where V varies from 1.5 to 2.0.
5. What are the factors influencing the frictional loss in pipe flow? Frictional resistance for the turbulent flow is,
i. Proportional to v
ii. Proportional to the density of fluid. iiiProportional to the area of surface in contact. iv. Independent of pressure.
v. Depend on the nature of the surface in contact.
6. What is compound pipe or pipes in series?
When the pipes of different length and different diameters are connected end to end, then the pipes are called as compound pipes or pipes in series.
7. What is mean by parallel pipe and write the governing equations.
When the pipe divides into two or more branches and again join together downstream to form a single pipe then it is called as pipes in parallel. The governing equations are:
Q1 = Q2 + Q3 hf1 = hf2
8. Define equivalent pipe and write the equation to obtain equivalent pipe diameter.
The single pipe replacing the compound pipe with same diameter without change in discharge and head loss is known as equivalent pipe.
9. What is meant by Moody’s chart and what are the uses of Moody’s chart?
The basic chart plotted against Darcy-Weisbach friction factor against Reynold’s Number (Re) for the variety of relative roughness and flow regimes. The relative roughness is the ratio of the mean height of roughness of the pipe and its diameter (?/D).
Moody’s diagram is accurate to about 15% for design calculations and used for a
large number of applications. It can be used for non-circular conduits and also for open channels.
10. Define the terms a) Hydraulic gradient line [HGL] b) Total Energy line [TEL]
Hydraulic gradient line: It is defined as the line which gives the sum of pressure head and datum head of a flowing fluid in a pipe with respect the reference line.
HGL = Sum of Pressure Head and Datum head
Total energy line: Total energy line is defined as the line which gives the sum of pressure head, datum head and kinetic head of a flowing fluid in a pipe with respect to some reference line.
TEL = Sum of Pressure Head, Datum head and Velocity head
11. What do you understand by the terms a) major energy losses , b) minor energy losses Major energy losses : -
This loss due to friction and it is calculated by Darcy weis bach formula and chezy’s formula .
Minor energy losses :- This is due to
i. Sudden expansion in pipe .
ii. Sudden contraction in pipe .
iii. Bend in pipe .
iv. Due to obstruction in pipe .
12 . Give an expression for loss of head due to sudden enlargement of the pipe :- he =
Where he = Loss of head due to sudden enlargement of pipe .
V1 = Velocity of flow at section 1-1
V2 = Velocity of flow at section 2-2
13. Give an expression for loss of head due to sudden contraction : -
hc =0.5 V2/2g
Where hc = Loss of head due to sudden contraction .
V = Velocity at outlet of pipe.
14. Give an expression for loss of head at the entrance of the pipe : - hi =0.5V2/2g
where hi = Loss of head at entrance of pipe .
15. What are the basic educations to solve the problems in flow through branched pipes?
i. Continuity equation .
ii. Bernoulli’s formula .
iii. Darcy weisbach equation .
16. Mention the general characteristics of laminar flow.
• There is a shear stress between fluid layers
• ‘No slip’ at the boundary
• The flow is rotational
There is a continuous dissipation of energy due to viscous shear