To Investigate the Relationship Between Specific Energy (e) and Depth of Flow(y) In a Laboratory Flume.

Objectives:

1.      To study the variations in specific energy as a function of depth of flow for a given discharge in a lab flume.

2.      To validate the theories of E-Y diagram( S.E and Depth) diagrams.

Apparatus:

—  S6 glass sided Tilting lab flume with manometric flow arrangement and slope adjusting scale.

—  Point gauge (For measuring depth of channel)

Related theory:

Specific Energy:     

            It is the energy of cross-section of open channel with respect to the channel bed. S.E if the total energy per unit weight measured relative to the channel’s bed and mathematically,

Where:

E = Specific Energy per unit weight

y = Depth of Flow

If we put Channel Width = b

Then           and     

Hence

Specific Energy remain same or constant along the channel flow having uniform flow condition.

Specific Energy Diagram:           

            It is a plot between specific energy as a function of depth of flow.

For channel of known geometry

Figure 2.1:      Plot of Specific Energy Curves

Froude’s Number (F_r):

            It is the ratio of inertial forces to the gravitational forces. Mathematically it is:

Critical Depth:

            It is the depth of flow that occurs when specific energy is minimum for a given discharge and Froude No. is equal to one (F.N = 1)

Critical Flow:

            It is the flow that occurs when depth of flow is equal to critical depth.

Super Critical Flow:

            It is the flow in which Kinetic Energy (K.E) is more as compare to Potential Energy (P.E)

OR

Flow for which the depth of flow is less than the critical depth and velocity is high.

y < yc , v > vc

OR

Flow when Froude’s number is greater than one. (Fr > 1)

Sub Critical Flow:

            Flow for which the depth of flow is more than the critical depth and velocity is low.

           y  > yc , v < vc

OR

Flow when Froude’s number is lesser than one. (Fr < 1)

Critical Velocity:   

            The velocity of flow at critical depth is called as critical velocity.

Alternate Depth:

For any value of specific energy other than the critical value there are two depths of flow one greater than the critical depth and other less than the critical depth these are called as alternate depth.

Procedure:

• 1      Maintain the constant Discharge in open channel.
• 2      For one particular value of flow, find out the water depths at the different locations and calculate the average depth of flow.
• 3      Calculate the specific energy.
• 4      Repeat this by varying the value of slopes.
• 5      Draw E – y curves.
• 6      Find out the critical depths and E_min

Precautions:

·         Take discharge readings only when flow is steady.

·         The height should not be measured near the joints or at points where there is turbulence in flume.

·         The height measuring needle must be adjusted precisely.

·         The tip of the needle must be just touching the water surface while taking observations.

Observation and Calculation

Width of Channel b = _______________

Length of the Channel = _____________

Sr No.	Discharge (Q)	Slope	Avg Depth 'y' (mm)				Area of Flow (A)	v	E
	m3/s		y1	y2	y3	yavg	m2	m/s	m
1
2
3
4
5
1
2
3
4
5
1
2
3
4
5

E – y graph

Comments