1. C.K.PITHAWALA COLLAGE OF ENGG. & TECH.
Absorption type dynamometer
Mechnical Engg.
Group No.:- P/20
Guided By :- Gaurang Sir
Prepared By :-
Nakrani Kalpesh
Panchani Vikas
Vasavada Jenish
Kakadiya Sharad

2. Introduction of dynamometer
Sometimes the brakes are not only used to retard or stop the motion but these also used to measure the power absorb during breking. Such brake which have provision to measure the absorbed power are called as “dynamometer”.
Dynamometer: dynamometer is an instrument for measuring the power
exerted by a source or the amount of power consumed by a load.
A dynamometer is a load device which is generally used for measuring the
power output of an engine. Several kinds of dynamometers are common, some of them being referred to as “breaks” or “break dynamometers”: dry friction break dynamometers, hydraulic or water break dynamometers and eddy current dynamometers.

3. Types of Dynamometer
The following two types of dynamometers are considered: Absorbtion dynamometer 1. Prony brake dynamometer 2. Rope brake dynamometer Transmission dynamometer 1. Balt transmission dynamometer 2. Epicyclic dynamometer 3. Torsion dynamometer

4. Prony brake dynamometer
Prony brake dynamometer is the simplest type of absorbtion type dynamometer.
It consist of two wooden block clamp together on revolving pulley fixed to the shaft of the engine known as brake drum whose power is to be measured.The bolts and nuts are used to clamp the blocks.
Prony brake serves to provide the well defined load to engine, with the output power of the engine dessipited as a thermal energy of the breking material.
By adjusting the load, output power of engine over the range of speed and throttel setting can be realized.

5. Absorbtion type dynamometer
Prony brake dynamometer

6. Construction of Prony brake dynamometer
Prony brake dynamometer consist of two wooden blocks together on revolving pulley fixed to the shaft of an engine known as brake drums.
In order to adjust the pressure on pulley to control its speed, helical spring is provided between nut and upper block.
Long lever is attached to the upper blocks and its outer end a weight W is attached.
At the other end of the lever counter weight is placed which balances the brake when unloaded.
Two stoppers are provided to limit the motion of the lever.

7. Prony brake dynamometer
Breking torque on the shaft,
T = W × L
Brake power of the engine = Torque × Angular speed
P = T × ω = T × 2πN 60
Therefore,
P = W × L × 2πN watt
Where,
W = weight of the end of the lever L = horizontal distance of weight from center pulley
N = speed of the shaft F = frictional resistance between brake and pulley
R = radius of the pulley
Above equetion will calculate the brake power without knowing the value of coefficient of friction between blocks and pulley and pressure exerted by tightening the nuts.

8. Rope brake dynamometer

9. Rope brake dynamometer
Rope brake dynamometer consist of one, two or more ropes wrapped over the rim of the pulley keyed to the shaft of the engine.
The upper end of the ropes is attached to the spring balance while lower end carries a dead weight.
In order to prevent the sliping of the rope over the pulley, 3 to 4 ‘U’ shaped wooden blocks are placed at the interval around the circumaference of pulley.
If high power is produced, then heat is generated due to friction between rope and pulley or drum. To prevent this, pulley is provided with internal flanges on the rim, forming chennel for flow of the water to cool the pulley or drum.

10. Rope brake dynamometer
Equation of brake power,
W = Dead Weight
S = Spring balance reading
D = Dia. Of pulley or drum
N = Speed of engine
d = dia. Of rope
(W-S) = Net brake load
Frictional torque due to ropes =
( W - S) × [ D + d ] 2
But, the torque transmitted by the engine at constant speed equal to frictional torque due to ropes.

11. Rope brake dynamometer
Brake power P = torque transmitted × angular speed of engine
P = (W – S) × [ D + d ] × ω 2
= (W – S) × [D + d] × 2πN
P = (W – S) (D + d) πN watt 60
If the diameter of the rope is neglected,
Brake power, P = (W – S) πND watt

12. T H A N K Y O U