Lab Manual-ENGI32651-Falling Ball Viscometer PDF

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FLUID MECHANICS (ENGI32651)

Laboratory Manual Falling Ball Viscometer

Objective In this experiment the aim is to determine the viscosity of one or several fluids at atmospheric pressure and constant temperature.

Introduction Viscosity of a fluid is that property of the fluid, which resists the action of a shear force. Since viscosity depends on the combined effect of molecular activity and cohesion, the viscosity of liquids, particularly at low temperature, has greater effect than molecular activity, it decreases as the temperature increases. One equipment used in the fluid viscosity experiment is the Falling Ball Viscometer. To derive the equation for the dynamic viscosity of a fluid, we shall consider a sphere with a diameter d and specific weight γ s , falling at a constant velocity V through the liquid with viscosity η , specific weight γ l , and density ρ . The forces acting on the sphere are shown in the figure below:

Fig: Free body diagram of the falling sphere After applying the equilibrium condition in vertical direction, the dynamic viscosity can be expressed as,

d ( γ S −γ l) η= 18 V 2

It is worth noting that due to wall effect, the velocity of the ball should be modified when:

spehere diameter (d ) 1 > tube dimatere( D) 3 The observed fall velocity

V 0 then must be corrected using:

( )

V 9d + 9d =1+ 4 D 4D V0

2

Prepared by: Mohammad Lutful Arefin

When a standard glass capillary viscometer such as the Cannon-Fenske Routine Viscometer is used, the dynamic viscosity is determined using the following formula:

η=K ∙ t Where K is the equipment constant and t is the time the ball took to travel between the two marks (upper and lower) on the viscometer.

Equipment There are many standard experimental techniques used to evaluate the viscosity of a fluid. Some of the simple an popular techniques make use of the following equipment: (i) Falling ball viscometer (ii) Cannon-Fenske Routine Viscometer

Procedure Follow instruction during the lab experiment and also consult other literature

Data Table 1: Data needed to evaluate specific weights of oils Test # Cylinder Mass when empty (gm) A B C

Cylinder A Cylinder B Cylinder C

Measure Measure Measure

Table 2: Data for the test balls Ball type Diameter (in) Steel Measure Glass Measure

Diameter (ft) Convert Convert

Mass when filled (gm) @volume (ml) Measure @300 ml Measure @100 ml Measure @100 ml

Density (gm/ml) 8.02 2.53

Type of oil TURBOFLO R&O 100 SAE 30 SAE 30

Density (Kg/m3) Convert Convert

Specific weight Find Find*

* convert density to Kg/m3, and then multiply with g (=9.81 m/s2) to find sp. weight ( γ ) * Also, remember to convert everything into imperial (US) –units as we are doing this experiment in imperial! Table 3: Date for speed calculation Test # Type of Oil Height of fall (in) A TURBOFLO 10 R&O 100 B SAE 30 6 C SAE 30 5

Height of fall (ft) Convert

Time taken (sec)

Convert Convert

Calculations 



Diameter , D =0.25∈×

1 ft =0.0208 ft 12 ¿

¿∗¿ ¿ × 1 ft =(¿∗¿) ft ¿∗¿ s 12 ¿ s Velocity of glass ball in cylinder B height of fall =¿ ¿ timetaken

Prepared by: Mohammad Lutful Arefin

Velocity (ft/sec)



gm kg m Specific weight of glass ball = ( Density ×Gravity ) =2.53 × 1000 × ml × 9.81 s2 3 ml gm



Density of fluid SAE 30: ¿



¿∗¿∗¿ ¿ N Specific weight of SAE 30 ¿∗¿∗¿ 3 m ¿ density × gravity=¿



8 0.020 ¿ ¿ ¿2 Viscosity of SAE 30 ¿ ( ¿∗¿−¿∗¿ ) ¿ (γ s −γ f )D 2 =¿ ¿ 18 v

mass of fluid ( gm ) volume of fluid ( ml)

Results Discussion Conclusion

Prepared by: Mohammad Lutful Arefin...