Viscometer Lab Report

INTRODUCTION

The capillary viscometers are very simple, inexpensive and used to measure the viscosity of liquids. Widely, it is used for measuring the viscosity of Newtonian fluids. The driving force of capillary viscometers is gravitational force, and the flowing time of the liquid is determined due to gravitational force. Disadvantage of the capillary viscometers is being not useful to find exact value.

Brookfield viscometer consists of single spindle attached to the device with vertical shaft. The spindle is rotated in the fluid and by this way viscosity is measured by Brookfield viscometer by using the data of torque. For choosing the suitable spindle size and speed, trial an error method is used. The estimation of apparent viscosity under

• To analyze the temperature dependence of viscosity by using a vibro viscometer.

METHOD AND MATERIAL

 Capillary Viscometer

By using Cannon-Fenske (U tube) viscometer, the experiment was performed for pure water and cherry juice. During this part of experiment, spherical chamber is filled with liquid and then the liquid was pulled up to upper elliptical chamber by means of puar being removed from system. Time data were recorded as well as the viscometer size.

 Brookfield Viscometer

This procedure was followed to measure the viscosity of baby food sample by observing the shear stress vs. shear rate relationship with Brookfield viscometer. Samples were put into the holder in which level of sample should be above the top of the spindle. After that, spindle was chosen and attached to viscometer. This procedure was repeated 6 times with the rotating of spindle.

 Vibro

According to Sahin and Sumnu, the variation of shear stress versus shear rate plot must be linear for Newtonian fluid and intercept should be zero (Sahin&Sumnu,2006). However, our plot has an exponential variation. Also, R2 is 0,5813 which is not suitable for linearity.

Then, we tried to apply power law model by taking logarithm of shear stress and logarithm of shear rate. As a result of our plotting, we got lnτ = 0,0032lnγ+4,4229 which is straight line. Also, R2 of this line is 0,8928 which shows close to linearity.

Finally, according to our plotting, results show that our puree sample is pseudoplastic fluid which has exponential variation in shear stress vs shear rate and linear variation in logarithm of shear stress vs logarithm of shear rate.

C) Vibro Viscometer

Temperature(1/K) ln(Viscosity)

0,003288 5,505331536

0,003268 5,351858133

0,003253 5,247024072

0,00321 5,030437921

0,003162 4,795790546

0,003124 4,123903364

0,002977 3,317815773

Temperature(oC) (Viscosity) (mPa.s)

31,1 246

33