TASK 1 - VISCOSIMETRY
INTRODUCTION

Viscosimetry is a measure of the resistance of fluids being deformed by stress. In everyday terms it means „thickness“ of a fluid. In extreme we speak about „thin“ fluids (e.g. water) or „thick“ fluids (e.g. honey).

Viscosity may be expressed as:

- kinematic viscosity ν (ni) = K . 10-6 . t [m2 s-1] , or

- dynamic viscosity η (éta) = ν . density of measured fluid [Pa s = Pascal second]

K - constant of viscosimeter = 0.02864 (Ostwald viscosimeter)
t - time
density: water = 1000 kg . m-3; blood serum = 1030 kg . m-3).
MEANING
Viscosity belongs to fundamental properties of liquids, and hence it is used to characterize various liquid foodstuffs (e.g. honey, fats, oils, soaps or soups).
Aim of the task: Measurement of viscosity of low viscous fluid (water, blood serum) with the Ostwald capillary viscosimeter, and of high viscous fluid (table oil) by the Höpler’s rheo-viscosimeter.

Ostwald's flow viscosimeter

1. OSTWALD'S CAPILLARY VISCOSIMETER
Aim of the task: Viscosity measurements of deionized water and blood serum.
PROCEDURE:
  1. Fill viscosimeter until the liquid level is between the two marks, and fix the instrument in its stand;
  2. Put on the viscosimeter a pipette pump, and suck the liquid above the 2nd mark (beware of air bubbles); narrow side tube must be closed with a finger;
  3. Put off the pipette pump and measure time of passage of the level between two marks;
  4. Measure deionized water and blood serum, each 10times;
  5. Create table, supplement with statistical analysis (standard deviation, relative standard deviation, standard deviation of the mean), and calculate ν and η for mean values of both substances (for formulas see Introduction).

Höpler's rheo-viscosimeter

2. HÖPLER'S RHEO-VISCOSIMETER
This  viscosimeter is used for measurements of highly viscose liquids (oils, fats, soups, etc.). The measurement is based on the movement of a ball immersed into the measured fluid. The movement of the ball that travels through a specific path is mechanically transferred to a round scale.
PROCEDURE:
  1. Using the excenter (move clockwise) lift the lever until the pointer of the instrument occurs in front of the 0 value and wait for 10 sec.;
  2. Release the excenter and measure the time of movement through a specific path.
    The optimum time (from 10 to 20 sec) is get using the corresponding weight constant P;
  3. Measure 3 paths, each 10times. Results insert into the table and supplement with the statistical analysis (standard deviation, relative standard deviation, standard deviation of the mean). For mean values of each path calculate the dynamic viscosity.
    3.1. path 30 mm (constant K = 0.9755)
    η = 0.1 . K . P . t [Pa s]    ;
    3.2. facultative path (25 mm recommended) (constant K = 0.9755)
    η = (0.1 . K . P . t . 30)/path [Pa s];
    3.3. corrected path (29.27 mm) (constant K0 = 1)
    η = 0.1 . K0 . P . t [Pa s].
  4. Significance of results express with the percentual conformity interval.


VIDEO-CLIP DEMONSTRATING PROCEDURE OF THE TASK

Version for HIGH SPEED connexion to internet!

Version for LOW SPEED connexion to internet!

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