Viscosity measurement using ostwald viscometer

Simple procedure to measure dynamic Viscosity of fluids using Ostwald Viscometer

1. Dynamic Viscosity Measurement using ostwald viscometer Presented by Tenison Basumatary , PhD student Department of Electronics & communication Technology, Gauhati University, Guwahati , Assam-781014 e. mail:- [email protected] 1

2. What is viscosity……………? Viscosity describes the liquid’s resistance to flow. Mathematically, viscosity  is the ratio of the shearing stress  to the velocity gradient in a fluid. Viscosity measurement for different fluids is very much important in food processing industries, pharmaceutical, cosmetic and petrochemical industries. It is also extremely needed during design of aerodynamic and hydrodynamic systems. 2

3. Ostwlad viscometer:- I Fig. 1:- Ostwald Viscometer 3

4. Ostwald Viscometer:-Experimental set up Fig. 2:- Laboratory set up to perform Ostwald Viscometer 4

5. Principle of ostwald viscometer Ostwald viscometer is based on Poiseuille’s law. According to this law, the rate of flow of liquid through a capillary tube having coefficient ɳ, is given by:-   Where, v= volume of liquid in ml t=flow rate in second through capillary r=radius of the capillary in cm l=length of the capillary in cm p=hydrostatic pressure in dyne/sq. cm ɳ=viscosity coefficient in poise   SI unit of Viscosity is pascal -second ( pa.s i.e., kg.m -1 .s -1 ), and the cgs unit of viscosity is poise (i.e., g.cm -1 .s -1 ) 5

6. Determination of dynamic viscosity of the glycerin at different temperatures Apparatus:- Ostwald Viscometer, Beaker , 20-25 mL syringe, T hermostat , S tand, Liquid samples and Digital balance 6

7. Steps to perform Ostwald Viscometer Prepare 0%, 30%, 50%, 70%, 90% and 100% solution of glycerin in pure water. Set up the temperature using thermostat. Put both the Viscometer and thermostat into a beaker with water and make sure that Viscometer is clamped vertically and check the viscometer with pure water what volume is required to fill the viscometer. Measure the weight of the empty beaker. Fill the beaker with each solution as mentioned in step 1 one after another and measure the weight of the beaker. Heat the Viscometer kept in a beaker on magnetic stirrer and notes the temperature shown by thermostat to make measurements for different temperatures. Now fill the Viscometer with solution through Arm 1 till it reaches to the mark II as shown in fig. 1 using syringe. Now pull the liquid using syringe as seen in fig. 2 so that liquid flow through fine capillary tube till it reaches to the mark above IV as shown in fig.1. Remove the syringe attached to arm 2 and observe the upper meniscus of the liquid. When the meniscus is aligned with mark “IV”, start the stop watch to measure time. Measurement terminates when the meniscus is completely aligned with the mark III and stop the stop watch. Record the total time taken by each sample. After performing each sample rinse the viscometer with pure water and waste with acetone and dry up. Repeat the measurement 3 - 4 times for each sample for each temperature and take the average of the time. 7

8. Mathematical expression for Determination of dynamic viscosity of the glycerin The viscosity of liquid is calculated using:- 8