pp2.pptx

Viscoty determination

1. Determination of Viscosity - By Sourabh Chauhan

2. Name : SOURABH TARAKESHWAR CHAUHAN Class : S.Y.B pharm Roll no : 18 Division : A Subject : Physical pharmaceutics – Ⅱ College: Shree D.D. Vispute college of Pharmacy and research center , gate no-04, vichumbe , new Panvel .

3. Determination of viscosity: In case of Newtonian systems the rate of shear is directly proportional to the shearing stress. Therefore, single point viscometer i.e. the equipment that works at a single rate of shear, is sufficient. For evaluation of Non-Newtonian fluids multipoint viscometers are required, because the apparent viscosity is to be determined at a several of rates of shear to get entire consistency curve.

4. Viscometer Single point At a single rate of shear one point on the curve Equipment: Ostwald viscometer, Falling sphere viscometer Application: Newtonian Fluids M u l t ip o i n t Several rates of shear many points on the curve Equipment: Cup and bob Cone and plate Application: Non Newtonian fluids & Newtonian Fluids

5. CA P I LLA R Y V I S CO M ETER Also known as U-tube viscometers, capillary viscometers include the Ostwald and Ubbelohde variations. They’re straight-forward and simple to use, consisting of a U-shaped glass tube with two bulbs (one higher and one lower). Fluid passes from the higher bulb to the lower bulb through a capillary, and viscosity is measured by timing how long it takes the fluid to pass through the tube

6. Introduction: These viscometers are suitable for only Newtonian systems. Principle: Capillary Viscometer based on Poiseuille’s law. This method of measurement, Measures time taken for defined quantity of fluid to flow through a capillary with known diameter and length. It is then compared with time required to flow by a liquid of known viscosity (usually water) . The viscosity of unknown liquid can be determined by using equation: η1/η2= ρ1t1/ ρ2t2

7. η1/ η2= RELATIVE VISCOSITY OF LIQ. The above eq. is based on POISEUILLE’S LAW for liq. flowing through capillary tube η= π r⁴tΔP/ 8lV Where, r = radius of inside capillary t= time flow ΔP=Pressure under which liq. Flow L= length of capillary V= Volume of fluid flowing This e.q can also be written as η= KtΔP

8. Capillary Viscometer Ostwald viscometer Suspended level viscometer Couette type Or revolving cup type or Mac Michael viscometer Searle type or revolving bob type or stormer viscometer

9. OSTWALD’S VISCOMETER: Ostwald’s viscometer also known as U-tube viscometer A device which is used to measure the viscosity of the liquid with a known density. This device is named after “Wilhelm Ostwald Working & Principle: The viscometer is filled with liq. Upto bulk A through 1 st arm. Then suck the liq. Through 2 nd arm to upper point C of the bulk B . Now allow the liq. To pass from upper marked C to lower marked D. And note the time of flow from upper marked C to lower marked D. Now the viscosity of liq. Can be calculated by using formula; η1/η2= ρ1t1/ ρ2t2

10. SUSPENDED LEVEL VISCOMETER: It is a modified form of Ostwald’s viscometer. In it ,there is third vertical arm attached to the bulb below the capillary part of the right arm. Liquid is introduced into the viscometer through the left arm In quantity sufficient to fill the bulb in the left arm. FALLING SPHERE VISCOMETER INTRODUCTION: Falling sphere viscometer is suitable for Newtonian systems. PRINCIPLE: Stoke’s law is the basis of the falling sphere viscometer, in which the fluid is stationary. Stoke’s law: “It states that when a body falls in viscous media, it experiences a resistance which oppose the motion of the fluid.” WORKING The sample &ball are placed in the inner glass tube & allowed to reach temperature equilibrium with the water in the surrounding constant temperature jacket. The tube and jacket are then inverted. Which effectively placed the ball at the top of inner glass tube. The time for the ball to fall between two marks is accurately measured and repeated several time.

11. FORMULA: Viscous drag on body = force responsible for the downward movement, thus : 3пηdv = п/6d³g x Ps– P1 where, D = diameter of the sphere g = acceleration due to gravity v = terminal velocity Ps = density of sphere P1= density of liquid by rearranging formula : η = d²g ( Ps – p1 ) / 18v

12. CUP AND B O B V I SCO M ETE R: This is a multipoint viscometer and belongs to the category of rational viscometer. It is consist of two coaxial cylinders of different diameters. The outer cylinder forms the cup into which the inner cylinder or bob is fixed centrally. The torque set up in the bob is measured in terms of angular deflection Q of a pointer that exhibit on the scale. Principle: The sample is placed in the cup and the bob is placed in the cup upto an appropriate height. The sample is accommodation between the gap of cup and bob. Now wither the cup or bob is made to rotate and the torque resulting from the viscous drag is measured by a spring or sensor in the drive of the bob.

13. Couette type Or revolving cup type or Mac Michael viscometer Searle type or revolving bob type or stormer viscometer TYPES

14. COUETTE TYPE VISCOMETER In this the cup is rotated and the viscous drag on the bob produced by the liquid results in a torque which is proportional to the viscosity of the liquid. Example: MacMichael viscometer

15. SEARLE TYPE VISCOMETER In searle type viscometer, the bob is rotated while the cup is held stationary. Examples: Stormer viscometer &Brookfield viscometer F ORMU L A η=kv w/v Where Kv =instrument constant W=weight in gram V=rpm generated due to w

16. CONE AND PLATE VISCOMETER A cone-plate is precise torque meter which driven as discrete rotational speed. The torque measuring system which consist of a calibrated b e r y l l ium c opp e r spring c onn ec t i ng the d r iven m ec h a nism to rot a t i ng cone, sense of resistance to rotation caused by presence of sample fluid between the cone and stationary flat plate

17. T h ank Y o u