types of viscometers (1)physical pharmacetics.pptx

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1. 1 PHARMACEUTICS-1 (PHYSICAL PHARMACY)

2. 2 Rheology

3. Viscosity Definition Formula and Units Viscometer Introduction Importance Types of Viscometer 3 Contents

4. A fluid flow property . Internal property of a fluid that offers resistance to flow. It is a measure of how easily a fluid can flow. It can also be viewed as a resistance to shear force, more viscous the fluid is, higher the resistance. 4 Viscosity

5. Formula: Viscosity = shear stress shear rate SI unit: The units of viscosity is: pious centi -pious 5 Formula & units

6. Definition: “A viscometer is an instrument used to measure the viscosity of a fluid.” It is also known as “ Viscosimeter .” Viscometer only measures under one flow condition The measure of the resistance is taken by measuring the drag resistance during relative motion through the fluid. 6 viscometer

7. Measuring viscosity is important when considering process conditions for materials that need to be pumped or piped . It effects dipping and coating performance , which is particularly relevant to syrups and lotions. Viscometer can be used to monitor batch consistency and quality control. They are also used to characterize plastics. 7 importance

8. 8 Types of viscometer

9. 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.and is then compared with time required to flow by a liquid of known viscosity (usually water) 9 CAPILLARY VISCOMETER

10. If η1 and η 2 are the viscosities of unknown and standard liquid ,   ρ1 and   ρ2 are densities and T1 and T2 are time required to flow in sec then; η1/η2= ρ 1t1/ ρ2t2 . η 1/ η2= RELATIVE VISCOSITY OF LIQ. The above eq. is based on POISEUILLE’S LAW for liq. Flowing through capillary tube . η = π r ⁴t Δ P / 8l V Where , r = radius of inside capillary t= time flow Δ P=Pressure under which liq. Flow L= length of capillary V= Volume of fluid flowing This e.q can also be written as η = Kt Δ P k=constant 10 Formula

11. 11 Type of capillary Viscometer

12. 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”. 12 OSTWALD’S VISCOMETER

13. 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= ρ 1t1/ ρ2t2 13 Working Principle

14. 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. 14 Ubbelohde Suspended level viscometer

15. 15 Other Types of capillary viscometers

16. Advantages Disadvantages No single tube is suitable for all viscosities Basic models can only be used for translucent fluids Difficult to clean the capillary tubes 16 Advantages & DISADVANTAGES Measure precise viscosities for many diverse fluids Small $ Portable Inexpensive Easy to use Can use a wide verity of capillary tubes on the same viscometer

17. 17 Falling & rising body apparatus

18. 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.” 18 Falling sphere viscometer

19. 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. 19 Working

20. 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 20 Formula

21. HOEPPLER BALL VISCOMETER: It is a falling ball instrument which uses a short , nearly vertical glass tube of large diameter and closely fitting ball of either steel or glass. The sample and the ball are loaded into the inner cylinder and brought to the temperature of measurement by means of a constant temperature outer jacket. The loading pin is released and the apparatus is inverted to place the ball in the initial stating position . The time for the ball to transverse the distance between two marks is measured A minimum 30 sec time is used for best result. 21 example

22. Rising sphere viscometer is also named as Rheometer. It is an important instrument to study the yield value of Non –Newtonian systems. In it 1.9 cm diameter stainless steel sphere connected to a strain gauze via a platinum-rhodium wire is lifted through the material under test at a very slow rate by a motor driven arm. The shearing stress caused by strain in the gel structure is recorded continuously. 22 RISING SPHERE VISCOMETER

23. ADVANTAGES High shear devices, This is incredibly important when dealing with non- Newtonian fluids which includes most of the fluids used in printing and coating today. DISADVANTAGES Can be maintenance intensive Can be parts intensive Replacement parts can be costly 23 Falling & rising body apparatus

24. INTRODUCTION: These viscometers are suitable for both Newtonian and non-Newtonian systems. Amongst the most widely used meter PRINCIPLE : Based on the principle that the fluid whose viscosity is being measured is sheared between two surfaces .In these viscometer one of the surface is stationary and other is rotated by an external drive and fluid fills the space in between .The measurements are conducted by Appling either a constant torque and measuring the changes in the speed of rotation or applying a constant speed and measuring the changes in the torque . 24 Rotational viscometer

25. 25 Types

26. 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. 26 Cup and bob viscometer

27. Two types of instrument exist depending on whether the cup or the bob rotates. 27 types

28. 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 28 Couette type viscometer

29. η=KM/w 29 Formula

30. In searle type viscometer, the bob is rotated while the cup is held stationary. Examples: Stormer viscometer Brookfield viscometer 30 Searle type viscometer

31. η= kv w/v Where Kv =instrument constant W=weight in gram V=rpm generated due to w 31 Formula

32. A cone-plate is precise torque meter which driven as discrete rotational speed. The torque measuring system which consist of a calibrated beryllium copper spring connecting the driven mechanism to rotating cone, sense of resistance to rotation caused by presence of sample fluid between the cone and stationary flat plate. 32 Cone and plate viscometer

33. Viscosity in pioses of a Newtonian liq. Is calculated by eq. h=CT/v Where C is an instrument constant V=speed of cone in revolution/min T= torqe reading 33 Formula

34. ADVANTAGES Can measure viscosities of opaque, settling, or non-Newtonian fluids. Useful for characterizing shear- thinning and time-dependent behavior. Speed of the rotating part easily adjusted. Often linked to computers for semi-automated measurement. DISADVANTAGES Can be relatively expensive. Often large and not portable. 34 Rotational viscometer

35. Vibrational viscometers Bubble viscometers Oscillating viscometers Orifice viscometers. Stabinger Viscometers Electromagnetically spinning sphere viscometer (EMSV) Rectangular-slit viscometers 35 Other types of viscometers

36. PHYSICAL PHARMACY BY AGARWAL KHANNA 36 reference

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