Physicochemical parameters of Viscometer & Stagalmometer
1 like550 views
This document discusses viscosity measurement techniques. It describes viscometers like the capillary viscometer and Ostwald's viscometer. The capillary viscometer uses Poiseuille's law to measure the time taken for a fluid to flow through a capillary tube, compared to a standard fluid. Ostwald's viscometer is a U-tube device that measures the time for a liquid to flow between two points at different heights. Surface tension is also examined using the stalagmometer drop volume method based on Tate's law. Precautions for accurate surface tension measurements are provided.
Physicochemical parameters of Viscometer & Stagalmometer
- 1. STUDY OF PHYSIOCHEMICAL PARAMETERS –VISCOMETER & STALAGMOMETER By DR. V.B. Khobragade Associate professor in Chemistry
- 2. ◾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. VISCOSITY 2
- 3. ◾Formula: Viscosity = shear stress/shear rate ◾SI unit: The units of viscosity is: poise (MKS) & centi-poise(CGS) FORMULA & UNITS 3
- 4. ◾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. VISCOMETER 4
- 5. ◾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. IMPORTANCE 5
- 6. TYPES OF VISCOMETER 6 Capillary viscometer Falling and rising body apparatus Rotational viscometer
- 7. ◾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). CAPILLARY VISCOMETER 7
- 8. FORMULA If η1 and η2 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= ρ1t1/ ρ2t2 η1/η2 = Relative Viscosity of liquid 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 liquid flow L = length of capillary V = Volume of fluid flowing This eq. can also be written as η= KtΔP where K is constant
- 9. OSTWALD’S VISCOMETER 9 Suspended level viscometer TYPE OF CAPILLARY VISCOMETER
- 10. ◾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”. OSTWALD’S VISCOMETER 10
- 11. ◾The viscometer is filled with liq. Upto bulk A through 1st arm. ◾Then suck the liq. Through 2nd arm to upper point C of the bulkB . ◾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 WORKING PRINCIPLE 11
- 12. ◾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. 12 UBBELOHDE SUSPENDED LEVEL VISCOMETER
- 13. OTHER TYPES OF CAPILLARY VISCOMETERS 13
- 14. 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 ADVANTAGES & DISADVANTAGES 14 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
- 16. Surface is the boundary between a solid/liquid and air/vaccum. Interface is the boundary between two or more distinct phases exist together.
- 17. Surface tension is defined as the force per unit length parallel to the surface to counter balance the Surface tension is defined as the force per unit length parallel to the surface to counter balance the net downward pull. Unit: dynes/cm ergs/m N/m
- 18. STALAGMOMETERMETHOD DROP VOLUME METHOD This method was first time described by Tate in 1864 who formed an equation, which is now called the Tate’s law. 𝑾 = 𝟐𝝅r𝜸 W is the drop weight, r is the capillary radius, and 𝛾 is the surface tension of the liquid.
- 19. In the case of a liquid which wets the stalagmometer's tip the r value is that of the outer radius of the capillary and if the liquid does not wet – the r value is that of the inner radius of the capillary. The drops wetting area corresponding to the outer and inner radii of the stalagmometer's tip.
- 20. The relative surface tension is given by: 𝛾 𝑚 2/3 = 𝑑1 1 = 1 𝛾2 𝑚2 𝑑2 2/3 Having known the drop volume the surface tension can be calculated from : = 𝑚𝑔 𝑚𝑔 𝑉𝑑𝑔 𝛾 = 2𝜋𝑟𝑓 = 𝑘 𝑘 𝜸 = 𝑽𝒅𝒈 𝒌 RELATIVESURFACETENSIONMEASUREMENTUSING STALAGMOMETER
- 21. PRECAUTIONS TO BE TAKEN Tip of pipette should have no imperfection in the outer circumference. Drops should be formed slowly About 20 – 30 drops should be collected to find the average weight Temperature should be maintained constant
- 22. EXAMPLES OF SURFACE TENSION