Presentation on theme: "Mer331 Lab – Week 2 - Viscosity Background: Viscosity n A fluid is a state of matter that does not permanently resist shear and the resistance to deformation."— Presentation transcript:
Mer331 Lab – Week 2 - Viscosity Background: Viscosity n A fluid is a state of matter that does not permanently resist shear and the resistance to deformation (shear stress) is a function of the rate of deformation (shear rate) n Rheology = science of deformation n Viscometry = measurement of rheological properties n Viscosity is the property of a fluid that resists deformation: u molasses vs water, u molasses in January vs molasses in July. n Newton Law of Viscosity (for Newtonian fluids)
Shear stress as a function of deformation Background: Viscosity Shear Thickening
Background Ketchup, Toothpaste : shear thinning Leaping Shampoo! Versluis M, Blom C, Meer D, Weele K, Lohse D (2006) Leaping Shampoo and the Stable Kaye Effect. Journal of Statistical Mechanics: Theory and Experiment 2006P07007.
Absolute (or Dynamic) Viscosity, Units: 1 Poise = 1 g/(cm sec) 1 Pa sec = 1 kg/(m sec) = 1 N sec/m 2 1 Poise = 100 cP = 0.1 Pa sec Kinematic Viscosity: = /ρ Units: 1 stoke = 1 cm 2 /sec = m 2 /sec Background: Viscosity Units
Techniques for Measuring Viscosity n Capillary Viscometers n Rotary Viscometers n Falling “Object” Viscometers n And many others….
Capillary Viscometers n Capillary Viscometers u Measure the flow rate of a fixed volume of fluid through a small orifice u From laminar flow theory we can relate the flow rate, pressure drop to viscosity = K*time K is a calibration constant Time is measured in seconds is given in cSt
Rotary Viscometers n Use the torque on a rotating shaft to measure a fluids resistance to flow = F * torque F is a calibration constant which you look up in the instrument manual
Falling “Object” Viscometers n Apply F=ma n At terminal speed a=0 F G = F B + F D F G = mg D 3 g/6 F B = fluid D 3 g/6 The drag on a sphere depends on the flow field: …. F B = Buoyancy F D =Drag F G = Weight
Falling “Object” Viscometers The drag on a sphere depends on the flow field: Reynold’s Number: For Stokes Flow: Re < 0.1 Therefore: Restrictions: terminal velocity, Re < 0.1
Gilmont Viscometer = Kt( ball - fluid ) K = 35 ball,ss = 8.02 (gm/ml) ball,glass = 2.53 (gm/ml) in Cp t in minutes
Lab Write Up You will write a full lab report. Review the information on the course webpage: Include detailed information on the uncertainty analysis: u Table of uncertainty values for each thing you measure (i.e. mass, volume etc). u Report all data with an uncertainty value u Include (hand written) derivation of uncertainty equations with a sample calculation in an appendix. u See handout on lab report expectations.