Newtonian fluid and Non- Newtonian fluid.
- 1. Newtonian And Non- Newtonian Fluids Prepared by PREETI MAURYA
- 2. What is fluid • A fluid is a state of matter in which its molecules move freely. • A fluid is a substance that continually flows under an applied shear stress. Fluids can be classified as Types of Fluid Ideal Fluid Real Fluid Newtonian Fluid Non-Newtonian Fluid Compressible Fluid Incompressible Fluid Ideal Plastics fluid
- 3. Continued…. • Ideal fluid: A fluid, which is incompressible and having no viscosity, is known as an ideal fluid. Ideal fluid is only an imaginary fluid as all the fluids, which exist, have some viscosity. • Real fluid: Real fluid can be defined as the fluid which deforms continuously for certain amount of shear stress and it consists of viscosity. Example : Water, Air etc. • Ideal plastic fluid: A fluid, in which shear stress is more than the yield value and shear stress is proportional to the rate of shear strain or velocity gradient, is known as ideal plastic fluid. • Incompressible fluid: A fluid, in which the density of fluid does not change which change in external force or pressure, is known as incompressible fluid. All liquid are considered in this category. • Compressible fluid: A fluid, in which the density of fluid changes while change in external force or pressure, is known as compressible fluid. All gases are considered in this category.
- 4. Introduction • Viscosity of a polymer solution depends on concentration and size (i.e., molecular weight) of the dissolved polymer. • By measuring the solution viscosity we should be able to get an idea about molecular weight. Viscosity techniques are very popular because they are experimentally simple. • They are, however less accurate and the determined molecular weight, the viscosity average molecular weight, is less precise. • For example, Mv depends on a parameter which depends on the solvent used to measure the viscosity.
- 5. What is Viscosity • Viscosity is a measure of a fluid's resistance to flow. OR • The viscosity of a fluid is a measure of its resistance to deformation at a given rate. • Viscosity is a measure of the internal friction of a fluid. i. Molasses is highly viscous ii. Water is low viscous Low Viscous High Viscous Fig. 1
- 6. Continued…. Formula of Viscosity :- Units – Pa.s , mPa.s, Poise (P), kg·m−1·s−1 Shear Stress(τ) :- Shear stress is define as force per unit area OR Shear stress, force tending to cause deformation of a material by slippage along a plane or planes parallel to the imposed stress. Unit - N/m² or Pa Fig. 2 Viscosity (η) = Shear Stress(τ) Shear Rate(ϒ)
- 7. Continued…. Shear Rate( ϒ) :- Shear rate is the measure of the speed at which the intermediate layers moves with respect to each other. Unit - Sec⁻¹. Where, v = velocity and dx = relative distance of layers. Types of Viscosity a) Dynamic Viscosity b) Kinematic Viscosity. Factor affecting Polymer Viscosity I. Temperature II. Concentration III. Molecular weight IV. And shear rate. ϒ = dv/dx
- 8. Newtonian Fluid • A fluid, whose viscosity does not change with the rate of deformation of shear stain. OR • A fluid which obeys Newson's law of viscosity is termed as Newtonian fluid. OR • Fluid flow which the shear stress is linearly proportional to the shear rate. OR • Fluid have a constant viscosity at a given temperature. For these fluid , the viscosity is independent of the shear stress rate change. • A shear diagram for Newtonian fluid is shown below. Note that the slope is constant. Fig. - 3 Fig. - 4 Shearstress Shear rate Newtonian Fluid Viscosity Shear rate Newtonian Fluid
- 9. Continued…. Newton’s law viscosity Where, μ = Viscosity τ = Shear stress (F/A) du/dy = rate of shear deformation. Examples – Water, Mineral oil, Gasoline, Alcohol, Ethyl alcohol, Hexane Fig.- 5 Fig.- 6 τ = μ du/dy
- 10. Non – Newtonian Fluid • When the ratio of shear stress to shear strain is variable or not constant. Other words, the variation in shear rate and shear stress is not proportional. OR • A fluid which does not obeys Newton's law of viscosity is termed as Non - Newtonian fluid. • In reality most fluids are non-Newtonian, which means that their viscosity is dependent on shear rate (Shear Thinning or Thickening) or the deformation history (Thixotropic fluids). Examples – Plastics, Ketchup, Blood, Toothpaste, Yogurt. Fig.- 7 Fig.- 8 Fig.- 9
- 11. Classification Non-Newtonian fluid Non- Newtonian Fluid Time Independent • Pseudo plastics • Dilatant • Bingham plastics Time Dependent • Thixotropic • Rheopectic
- 12. Time Independent Non-Newtonian fluid Pseudo plastics(Shear Thinning) : Fluid displays a decreasing viscosity with an increasing shear rate. This type of behaviour is called shear-thinning. OR • A fluid whose apparent viscosity or consistency decreases instantaneously with an increase in shear rate • Examples : Plastics melts, Polymer solution, Printing ink blood etc. Fig.- 10 Fig.- 11 Shear Rate ShearStress Viscosity Shear Rate
- 13. Continued…. • Most polymer solution and melts exhibit shear thinning (Pseudoplastic), Whereas shear thickening (Dilatant) behaviour is rarely observed. • The observed shear thinning polymer melts and solutions is caused by disentanglement of polymer chains during flow. • Polymers with a sufficiently high molecular weight are always entangled and randomly oriented when at rest. • When sheared, however, they begin to disentangle and to align which causes the viscosity to drop. • The degree of disentanglement will depend on the shear rate. • At sufficiently high shear rates the polymers will be completely disentangled and fully aligned. • In this regime, the viscosity of the polymer melt or solution will be independent of the shear rate, i.e. the polymer will behave like a Newtonian liquid again. • The same is true for very low shear rates; the polymer chains move so slowly that entanglement does not impede the shear flow. The viscosity at infinite slow shear is called zero shear rate viscosity (η0).
- 14. Dilatant ( Shear Thickening) • The rheological behaviour of dilatant (Shear thickening) fluid is exactly opposite to that of pseudoplastic fluid, their viscosity increases with the rate of shear. • Some liquids with dilatant behaviour are slurries, candy compounds, and corn-starch & water mixtures. Fig.- 12 Fig.- 13 Shear Rate ShearStress Viscosity Shear Rate
- 15. Continued…. Fig.- 14 Fig.- 15 Pseudoplastic & Dilatant Viscosity Shear Rate Newtonian Fluid ShearStress Shear Rate
- 16. Current and Future Applications of Dilatants • Materials and Fluids that exhibit Non-Newtonian behaviour such as Dilatants offer a diverse range of potential opportunities and future applications. • Potential Applications of Dilatants: • Shock absorption Systems • Automotive Suspension - Magnetic particles suspended • Impact Stress Cushioning - Sport / Athletics • Accident damage and injury mitigation - Transport • Impulse Distribution Systems • Smart Body Armour
- 17. Bingham Plastic Fluid • These fluids do not flow unless the stress applied exceeds a certain minimum value. Beyond a minimum value of shear stress, a Bingham body shows a linear relationship between stress and strain. • Bingham plastic is a material that behaves as rigid body at low stresses but flows as a viscous fluid at high stress. • This behaviour is exhibited by slurries, suspensions of solids in liquids, paints, emulsions, foams, blood, ketchup, tooth paste,etc. Low shear High shear Fig.- 16 Fig.-17 ShearStress Shear Rate
- 18. Shear stress and deformation rate relationship of different fluids Fig.- 18 ShearStress Shear Rate
- 19. Time Dependent Fluid • The time dependant fluid are those fluids, which show either a decrease or increase in the viscosity with time at a particular shear rate. • If these fluid are subjected to a constant shear rate, the shear stress will either decrease or increase. • These fluids are classified as thixotropic ( if viscosity decreases with time ) and rheopectic ( if viscosity increases with time ) respectively.
- 20. Thixotropic Fluid • The apparent viscosity decrease with time .Result break down in the microstructure of the material as shearing continues. • When at a constant shear rate, the stress decreases over a period of time due to structure breakdown until eventually it reaches a steady value, the product is said to be thixotropic. Examples : Aged condensed milk, cream and ice cream mix, egg white, paint, iron oxide gels etc. Rheopectic Fluid • Rheopectic liquids increase in viscosity as stress over time increases OR . • This essentially the opposite of thixotropic behaviour, in which the fluid viscosity increases with time as it is sheared at a constant rate. • Rheopectic fluid are rarely encountered. Both thixotropic and rheopectic may occur in combination with any of the previously discussed flow behaviour, or only at certain shear rates. Examples : Printer ink, gypsum paste.
- 21. Continued…. Fig.- 19 Fig.- 20 Viscosity Stress Over time Rheopectic Thixotropic Thixotropic Rheopectic Shear Rate ShearStress
- 22. The table below summaries four types of non-Newtonian fluids Type of behaviour Description Example Thixotropic Viscosity decreases with stress over time Honey – keep stirring, and solid honey becomes liquid Rheopectic Viscosity increases with stress over time Cream – the longer you whip it the thicker it gets Shear thinning Viscosity decreases with increased stress Tomato sauce Dilatant or shear thickening Viscosity increases with increased stress Corn-starch
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