Newtonian fluid and Non- Newtonian fluid.

Brief description of 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. M olasses is highly viscous W ater is low viscous Low Viscous High Viscous Fig. 1

6. Continued …. Formula of Viscosity :- Units – P a.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 Dynamic Viscosity Kinematic Viscosity. Factor affecting Polymer Viscosity Temperature C oncentration M olecular weight 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 Shear stress Shear rate Newtonian Fluid Slope = 1/ μ 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) : F luid 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 R ate Shear Stress 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 (η ). 

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 Shear Stress Viscosity Shear Rate

15. Continued…. Fig.- 14 Fig .- 15 Pseudoplastic & Dilatant V iscosity Shear Rate Dilatant Fluid Newtonian Fluid Pseudoplastic Fluid Shear Stress Shear Rate Newtonian Fluid, n=1 Pseudoplastic(Shear Thinning<1) Dilatant(Shear Thickening, n>1

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 Shear Stress Shear Rate Bingham Plastic

18. Shear stress and deformation rate relationship of different fluids Fig.- 18    Shear Stress Shear Rate Bingham plastic Psuedoplastics Newtonian Dilatant(Shear Thickening)

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 Shear Stress

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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