Non Newtonian Fluids

Introduction:

Non Newtonian fluid is a fluid which can change its flow rate. The flow rate change is dependent on applied stress and duration of applied stress. The reason no fluid can be follow Newtonian fluid behavior has extended research activity in non Newtonian fluids. Non Newtonian fluids exist in nature as well. For instance ice, lava, snow, clay suspensions, paints, emulsions, molten rubber, tomato ketchup, and blood flow. The motion of fluid was studied by Sir Isaac Newton. By changing the temperature, liquid can be either solid ice or gaseous vapor. Fluid which follows this flow behavior independent of applied stress is referred as Newtonian fluids. The fluids which do not follow this are referred as strange fluids or non Newtonian fluids.

Stress and strain:

Applied force on body is referred as stress and stress results in strain formation. For instance hammering metal, where hammering is applied stress and deformation of the metal or distortion of metal results in strain. In contrast Newtonian fluid will not resist the applied stress. For instance hammering water will not have any reflection of stress or strain. However non Newtonian fluids will change its flow behavior or viscosity under stress. Sudden stress application results in behaviors of fluids as solids. Some times it moves in opposite direction and ruins the process. When the stress is removed from the fluid, the fluid returns to its original state.

Types of non Newtonian fluids:

All non Newtonian fluids do not behave in similar fashion. Some behaves as solids rather than fluids. Following are non Newtonian fluid behavior types.

• Thixotropic: Fluid viscosity decreases with applied stress. For instance stirring of honey results in liquefying of solid honey.
• Rheopectic: Fluid viscosity increases with applied stress. For instance whipping of cream.
• Shear thinning: Fluid viscosity decreases with applied stress. For instance tomato sauce.
• Dilatant or Shear thickening: Fluid viscosity increases with applied stress. For instance Oobleck, a mixture of corn flour and water.

Questions:

• Why do non Newtonian fluids matter?
• What are the implications of non Newtonian fluid?
• What are microscopic and macroscopic behaviors of non Newtonian fluid?
• Give governing non Newtonian fluid equations.