viscosity

Examples of viscosity in the following topics:

• Viscosity

  • The units of viscosity in the SI system are $N \cdot sec /m^2$ (or $Pa \cdot sec$ ).
  • When measuring viscosity, strain is applied at a certain rate, called shear rate.
  • Fluids that display a constant viscosity over a range of shear rates are called Newtonian, while those with a non-constant viscosity are non-Newtonian.
  • We can see that viscosity is highly dependent on temperature.
  • Therefore, we say water is thin, having a low viscosity, while honey is thick, having a high viscosity.

• Accretion Disks

  • Without viscosity the accretion will cease, so the crucial ingredient to move further is a prescription for the viscosity.
  • Unfortunately, natural estimates for the microscopic viscosity of astrophysical gas are too small by many orders of magnitude to account for the structure of accretion disks.
  • It is likely that accretion disks are turbulent magnifying the effects of small-scale viscosity to larger scales.
  • However, without simulating the turbulence directly, it is difficult to estimate the effective viscosity.
  • Instead let's assume there is some viscosity that we don't know exact and look at the angular momentum transport needed to maintain accretion.

• Poiseuille's Equation and Viscosity

  • Virtually all moving fluids exhibit viscosity, which is a measure of the resistance of a fluid to flow.
  • Viscosity is a basic property necessary for the analysis of fluid flow.
  • The greater the viscosity, the ‘thicker' the fluid and the more the fluid will resist movement.
  • The viscosity of the fluid is then its inherent resistance to undergo this displacement.
  • Viscosity in fluids generally decreases with increasing temperature.

• Motionof an Object in a Viscous Field

  • Objects moving in a viscous fluid feel a resistive force proportional to the viscosity of the fluid.
  • One of the consequences of viscosity is a resistance force called viscous drag $F_V$ that is exerted on a moving object.
  • For laminar flow around a sphere, $F_V$ is proportional to fluid viscosity , the object's characteristic size L, and its speed v.
  • For the special case of a small sphere of radius R, moving slowly in a fluid of viscosity , the drag force $F_S$ is given by
  • There is a force, called viscous drag FV, to the left on the ball due to the fluid's viscosity.

• What is a Fluid?

  • The distinction is made by evaluating the viscosity of the substance.
  • a) not resisting deformation or resisting it only lightly (viscosity), and
  • Real fluids display viscosity and so are capable of being subjected to low levels of shear stress.

• Velocity of Blood Flow

  • Resistance is the force which  must be overcome by pressure in order for flow to occur and is a factor of vessel length, diameter and surface composition and the viscosity of the liquid flowing through.
  • As such its viscosity is relatively changeable depending on osmotic balance and cell load.
  • Increases in viscosity, for example by reducing water content, lead to increases in resistance and thus reduction in flow.

• Blood Flow

  • Typical values for the viscosity of normal human plasma at 37°C is 1.2Nsm-2.
  • The viscosity of normal plasma varies with temperature in the same way as does that of its solvent, water.
  • (a 5°C increase of temperature in the physiological range reduces plasma viscosity by about 10%).

• Properties of Sulfur

  • Again, this is accompanied by a lower density but increased viscosity due to the formation of polymers.
  • At even higher temperatures, however, the viscosity decreases as depolymerization occurs.

• Angular Momentum Transport

  • The viscous stress is proportional to the viscosity and the angular velocity gradient,
  • We can combine these two equations to yield the value of the coefficient of dynamical viscosity, $\eta$,

• Long-Term Renal Regulation

  • As well as vessel morphology the viscosity of blood is one of the key factors influencing resistance and hence blood pressure.
  • A key modulator of blood viscosity is the renin–angiotensin system (RAS) or the renin–angiotensin–aldosterone system (RAAS); a hormone system that regulates blood pressure and water balance.