Extensional viscosity is the viscosity coefficient when applied stress is extensional stress valid for non-Newtonian fluids.Shear viscosity is the viscosity coefficient when applied stress is a shear stress, valid for non-Newtonian fluids.Bulk viscosity is the same as volume viscosity.Volume viscosity is the viscosity coefficient that determines the dynamics of compressible Newtonian fluid.Kinematic viscosity is the dynamic viscosity divided by the density for Newtonian fluid.Dynamic viscosity is the viscosity coefficient that determines the dynamics of incompressible Newtonian fluid.They are introduced in the main books on hydrodynamics and rheology. There are several different viscosity coefficients depending on the nature of applied stress and nature of the fluid. When looking at a value for viscosity, the number that one most often sees is the coefficient of viscosity. A viscous glue was made from mistletoe berries and used for lime-twigs to catch birds.

The word 'viscosity' derives from the Latin word ' viscum' for mistletoe. 5.1.1 Effect of temperature on the viscosity of a gas.4.1.3 Dynamic versus kinematic viscosity.4.1.1 Viscosity (dynamic/absolute viscosity).In this case, the volume of foam will increase and the foam concentrate will not mix properly, thus it will reduce the chances of successful fire extinguishment. Regarding large fire installations, pressure and length of pipe are important factor for correct proportioning of Non-Newtonian foam.įinally, when viscous foam agent is handled with non-adapted pump, it may cause air trapping into the concentrate. It will result in trouble or longer fire extinguishment. If foam discharge and mixing devices are not fitted to Non-Newtonian foam concentrate, they can have difficulties to provide the correct amount of foam agent and underdose it. Some of them are calibrated to handle non-Newtonian foam concentrates (for example LEADER MIX AB foam proportioners), and others may require special settings.ĮN 1568 standard tells that if a pseudoplastic foam with a viscosity above 120 mPa.s (at a lowest temperature of use and at 375 s-1) or a Newtonian foam above 200 mm2/sec (at a lowest temperature of use and at 375 s-1), it could need special adjustment on proportioning systems. Indeed, foam viscosity may impact transport in pipelines and injection processes.įoam concentrate viscosity is not handled in the same way on foam equipment. Foam physical properties have to be compliant with foam equipment settings.

The foam concentrate is selected depending on the fire risk faced (class A combustible material, class B water-miscible fuel, class B water-immiscible fuel…). The success in firefighting depends, to a great extent, on combination of fire extinguishing system (mixing and discharge devices), fire foam concentrate, temperatures, water flow and pressure. What are the relations between foam viscosity and foam equipment? To have an idea of viscosity in product of our everyday life, here is some examples: Fluids Viscosity measurement is done at a defined temperature. Pseudoplastic foam viscosity may be measured using a rotary viscometer, cone and plate viscometer, or Rheometer. I.e., some AR-AFFF and FFF (Fluorine-Free Foams) are pseudo-plastic foam concentrates. Pseudoplastic foams have dynamic viscosity, usually expressed as millipascal seconds, in mPa.s unit or in Centipoise, in cP unit. Liquids such as shampoo are viscous and flows slowly without force. It becomes fluid as the aspiration progresses.Ī highly viscous fluid is very thick compared to low viscous fluid. Non-Newtonian firefighting foams will require a larger amount of energy to move, especially when priming the pump. It shows an instantaneous decrease in the apparent viscosity with an increase in the shear rate. Non-Newtonian foam concentrate viscosity is not constant and is related to the shear rate. Non-Newtonian firefighting foams: There are commonly called pseudo-plastic foams or viscous foams.Generally, AFFF and class A foams are Newtonian (not viscous), such as BIOEX AFFF BIOFILM and class A foam BIO FOR. Newtonian foams have kinematic viscosity, usually expressed as Centistokes, in cSt unit or in mm²/s. Liquids, like gasoline or water, flow very readily. A Newtonian fluid have constant viscosity, it is not affected by shear rate. Their movement are generally proportional to the force applied. Viscosities of firefighting foam concentrates are separated into 2 categories: It depends on the type of foam concentrate.

There are various ways to measure foam viscosity. Viscosity may impact transport in pipes and injection process.

The lower the viscosity is, the more fluid it is. First, the viscosity is the physical property that characterizes the flow resistance of fluids.

Water dynamic viscosity pa s