![]() For instance, the table below shows that viscosity increases monotonically with concentration for sodium chloride and calcium chloride, but decreases for potassium iodide and cesium chloride (the latter up to 30% mass percentage, after which viscosity increases). The viscosity of an aqueous solution can either increase or decrease with concentration depending on the solute and the range of concentration. This is also the reason oils tend to be highly viscous, since they are usually composed of long-chain hydrocarbons. More dramatically, a long-chain hydrocarbon like squalene (C 30H 62) has a viscosity an order of magnitude larger than the shorter n-alkanes (roughly 31 mPa This effect can be observed for the n-alkanes and 1-chloroalkanes tabulated below. Substances composed of longer molecules tend to have larger viscosities due to the increased contact of molecules across layers of flow. One of the key predictions of the theory is the following relationship between viscosity μ \mu, thermal conductivity k k, and specific heat c v c_ For this reason, measured viscosities of the noble gases serve as important tests of the kinetic-molecular theory of transport processes in gases (see Chapman–Enskog theory). ![]() The simple structure of noble gas molecules makes them amenable to accurate theoretical treatment. By contrast, pressure is omitted since gaseous viscosity depends only weakly on it. The temperatures corresponding to each data point are stated explicitly. Where data points are unavailable for 25 ☌ or 1 atmosphere, values are given at a nearby temperature/pressure. Here "standard conditions" refers to temperatures of 25 ☌ and pressures of 1 atmosphere. Viscosities at or near standard conditions Consequently, its kinematic viscosity is around 2 to 40 centiStokes. The density is usually on the order of 0.5 to 5 kg/m^3. Consequently, if a liquid has dynamic viscosity of n centiPoise, and its density is not too different from that of water, then its kinematic viscosity is around n centiStokes.įor gas, the dynamic viscosity is usually in the range of 10 to 20 microPascal-seconds, or 0.01 to 0.02 centiPoise. The density is usually on the order of 1000 kg/m^3, i.e. In engineering, the unit is usually Stoke or centiStoke, with 1 Stoke = 0.0001 m^2/s, and 1 centiStoke = 0.01 Stoke.įor liquid, the dynamic viscosity is usually in the range of 0.001 to 1 Pascal-second, or 1 to 1000 centiPoise. In engineering, the unit is usually Poise or centiPoise, with 1 Poise = 0.1 Pascal-second, and 1 centiPoise = 0.01 Poise.įor kinematic viscosity, the SI unit is m^2/s. This page lists only dynamic viscosity.įor dynamic viscosity, the SI unit is Pascal-second. Kinematic viscosity is dynamic viscosity divided by fluid density. The values listed in this article are representative estimates only, as they do not account for measurement uncertainties, variability in material definitions, or non-Newtonian behavior. Of all fluids, gases have the lowest viscosities, and thick liquids have the highest. Viscosity is measured using a viscometer. For instance, honey hasĪ much higher viscosity than water. It corresponds roughly to the intuitive notion of a fluid's 'thickness'. A poise (P), named after Jean Léonard Marie Poiseuille, who also derived the Poiseuille's law equation, has a value equivalent to 0.1 pascals-second (Pa⋅s).Dynamic viscosity is a material property which describes the resistance of a fluid to shearing flows. Now that we know the difference between the two types of viscosities, let's go back to the measurement units. By determining the viscosity of fuels in terms of kinematic viscosity, we get to model the speed fuel droplets that will be sprayed out of an injection nozzle due to applied pressure. One particular use of kinematic viscosity is for fuels. On the other hand, we use kinematic viscosity to describe the speed of the fluid due to an applied force. Learn more about squeezing pressure on a container with fluids by checking out our manometer calculator. That way, it won't be either too hard to squeeze the paste out of the tube or too runny that a lot of paste comes out, even with a little squeezing pressure. When formulating the mixture of, let's say, a paste in a tube, we want the paste to have a specific dynamic viscosity. The dynamic viscosity tells us how much force is required for a fluid to move at a particular speed. Viscosity, which describes a fluid's consistency or "thickness," comes in these two types for some distinct reasons. Poise is a unit of measurement used particularly for dynamic viscosity, while stokes is for kinematic viscosity. Poise and stokes are units of measure used to quantify viscosity.
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