So when you calculate $Re = s L / \nu$, you come out with a pure number that has no units. The kinematic viscosity is an atmospheric variable defined as the ratio between the dynamic viscosity () and the density () of the fluid and depends on. Note that is the same units as kinematic viscosity. The kinematic viscosity, often represented by the greek letter and used mainly for liquids, is a measure of the viscosity in the particular situation where. We could have just kept the original two quantities.Īs for the units, the other two quantities in the reynold's number equation are length and velocity. Now it's 3 equations, exactly 1 of which has to do with the type of fluid, and 2 that have to do with the particular situation. Because it comes up so often, and because both density and viscosity are intrinsic to the type of fluid, we simplify the Reynold's number equation to just $Re = s L / \nu$, where $\nu$ is kinematic viscosity. The reynold's number is super important and it comes up all the time in fluid mechanics. Of these four quantities, 2 are intrinsic to a particular fluid (density and dynamic viscosity) and 2 are more to do with the situation (the length and the velocity). The Reynold's number is defined as $Re = \rho s L / \mu$, where $\rho$ is density, $s$ is velocity, L is a length, and $\mu$ is dynamic viscosity. Flows with high reynolds number will behave completely differently than flows with low reynolds number. One of the fundamental distinctions has to do with the ratio of inertia forces to viscous forces, which is called the Reynold's number. The kinematic viscosity ( 'nu') is the dynamic viscosity of the medium divided by its density. Relationship between dynamic and kinematic viscosity v. If your density is not in kg/m, you can use our density converter or: If the density is in g/cm, multiply it by 1000 to convert it to kg/m. Dynamic viscosity increases for gases as temperature rises. To convert kinematic viscosity to dynamic viscosity (centistokes to centipoise): The first step to converting cSt to cP is determining the fluid density in kg/m. To understand what it is, you have to understand that there are many different types of fluid flow, and they behave very differently. The dynamic viscosity drops off very quickly for liquids as their temperatures increase. Thinking of it as so many $m^2$ of fluid flowing per second is not what it is about. Don't try to think of it as resistance of fluid to flowing, because that's not what it is. Kinematic viscosity is something totally different. A more common unit of kinematic viscosity is the square centimeter per second cm 2 /s, which is given the name stokes St after the Irish mathematician and physicist George Stokes (18191903. This unit is so large that it is rarely used. honey has much higher dynamic viscosity than water, or cold motor oil has higher dynamic viscosity than warm motor oil. The SI unit of kinematic viscosity is the square meter per second m 2 /s, which has no special name. High dynamic viscosity = more resistance to flow. This is what lay people think of when they think viscosity. On the other hand, the kinematic viscosity tells about the speed the fluid reaches when a particular force is applied to the fluid.Dynamic viscosity represents the resistance of fluid to shear forces as you said. When choosing between the two viscosities, it is worth noting that dynamic viscosity tells us about the force required to move the fluid at a certain speed. The larger the force or stress needed to move the plate, the more viscous the fluid is.
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