Reynolds Number

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lab on reynolds number
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  TABLE OF CONTENTS Content page number Introduction Aim  Introduction Introduction Liquids do not always flow in a perfect, smooth stream. Once velocity increases past a certain threshold (determined by the diameter of the pipe, density and viscosity of the liquid, and velocity), puffs begin to develop in the liquid and produce turbulence. A smooth flow of liquid is called laminar while an uneven flow is called turbulent. In order to observe and study these types of flow, an engineer, by the name of G.H.L Lagen in 1839, carried out experiments and deduced an equation with an unknown constant in relation to the viscosity of a liquid. In 1883, however, an engineering professor, Osborne Reynolds, discovered the identity (equation) o f the unknown number in Lagen’s equation.  This is the equation we now call the Reynolds number. This laboratory, based on the concept of Reynolds number and its application, entails the duplication of the experiment he used to generate results presented in this report. The significance of the Reynolds number is that it relates given values (density, velocity, length/diameter, and viscosity) to the type of flow that the liquid will experience. The larger the Reynolds number, the more turbulent the flow. The accepted Reynolds number for transition from laminar to turbulent flow in a smooth, circular pipe is 2300 (White 352).    AIM To observe the different types of fluid flow and to determine the Reynolds number of each type of flow.  Theoretical information Fluid flow can be characterized as laminar, turbulent, or transitional. The dimensionless Reynolds number (Re) can be used to determine the fluid flow condition. The Reynolds number can be calculated mathematically using: Where ρ = the fluid density, V = the velocity of the fluid, d = to the diameter of the tube, μ = the dynamic viscosity of the fluid a given temperature. Re- Reynolds number can be interpreted as the ratio of the flow's inertial forces to its viscous forces. For large viscous forces (low Re, normally Re < 2000 for pipe flows), viscous effects are great enough to damp any disturbances or perturbations in the flow and the flow remains laminar. Any combination of low velocity, small diameter, or high kinematic viscosity which results in Re < 2000 for pipe flow will produce laminar flow. The flow is called laminar because the flow takes place in layers. The only mixing that occurs is molecular mixing between the layers or  between different parts of the flow. For large inertial forces (large Re, normally Re > 4000 for pipe flows), there is not enough viscous damping to remove any disturbances in the flow. Again, any combination of V and D giving Re > 4000 will produce turbulent flow. As Re increases, the viscous damping of flow disturbances or  perturbations decreases relative to the inertial effects. Because of a lack of viscous damping, disturbances are amplified until the entire flow breaks down into in irregular motion. There is still a definite flow direction, but there is an irregular motion superimposed on the average motion. Thus, for turbulent flow in a pipe, the fluid is flowing in the downstream direction, but fluid  particles have an irregular motion in addition to the average motion. The turbulent fluctuations are inherently unsteady and three dimensional. As a result, particles which pass through a given point in the flow do not follow the same path in turbulent flow even though they all are flowing generally downstream.
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