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Dimensionless numbers in fluid dynamics

By Chemical Engineering |

Dimensionless numbers refer to physical parameters that have no units of measurement. These numbers often appear in calculations used by process engineers. As long as consistent units are used, dimensionless numbers remain the same whether metric or other units are used in the equations. Here are some dimensionless numbers often used in chemical engineering fluid dynamics calculations: Reynolds number (Re). Reynolds numbers express the ratio of inertial forces to viscous forces in a flowing fluid, and represent a way to quantify the importance of these two types of forces under a given set of flow conditions. When calculating pressure, heat transfer or head loss in pipes, it is important to know whether a fluid is exhibiting laminar flow, turbulent flow, or a mixture of the two. Re is typically used as a criterion for determining whether pipe flow is laminar or turbulent. High Reynolds numbers are associated with turbulent flow, where inertial forces dominate and flow is chaotic and characterized by eddies and vortices. Low Reynolds numbers are associated with laminar flow, where flow paths are smooth and viscous forces dominate as defined by Equation (1). The term is named for U.K. physicist Osborne Reynolds.   Re =…
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