## REYNOLD'S NUMBER (Re) DEFINITION AND BASIC INFORMATION

Generally, the first thing a fluids engineer should do is estimate the Reynolds number range of the flow under study. Very low Re indicates viscous creeping motion, where inertia effects are negligible. Moderate Re implies a smoothly varying laminar flow.

High Re probably spells turbulent flow, which is slowly varying in the time-mean but has superimposed strong random high-frequency fluctuations. Explicit numerical values for low, moderate, and high Reynolds numbers cannot be stated here.

The pecking order changes considerably, and mercury, the heaviest, has the smallest viscosity relative to its own weight.

All gases have high relative to thin liquids such as gasoline, water, and alcohol. Oil and glycerin still have the highest , but the ratio is smaller.

For a given value of V and L in a flow, these fluids exhibit a spread of four orders of magnitude in the Reynolds number.