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Module 7
Dr. D. Penney

Reynolds Number:

There are four factors which are used to calculate the Reynolds number . The preferred equation is one that incorporates mean velocity of flow, times tube radius, times the specific gravity of the liquid, and this quantity divided by the viscosity. Other equations that are sometimes used contain diameter or flow rate instead of velocity. The equation incorporating flow rate is easily derived from those containing mean velocity and vessel dimension.

In 1883 Sir Osborne Reynolds found using a purely physical system that for a Reynolds number below 1000, streamline or laminar flow usually was present. When the Reynolds number was above 1000, turbulent flow was usually present. One-thousand seems to be the critical value when radius is used to calculate the Reynolds number, but the critical value is really more a zone.

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