Friday is here, and the weekly 'A Taste of Science for the Weekend' column is back — issue 59.
This time: laminar flow, dimensionless numbers, and their connection to piping systems, blood vessels, and aircraft.
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At first glance, this video looks like a still image.
The stream of liquid flowing from the tap into the sink is so steady that it appears completely motionless.
How does it work?
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In fluid mechanics, a distinction is made between turbulent flow — in which a gas or liquid flows with eddies and random motion — and laminar flow, in which the fluid moves uniformly in a fixed direction.
We encounter turbulent flow every time we turn on a tap or open a window; it is the form of flow we meet in most everyday situations.
Laminar flow can be observed when pouring honey. Its high viscosity makes the flow so smooth that it appears almost frozen in place.
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Laminar flow is of little consequence when we turn on the kitchen tap, but it is critical in many other contexts.
The design of piping systems places great emphasis on diameter, materials, and internal coatings to ensure laminar flow inside the pipe.
Turbulent flow in a pipe causes unbalanced pressures, high wear, and energy loss.
The body's circulatory system is turbulent in the large blood vessels — enabling better mixing of oxygen and nutrients in the blood — and laminar in the delicate vessels, to preserve their integrity.
The design of aircraft, museum ventilation systems, medical equipment, and spacecraft is carried out with careful attention to maintaining laminar flow as much as possible.
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The threshold above which laminar flow becomes turbulent is determined by the Reynolds number, calculated as follows:
(density × velocity × length) / viscosity = Reynolds number.
The number is not a fixed constant.
In a circular pipe, 2000 is generally the value above which flow becomes turbulent, but in other situations the transition occurs at a different Reynolds number.
The Reynolds number is a dimensionless number.
This means that regardless of which units of measurement you use in the calculation, the Reynolds number you obtain will be identical.
In this way, it makes it straightforward to obtain a clear result across any scale and any system of units.
Shabbat Shalom 😊
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