Convection Cell "Sea Breeze" Visualization

Convection cell demonstration narrated by Steven Wofsy for E-PSCI 338 February 2020. A heating element in the bottom-right side of a tank of water causes convective circulation. The warm water above the heater rises up to the surface and moves over to the left side of the tank, where it starts to cool. Losing buoyancy as it cools, the water gradually returns to the bottom, where it completes the cycle by being drawn back into contact with the heater.
One can draw an analogy with this demo and onshore breezes that occur along the coast on hot summer days. In that case, air heated by land rises up and is replaced by cooler air moving in from over the ocean.
The tank was custom built at Harvard Bio Labs Machine Shop in Cambridge, MA; it is about 14" x 10" x 2" and is made out of acrylic. The heater is a 125W Cenco Knife Type Immersion Heater connected to a Variac. About 20 drops of concentrated rheoscopic fluid were added to distilled water.

[@PlayNowWorkLater]

This has to be the best demonstration of convection currents in water on KZbin. The Aluminum particles really help illustrate the eddy currents

[@mmd488]

Even having such videos would have made learning Science so much fun during my childhood.

[@RyanHartwigOfficial]

Thanks! Helped me understand convection for my drone pilot training class.

[@奇覆木星稱屬氫]

these kind of videos calm spirits.

[@klemens8565]

It's beautiful, thank you

[@royalfolkspark]

You must believe in Santa Claus, The Tooth Fairy,, The Easter bunny, Oswald killed Kenndy, 9-11, and.. last but not least....(covid 19).

[@Winterzz838]

@@royalfolksparkyou think COVID was fake? 😂

[@brokenbagus]

i like your funny words magic man

[@mujinaumemiya3130]

Flow is generated at heated end, diffused around the cold side; no flow from the cold end. It is consistent with the ocean flow.

[@14jessek]

How much of an effect is caused by this being a closed container, seeing as in real life there wouldn't be a barrier preventing the horizontal motion from continuing, and converting it into downwards motion? One thing about seabreezes I've not been able to figure out, is why they have a clear frontal boundary, as opposed to gradually changing the wind direction over time as ground temp rises. It's almost as if they "take off" in real life, similar to a spring being released. It slowly builds and stores energy, that is suddenly released, causing a clear defined frontal boundary.

[@Starbuck.Laniakea]

Thank you for sharing

[@eliotvarda]

Beautiful

[@mchohatai]

How, what will happen if the heating strip in the middle? 🙄

[@Rolembeek33]

Can anyone give me some more information about the rheoscopic fluid used ? (brand/name/exact composition) In the past,I used mica powder to make flow visible (works quite well) but after a few tens of minutes, this settles to the bottom and have to be stirred up before a each new demonstration. (used to do demonstrations for kids)

[@NatSciDemos]

We use concentrated fluid from Steve Spangler Science

[@igorstaszak133]

What has been added to the water?

[@NatSciDemos]

Tiny aluminum flakes

[@tinytiny3704]

How can I use convection cell in a sentence

[@ravimakwana992]

so the fluid right in the middle stays "nearly" static?

[@samuelwhitt1050]

It slowly warms and rises only to cool and warm again.

[@AustinShoeman]

Does this have to do with the Intermolecular forces of the water. Since IMFs become weaker when heated and stronger when cooled. Just recently learned about them so I was wondering if that’s it.

[@NatSciDemos]

The forces stay the same when the H2O is heated. However, the thermal energy increases, and that leads to a decrease in density, which causes an increase in buoyancy.

[@NatSciDemos]

An increase in temperature is an increase in the average kinetic energy of the molecules, so they will be zooming around at high speed and occasionally crashing into each other, which means there will be less molecules per unit of volume at a given time. Sure, the forces between molecules will be less because they're further apart from each other as they zoom around with thermal energy. The point is that the density decreases as a result of their kinetic energy, not as a result of the forces changing. Does that make sense?

[@AustinShoeman]

Harvard Natural Sciences Lecture Demonstrations ah, yeah that does clarify a lot. So some of the molecules moving faster in the area with the heater move in a direction away from the right side of the container? This decreases the density of water on the right side of the container but also increases it in other areas. Also, the reason why the flow continues from the top right to top left is because the less dense water continues to rise to the top until it cools back down and falls?

[@FigmentVFX]

Where did you get a tank like that?

[@NatSciDemos]

It was fabricated in our machine shop.

[@chrisgoldbach4450]

Is tjis how waves work in the ocean?

[@NatSciDemos]

Yes and no. Water does move in a (more or less) elliptical path below ocean waves, but it's not due to convection.

[@wiiuwiiu2020]

Why does the cooling water not have microstructure and eddies?

[@NatSciDemos]

The turbulence near the heater happens because the hot water that was in contact with the heater is moving much more quickly than the relatively cool water surrounding it, to the point where the flow changes from laminar motion (characterized by smooth streamlines) to turbulent motion (chaotic). Away from the heater, the temperature--and hence the density--is more uniform, and so the fluid is moving with a more uniform velocity and laminar motion dominates.

[@wiiuwiiu2020]

@@NatSciDemos That's super interesting! What mathematics governs such a bifurcation of behavior? What describes the threshold for temperature difference to go from laminar to turbulent?

[@NatSciDemos]

To calculate the onset of turbulence you could use the Reynolds number, but some hand-waving would be needed since we're not talking about flow in a tube of well-defined diameter. You could also use Naiver-Stokes equations, but in that case we're talking really complicated math. ;)

[@butterflywing61]

@@wiiuwiiu2020 Great question! Mathematics as us non PHD folks understand it can only predict at the macro (time averaged) level. I can only imagine the calculations would have to be done at the nano level involving billions of calculations based on the actual structures of the materials involved. What appears to us as random chaos probably can be described mathematically.

[@royalfolkspark]

Please explain how a wood fire at 800 degrees can melt steel ?

[@butterflywing61]

WTC 7

[@royalfolkspark]

Plz do a video on the (space shuttle). NASA stated it was a glider (no engine). (Shotgun microphones picked up engine sounds when landing). Please be honest with your audience.

[@samuelwhitt1050]

Video link? (biased claims dont do the world any good)

[@royalfolkspark]

@@samuelwhitt1050 Three questions for you... 1. How many times is the earth bigger than the moon. (approximate). 2. How many (photos) were taken by the astronauts while on the moon ? (five trips)(500 or 1000 perhaps) ? 3. Why were there no photos of the earth taken from the moon ? Please answer follow earthling.