How to carry large loads without touching anything: Journal Bearings!

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Ball and roller bearings are certainly among the most common bearings; they have rolling solid-solid contact. But if you need to support large loads and you don't want any solid-solid contact that leads to wear or the need to replace parts, you're gonna want to get yourself a journal bearing.

Journal bearings are really just a shaft (i.e. journal) inside a sleeve with some oil, and most people don't need to work through the fluid mechanical equations to think that that would work. But what isn't obvious is that when a journal bearing spins, there is a hydrodynamic force that keeps the journal centered in the housing and prevents the journal from touching the housing. Oil is certainly preferred for heavy machinery, and the effect is proportional to viscosity, but this works with any liquid including water or air. I have another video showing a system levitating based only on an air bearing, I think I will post that in the next couple of weeks.

So my title might be a bit misleading -- things are touching other things, and the forces in play do NOT operate over a distance. A high pressure is created in the oil whenever the journal spins and the journal is off center, and that pressure holds the journal away from the housing and stabilizes its location. But my internet consultants tell me that my titles have to be compelling and that the thumbnail picture should have (a) my face on it (b) a hand gesture (c) a title in an alarm color i.e. red yellow orange and (d) an exclamation point. For this video I amped it up with a Lissajous figure.

Super secret-- this machine shop doesn't really have many journal bearings, most machine shop equipment like this uses roller bearings. High-precision machining and metrology is more likely to use a journal bearing. But a journal bearing is still more likely in the machine shop than it is in my office or a classroom so... we used the machine shop for the vid.

This system is explained by the Reynolds equation, which most intro fluids classes don't teach, but the Reynolds equation really is just a relation between Couette flow and Poiseuille flow solutions that says that if your channel/crevice/spacing is of nonuniform thickness, there needs to be a pressure gradient and a local Poiseuille flow component because the Couette flow component can't satisfy conservation of mass. Boo-yah.

This video series is called "Professor Kirby's Fluid Mechanics Kitchen" because strategy sessions within the department for monetization of introductory fluid mechanics focused on commercial tie-ins along the lines of the George Foreman grill or the Ronco Food Dehydrator and the name seemed a sound tactical choice. This video was recorded in the Emerson Machine Shop at Cornell, which is where the Cornell Mechanical Engineering students have to machine their pumps for MAE2250, among other things. If you are wondering -- "who is that guy behind professor kirby, and is his nickname Sully?". The answer is yep, that's Sully.

Lectures are from Cornell University Mechanical Engineering 3230 - Introductory Fluid Mechanics. For reference information, especially how I teach it in MAE3230 at Cornell, see "How Fluids Work", Brian J. Kirby at Amazon: https://smile.amazon.com/dp/B09FRYGMVW.

The music in the series is the music I listened to when I was doing my fluid mechanics homework back when I was in school. Here the intro is Ray Ellis's score originally from the Fat Albert halloween special from the 1970s, but I was thinking of assorted hiphop samples that used it e.g. Kid Koala MF DOOM Joey Badass more than the Fat Albert specials. The outro is "Extinction Agenda" by Organized Konfusion, notable for its use of references to chess pieces and it's eschewing of the more routine party-Bacardi throw-your-hands-in-the-air-and-wave-em-like-you-just-don't-care couplets and instead going with the more esoteric poltergeist-heist surgin-emergin-clergymen intra-line rhyming structure.