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Question about centrifugal force and Bernoulli's law.

What I want to do is maintain a gas at very high pressure and temperature for propulsion purposes. The problem is containing a gas at high pressure requires a thick walled tank, and the resulting mass would obviate the advantage of having the gas at high pressure. So what I'm considering is moving the gas at high speed within the tank. By the Bernoulli principle the tank should see the pressure on its walls as much less. However, if the gas is moving around a cylindrical tank or a toroidal tank, then by centrifugal force that would seem to indicate it should increase the pressure(!) Which one wins out? Here's one possible way to address this problem. You could have the tank consist of long straight portions on either side but be curved at the top and bottom. Then you would only have to keep the portions at the top and bottom to be thick walled to maintain the pressure increase due to centrifugal force. If the straight portions are much longer than the curved parts at top and bottom, you could get a large volume without having to add too much to the tank mass.

Bob Clark

Reply to
Robert Clark
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why not store the gas in a much smaller solid form, then ignite it so it changes state from a solid to a gas ?

Reply to
Tom

This won't work. The way Bernoulli's law works is that it has to be applied along a streamline. Then an increase in speed along that streamline results in a reduction in the pressure. What I was envisioning is that if you have a flow at steady speed and it flows horizontally over a surface, while maintaining the same constant speed, then the pressure applied to the surface will be less than the pressure far from that surface. This is not how Bernoulli works. It only applies when the velocity is different between two points in the flow.

Bob Clark

Reply to
rgregoryclark

| >

| > Bob Clark | | This won't work. The way Bernoulli's law works is that it has to be | applied along a streamline. Then an increase in speed along that | streamline results in a reduction in the pressure. | What I was envisioning is that if you have a flow at steady speed and | it flows horizontally over a surface, while maintaining the same | constant speed, then the pressure applied to the surface will be less | than the pressure far from that surface. This is not how Bernoulli | works. It only applies when the velocity is different between two | points in the flow. | | | Bob Clark

Sounds like a jet engine to me.

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Reply to
Sorcerer

Offhand this doesn't sound promising, but let's be analytical.

One problem with your scheme, ahem, is that the pressure term in Bernoulli's equation is the real internal pressure of the gas. No matter what your set up, low gas pressure is low gas pressure, not high gas pressure -- you are not getting compression associated with a high internal pressure while only seeing the effects of a low pressure on the vessel.

Reply to
Edward Green

Use a bolloon inside a ballon inside the tank? Inside balloon holds moving gas while outside balloon regulates pressuue along length of the tank?

Reply to
sugna41

What I really want is the high speed. So perhaps I can just inject the fuel into a tank at the speed I want. The problem is you want it to have the exhaust speed of a rocket, thousands of meters per second. So again you have to be concerned with the high pressure that would be created by the centrifugal force. How do you calculate this for a *compressible* gas?

Bob Clark

Reply to
Robert Clark

I thought you wanted to store gas at high pressure and cheat on wall thickness by applying Bernoulli's principle? Which won't work, for reason I indicated.

So you just want to know the contribution to pressure as a high speed gas rounds a corner? Roughly, Newton's second law should work: dP/dt = net force around the elbow or U; average the force over the projected wall area; pressure. Compressibility doesn't enter on this level.

Reply to
Edward Green

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