Laminar Flow versus Turbulant Flow

[dlarson]

Just to be clear, I am not arguing against turbulence or laminar flow in a stove.
I just think that it's perfectly correct to describe gas flows in a stove with those terms.

Zelph, your post mentions mechanical machines and nozzle tips as usually having turbulent flows. If this is the case, perhaps the the gas jets in a pepsi jet stove are also turbulent. In contrast, I would think that the open type stoves are more laminar flow, at least towards the base of the flame. When there is no pot I have watched the flame flow nicely up but then break up a little towards the top.

And then there's this transient business... I'll have to read up some more on that.

[zelph]

Let's take a step backwards and see what Brian Robinson said:

If you've ever watched a creek flowing across a
smooth granite surface, you've seen both. At first, the water is clear, then
white. The clear water is laminar flow. It moves faster than the turbulent
white water ahead of it, thus it is shallower. The turbulent white water
ahead is deeper because it's moving more slowly.

Ok, we learned that water/air flowing over a smooth granit surface will be laminar.

White water in a creek is caused by the downward flow of water over rocks/boulders(rough surface) which cause turbulance. The water increases speed as it moves downward at a greater angle. What he said seems totally mixed up. He says the clear water is laminar flow. It moves faster than the turbulant water ahead of it. That sure do sound bogus.

[dlarson]

In the laminar flow of fluid through a hose, the fluid against the inner surface is actually quite stationary while the fluids in the middle are moving. So perhaps the laminar flow of water over smooth granite is faster but we can't tell very easily.

Also, when rafting down a river, rapids are usually steeper but full of rocks. If they where just steep and the river bottom was a smooth sheet of granite I believe the water would move faster since it's not getting hung up and redirected by the rocks. The thing is, rapids are kind of like damns in that they tend to hold back the water upriver. Once you hit the rapids the flow rate is faster than the pooling liquid behind them. If there was actually a steeper part of the river that had a smooth granite surface I don't think we would know because the water before and after it would be the same level. The only exception to that is if the smooth steep surface was long enough and/or steep enough to significantly thin the water to create a differential between the two sides.

Have you ever poured a glass of soda from a 2 liter bottle? We learned in high school physics class that pouring the liquid at the proper angle to create a laminar flow would fill the glass faster than just tipping the bottle vertical and letting the liquid 'plop' out in a turbulent flow.

[oops56]

I just hope there is no test on this i did not read it much just the first few word that i could not say or understand and i was not going to look it up. All i know is fire burns hot that all one needs to know I don't care if its up down side ways in a circle just don't burn the eye brows

[zelph]

In the laminar flow of fluid through a hose, the fluid against the inner surface is actually quite stationary while the fluids in the middle are moving. So perhaps the laminar flow of water over smooth granite is faster but we can't tell very easily.

Also, when rafting down a river, rapids are usually steeper but full of rocks. If they where just steep and the river bottom was a smooth sheet of granite I believe the water would move faster since it's not getting hung up and redirected by the rocks. The thing is, rapids are kind of like damns in that they tend to hold back the water upriver. Once you hit the rapids the flow rate is faster than the pooling liquid behind them. If there was actually a steeper part of the river that had a smooth granite surface I don't think we would know because the water before and after it would be the same level. The only exception to that is if the smooth steep surface was long enough and/or steep enough to significantly thin the water to create a differential between the two sides.

Have you ever poured a glass of soda from a 2 liter bottle? We learned in high school physics class that pouring the liquid at the proper angle to create a laminar flow would fill the glass faster than just tipping the bottle vertical and letting the liquid 'plop' out in a turbulent flow.

Waterover a spillway that has a 45 degree ramp on the down side give a good example of the uninterupted flow of water. Just the other day on the tube was a program about people that jump off the golden gate bridge. They're not going very fast when they first let go of the top rail but by the time they get to the bottom their doing 75 miles per hour. Water going down hill in creeks and rivers picks up speeed also. I'm inclined to beleive the gases coming out of a pop can side jet are laminar just as is an open top. Like Tony said, he has not seen alcohol stoves that burn turbulent.

I've poured a few quarts of brewskis in both ways Lots of bubbles straight down, tilt to the side no bubbles. Too many quarts made me tilt to one side. Don't do that any more

[Tony]

Studying fluid dynamics is what I do for a living.

If you look closely at this shadow graph image of a flame from a cat can side burner stove under a pot you can see the flame coming out of the side of the stove, there is no sign of turbulence until the flame goes up the side of the pot and starts to mix with the (or entrains) surrounding air.

I have also included some shadow graph pictures of the flames from other alcohol stoves and until the flame goes up the side of the pot in my opinion there is no sign of turbulence.

Tony


Side jet burner


My volcano which has a fairly high velocity flame jet for an alcohol stove


Zelphs Starlyte


Open top burner

[zelph]

Studying fluid dynamics is what I do for a living.

If you look closely at this shadow graph image of a flame from a cat can side burner stove under a pot you can see the flame coming out of the side of the stove, there is no sign of turbulence until the flame goes up the side of the pot and starts to mix with the (or entrains) surrounding air.

I have also included some shadow graph pictures of the flames from other alcohol stoves and until the flame goes up the side of the pot in my opinion there is no sign of turbulence.

Tony

These shadowgraphs are totally awesome how they show where the turbulance occurs. There is no doubt in my mind that Robinsons' statement was on the verge of an urban legend in the making. Your photos show there is no turbulance around the holes of the Supercat stove.

Studying fluid dynamics is what I do for a living.

[/quote]

sombody has to get the fun jobs that offer the chance to make stoves and see how they apply to your work

I've got to make a shadow graph, I do, I do !!!!!!!

I really do appreciate the time and effort you put into those photos for us to actually see what is going on around the pot as the burner is aflame. We appreciate your talents to no end. Thank you Tony

[dlarson]

I agree. The flames do not appear turbulent until after they drift up the side of the pot. I spent a lot of time looking around the net prior to that post and it seems to fall in line with what I found. Hooray for laminar!

[zelph]

Urban Legend busted!!!!!

[seudo_411]

Hi guys, Been away for a while, but i'm back and i have an idea i want to bounce off you guys, and it is based on the article on the Cat stove. I found that an air hole in the middle of my open top burner concentrated the flame in the center of the pot i am using. so I went with this design. it has standard cat stove type side air holes, as well a a cone shaped one in the center, the outer holes will have a simmer ring as the Turbo cat stove has, but also the center hole. I'm currently working with a friend who builds safes, and he is going to help me build the entire stove from SS sheet. what i intend is to make use of the smoother laminar flow for efficient combustion, and the top the outlet with gauze as this will reduce the gas velocity and allow more contact with the pot. looking to get a Jetoil PCS type cup with heat exchanger.

Here's the Quick and Dirty drawing.



I would appreciate any input you guys have.