pot pot boat

[jaket]

http://www.youtube.com/watch?v=g3OLhFx8 ... re=related

hi

is the 'pot pot boat' engine basicly a stirling engine, (thermoacoustic engine?) it basicly has just a chamber and a tube(or multible tubes), I think the water column in the tube acts as a piston.

JT

[Lucien01]

hello jacket,

Very clever. Well done!


I'd like to know exactly how it works.

[Ian S C]

Hi Jacket, they,r quite interesting little motors. When I was about 10 yrs old I made my first one, it consisted of a length of 1/4" dia copper tube. I made a 3 turn coil on it by wrapping it around a bit of broom stick. I made a little tin boat with 2 holes out the back, and soldered in the copper coil, I put a little container of meths under the coil (coil mounted vertically), and put the boat in water, and squerted some water into the tube, and away it went. When Dad came home, he told me about Pop Pop boats, and how he had one when he was a kid. I thought I had invented some thing new, I'd never seen or heard of them before that.
In latter years I,v had a similar motor in a bigger tin boat, and sailed it on the lake at the local park. Ian S C

[jaket]

I think it works like this.

there needs to be small amount of water in the chamber(even just a drop). when it boils it pushes the column of water in the pipe away from the chamber, but the mass of the column causes it to go too far, this causes vacuum to the chamber and the column of water starts to move back. some water droplets are injected to the chamber again, and the loop starts again.

the reason these engines usually have two pipes, is just because it's easier to prime it when there is two pipes. inject water to one and when it comes back from the other pipe, it's ready. it would work with one tube, or I've seen ones with 5 or more tubes.

sometimes these engines have diaphram that makes the poping sound, but it's not necessary.

[jimlarsen]

This would not be a Stirling. It is more closely related to a steam turbine.

[Ian S C]

Jim, I think it could possibly be called a thermo acoustic motor, with a hydraulic piston. actually its a flash steam boiler, the small amount of water in the boiler almost instantly turns to steam, that expands (1200 times in volume I think), it pushes out the tail pipe, and a partial vacuum is formed, sucking in another few drops of water, and so the cycle goes on. I don't know how or why I designed my first one all those years ago, I got my first steam engine a few months later,a Mamod SE 2, still got it. Ian S C

[jaket]

actually you could probably modify similar design to be a stirling engine too. if would need to have the cold end, maybe longer tube style pressure chamber and steel wool inside the end cold end. heat it from the middle were the wool ends. and that water would act as a piston. water would move the air from hot end to the cold end.

[Carnot]

Stirling engines use a closed system that heats and cools the working fluid, so a pot pot boats isn't a Stirling.
They are fun though, I remember having a tiny little one, only a few inches long made out of tin that ran around the bathtub.

[Ian S C]

Carnot, you could(stretch a point) say that the water at the end of the tubes closes the tubes, and the steam from the boiler(now condensed) is the piston, the slug of water oscillates ack and forth in the tubes, flashing to steam , then condensing. Ian S C

[speedless]

Hi
Its not a stirling or steam engine,its a ressonant waterjet.
The princip is also used in pulsjetmotors.
If you like to make a simple putt putt see this:http://www.sciencetoymaker.org/boat/makeBoat4_07.htm
Jan

[Carnot]

Hi
Its not a stirling or steam engine,its a ressonant waterjet.
The princip is also used in pulsjetmotors.
If you like to make a simple putt putt see this:http://www.sciencetoymaker.org/boat/makeBoat4_07.htm
Jan

This link describes a nice all-metal soldered putt putt - no glue in sight - and without a noisy diaphragm.....
http://www.nmia.com/~vrbass/pop-pop/buildpop.htm

[tibsim]

Pot pot is essentially the same as the rice thermoacoustic machine. This and many other things could be two-stage also:

or we can probably use possible an suitable alcohol- water mixture, and with this also we could to increase the temperature difference between the cold and hot sides of the machine (only to a slightly lesser extent.).

[Tom Booth]

Thanks for bringing up this old topic! Very interesting.

It appears from the way the boat is started, by getting nearly all the air out of the boiler, that it depends on the *saturated vapor" principle.

I'm skeptical that it actually requires a temperature difference to run. I"ve watched some videos where the "sink" seems minimal or absent. (Tubes made of glass or plastic, hull made of styrofoam)

I'd be interested to see if the boat would still operate if put into a pot of boiling hot water. With all the pop pop boat experiment videos, I haven't been able to find an example of anyone trying to run the boat in a bath tub of hot water.

[tibsim]

I think that if the water is boiling in the boiler, and the pipe is in a colder place, e.g. in the air above the water, then the boiling pot also works in water. The water in the pipe must be able to condense.

[Tom Booth]

I think that if the water is boiling in the boiler, and the pipe is in a colder place, e.g. in the air above the water, then the boiling pot also works in water. The water in the pipe must be able to condense.

Some boats (in youtube videos have plastic tubes which I don't think could rapidly cool the water vapor.

The water vapor could be cooling/condensing in part due to the 'saturated vapor" effect lowering the condensation/boiling point and cooling from "expansion work" pushing water out of the tube.