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mooeypoo

Rotating candle... Convection cycle?

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So, I'm looking for fun home experiments in thermo.

 

I found this video:

 

I'm going to test it out soon (need to buy a proper candle, I only have the small round scented ones). BUT Before I can put this in a proper official "DIY" kit, I need to know what's going on.

 

I *think* I know, but I need some help with this. Is this due to a convection cycle or something else? If so, I'm having a bit of difficulty understanding how BOTH sides are lit (which also means they warm up the air above them, respectfully) and yet it rotates, one side goes up while they other goes down.

 

What's going on here? Is the heat engine more towards the "center" (as in, the center is cold and the tips are hot, so the cycle is really 2 circles from the center) ?

 

I'm a bit confused. Help?

 

Thanks!

 

~mooey

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I think it involves the relative melting speeds as function of the angle between flame and wax.

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Could it have to do with the amount of wax? That's my guess. As wax burns/drips off one end it becomes lighter, and the heavier end will fall. I would guess a downward-tilted candle will burn more rapidly, since the flame is closer to the wax.

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I don't think this has anything to do with thermo, more the effects of levers.

 

the lower end will lose mass faster (this is demonstrated by the lower flame being larger) both by burning and by wax being able to drip off the candle to the work surface.

 

The higher side loses mass slower because the only flow of wax to the flame is via capillary action and not also gravity feed. alls molten wax will remain part of the candle.

 

as the lower end burns off mass it becomes lighter causing itself to rise and the other end loses less mass and becomes the heavier side.

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Could it have to do with the amount of wax? That's my guess. As wax burns/drips off one end it becomes lighter, and the heavier end will fall. I would guess a downward-tilted candle will burn more rapidly, since the flame is closer to the wax.

 

I thought about that too, like the "Drinking Bird" but if you notice, the candle isn't entirely balanced to begin with... not sure how much wax it loses. Also, at some point it rotates almost all the way through.

 

My coworker here suggests that the flame that's slightly higher is all-exposed, so it heats the air above it and creates negative pressure layer. The flame that's lower is partially hidden by wax, so there's LESS heated air and hence lesser pressure, and so the candle rotates.

 

That might be ...

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I thought about that too, like the "Drinking Bird" but if you notice, the candle isn't entirely balanced to begin with... not sure how much wax it loses. Also, at some point it rotates almost all the way through.

It looked to me that the larger rotations happened after you could see drops of wax coming off. The weird thing (to me) is that it rotates past vertical and then reverses direction.

 

My coworker here suggests that the flame that's slightly higher is all-exposed, so it heats the air above it and creates negative pressure layer. The flame that's lower is partially hidden by wax, so there's LESS heated air and hence lesser pressure, and so the candle rotates.

 

That might be ...

 

If the exposed flame creates a low pressure area above it, the high pressure below would push up on it.

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I thought about that too, like the "Drinking Bird" but if you notice, the candle isn't entirely balanced to begin with... not sure how much wax it loses. Also, at some point it rotates almost all the way through.

 

My coworker here suggests that the flame that's slightly higher is all-exposed, so it heats the air above it and creates negative pressure layer. The flame that's lower is partially hidden by wax, so there's LESS heated air and hence lesser pressure, and so the candle rotates.

 

That might be ...

 

I somehow agree with him. It seems a fit-able explanation.

 

And about the complete rotation of the candle, it would occur after sometime. IN 'sometime' period, a lot of less pressure area is created above the apparatus. This would result in a lot of air-flow from down to top, resulting in complete conversion.

 

But, it won't be the first step. I would happen after some semi circular movements are done.

This could be tested by taking a candle (of small thickness as shown in video ) and applying molten wax on both sides. The molten wax should form a box type formation on the end. Now, before planting more wax, you should thicken the wick by attaching thicker cotton threads.

Now, set the apparatus. If it shows complete cycle early as compared to other candle. Then, our idea would be correct.

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