Shushing, Hushing, Shooshing a candle?
May 9, 2017 8:18 PM Subscribe
The other day I was hanging out with a friend, and when I went to blow out a candle I blew too hard and spattered wax everywhere. She suggested that I hold my finger halfway between my mouth and the flame to protect against this happening, and that it also allowed for a much smaller quantity of air. I tried it out, and sure as hell it worked, I've been doing it every night since. I started thinking about it and it makes perfect sense; utilizing turbulence in the air to blow out the flame with less volume of air. My question is: WHAT IS THIS CALLED?
There has to be some term for it...I remember seeing a specific Christmas illustration when I was a child showing someone putting out a candle this way, and I used to joke with my brother that they were telling the candle to be quiet. Only now, a couple of decades later, do I realize what it was depicting. Is this super common? If so, why can't I find any words or terms that describe the action?
There has to be some term for it...I remember seeing a specific Christmas illustration when I was a child showing someone putting out a candle this way, and I used to joke with my brother that they were telling the candle to be quiet. Only now, a couple of decades later, do I realize what it was depicting. Is this super common? If so, why can't I find any words or terms that describe the action?
Possibly Bernoulli effect/principle.
Works really well with a wine bottle, btw.
posted by scruss at 6:44 AM on May 10, 2017
Works really well with a wine bottle, btw.
posted by scruss at 6:44 AM on May 10, 2017
If you really are using the turbulent action, this is not the Coanda effect, it's simple Vortex Shedding. Not specific to candles of course, it's just the term for the physics concept you're using. The animated GIF Wikipedia presents will actually be a pretty relevant for blocking near-laminar flow from your mouth with a finger.
FWIW, I've never heard of it or seen it, but I've also never had problems blowing wax around, I just get close and use a small puff of air.
posted by SaltySalticid at 9:32 AM on May 10, 2017 [1 favorite]
FWIW, I've never heard of it or seen it, but I've also never had problems blowing wax around, I just get close and use a small puff of air.
posted by SaltySalticid at 9:32 AM on May 10, 2017 [1 favorite]
Here is a visualization of 5 regimes of fluid flow past a cylinder as determined by Reynold's number, which has a linear relationship with flow speed in this situation.
Vortex shedding appears by R 2000, turbulence in the shed vortices by around R 10,000 (5X greater flow speed), and a full turbulent wake by R 100,000 (50X greater flow speed).
Figuring out which regime you were in as you blew past your finger according to this scheme wouldn't be too hard using the simple formula in the link, as long as you felt confident in estimating the speed of your breath as it blew past your finger.
posted by jamjam at 10:56 AM on May 10, 2017 [1 favorite]
Vortex shedding appears by R 2000, turbulence in the shed vortices by around R 10,000 (5X greater flow speed), and a full turbulent wake by R 100,000 (50X greater flow speed).
Figuring out which regime you were in as you blew past your finger according to this scheme wouldn't be too hard using the simple formula in the link, as long as you felt confident in estimating the speed of your breath as it blew past your finger.
posted by jamjam at 10:56 AM on May 10, 2017 [1 favorite]
That is a great link jamjam; I was conflating smaller vortex chains with true turbulence in my previous response.
I will bet a donut that regimes 3-5 are what matters for most candle-finger cases, with 3.5-4 being the main action. All of those will be more effective at blowing out a candle than 1,2, or the unimpeded flow for the same laminar steady-stream velocity. 5 is conceptually effective, but I don't think it's that commonly realized in real candle-finger blowing out events.
posted by SaltySalticid at 3:02 PM on May 10, 2017 [1 favorite]
I will bet a donut that regimes 3-5 are what matters for most candle-finger cases, with 3.5-4 being the main action. All of those will be more effective at blowing out a candle than 1,2, or the unimpeded flow for the same laminar steady-stream velocity. 5 is conceptually effective, but I don't think it's that commonly realized in real candle-finger blowing out events.
posted by SaltySalticid at 3:02 PM on May 10, 2017 [1 favorite]
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posted by Miko at 8:53 PM on May 9, 2017 [2 favorites]