What-If 0071: "Stirring Tea"

[thanksbastards]

Stirring Tea

I was absentmindedly stirring a cup of hot tea, when I got to thinking, "aren't I actually adding kinetic energy into this cup?" I know that stirring does help to cool down the tea, but what if I were to stir it faster? Would I be able to boil a cup of water by stirring?

Will Evans

A lot of strong points made, but I think the physics could probably be defeated, but losses and vorticies would be very hard to account for in a numbers sense. Let me see if I can't put together a scenario where you could actually get the energy into the cup. giddy-up horsey, I got a treadmill I need you to run on. Gonna go ahead and post this first so we don't dupe...

[Klear]

Maybe if you stirred it with a lightsaber...

Also, the dictionary of numbers wrote that the 700 wa.tts is "approximately the amount of sunshine falling on a square metre of the Earth's surface on a clear day in March for northern temperate latitudes". So you just need to deflect a square metre of sunshine into the cup and it boils in close to 2 minutes. Cool!

[thanksbastards]

now if you had a robust, possibly adamanitum cup and paddle whisk, like those things used to stir 5 gal buckets of paint, but small enough to fit in a cup, and capped the top of the tea cup, you could retain the tea. allow zero air space above the tea and then feed the whisk shaft out thru the lid (duh) and use some kind of bevel gear/pully system to connect the hoovemill[1] to the whisk, carefull to maximize effeciencey as a horsepower is 750 watts or so iirc. The value over-estimates the power of a horse to avoid farmers getting all huffy about thier horses being accused of only producing some measly amount of a new unit dervied which I am sure is a thing farmers worried about back then.[2] This leaves you little overhead to waste in bad gear trains. Now as the itty bitty whisk kicks around at rediculous speeds I realize a gear train probably won't cut it and you'll need some kind of hydrodynamic speed multiplier i guess, sorry. But now that your contraption is really whizzzing about, you should be imparting some interesting power to the tea. cavitation will continue to occur as the tea is probably compressible at these force magnitudes, but that means there is a gnarly pressure wave [3] in front of the paddles and I suspect that will be imparting a good amount of energy. Baffling would be neededto avoid simply rotating the tea at higher and higher speeds till time travel via bad super man science[4] occurs within the teacup[5], although a simpler teacup can be used if your hoovemill contraption can reverse speed rapidly and repeatedly. the second method would probably put more energy into the tea anyways, so lets go with that. slap that tea!

any failure modes I missed here? surely it can't be this simple....


[1] a treadmill is run on with the treads of your shoes, I only assume a horse would run w/ its hooves on a hoovemill
[2] Urban legend proudly brought to you by my high school science teacher
[3] You can not surf this brah
[4] no
[5] suddenly struck by the thought of how did Randall avoid a "tempest in a tea***" snark throughout that entire installment?

[Thorbard9]

Interesting that this article became available at about morning tea time (not to be confused with teatime, which is a different time of day from the other end of the country).

Also, the dictionary of numbers wrote that the 700 wa.tts is "approximately the amount of sunshine falling on a square metre of the Earth's surface on a clear day in March for northern temperate latitudes". So you just need to deflect a square metre of sunshine into the cup and it boils in close to 2 minutes. Cool!

Actually this can be a very efficient method of heating water. People have built parabolic reflectors for just such a purpose.

[KarMann]

Where's footnote 1? Where's footnote 1?!?

This might be even worse than unclosed parentheses.

ETA: The math formatting for footnote 4 is messed up, too.

[mccdyl001]

As a side question. in the scenario of a tea cup without baffles, would it be possible to stir fast enough that you could accelerate the speed of the rotating tea until centrifugal forces pushing outward (on the inside of the tea cup) could shatter a standard porcelain tea cup?

[superlinkx]

I also noticed that in footnote 2, ammonia is referenced as an element. It's actually NH3, which is a compound.

[leeharveyosmond]

No matter how hard you stir your tea, it's not going to get any warmer.

Actually it might; as per the discussion you are adding kinetic energy, even if you are as per the discussion accelerating other processes by which energy is lost. But you wouldn't detect an increase in temperature.

If on the other hand you did this in a fancy insulated copper can, and your family background in brewing gave you knowledge of how to make thermometers to measure temperature changes to within 0.01 deg F, then you might.
http://en.wikipedia.org/wiki/Mechanical_equivalent_of_heat
http://en.wikipedia.org/wiki/James_Prescott_Joule

Or you might not. This could well be the experiment about which I read in a thermodynamics textbook "paradoxically, if he had detected the temperature rise this would have set back the development of thermodynamics by approximately thirty years".

[Popup]

While it's certainly impractical to heat the tea - it should not be impossible to heat a teacup. At least if it's made of metal.

The concept of 'Friction stir welding' uses what's basically a fancy teaspoon (made out of tungsten) to stir metal until it melts enough to form a small pool of molten metal.

http://en.wikipedia.org/wiki/Friction_stir_welding

[KarMann]

*twitch* Footnote 1 goes between 5 & 6 now?

I may have to go lie down for a bit.

[rcroonenberghs]

It is only not possible because you use tea. If you use a more dense fluid like paint, it would heat up when stirring. (when you mix paint in the shop, it heats up in the machine)

[spOTTy]

If a microwave has been involved, you're not making tea! Someone get the poor man a kettle.

/British

[Higure]

At physics.stackexchange there is a question regarding this (slightly altered, though; it asks if sirring actually hastens cooling or dampens it). I cannot post a link (probably my post count), but it's question number 5265, with the title "Cooling a cup of coffee with help of a spoon". Google should help (or the internal search engine on physics.SE).

[peewee_RotA]

I've got two things that I think drastically change the article.

First, there's an experiment that was able to "boil" water with very little energy.
http://news.rice.edu/2012/11/19/rice-un ... echnology/
http://pubs.acs.org/doi/abs/10.1021/nn304948h


Second, no stirring at an industrial level was considered. Tank stirrers remove the considerations of airflow. I'm trying to research this better, but it sounds like it's technically possible to boil water in an industrial tank stirrer or agitator.

[Klear]

convert solar energy directly into steam

Wut? They turn photons into H₂O?

Edit: I read the rest of the article and I get what they wanted to say, but I still find it funny.

[cellocgw]

I was going to suggest stirring it with a spoon made of solid U-238, but a light saber might work, so long as you don't accidentally slash the teacup in half.

On the sunlight thing: it's trivial to focus a square meter's worth of sunlight into a mug -- measuring one on my desk, D=8 cm, so A = pi*(4^2) = 50.26 cm^2, vs. the 10^4 cm^2 collection area.
You do have to account for the spectral absorption of tea (subscription required, sorry) . You might get a reasonable approximation by using this curve for water (a good idea anyway, since you should boil the water before adding the tea leaves).

Maybe if you stirred it with a lightsaber...

Also, the dictionary of numbers wrote that the 700 wa.tts is "approximately the amount of sunshine falling on a square metre of the Earth's surface on a clear day in March for northern temperate latitudes". So you just need to deflect a square metre of sunshine into the cup and it boils in close to 2 minutes. Cool!

[cellocgw]

now if you had a robust, possibly adamanitum cup and paddle whisk, like those things used to stir 5 gal buckets of paint, but small enough to fit in a cup, and capped the top of the tea cup, you could retain the tea. allow zero air spaaace above the tea and then feed the whisk shaft out thru the lid (duh) and use some kind of bevel gear/pully system to connect the hoovemill[1] to the whisk, carefull to maximize effeciencey as a horsepower is 750 watts or so iirc. [snip]
[1] a treadmill is run on with the treads of your shoes, I only assume a horse would run w/ its hooves on a hoovemill

Yeah, but if you have Pegasus on the hoovemill, will he ever get airborne?

[hamjudo]

Randall forgot to ramp it up. Try an insulated teacup, with lid, and a magnetic stirrer. Wait. If still too much heat loss, upgrade to a vacuum thermos. You'll need a vacuum thermos that is transparent to the magnetic field, so you may have to have the chemlab's glassmaker make one for you.

You can also upgrade the stirrer. There are aquarium pumps where the electric coils are on the outside of a sealed cylinder, and a magnetic shaft is on the inside. Only the magnetic field goes through the seal. They aren't as efficient as a standard motor, but it would not be out of the question to design one that could develop 700 watts of power at the turbine. To avoid cheating, the waste heat from the motor would have to be kept away from the tea.

Once the container is sealed, cavitation is an effective way to turn mechanical energy into heat.

In the preview, I see that some of my text has been enhanced. electric coils is definitely an enhancement.

[Zassounotsukushi]

Of course insulating the system would cause the temperature to rise. The core concept of this What-If claim is that stirring increases the heat transfer to the environment faster than it deposits heat itself. That means that in a differential sense you won't increase the temperature - you'll only lower it.

You could practically insulate a cup to be stirred. There's still the matter of electrical or magnetic connection to power the stirrer, but it would probably be workable. If the majority of the cup was thermally isolated by vacuum insulation, you could still run two wires into it to power the motor. It's not difficult to transmit power.

Happy to see physics SE mentioned! http://physics.stackexchange.com/questions/5265/cooling-a-cup-of-coffee-with-help-of-a-spoon/5510#5510

My own best experimental answer was also related to rotors, albeit a pedestal fan http://physics.stackexchange.com/questions/13571/home-experiments-to-measure-the-rpm-of-a-pedestal-fan-without-special-equipment

Things get to be quite a lot of fun once you cross into home-experimental.

[Milnoc]

What if you used a Blendtec blender? Apparently, you can heat liquids to 110 degrees Fahrenheit. http://www.blendtec.com/support/faq (look for "hot soup")

[Qaanol]

I am disappointed in the lack of mention of vertical-axis wind turbine water heaters that work directly by stirring the water in a tank. It is a real thing and it really works to heat real water. Really.

[davidstarlingm]

Also, the dictionary of numbers wrote that the 700 wa.tts is "approximately the amount of sunshine falling on a square metre of the Earth's surface on a clear day in March for northern temperate latitudes". So you just need to deflect a square metre of sunshine into the cup and it boils in close to 2 minutes. Cool!

As someone else hinted at, you have to deal with reflection and absorption and transmission curves, so the actual energy going in will be significantly less than 700 watts.

Then again, concentrated sunlight can melt concrete easily, so you're on the right track.

Once the container is sealed, cavitation is an effective way to turn mechanical energy into heat.

It is, but sealing the container prevents normal cooling, which was part of the equation.

What you'd need would be a container which keeps the tea pressurized without preventing heat from being conducted away. That's going to be tricky.

[Arancaytar]

The horse looks unamused.

"Dude, I have had it with your thought experiments and your freaking battery staples. Unless you want to hear a thousand annoyingly useless things about shadows again, shut. up."

Yeah, but if you have Pegasus on the hoovemill, will he ever get airborne?

In ten seconds flat.

[cellocgw]

I am disappointed in the lack of mention of vertical-axis wind turbine water heaters that work directly by stirring the water in a tank. It is a real thing and it really works to heat real water. Really.

But not disappointed enough to bother enlightening us with even one reference?

BTW, efficiently transferring heat is not the same as raising the temperature. Your wind turbine water heaters will not succeed in producing temperatures anywhere near 373 K .

[airdrik]

At least the tea cup wasn't half empty

Classic!

Examining the splatterings, I believe I see a map of an elongated Germany drooling on its neighbors to the south (this also looks like the head of a dog, similarly drooling), a hat with a stick through it, a tree, a dance shoe (men's), New Zealand (one of the islands is rotated) and of course the Grim.

[BunsenH]

If you're stirring the tea by hand, how long until you die from hyperthermia?

[nerobro]

I don't like the answer here...

I know that high power blenders have a problem where they boil the fluids put into them. For testing, Blendtec has blender bowls with holes in the side so they can continuously feed water into them. The reason being that when you're pumping 800w into water.. it boils pretty quickly.

I bet, that with a 700w motor, and a cup with a lid, you could reasonably increase the temperature of a cup of tea by stirring.

..... I want to try this....

[rhomboidal]

I've heard that meteorologists have always known how to make a tempest in a teapot.

[dphilli1]

I've seen video of water being boiled in a blender -- shear friction is sufficient to heat the water to boiling...

[peewee_RotA]

I've been looking into this a bit from two angles. First, is there a reasonable way that any average person could mix a liquid really fast? Second, what happens if the convection problem is mitigated by using a closed container?

The first thing I looked into were industrial mixing drums. There didn't seem to be any data on whether or not they normally generate a great amount heat, and therefore have to be cooled to protect things like whipping cream or ice cream during production. I tried to contact a few companies, but have not gotten responses yet. I'll post them when I get them.

The second thing I looked at were things that most people have, blenders. The very first thing I did was try to contact Blend Tec who responded with a confident yes. Then I found plenty of examples of hot soups being made with room temperature water. Apparently the Vitamix blender is the one that advertises this more than blend-tec. Although both boast the functionality in their blenders.

It's pretty much a fact, the friction of the blades contacting with the liquid around them can eventually boil water. Below is a fun read on the subject because it really takes something like this to get a group of nerds so interested in kitchen appliances. (The comments are what really take the boiling water conversation further)

http://www.cookingforengineers.com/arti ... ions/print

[rjsteg]

When I was young, I saw this exact experiment in a "science" book...maybe World Book Encyclopedia from the 70s.

As I set it up and turned on my mom's mixer, I realized that it had no way of working as described. Sigh.

It also had an "ion" rocket prototype powered by a car battery. That didn't work either.

(Maybe it was just me

[keithl]

The boiling point of water goes down with reduced pressure. Make a vacuum pump with the spoon (you figure out how, do I have to do all your work for you?) and evacuate a closed chamber around the tea. It will boil away even at room temperature, though it will get rather cold because the enthalpy of vaporization pulls heat energy out of the tea. So you probably wouldn't boil all the tea; it would freeze, and then slowly sublimate.

(oopsie edit)

[keithl]

Another way to "stir tea" is to accelerate the spoon to hundreds of kilometers per second velocities, downwards into the teacup. It will be moving far too fast for the tea to get out of the way, so the tea will mechanically compress to tens of thousands of atmospheres and incandescent temperatures. The result will be tea flavored plasma, mixed with spoon and cup and table and floor plasma. Yum!

[Klear]

I've seen video of water being boiled in a blender -- shear friction is sufficient to heat the water to boiling...

But will it blend boil?

[sorsoup]

(Note: Pushing almost-boiling water to boiling takes a large burst of extra energy on top of what's required to heat it to the boiling point—this is called the enthalpy of vaporization.)

I don't think this is right. As I understand it, the enthalpy of vaporization is the heat that would be required to vaporize, or boil away, the water in its entirety, leaving an emtpy cup. Pushing almost-boiling water to boiling takes almost no energy.

[senor_cardgage]

At least the tea cup wasn't half empty

Classic!

Examining the splatterings, I believe I see a map of an elongated Germany drooling on its neighbors to the south (this also looks like the head of a dog, similarly drooling), a hat with a stick through it, a tree, a dance shoe (men's), New Zealand (one of the islands is rotated) and of course the Grim.

No, they are all maps of New Netherlands.

[BunsenH]

(Note: Pushing almost-boiling water to boiling takes a large burst of extra energy on top of what's required to heat it to the boiling point—this is called the enthalpy of vaporization.)

I don't think this is right. As I understand it, the enthalpy of vaporization is the heat that would be required to vaporize, or boil away, the water in its entirety, leaving an emtpy cup. Pushing almost-boiling water to boiling takes almost no energy.

Close. The enthalpy of vaporization of water is the amount of energy needed to transform liquid water at the boiling point to water vapour at the boiling point, per unit of water. This is usually given as 40.68 kJ/mol or 2260 kJ/kg at its standard boiling point (i.e. 100' C, 1 atm pressure). Multiply by the amount of water in the cup and you get the amount of energy. And yes, the enthalpy of vaporization is much larger than the heat capacity of liquid water (75.3 J K^-1 mol^-1) multiplied by a small temperature change.

[rmsgrey]

(Note: Pushing almost-boiling water to boiling takes a large burst of extra energy on top of what's required to heat it to the boiling point—this is called the enthalpy of vaporization.)

I don't think this is right. As I understand it, the enthalpy of vaporization is the heat that would be required to vaporize, or boil away, the water in its entirety, leaving an emtpy cup. Pushing almost-boiling water to boiling takes almost no energy.

You seem to be vehemently agreeing about the physics, but disagreeing about your terminology - Randall is talking about the energy required to actually boil the water rather than simply raise it to boiling point...

[sorsoup]

(Note: Pushing almost-boiling water to boiling takes a large burst of extra energy on top of what's required to heat it to the boiling point—this is called the enthalpy of vaporization.)

I don't think this is right. As I understand it, the enthalpy of vaporization is the heat that would be required to vaporize, or boil away, the water in its entirety, leaving an emtpy cup. Pushing almost-boiling water to boiling takes almost no energy.

You seem to be vehemently agreeing about the physics, but disagreeing about your terminology - Randall is talking about the energy required to actually boil the water rather than simply raise it to boiling point...

But Randall wrote "from room temperature to nearly boiling in two minutes" (my emphasis), and seems to think that raising it to nearly boiling uses much less energy than raising it to boiling point.

[rmsgrey]

(Note: Pushing almost-boiling water to boiling takes a large burst of extra energy on top of what's required to heat it to the boiling point—this is called the enthalpy of vaporization.)

I don't think this is right. As I understand it, the enthalpy of vaporization is the heat that would be required to vaporize, or boil away, the water in its entirety, leaving an emtpy cup. Pushing almost-boiling water to boiling takes almost no energy.

You seem to be vehemently agreeing about the physics, but disagreeing about your terminology - Randall is talking about the energy required to actually boil the water rather than simply raise it to boiling point...

But Randall wrote "from room temperature to nearly boiling in two minutes" (my emphasis), and seems to think that raising it to nearly boiling uses much less energy than raising it to boiling point.

It takes 420kJ to raise 1kg water from 0C to 100C, and 2260kJ to actually boil that same 1kg of water once it's at boiling point. Randall's point is that you need a lot of extra energy to boil the water once it's at boiling point, not that it requires a lot of energy to get from nearly-boiling to boiling-point.

By talking about nearly boiling, Randall is simply avoiding the ambiguity of whether the boiling water should count some, all, or none of the enthalpy of vaporisation, particularly since it outweighs the heat required to get the water from absolute zero (as ice) to almost boiling - including the enthalpy of fusion - never mind from room temperature to almost boiling...