What-If 0071: "Stirring Tea"

[Djehutynakht]

Yeah, that Horse does look really considerably ticked off.

Also, I wish someone would get a flat version of Randall's splatter up for use. It'd make a great map.

[peewee_RotA]

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!

A pistol shrimp can boil tea just by stirring it:

http://www.youtube.com/watch?v=eKPrGxB1Kzc

[tups]

I cannot express my disappointment enough about the horse. It has eyes, a mouth and nostrils. I would so like to see Randall's redition of a stick horse ... I am sure he would nail it. Please, Randall, give us a stick horse in a future cartoon ...

[ronzie9]

Boiling water and heating it do not necessarily mean the same thing. As was pointed out earlier in this thread, lowering the air pressure above the water will cause it to boil without raising the temperature. Since cavitation causes localized volumes of low pressure in the liquid, with the vapor pressure rising above the ambient pressure, it can technically be said to be boiling there. It probably wouldn't make for a tasty cup of tea, though it might be pleasantly effervescent, which some may find stirring.

[blademan9999]

I'd say this is relevant http://www.youtube.com/watch?v=90WznJlh3Ew

[nerobro]

A secondary method of "boiling tea" is to use a very big spoon, and use it very fast, lowering the pressure nearby. Reducing the local pressure will allow "hot tea" to boil.

But I think that misses the point of the exercise doesn't it?

[ramk13]

I've seen a Vitamix blender put out hot soup from room temperature ingredients. Saying that the blender motor is putting several hundred watts of power into the water, and the blender container is plastic that isn't going to sink/transport heat very quickly, it would stand to reason that you could boil water in one. I dont' know how the performance of the blender would change (bearings, etc) at that temperature, but I'm guessing the built the blender to withstand that temperature.

[Kieryn]

I have a Vitamix at home and it of course occurred to me that Randall might have missed something. Glad to see others have already covered the topic. Carry on!

[peewee_RotA]

Got a reply from Honest Tea. I had a feeling that a natural foods company would not use any kind of industrial stirrers, but figured it was worth a shot. (Small companies tend to actually reply to random, ridiculous questions)

Fortunately for drinkers of their product, and unfortunately for me, they couldn't help with any information on the use of tank stirrers.

[peewee_RotA]

Oh me yarm, this deserves a double post. I've contacted a manufacturer of industrial mixers/agitators to ask about how much unwanted heat the process typically generates. The best example is the creation of dairy products. Whipping cream, ice cream, and even butter can be temperature controlled processes. So I phrased the question as such.

I think I've received the best e-mail response in the history of the internet:

Your questions are extremely unusual. What is the purpose of your inquiry?

[Mikeski]

Gee Willikers, this deserves a double post. I've contacted a manufacturer of industrial mixers/agitators to ask about how much unwanted heat the process typically generates. The best example is the creation of dairy products. Whipping cream, ice cream, and even butter can be temperature controlled processes. So I phrased the question as such.

I think I've received the best e-mail response in the history of the internet:

Your questions are extremely unusual. What is the purpose of your inquiry?

Well, which is the most likely?

a) I'm an actual ice-cream manufacturer who doesn't already know the answer to this
b) I work for your competition, and I'm trying some really cheeky industrial-espionage techniques
c) I'm trying to set up a heavy-duty methamphetamine/explosive manufacturing rig in my garage, and I'd like you to reassure me that I'm not about to relocate my operations to Mars
d) I'm trying to refute a webcomic

[peewee_RotA]

a) I'm an actual ice-cream manufacturer who doesn't already know the answer to this
b) I work for your competition, and I'm trying some really cheeky industrial-espionage techniques
c) I'm trying to set up a heavy-duty methamphetamine/explosive manufacturing rig in my garage, and I'd like you to reassure me that I'm not about to relocate my operations to Mars
d) I'm trying to refute a webcomic

Personally, after pressing send I was worried he'd go for c) and I'd be getting a knock on the door by the local authorities.

[abatie]

I have a friend who cleans his vitamix by boiling water in it. Also, if you search for the vita-mix blender faqs (including the url gets this post flagged as spam ), it says "Q: How can the same machine cook soups AND freeze ice cream?
A: High-speed blade action is the secret to friction cooking and making frozen treats in the Vita-Mix! For frozen treats, the high-performance hammermill and cutting blades crush frozen ingredients and release coldness. Vita-Mix processing is so fast, there is no time for melting and the mixture refreezes itself. For cooking soups, the blade speed builds a friction heat that can bring fresh ingredients to boiling in 4-6 minutes."

[freezer]

I expected the horse to say "That's a battery staple".

[Plasma Man]

"For frozen treats, the high-performance hammermill and cutting blades crush frozen ingredients and release coldness."

No. Just no. There is no such thing as "coldness". Saying that crushing frozen ingredients releases coldness is like saying that a lamp sucks in darkness.

[Klear]

"For frozen treats, the high-performance hammermill and cutting blades crush frozen ingredients and release coldness."

No. Just no. There is no such thing as "coldness". Saying that crushing frozen ingredients releases coldness is like saying that a lamp sucks in darkness.

It's more like saying a lamp dissolves darkness. A lamp sucking up darkness is just plain wrong =P

[Kingy]

I have a problem with my fire trucks boiling the water in the pump if we are not actually using water out of the hoses. One truck has a 20hp motor that boils about 10 litres in ten minutes(rough guess), so we open a bypass valve to run it back into the tank. Our new truck has a 200hp engine that boils about 100lt of water in a few minutes if not bypassed. It's not cavitating, just the impellers turning in it is enough to heat it.

[hansen.d]

I have a mixer at home (like the ones they use in the smoothie shops) that will heat water, the heat clearly isn't from conduction at the motor, I'd always thought it was from the friction of stirring. what am I missing?

Dave

[Zassounotsukushi]

I have a problem with my fire trucks boiling the water in the pump if we are not actually using water out of the hoses. One truck has a 20hp motor that boils about 10 litres in ten minutes(rough guess), so we open a bypass valve to run it back into the tank. Our new truck has a 200hp engine that boils about 100lt of water in a few minutes if not bypassed. It's not cavitating, just the impellers turning in it is enough to heat it.

Cavitation is boiling occurring in the lowest pressure point in the system - the volume right behind the impeller. In order for boiling to happen without cavitation, there would have to be a point in the system at lower pressure than that. That could be accomplished, for instance, by some higher point in the system. However, that seems awfully unlikely.

[peewee_RotA]

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)

So apparently they've already done this one... 7 years ago.

http://www.youtube.com/watch?v=MZnURf9cmnc

[peewee_RotA]

Oh and while I'm waiting, most impatiently, for the next What If?, I thought I'd share what I found out in that strange e-mail exchange.

Regular stirring blades in industrial applications don't normally generate much heat. The best I can tell is that the volume of material is huge compared to the blade, meaning that the amount of friction is low and the volume of material to heat is high. Even if it generates a lot of heat, it has to transfer to all of the material. The most common type of industrial stirrer that I saw was an attachment for barrels. Others mostly had metal, non-insulated, drums. So heat probably dissipates quickly.

However, they did point out that a couple types of mixing blades DO generate unwanted (or wanted) heat. A dispersion blade stirs differently than regular blades. It creates a double vortex. It also has a lot more surface area to create friction. I didn't finish any kind of research yet on it, which is why I didn't post. But that's the basic part of it.

Homogenizes are much bigger mixers with much more surface area and surface contact. I didn't even start looking into this one, other than to see what they look like. A typical mixer looks like a propeller blade. These look replicas of the DNA storage tank in Jurassic Park. So we're talking exponential surface area increase. Now I seem to remember watching some show at some point that mentioned a homogenization process in which heat was desired. I can't for the life of me remember why, but the heat might not be a byproduct after all.

Anyway I'll do actual research eventually. Just thought that typing this out would pass the time.

[5th Earth]

A thought on simplifying the various sealed container mixing apparatuses.

Instead of using a device inside the container to do the stirring, requiring some sort of means of transferring power into the sealed vessel, use the vessel itself to do the stirring. Construct a vessel with, for example, paddle-like extrusions on the interior surface, then vigorously rotate the container back and forth. You still need to get a temperature probe in there to verify your results, but the mechanical setup is a lot simpler.

[theme]

I believe everyone missed something.
If stirring causes a vaccum cavity, I think it would lead to the case of a glass half empty http://what-if.xkcd.com/6/ .
The force of air pressure pushing tea onto the cup would definitely cause at least some heat, (possibly repeating over and over) assuming it doesn't generate some glass/ceramic fragments flying around.

[peewee_RotA]

A thought on simplifying the various sealed container mixing apparatuses.

Instead of using a device inside the container to do the stirring, requiring some sort of means of transferring power into the sealed vessel, use the vessel itself to do the stirring. Construct a vessel with, for example, paddle-like extrusions on the interior surface, then vigorously rotate the container back and forth. You still need to get a temperature probe in there to verify your results, but the mechanical setup is a lot simpler.

The average person also has access to this. It's called a washing machine. (A dryer can reasonably be modified to do the same thing though)

Anyway, I never followed this path because I wanted to draw the line between agitation and stirring. There are plenty of agitators in factory use. The big one I could think are polishers that rotate with rocks, or other grit, polishing the finished product. But there are also screw shaped stirring drums and things like that. I think that this will complicate the basic principals so much that it's another league of questioning.

"Can I boil tea in a rock polisher?"
"Yes, if your rock polisher doesn't melt in the oven."

[theme]

I believe everyone missed something.
If stirring causes a vaccum cavity, I think it would lead to the case of a glass half empty http://what-if.xkcd.com/6/ .
The force of air pressure pushing tea onto the cup would definitely cause at least some heat, (possibly repeating over and over) assuming it doesn't generate some glass/ceramic fragments flying around.

Excuse me, anyone wanna discuss about this?

[Cynical Idealist]

It doesn't create a hard vacuum. It does create a region of lower pressure, which in extreme cases is enough to create a region of gaseous water. The force of that region collapsing is impressive (it can cause a lot of damage to steel), and it does generate elevated temperatures in a small area, but I don't believe you get any "extra" heating through cavitation. It's the same amount of energy as you'd get from stirring at the same power without cavitation (a better-designed spoon?), just more localized.

[SuperSteve]

(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...

Putting aside the debate about the meaning of "nearly", Randall's calculation 1 cup × Water heat capacity × (100∘C−20∘C)/2 minutes=700 watts is wrong, because not all of the energy used by the microwave oven ends up being thermal energy of the liquid, for the following reasons:

1. Before the water reaches the boiling point (or nearly the boiling point), it starts to evaporate fairly rapidly, and some of the energy is consumed by this process (equal to the heat of vaporization times the amount of water that evaporates.

2. Some of it heats the air in the microwave oven, and the microwave oven itself.

[snowyowl]

I wouldn't count the enthalpy of fusion in this case. It's a lot easier to make tea using liquid water than water vapour.

[hankwang]

According to the article:

Based on figures from industrial mixer engineering reports,[4] I estimate that vigorously stirring a cup of tea adds heat at a rate of about a ten-millionth of a watt. That's completely negligible.[5]

I don't have that particular reference [4] at hand, but I highly doubt that the number of 1E-7 W applies to typical teaspoon-based stirring. With vigorous stirring, you have about F = 1 N of force at v = 0.5 m/s, which makes about 0.5 W of dissipation. Of course, it would still take you quite a while to bring the water to a boil.

I'm surprised that nobody mentioned this so far; I registered here especially to make this point.

I suspect that the engineering book was describing an empirical formula for large vessels (some expression involving diameter, viscosity, density, and speed), scaled down to a tea cup. However, typically those expressions are valid only for a particular range of Reynolds numbers (speed*diameter*density/viscosity), which could be orders of magnitude different for a tea cup with hot water versus a vessel with sugar syrup.

The term "cavitation" was mentioned a couple of times here. In order to get cavitation in cold water, you need to get dynamic pressures (0.5 rho v^2) on the order of the atmospheric pressure (1e5 Pa), which is 14 m/s. You would need to stir your tea 110 Hz, assuming a circular trajectory of 4 cm diameter. Not very likely to happen.

[gladiolas]

I wanna know if peewee_RotA told them about xkcd? It'll be one more thing for the folks in that office to pass the time looking at.

What if you had a miniature rocket ship flying around inside the tea? Better yet, an FTL ship?

[Submarine]

Yeah, well, so I was ''studying'' (reading What If, that is), and when I reached #71 (I might be going to fail Dynamics next week) it occured to me that the answer should, in the end be, yes. The question if it is possible to boil the water by stirring is quite easily interpreted as if it is possible to heat water by stirring, and from that point the answer revolves around that, but raising the temperature of a liquid is not the only way to boil it. The other is decreasing the pressure, which is exactly what happens when cavitation occurs. The liquid doesn't actually get hotter, but due to a fall in pressure bubbles of steam form near and on the spoon surface, to rapidly collapse under pressure from surrounding regions, damaging the spoon severely in the process (this is also one of the problem is ship propellor design).
It would be useless to make tea, but it would be boiling.

[Caprice]

Since the tea doesn't do anything dramatic like rise into the air or emit light, the energy must be turning to heat.

If the tea does do something dramatic like rise into the air or emit light, then it is not tea, and you should probably not drink it.