B Is it possible to boil water by stirring it?

[Thalita Luna]

According to the Joule experiment, work can increase the temperature of a liquid. Is it possible to boil water simply by stirring it? How much energy would be required?

 

[Drakkith]

Theoretically, yes. But in reality you'd lose enough energy through heat transfer to the environment that it would probably never boil without a very, very specific setup.

 

[fresh_42]

Theoretically, yes. But in reality you'd lose enough energy through heat transfer to the environment that it would probably never boil without a very, very specific setup.

Practically, too, by cavitation.

 

[PeroK]

According to the Joule experiment, work can increase the temperature of a liquid. Is it possible to boil water simply by stirring it? How much energy would be required?

Why not do an experiment with a bucket of water, a stirrer and a thermometer?

 

[berkeman]

Is it possible to boil water simply by stirring it? How much energy would be required?

It might depend on the starting temperature of the water. Can you say why?

 

[fresh_42]

It might depend on the starting temperature of the water. Can you say why?

And atmospheric pressure. It depends on the entire setup of the experiment. @PeroK's bucket is probably doomed to fail, but if you have a vacuum chamber or a submarine, or a small volume with a really fast stirrer ...

 

[Baluncore]

Is it possible to boil water simply by stirring it?

YES.
It happens in centrifugal pumps when you fail to open the outlet valve. The water that remains in the pump does not carry the "inefficiency heat" away, so it increases in temperature, until it boils. The lower steam density then reduces the centrifugal pressure, and the motor power consumption. The pump maintains the steam and boiling water, until the outlet valve is opened.

 

[Nugatory]

According to the Joule experiment, work can increase the temperature of a liquid. Is it possible to boil water simply by stirring it? How much energy would be required?

You should try doing some calculations for yourself…. make some sensible assumptions about how much power is going into turning the paddles and how much heat escapes from the water…. @Baluncore has given you an example of an extreme case.

 

[PeroK]

@PeroK's bucket is probably doomed to fail, ...

Apparently not!

https://www.kidzsearch.com/kidztube...er-stirring-challenge-accepted_4db227f9f.html

 

[fresh_42]

https://www.kidzsearch.com/kidztube...er-stirring-challenge-accepted_4db227f9f.html

I associated a setup with a real bucket and a painter's stirrer by your description, something like that:

 

[Drakkith]

YES.
It happens in centrifugal pumps when you fail to open the outlet valve. The water that remains in the pump does not carry the "inefficiency heat" away, so it increases in temperature, until it boils. The lower steam density then reduces the centrifugal pressure, and the motor power consumption. The pump maintains the steam and boiling water, until the outlet valve is opened.

Huh. I wouldn't have thought it would be practical. Looks like I was wrong.

 

[Baluncore]

Huh. I wouldn't have thought it would be practical. Looks like I was wrong.

It is so simple a mistake, that you are unlikely to meet anyone prepared to admit that they have done it. We learn by other's mistakes. The others remain anonymous, but go by the nickname "tea's up".

 

[phinds]

Huh. I wouldn't have thought it would be practical. Looks like I was wrong.

 

[Vanadium 50]

I wouldn't have thought it would be practical.

Well. it kind of isn't. The effect is nonzero, but remember that the latent heat of vaporization is 540 cal/g - if it weren't for the phase transition, you'd need to heat your water to 640 C )almost 1200 F). It takes a huge amount of energy to boil water.

If you want steam, there are better ways to get it.

 

[Baluncore]

Here are a couple of real world examples.
https://im-mining.com/2012/12/31/preventing-dangerous-centrifugal-pump-overheating/

https://www.quora.com/Why-does-my-w...th-cutting-and-replacing-new-pipes-many-times

https://blog.bermad.com/fire-protec...circulation-or-fire-pump-casing-relief-valves

 

[Vanadium 50]

Sure, It can be done. I've done it myself. I've done it myself when it was an undesired side effect, in fact. But there's a reason that most people who want steam buy a boiler and not a giant spoon.

 

[DrClaude]

Sure, It can be done. I've done it myself. I've done it myself when it was an undesired side effect, in fact. But there's a reason that most people who want steam buy a boiler and not a giant spoon.

-My arm is tired!

-Shut up and continue stirring. I want to brew my coffee!

 

[Vanadium 50]

I want to brew my coffee!

Maxwell's Demon House?

 

[russ_watters]

The OP doesn't say anything about practicality...

Also, more broadly, this issue is very significant for some industrial processes, like food processing. I once did some work at a cocoa bean processing facility where the beans were chopped up by giant blenders into a viscous mixture of cocoa powder saturated with cocoa butter. If I remember correctly the motors were 100 kW and the blender vessels had chilled water jackets to remove that 100 kW of heat so as not to cook/burn the products. The process heat kept the products liquid at 95F or so, and the room was heavily insulated and cooled year-round to 95F to keep the products flowing from process to process at the right temperature.

 

[Baluncore]

Steam explosions of pumps, cause severe injuries, with some fatalities.
This 1.6 Mbyte paper includes pictures of the damage caused.
https://www.ketopumps.com/media/1342/keto-green-paper-centrifugal-pump-explosions.pdf

 

[OmCheeto]

-My arm is tired!

-Shut up and continue stirring. I want to brew my coffee!

I analyzed the video from PeroK's post #9 and determined that the effective power input to the water from the blender was about 530 watts. I then googled and discovered that top athletes arms have a maximum continuous output of 30 watts. I decided that Drakkith was correct stating that it was theoretically possible but practically improbable. Can you imagine 18 Arnold Schwarzenegger sized arms trying to stir up 16 ounces of water? That would be quite the contraption to do something like that. I suppose we could give each of them one ounce containers with arm powered blenders specifically designed for the task.

Another interesting thing was that his blender heated the water about as fast as my microwave. It takes my microwave 7 minutes to bring 16 ounces of tap water to a rolling boil. In the video, the amount of water varied from between 18 to 14 ounces, so I took the average.

Much eyeballing was utilized in the creation of the graph.

 

[russ_watters]

Another interesting thing was that his blender heated the water about as fast as my microwave. It takes my microwave 7 minutes to bring 16 ounces of tap water to a rolling boil.

7 minutes? You know you're supposed to keep the door closed, right?

 

[gmax137]

As another real-world example, when it is time to bring a nuclear reactor from cold to operating conditions (550F, 2250 psia), we run the reactor coolant pumps (first one, then two, eventually four). Even with unburned fuel (no decay heat), this "stirring" works pretty quickly (half a day maybe). The pumps are about 2 MW (or 67,000 Arnolds for you non-metric types).

 

[jtbell]

I analyzed the video from PeroK's post #9 and determined that the effective power input to the water from the blender was about 530 watts. I then googled and discovered that top athletes arms have a maximum continuous output of 30 watts.

Legs would be more effective, via a stationary bicycle or a Peloton or similar device. A fit recreational bicycle tourist like I used to be can probably put out 75-100 W for hours. A Google search seems to indicate that a highly fit racer can do 400 W in a sprint.

 

[fresh_42]

Legs would be more effective, via a stationary bicycle or a Peloton or similar device. A fit recreational bicycle tourist like I used to be can probably put out 75-100 W for hours. A Google search seems to indicate that a highly fit racer can do 400 W in a sprint.

Up to 600W for 30 seconds in the lead in team time trials.

 

[Vanadium 50]

Stationary bike? I wonder if you evaporate more water by sweating or stirring.

 

[OmCheeto]

Guessing you'd lose more blood than water when your spouse learns how much you paid for a pedal powered blender to do a science experiment: $2955.00

ref: https://rockthebike.com/shop/bike-blenders/electric-fender-blender-pro/

 

[Vanadium 50]

PF spouses are the most understanding people on the planet.

 

[russ_watters]

Legs would be more effective, via a stationary bicycle or a Peloton or similar device. A fit recreational bicycle tourist like I used to be can probably put out 75-100 W for hours. A Google search seems to indicate that a highly fit racer can do 400 W in a sprint.

And it's actually a thing:

https://wheelygoodsmoothies.com/

 

[JT Smith]

I wonder how much the heat from the motor and shaft friction added? Probably it doesn't change the result, just the amount of time.

I would have guessed you couldn't do it. But now having seen it I don't know why I thought that. Provided heat loss isn't too great it seems like you could keep adding heat endlessly. With the right liquid perhaps in addition to destroying his thermometer probe he could have melted down his blender as well.