Will a liquid boil quicker if it is stirred versus if it is not stirred

Question

Will the whole liquid boil quicker on a stove-top if it stirred versus if not stirred? What should be the frequency of stirring to get to boiling point quickly? please explain your hypotheses with experiments(or links to) preferrably

depending on material of object used to stir, the liquid will boil slower, the object will absorb an amount of heat which could be transfered to the liquid to boild faster — Nikos M., Aug 11 '14 at 17:09
Not well-enough defined to answer. How are you applying heat (e.g. stovetop burner to pot vs placing in a convection oven)? Do you want some or all the fluid to reach the boiling point? and more... — Carl Witthoft, Aug 11 '14 at 17:13
it will still absorb heat, now depending on material and type of strirring the heat lost to the object could be compensated by the stirring process, but this requires very specific process and not just kitchen materials — Nikos M., Aug 11 '14 at 17:13
By what percentage will the temperature be affected by an object — Pranay Aryal, Aug 11 '14 at 17:13
Essentially the reverse of our top-voted question. I'm unsure if the same reasoning applies, though. — ACuriousMind, Aug 11 '14 at 17:18
"please explain your hypotheses with experiments(or links to) preferrably" Indeed, this is a question that can be best answered by experiment. You should do it. — Ján Lalinský, May 23 '15 at 10:54

score 3 · Answer 1 · answered Aug 14 '14 at 18:55

I think the answer is, it depends. There are two opposing effects here. Suppose you have a liquid-filled pot over a burner. If a layer of hot liquid forms against the bottom of the pot, that will reduce the rate of heat transfer from the burner. Stirring might keep cooler liquid in contact with the bottom of the pot, and therefore increase the efficiency of the heat transfer. On the other hand, in an unstirred pot, a cooler layer of liquid may form on the top of the pot, decreasing the rate of heat transfer to the air. Stirring the pot will bring hotter liquid to the surface, resulting if more heat transfer to the air. Which of these two effects dominates depends on lots of things, like the precise dimensions of the pot, the temperature of the burner, and the temperature of the air. However, in general, the expansion of the liquid due to heating will create convection currents that will naturally stir the mixture, bringing hot liquid to the top and cool liquid down to the bottom. So unless the "liquid" is fairly viscous, stirring probably won't make much difference one way or the other.

If you're asking this for practical reasons such as how best to bring water to a boil in order, say, to cook spaghetti, the answer is that leaving the cover on while it heats is your best strategy, since this limits the loss of heat to the air. And or course, you can't stir it with the cover on.

But what percentage of total heat is lost through air and how much time is saved by covering it? — Pranay Aryal, Aug 14 '14 at 19:00

score 0 · Answer 2 · answered Nov 27 '21 at 16:34

I agree that it depends but I don’t think the problem is under constrained given a few assumptions:

The temperature is measured at a spot farthest from any wall of the pot (the coldest point in the body of water). Boiling is actually a localized function only representing the temperature/pressure of the water at the point the gas bubble is created.
Boiling point is defined as 1° below the actual boiling point for that atmosphere (211° at sea level)
The pot is not particularly tall or squat. A very squat pot would favor a lid and a very tall pot would favor stirring.

My hunch is that the stirred pot will reach temperature faster than the covered pot. I came across this question because I son’s thinking about doing this for his school science project. I will report back.

score 0 · Answer 3 · answered Nov 27 '21 at 17:47

Yes! But the effect would be so tiny and nearly not possible since the molecules are so bonded to each other that the disturbance caused due to stirring is spread equally to every molecule and the effect of this is the same for nearly every nearby molecule consequently resulting in almost no collision which is, of course, responsible for temperature.

There is a phenomenon in physics if u know, called Edde Current, where a metallic object, if kept in a varying current (loosely speaking AC), there is a current produced in the metal object and since the current is changing, so does the speed of ions(electron) and hence the collision. In fact, this method is used to melt metals.

Now back to the boiling part. Add some salt in water, to make it a little conducting, and now if u do the Edde current thing with water, it will boil faster than expected.

Will a liquid boil quicker if it is stirred versus if it is not stirred

3 Answers3