0
$\begingroup$

Assuming the thermos to be ideal and the fluid stored inside it also ideal and non-viscous. For a cold fluid, is it possible to increase the fluid's temperature by shaking the thermos flask? Can the kinetic energy provided by the motion be used to increase the energy of the fluid and thereby its temperature? How efficient will the process be?

$\endgroup$
  • $\begingroup$ Sorry only saw ideally insulated thermos. See my edited answer $\endgroup$ – Bob D May 3 at 17:04
  • $\begingroup$ By the way I believe no such fluid exists $\endgroup$ – Bob D May 3 at 17:08
  • $\begingroup$ Check out Joule, Rumford and cannon barrels with a publication in 1798 about heat. $\endgroup$ – Solar Mike May 3 at 17:56
0
$\begingroup$

Assuming the thermos to be ideal and the fluid stored inside it also ideal. For a cold fluid, is it possible to increase the fluid's temperature by shaking the thermos flask?

Yes, but only if it were a real and not ideal fluid. The rest of my answer assumes a real fluid.

Can the kinetic energy provided by the motion be used to increase the energy of the fluid and thereby its temperature?

Shaking the contents can raise the temperature of the fluid. This causes viscous friction within the fluid due to your shaking. It's the viscous friction within the fluid that causes the temperature rise. When you shake the contents it is similar to what is called "stirrer work"- i.e. as if there were a paddle wheel inside the chamber that is rotated by a shaft extending outward. This was the basis of the famous Joule stirrer experiment where he demonstrated the equivalence of mechanical work and heat. You can look it up on the internet.

How efficient will the process be?

Not very. I believe the temperature rise was very little in the Joule experiment

ADDENDUM:

The process you described and I responded to is a work transfer to the fluid not a heat transfer. Heat is energy transfer due solely to temperature difference. No heat transfers to an ideal thermos contents. I have taken the liberty to edit your title. Feel free to reject it if you want.

Hope this helps.

$\endgroup$
  • $\begingroup$ Ideal fluids don't have viscous forces right? (please see edit) $\endgroup$ – evamPUNdit May 3 at 16:50
  • $\begingroup$ Correct. my answer was for a real fluid. I believe an ideal fluid does not exist. I edited my answer. Also, your title to the question is not applicable. What is involved is a work transfer to the fluid, not a heat transfer. See my ADDENDUM. $\endgroup$ – Bob D May 3 at 18:27
  • $\begingroup$ Thanks for the answer. Sure did clear my doubts. $\endgroup$ – evamPUNdit May 4 at 1:43
  • $\begingroup$ "Yes, but only if it were a real and not ideal fluid." , Won't kinetic energy be imparted to the fluid irrespective of whether its viscous or not? Shaking of thermos can also lead to more movement of fluid. $\endgroup$ – evamPUNdit May 4 at 1:49
  • $\begingroup$ @ImmortalUchiha I think it would be better to answer that my amending my answer. Please stand by. $\endgroup$ – Bob D May 4 at 1:52
0
$\begingroup$

Heating 1 kg of water 1°C requires 4182 J. Dropping 1 kg of water from a height of 1 m imparts 9.81 J of kinetic energy to the water, which ultimately turns into heat energy when the water slams into the ground. This raises the temperature by $9.81/4182 = 0.0023$ °C, so the effect is quite small.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.