Go Back   Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old May 15th 2019, 06:07 AM   #1
Junior Member
 
Join Date: May 2019
Posts: 2
Question Drinking bird temperature

In a drinking bird, water from the wet on the outside of the head evaporates, causing the vapor inside the head of the bird to cool. This reduces the pressure of the vapor at the top, allowing the higher pressure in the lower bulb to push up the column of liquid.

But the bird's body (including the rump and neck) is also a bit colder than the ambient temperature (but not as cold as the beak). Why is that?

My idea is that when the liquid rises in the bird, the vapor pressure in the rump decreases. As a result, a part of the liquid evaporates. The necessary entropy is removed from the remaining liquid, which thus cools.

Is that a conclusive argument? Are there any other reasons why the drinking bird is colder than the ambient temperature?

On the other hand: Shouldn't there be a temperature compensation by heat absorption from the environment? Why is the bottom bulb colder than the environment at all?

Another idea: The liquid might cool when it rises to the head. So when the liquid flows back into the bottom bulb, as the bird goes back into the verticale, it's colder than originally.


I would be very grateful if somebody who understands this better than I do could explain it to me. Thanks in advance!

PS: English is not my mother tongue, so please excuse my linguistic mistakes.
NPhantom is offline   Reply With Quote
Old May 15th 2019, 08:05 AM   #2
Senior Member
 
Woody's Avatar
 
Join Date: Jun 2016
Location: England
Posts: 842
The drinking bird works by creating a temperature difference between the bulb and the head.

If it is in direct sunlight, the birds rump might actually be hotter than ambient.
but the key is that the head must be colder than the rump for the nodding bird to work.
__________________
~\o/~
Woody is online now   Reply With Quote
Old May 15th 2019, 09:29 AM   #3
Junior Member
 
Join Date: May 2019
Posts: 2
Originally Posted by Woody View Post
The drinking bird works by creating a temperature difference between the bulb and the head.

If it is in direct sunlight, the birds rump might actually be hotter than ambient.
but the key is that the head must be colder than the rump for the nodding bird to work.
It's clear that the temperature difference is decisive for the bird to work.

I was only asking out of interest, because with a thermal camera you can see that the bulb is colder than anbient (ok, of course not in sunlight).
Is this simply because of convection or because the liquid in the bulb evaporates, when liquid rises, as the vapor pressure decreases?
NPhantom is offline   Reply With Quote
Old May 15th 2019, 07:34 PM   #4
Senior Member
 
Join Date: Apr 2017
Posts: 476
Originally Posted by NPhantom View Post
In a drinking bird, water from the wet on the outside of the head evaporates, causing the vapor inside the head of the bird to cool. This reduces the pressure of the vapor at the top, allowing the higher pressure in the lower bulb to push up the column of liquid.

But the bird's body (including the rump and neck) is also a bit colder than the ambient temperature (but not as cold as the beak). Why is that?
As you say the bird moves by the cooling effect of evaporation. The head is the source of the reduction in temperature, but this will inevitably be transferred to the lower regions , liquid from there moves up and down , reducing the temperature of the whole volume of fluid in the bird.
oz93666 is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Tags
bird, drinking, drinking bird, entropy, temperature



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Unit to see from the bird's eye philipishin Philosophy of Physics 13 May 20th 2019 02:57 AM
lowest frequency of a water with drinking straw ling233 Waves and Sound 2 Jul 22nd 2014 04:30 PM
Bird feeder's force spartan301 Kinematics and Dynamics 6 Mar 27th 2011 05:15 PM
Bird-and-trains problem omirs Kinematics and Dynamics 2 Sep 26th 2010 06:13 PM


Facebook Twitter Google+ RSS Feed