Liquid Hummingbird Feeder Explanation, Please ?

[Robert11]

Hello,

 

I realize that this isn't as interesting as, e.g., quantum theory, but I've thought

about this a bit, and just can't determine the force balance for it:

 

So, let me please ask:

 

On the typical liquid hummingbird feeders, the liquid is first place into an inverted

(one end) closed bulb, thumb put over the open end, and then inverted into the base.

 

The liquid level typically drops about 1/3 of the way down.

As the sector is withdrawn by the birds from taking it at the base, the bulb's level, of course, drops a bit.

 

It is reasonable to assume that there is a partial vacuum created.

 

But, I still can't see how an equilibrium is being established.

14.7 atm p is of course equiv. to about 34 feet of water (or nectar).

 

Lots of explanations on the web, but I am fairly convinced

most of them are wrong.

 

Can someone explain all of this for me, please ?

 

Thanks,

Bob

[exchemist]

Hello,

 

I realize that this isn't as interesting as, e.g., quantum theory, but I've thought

about this a bit, and just can't determine the force balance for it:

 

So, let me please ask:

 

On the typical liquid hummingbird feeders, the liquid is first place into an inverted

(one end) closed bulb, thumb put over the open end, and then inverted into the base.

 

The liquid level typically drops about 1/3 of the way down.

As the sector is withdrawn by the birds from taking it at the base, the bulb's level, of course, drops a bit.

 

It is reasonable to assume that there is a partial vacuum created.

 

But, I still can't see how an equilibrium is being established.

14.7 atm p is of course equiv. to about 34 feet of water (or nectar).

 

Lots of explanations on the web, but I am fairly convinced

most of them are wrong.

 

Can someone explain all of this for me, please ?

 

Thanks,

Bob

Yes it will be a partial vacuum. if there is no air in the system then when you invert it, the pressure above the liquid will be just the vapour pressure of the liquid. But there will be some air, no doubt, from air pockets, leakage past your thumb, bubbles and from air dissolved in the liquid. So that will add to the pressure above the liquid. As the birds feed, bubbles of air enter and contribute further to the pressure above the surface. 

 

In fact, you can do the calculation the other way round. From the height of the column of nectar the air supports, you can work out the pressure difference from atmospheric. It won't be that much below atmospheric, by your description.   

[DaveC426913]

Since you've already done some research and rejected what you've found, it would be moot to give you standard answers. So let's turn it on its head.

 

What do you expect should happen, and why?