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Richard

Richard

Final Approach
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Ack...city life
You close the refrigerator door and then try to open it. There is resistrence to the door opening. This is caused by warmer air being cooled inside the appliance causing a negative pressure which results in the resistence.

T or F?


BONUS Q:
You open the refrigerator door, close it, try to open the freezer door almost immediately. There is resistence to opening the freezer door. How do you explain this?
 
Richard said:
You close the refrigerator door and then try to open it. There is resistrence to the door opening. This is caused by warmer air being cooled inside the appliance causing a negative pressure which results in the resistence.

T or F?


BONUS Q:
You open the refrigerator door, close it, try to open the freezer door almost immediately. There is resistence to opening the freezer door. How do you explain this?
Click to expand...
Don't know if the first question is true or false (I think T) but the second question is because the two are interconnected in most refrigerator/freezer combinations, the fridge is cooled by cold air flowing down through vents from the freezer.

Actually, upon reflection I always thought the door was harder to open because moisture from the warmer air caused condensation on the door seal making it adhere a little better to the metal of the refrigerator body.
 
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I'm just going to guess at this one:

Opening the refrigerator door lets warm air enter, pushing cold air out. Warm air occupies less space than cool air because it is less dense. When the door closes, it seals (because of the fancy white gaskets), and the warm air begins to cool down (because of the way the refrigerator works). This leaves a void, and if the door were made of weaker material, it would buckle. Since it is not made of lesser quality material, it instead gets pulled in tight and it seals, causing the resistance.

As for the freezer...no clue. edit: Unless it is because they both share a ventilation system (I just looked at my fridge to see for sure).
 
The magnetic strip around the door helps to keep the door closed.
 
I always thought it was the little guy inside that controls the light. He decides that you've had enough food and tries to hold the door shut.
 
The volume of the room air that mixes with the fridge air inside the fridge condenses when it cools, which lowers the air pressure inside the fridge. The higher air pressure outside holds the door closed. It can be really hard to open a refrigerated or freezer case in a store due to that effect.
 
NC Pilot said:
The magnetic strip around the door helps to keep the door closed.
Click to expand...

This is most usually the reason. Go into an appliance store where the machines are off, and you still get the resistance when you try to open the doors.

At least one manufacturer, SubZero, has a vacuum pump that runs for 15 seconds or so, to suck the door tightly closed. If you try to open the door immediately after closing it (while the pump is running), it is much harder to do. Wait until the vacuum pump stops (you can hear a hissing sound as air leaks through the door seals subside when the pump stops) and the door is easier to open once again. But it still "sticks" because of the magnetic seals.

Conclusion: The door seals are meant to stop convection currents but are not pressure tight. Ditto freezer door seals. Since pump-created vacuum is soon lost by outside air seeping in, so would a vacuum created by closing the door on a refrig full of warm air and cooling it.

-Skip
 
NC Pilot said:
The magnetic strip around the door helps to keep the door closed.
Click to expand...

Hehehe.. I like the way you think..

"Well, it could be the variation in the flux capacitor reacting with the density altitude variance in regards to the solar panel array of the hubble telescope."

OR

"The magnets make the door stick."
 
I know that right after I replaced the De-ionized Cataclysmic Regurgitator in my fridge, it was really hard to open after 10 beers or so.
Coincidence??? I don't think so.......
 
Inside the rubber door seal is a magnetic strip that holds the door closed. It's not temperature related because you get the same resistance if it's cold or ambient inside.

As for the freezer: The two compartments are not physically separate. There are at least some fridges you can see the light from the refrigerator compartment coming through the gaps into the freezer section. Closing the door rapidly pushes air out as it slams shut. The end effect is a slightly lower air pressure inside both compartments. You can hear the air seeping in around the seals sometimes after slamming the door. Both doors, not just the freezer, are harder than normal to open for a few minutes.

BONUS #2: How hard do you have to slam the door to get adequate low pressure inside to pull the entire fridge across the kitchen by the door handle without the door opening?

FWIW: Based on advanced scientific research techniques (I.E. I climbed inside and closed the door) I can assure you that the light does in fact turn off when the door closes. Actually, depending on the switch design, it will turn off a little before the door completley closes.
 
A "T" or a "F" wasn't good enough for y'all? Ron came the closest with his one word response. I bet y'all gave your teachers the fits...I know I did! :yes:
 
Richard said:
You close the refrigerator door and then try to open it. There is resistrence to the door opening. This is caused by warmer air being cooled inside the appliance causing a negative pressure which results in the resistence.

T or F?
Click to expand...

I'd have to say false because I don't think the air cools fast enough for the effect to be apparent when opening immediately. My guess as to the cause of the resistance is two things: the magnetic seals and the expansion of the refrigerator volume as the door opens.
 
lancefisher said:
I'd have to say false because I don't think the air cools fast enough for the effect to be apparent when opening immediately. My guess as to the cause of the resistance is two things: the magnetic seals and the expansion of the refrigerator volume as the door opens.
Click to expand...
Aren't the magnetic strips always 'activated'? If so, how to explain the temporary increased resistence as I described?

Someone would need to calculate what temp drop in a given volume of air would be sufficient to induce a given increased resistence to a door of n sqare footage.
 
Richard said:
Aren't the magnetic strips always 'activated'? If so, how to explain the temporary increased resistence as I described?
Click to expand...
Well for one thing magnetic force is not linear. The strength decrease by the radius2. That means the force is much greater close by than just a little bit a way from the magnet.
 
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smigaldi said:
Well for one thing magnetic force is not linear. The strength decrease by the radiius[sup2[/sup. That means the force is much greater close by than just a little bit a way from the magnet.
Click to expand...
Let's get off the paper and take it to the field. A closed door is a closed door. Yet a closed door immediately after an opening will demonstrate a perceptable increase in force to open again.
 
Richard said:
A "T" or a "F" wasn't good enough for y'all? Ron came the closest with his one word response. I bet y'all gave your teachers the fits...I know I did! :yes:
Click to expand...

Of course we gave the teacher fits. There's nothing more infuriating than being told you're wrong when you know you're right and can easily dig up the well researched proof to back yourself up. (So what if the real answer is in a 1st year college physics book and you're in 3rd grade)
 
fgcason said:
Of course we gave the teacher fits. There's nothing more infuriating than being told you're wrong when you know you're right and can easily dig up the well researched proof to back yourself up. (So what if the real answer is in a 1st year college physics book and you're in 3rd grade)
Click to expand...
How serendipitous it was I swallowed my coffee nanoseconds before I read that last line.
 
Richard said:
Let's get off the paper and take it to the field. A closed door is a closed door. Yet a closed door immediately after an opening will demonstrate a perceptable increase in force to open again.
Click to expand...

When you close the main door quickly, the attached freezer door that wasn't opened will demonstrate a similar increase in required force to open. The only direct connection between the two doors under those conditions that I can see is air pressure..or the food inside is trying to hold the door closed so it won't get eaten. :dunno:
 
lancefisher said:
I'd have to say false because I don't think the air cools fast enough for the effect to be apparent when opening immediately. My guess as to the cause of the resistance is two things: the magnetic seals and the expansion of the refrigerator volume as the door opens.
Click to expand...

I have to say false too. In the SubZero there is a vacuum pump that, when running, makes it very hard to open the door. Almost immediately after the vacuum pump turns off, the door is once again easy to open. The fridge is not pressure tight. The fridge is not pressure tight. The fridge is not pressure tight.

Put it on a treadmill and it still is not pressure tight!

-Skip
 
It is pressure tight enough to result in a perceptable increase in resistance. Either that or I'm hallucinating because this very simple practical demonstration is not repeatable.

What causes the increased suction?
 
One just needs to be able to open the freezer door freely since that is where the ice is kept and ice is necessary for a margarita which is necessary. Need I say more?
 
Laurie said:
One just needs to be able to open the freezer door freely since that is where the ice is kept and ice is necessary for a margarita which is necessary. Need I say more?
Click to expand...

And in my case it's where anything that I might be able to
cook (in the microwave) is kept.

;-)
 
Skip Miller said:
I have to say false too. In the SubZero there is a vacuum pump that, when running, makes it very hard to open the door. Almost immediately after the vacuum pump turns off, the door is once again easy to open. The fridge is not pressure tight. The fridge is not pressure tight. The fridge is not pressure tight.

Put it on a treadmill and it still is not pressure tight!

-Skip
Click to expand...

What if another refrigerator leaves Chicago on the 7:25 treadmill, headed in the opposite direction? What then?


What... then????

:goofy: :rofl:
 
I guess you guys don't remember when refrigerator door latches were replaced because a couple of two-year-olds managed to climb into refrigerators. The doors closed and latched. The children suffocated and were eventually found by their distraught mothers.

After latches were replaced with magnets in the seals (so that tots could push them open from inside), the problem still happened, so now when a refrigerator or freezer is discarded, you MUST completely remove the door at the hinge.
 
I seem to remember watching a Punky Brewster episode about that when I was a kid...
 
This obviously calls for a test.

So.. When I got home from work I opened my fridge using two fingers and carefully noting the effort it took, deposited a twelve pack on the shelf :D, and closed the door. I then re-opened the fridge using the same two fingers, also noting the required effort.

After turning on my computer and logging on I returned to the fridge and noted the effort to open it with two fingers. I removed one beer, closed the door, and re-opened the door.

From this test I will have to conclude that it takes slightly less force to open the door the second time.
 
GaryO said:
This obviously calls for a test.

So.. When I got home from work I opened my fridge using two fingers and carefully noting the effort it took, deposited a twelve pack on the shelf :D, and closed the door. I then re-opened the fridge using the same two fingers, also noting the required effort.

After turning on my computer and logging on I returned to the fridge and noted the effort to open it with two fingers. I removed one beer, closed the door, and re-opened the door.

From this test I will have to conclude that it takes slightly less force to open the door the second time.
Click to expand...

OK, maybe next week I'll try this with a digital force gauge at work (except for the beer part).
 
lancefisher said:
OK, maybe next week I'll try this with a digital force gauge at work (except for the beer part).
Click to expand...

Lance,

You give this a try yet? I'm curious to see the results. Put me in the "I doubt there's a significant effect from much of anything besides the magnet" camp.
 
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