Why is there a under pressure effect after opening of a refrigerator door?

Yuri B.

When we heat air inside a hermetic container, the air expands, its pressure increases. On the other hand, when we cool the air, it "shrinks" , and, as the space inside the fridge is almost "hermetic", the air pressure inside the fridge decreases.

They put air pressure equalizing valves on industrial refrigerators (cold rooms). Without them personal has difficulty in opening the doors after the (temperature) pulling down has started.

A.T.

Yeah, but because it is a fridge some think that every effect must have something to do with temperature.

There is an easy test guys: Try it with a fridge that is off.

sophiecentaur

Good idea but what about the contents?

I must say, though, the notion that a fridge is "hermetically" sealed is questionable. Why should they be? It's not a Tupperwear seal is it?

Yuri B.

"Hermetically sealed" in the sense that cooling down of the air entered happens faster than its pressure equalisation with the ambience.

sophiecentaur

OK. Do the following experiment that I did just then (with an ordinary Fridge, which was the subject of the OP).
Open the door: hear the 'slight hiss' of air going in.
Close the door and immediately open it again. When I did this, the 'hiss' was exactly the same and I could repeat the operation as many times as I cared to. The same noise and, I conclude, the same pressure difference on each occasion. I don't know just how fast you reckon the air inside would cool down but could you really believe it cooled by the same amount after one second as it had done since the door was closed earlier in the day?
The only effect that could be regarded as common to the long and short period could not be thermal.
Why don't you like my 'accordion' explanation?