How long does it take for the cold air to leave the refrigerator?
We all hear that keeping the fridge door open a long time lets the
cold out, but how long does this really take?
If most of the cold air falls out in the first 10 seconds, and only 10
percent more in the next 10, and 3 percent more in the next 10, then
after the first 10 seconds, there's really no rush.
Except I made up those numbers. Does anyone know any real numbers
I is going to take a few more variables to get a good number. Is the
frig full, how full, does the stuff there repaint a lot of heat or loose it
quickly? Fill that thing up with cartons of milk and you could leave it
open a long time while loosing little, empty opening it for just five
seconds would likely dump most of the cold air.
One empirical chimney formula says cfm = 16.6Asqrt(HdT), so a 2'x2'x4'-tall
36 F fridge box with V = 16 ft^3 and A = 2'x2' top and bottom vents might
fill with 70 F room air in 16/cfm = 0.02 minutes, ie 1.2 seconds.
But if it's full of thermal mass with lots of surface, eg milk cartons and
jars, 70 F room air at 50% RH would keep flowing through the fridge box for
a long time and condense water vapor onto the mass surface and add lots of
heat to the fridge contents.
So it's best to keep the fridge nearly empty, given long door openings.
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