What is the relative humidity in a freezer?

Question

What is the relative humidity in a freezer?

Answer 1

The relative humidity can vary.  Moisture from foods and the outside air which is introduced when the door is opened can raise the RH, especially when that outside air is then chilled, which is why they get frost buildups in some cases.  Since the air is cold, it cannot hold much moisture, thus any moisture raises the relative humidity.

Answer 2

The 2nd & 3rd answers are correct.  Relative humidity will vary in a freezer.

The higher the air temperature, the more water the air will hold.  If air temperature rises and there's no change of water in the air, the relative humidity will lower.  Conversely, if air temperature falls with no water change in the air, relative humidity will rise.

If air temperature falls so low that it can't continue to hold the amount of water it has, the water is shed from the air.  If the air is cool, it comes out as dew.  If it's really cold, it comes out as frost.

Getting back to your original question, the answer is it varies, but if there's frost in the freezer, it's probably high.

It took me a lecture or two of undergrad thermodynamics to get that, along with several lengthy and messy equations.  So for you, this knowledge comes cheap!

Answer 3

The relative humidity in a freezer is very low.

Answer 4

As Cyswxman says, it all depends on the humidity of the food you introduce and the ambient air outside. In my opinion, the relative humidity in a freezer is 100%.

Say you open the freezer and the air outside is 25 C. It can contain 20 grams water per cubic meter and it is then 100% saturated. Let's say that the air relative humidity is only 50% and the air contains then only 10 grams/m3.

If you cool down the air to say, freezing point, then the air can only contain about 3 grams/m3.

What happens to the other 7 grams? Well, it has to condensate in dew or frost.

Don't you see frost inside your freezer when you open it? Well, it must mean that there was too much humidity in the air to remain in suspension, doesn't it? Then, in my opinion, the relative humidity of the air inside your freezer must be 100%.