General Question

elbanditoroso's avatar

Does ice melt faster in humid conditions (high relative humidity), or low?

Asked by elbanditoroso (24933points) August 18th, 2018

Not temperature, but humidity.

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10 Answers

gondwanalon's avatar

Humid air is denser then dry air.

The more air molecules that there are surrounding the ice, the more heat exchange will take place over dry air (given a constant air and surface temperature and over a specific time interval).

The denser air will draw heat from the ice and cause it to melt more quickly than less dense dry air.

Call_Me_Jay's avatar

Actually, humid air is less dense than dry air!

I was very surprised to find this when I went looking for the numbers. The quick explanation is that water is mostly hydrogen, the lightest element.

You can see the math on this page – The Engineering Toolbox – ‘Note! Water vapor in air will dilute the other gases and reduce the total density of the mixture. Dry air is more dense than humid air!’

gondwanalon's avatar

Oops my bad. Thanks for the information.

Nevertheless. The nature of the high amount of liquid micro drops of H2O surrounding the ice will act as a greater heat exchanger than dry air and therefore melt the ice faster than dry air.

Call_Me_Jay's avatar

It appears that correct, humid air will melt the ice slightly faster, but the difference is negligible because humid air carries very little water.

Here’s a page about heating air, but cooling the air with ice takes the same energy (just moving in the opposite direction).

StackExchange/Physics – How air humidity affects how much time is needed for heating the air? – ” takes almost twice as much energy (per unit mass) to heat the water in the air than the dry air itself.

“But, only 10g in every 1kg of air is water vapour ( ie 1%) so you only have to do twice as much work to that 1%.

“In other words – no you won’t see any measurable difference.”

ARE_you_kidding_me's avatar

I don’t think we should negate the effects of sublimation, if you consider that “melting” I do. That’s a dry air thing.

gondwanalon's avatar

In science, the ultimate arbitrator for answering questions is experiment rather than theoretical arguments.

Try this experiment:
Put a 1 cm3 of ice (ice temp is 30ºF) on a table at 50ºF (air temp also 50ºF) on a day that the air measures 0 humidity. Then time how long it takes for the cube of ice to melt.

Then wait for a day that the air temperature is also 50ºF with 100% humidity and take a similar 1 cm3 of 30ºF ice and put it out in the 100% humid air (100% humid air means that it is raining) and again time how long it takes for the ice to melt.

I think that you will likely determine that there is a measurable and significant difference in melt down times.

LostInParadise's avatar

I would think that ice melts faster in low humidity. Water moves from higher concentration to lower concentration. High humidity means higher concentration of water in the air. The reason that we are more uncomfortable when the humidity is high is that sweat evaporates more slowly, so its cooling effect is diminished. Sweat evaporation would be analogous to ice melting.

gondwanalon's avatar

Liquid water (within sweat) evaporating into humid air is not analogous to solid water melting (from a solid to a liquid) in humid air.

The reason sweat won’t evaporate well when the air is very humid is because the capacity of the air to absorb the water vapor from the sweat is greatly diminished. The air can only hold a certain concentration of water vapor.

The ability of the world (at room temperature) to handle liquid water (at any air humidity level) melting from a cube of ice is limitless.

LostInParadise's avatar

What you say makes sense, I was confusing evaporation with melting.

It now seems that high humidity would case faster melting. High humidity would limit the rate at which the liquid loses heat to the atmosphere, which would make the liquid warmer than if there were a higher evaporation rate. Does any of the ice go directly from solid to gas?

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