try this link for a good simple example of how heat transfers in space

http://www.straightdope.com/classics/a1_127.html

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'The eye can only see what the mind is prepared to accept'

Ah this takes me back to undergraduate studies of thermodynamics...

It's implied, but not clearly stated that a glass of water taken into a vacuum will boil until it freezes. The vaporization of the water from the surface removes heat from the only source it has - the liquid water itself, assuming the container is shielded from the sun. Once the water in the glass is frozen, it will continue to cool towards absolute zero as ice from the surface sublimes into the vacuum - again taking heat from the ice that remains behind. So the answer is water both boils and freezes in a vacuum.

That sounds about right, as the water boils it loses energy as the latent heat of vaporisation, which is fair quantity of energy per unit mass. Temperature drops until it is below the melting point of water in a near vacuum, and the water thus freezes.

The cool thing is you can repeat this on earth in an atmosphere. Take a saucer of water (or a puddle if you want) and pass dry air over it. Water will vaporise into the dry air cooling the temperature of the main body. Pass enough dry air over the water and you can freeze it, although this is quite difficult in practise due to conductive heat from the container that you use....

<font size=-1>[ This Message was edited by: Mainframes on 2003-02-19 05:19 ]</font>

<font size=-1>[ This Message was edited by: mainframes on 2003-02-20 05:52 ]</font>

When ice sublimes in vacuum, would the heat lost by the remaining ice, per unit of mass of the sublimed ice, be determined by heat of vaporization or heat of fusion?

Please excuse my ignorance. I ain't nevar bean to coleage.

Turning liquid water into vapor requires 540 calories per gram. Turning ice at the freezing point into water at the freezing point requires 80 calories per gram. Add the two numbers together and that's the amount of heat removed through sublimation - that is 620 calories to convert a gram of ice into a gram of water vapour at the same temperature.

The example given by Mainframes of water in a dish has a parallel much closer to us. Humans perspire in order to lose excess body heat. The evaporaton of sweat carries with it a lot of heat. That's why a humid day feels hotter than a dry day at the same temperature - the rate of evaporation (and consequent cooling of the skin) is less when the air is humid, but standing in a breeze will increase the rate of evaporation by constantly removing the saturated air layer at the skin and replacing it with dryer air.