# Thermodynamics in the Kitchen

1. Aug 27, 2004

### bjon-07

This may be a stupid, but here it goes,

When ever i stand in front of the freezer i always get yelled at for letting the cold air of of the freezer.

But according to thermodynamics (the 1st law a beileve) heat moves from hot to cold. So when i leave the freezer open am i letting IN HEAT, reather than letting out the colder air that is inside the freezer.

I also relazie that the deinsity of a gas is proprational to it temperature, so mabye the cold air falls out of the freezer.

Can someone please tell me what is happening when i open the freezer, i have taken G-Chem in college so i know the basics of thermo,

i

2. Aug 27, 2004

### chroot

Staff Emeritus
You've got it right. The cold air rolls out of the freezer and falls toward the floor. It is replaced by warm air already present in the room.

The freezer then has to expend energy removing the heat from the warm air now present in the freezer cavity.

- Warren

3. Aug 27, 2004

### Integral

Staff Emeritus
I am not sure that there is any difference between "letting in heat" or "letting out cold". The net effect is that the temperature inside the freezer increases, this must be accompanied by running the compressor to cool it back down, this work done increases the room temperature MORE then the decrease due to the "escaping cold" of the freezer. In the long run by keeping the freezer door open you heat up the room.

4. Aug 27, 2004

### Ivan Seeking

Staff Emeritus
Just to avoid confusion, maybe we should specify what type of transfer we are talking about: Convective, radiative, or conductive. Convection carries the cool air out of the fridge. Convection also allows the cool, escaped air to warm. Conduction allows heat to leak in through the walls into the fridge, Radiation wouldn't apply much here.

5. Aug 28, 2004

### Tide

It's not the cold air per se that is the problem since its heat capacity is usually negligible compared with that of the contents of the freezer and its walls. The problem is when the contents are heated by the warm air entering the freezer and it costs energy (\$) to remove the heat.

6. Aug 28, 2004

### MiGUi

Thats a very common question: Can we use the freezer to cool the kitchen? And the answer is obviously NO...

7. Aug 28, 2004

### HallsofIvy

HOWEVER! It would be really, really dumb to point this out to your parents the next time they tell you not to let the "cold" out!