If hot air goes up and cold air goes down, why does a horizontal freezer loses cold when opened?
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It’s too simple to say hot air “goes up” and cold air “goes down.” Hot air is less dense and cold air is more dense. That means they tend to go up and down respectively, but in the case of a horizontal open freezer, it’s a little different.
The cold air in the freezer suddenly has more room to spread into and “go down” to the floor level. So in the same way that a freezer full of liquid water would spill out when you open the door, the cold air spills out. Warm air from the room replaces some of it, and until the temperature inside evens out again, it will be slightly warmer in the upper part of the freezer.
Chest freezer are way more efficient than “upright” freezers for the exact reason you stated. However due the properties of air when the door is opened it creates a difference in pressure around it that mixes the air in the freezer with the outside air.
Lifting the lid causes strong air currents.
While what you posted IS true, it’s disrupted by air that isn’t still.
Think of it kinda like oil and water. Left alone they separate but mixed up you get a blend.
Same kind of thing only it’s all air just different temperatures.
Different law of physics. In the case of hot air going up, it’s Archimedes. But in the case of freezer, it’s thermodynamics.
The fact that the temperature of the air causes one to rise and the other to sink doesn’t mean there is no thermal exchance between the air masses. You’ll lose cold regardless of the orientation of the freezer because you’re exposing it to warmer air. Less so, but still.
1. Hot air rising and cold air sinking is only true on average. It’s not like all the molecules arrange themselves in an orderly fashion from hot to cold. We’re talking about gases, so molecules are flying around and bumping into each other. The colder ones tend to settle at the bottom, but it’s not like the air inside the freezer doesn’t mix with the air above it at all. It just doesn’t mix very fast. Also, by opening the lid, you are creating air currents that will speed up the mixing of air initially.
2. Even if the air from the freezer didn’t mix with the air above it, the air molecules are still bumping into each other. Every time a warmer molecule bumps into a colder one, some heat energy goes from the warmer to the colder molecule. So over time, heat from above the freezer is transferred down into the freezer. This happens even with the lid closed, but the lid and walls of the freezer are made of insulating material, which slows down the transfer of heat.
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