I Help me understand heating/cooling principles

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The discussion revolves around temperature variations in a closet with two shelves and fans installed above the doors. When fans blow ambient air into the closet, the lower shelves become hotter than the upper shelves, while reversing the fan direction results in the opposite temperature gradient. This phenomenon is attributed to the principles of convection, where warm air rises and cooler air sinks, causing uneven temperature distribution. The introduction of cooler ambient air mixes with the warmer air inside, gradually cooling it down over time. Understanding these principles can help optimize airflow and temperature regulation in the closet.
lavalin
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Hello

I have a closet with two double doors. There’s a 3mm gap between the doors and a 10mm gap down the bottom. I have a few fans mounted above the doors in the wall.

Ambient air is always 2-3deg cooler than inside the closet due to some electrical equipment I have running in there.

I have 2 shelves in the closet. On each shelf there’s a temperature sensor which are closely calibrated. Between the shelves and the doors is a 150mm gap.

When I orientate the fans to blow ambient air in, the lower shelves are about 2 degrees hotter than the upper shelves. When I orientate the fans to extra air out of the closet, the top shelf is about 2 degrees hotter than the bottom shelves.

Just curious to understand the science behind why this is happening.

Also if I pull air into the cabinet which is 2deg cooler than inside the cabinet, what happens to the warm air inside the cabinet? Does it simply mix and just cool down over time? Or is there another explanation
 
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lavalin said:
I have a few fans mounted above the doors in the wall.

... inside the closet due to some electrical equipment I have running in there.

When I orientate the fans to blow ambient air in, the lower shelves are about 2 degrees hotter than the upper shelves. When I orientate the fans to extra air out of the closet, the top shelf is about 2 degrees hotter than the bottom shelves.

Just curious to understand the science behind why this is happening.
When the fans blow air in at the top, the outflow of the heated up air is at the bottom.
When the fans blow air out at the top, the outflow of the heated up air is at the top.
 
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