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On the other hand, if the purpose is to express, say, smell, blowing the smell out is the better solution.
If this is because you want to feel cooler, place the fan so it blows cool air inwards onto you . You'll get far more benefit from having air blown on you than you will from just dropping the ambient temperature around you.
Better yet: keep yourself wet while using the fan. The evaporation of water molecules cools you down.
My 4rd grade teacher was convinced of the science of using two fans to cool off the classroom: one blowing cool air into the classroom from the hallway and one fan blowing hot air out of the classroom through a window. The kids that sat near the fan blowing in the room from the hallway were quite content, but the kids by the window were always complaining and they would secretly turn the fan in the window around so i…
My 4rd grade teacher was convinced of the science of using two fans to cool off the classroom: one blowing cool air into the classroom from the hallway and one fan blowing hot air out of the classroom through a window. The kids that sat near the fan blowing in the room from the hallway were quite content, but the kids by the window were always complaining and they would secretly turn the fan in the window around so i…
The problem is that the room probably has leaks such that if the fan in the hall is creating pressure, then the air doesn't all escape through the window. It'll escape through the path of least resistance or maybe even just spin inside the room (hot air rises too). If there is two doors for the room, some of it may be escaping under the other door. In that case, then air is just circulating back into the hallway. People also forget to take into consideration the expansion of hot air, which I've seen quotes for being up to 6x the volume. This complicates the pressures in the room.
As mentioned elsewhere in the discussion, the kids probably wanted to feel cool via evaporation since neither of the fans was moving nearly enough air to cool the entire room enough.
I run a couple large crypto mining farms in a pretty hot country. The 'kids' generate the heat and we have to move large amounts of air through them in order to keep them relatively cool. I've had to learn a lot about airflow design and it sounds very similar to what your teacher was trying to achieve.
Assumes small room with only one window and can't open anything else: Place the fan in the lower part of the window blowing down inwards. Sucks in air in bottom half, warm air goes out above the fan.
Assumes small room with only one window and can't open anything else: Place the fan in the lower part of the window blowing down inwards. Sucks in air in bottom half, warm air goes out above the fan.
You are answering a different question. To put it in your terms, do you think your solution is more efficient than putting fan in upper part sucking the air out, and what's your reasoning?
“Hacker News trips over themselves to invent HVAC basics from first principles”
If this is because you want to feel cooler, place the fan so it blows cool air inwards onto you . You'll get far more benefit from having air blown on you than you will from just dropping the ambient temperature around you.
Assuming temperature in room is lower than your temperature (likely). It only accelerates the speed at which your skin temperature moves to match the air temperature through convection. If you can move air elsewhere to lower the temperature of the room, that is better long term.
Earlier quoted context omitted.
Just to add, for computer cases, you want it to be a high pressure zone because intake fans generally have filters in front to catch the dust before it gets into the case. Negative pressure means dust gets sucked in from the cracks.
Also while extremely trivial here, higher pressure air has a higher capacity to transfer heat.
The highest performing PC fans create about 10mmH2O pressure while typically you can expect about 1mmH2O pressure compared to 10mH2O of the atmosphere. This translates to densening of the atmosphere around components by 0.1% or 0.01%, respectively.
Correct placement and design is by orders of magnitude more important than the increased efficiency due to higher density of air.
You could see much more effect by making your air more humid (humid air has higher heat capacity), which will be also much more pronuncable than the increased density due to pressure.
Everyone seems to be assuming that you have a big fan which actually changes the air flow in the whole room in a major way. If that's the case, great, put it any way you like - it doesn't matter. For people like me, who use a cheap fan in the summer. Put it in front of you facing towards you. You will feel cooler. If you are still interested in CFD I can give you a hand, but this is answer we are going to get from it…