# How fast does hot air rise?

by tmstauff
Tags: convection, fluid dynamics
 P: 1 So for a class I am designing a solar dehydrator and I want to know how fast the hot air will rise out of the dehydrator. For calculation purposes assume the hot air is 120°F @ 30% relative humidity (23 g/m3) and rising through a tube (if necessary assume the tube is 4 in. in diameter), the outside air is 80°F @ 60% relative humidity. In addition assume the hot air has a volume of 40 cubic feet. If anybody knows how to calculate how fast it will rise through the tube that would be awesome. Otherwise I will most likely doing an educated guess. Thanks.
 Mentor P: 10,853 How long is the tube? If you can calculate the air density inside and outside, multiply it with the volume inside and the gravitational acceleration of earth to get the total force. That will be used for friction and acceleration of the air, with some fraction to determine.

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