Calculating the Rise of Hot Air in a Solar Dehydrator

In summary, the individual is designing a solar dehydrator for a class and is seeking information on the speed at which hot air will rise through a tube. The hot air is at a temperature of 120°F and 30% relative humidity, while the outside air is at 80°F and 60% relative humidity. The volume of the hot air is 40 cubic feet and the diameter of the tube is assumed to be 4 inches. The individual is looking for a calculation to determine the speed of the hot air rising through the tube.
  • #1
tmstauff
1
0
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.
 
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  • #2
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.
 

1. How does hot air rise?

Hot air rises due to a phenomenon called convection. As air heats up, it becomes less dense and expands, causing it to rise. This upward motion creates a convection current, where hot air rises and cooler air sinks to take its place.

2. What factors affect the speed at which hot air rises?

The speed at which hot air rises depends on the temperature difference between the hot air and its surroundings, as well as the density and humidity of the air. The greater the temperature difference, the faster the air will rise. Higher humidity can also slow down the speed of hot air rising.

3. How is the speed of hot air rising measured?

The speed of hot air rising is typically measured in units of velocity, such as feet per second or meters per second. This can be measured using instruments such as an anemometer or a hot wire anemometer.

4. Is there a limit to how fast hot air can rise?

There is no specific limit to how fast hot air can rise, as it depends on the aforementioned factors. However, in most cases, the speed of hot air rising is relatively slow, usually no more than a few meters per second.

5. Why does hot air rise?

Hot air rises because of a principle known as the Ideal Gas Law. This law states that as the temperature of a gas increases, its volume and pressure also increase. This causes the hot air to become less dense and therefore rise, displacing cooler and denser air.

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