Calculating the Rise of Hot Air in a Solar Dehydrator

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SUMMARY

The discussion focuses on calculating the rise of hot air in a solar dehydrator, specifically at a temperature of 120°F and 30% relative humidity. Participants suggest calculating air density both inside and outside the dehydrator, using the formula that involves multiplying air density by volume and gravitational acceleration to determine the total force. This force will help in understanding the friction and acceleration of the hot air as it rises through a 4-inch diameter tube. Accurate calculations are essential for optimizing the design of the solar dehydrator.

PREREQUISITES
  • Understanding of thermodynamics, specifically the behavior of gases.
  • Knowledge of air density calculations based on temperature and humidity.
  • Familiarity with basic physics concepts, including force and acceleration.
  • Experience with fluid dynamics, particularly in relation to airflow in tubes.
NEXT STEPS
  • Research how to calculate air density using the Ideal Gas Law.
  • Learn about the effects of humidity on air density and buoyancy.
  • Explore fluid dynamics principles related to airflow in cylindrical tubes.
  • Investigate methods for measuring airflow rates in solar dehydrators.
USEFUL FOR

Engineers, designers of solar dehydrators, and anyone interested in optimizing airflow and thermal efficiency in solar energy applications.

tmstauff
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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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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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