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efekwulsemmay
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Homework Statement
Hot air balloons use a burner (typically around 2 MW of power output) to heat the air in
the envelope (the balloon part of the hot air balloon). Consider a typical envelope with a
volume of V = 2800 m3. The weight of the balloon (envelope, basket and passengers, but not including the air in the envelope) is 400kg. Assume that all the heat from the burner goes into heating the air in the envelope and that there is no conductive loss to the environment. (Note that as the air in the balloon expands, hot air will move out of the envelope; i.e., there will be convective loss of heat.) Treat the air as a diatomic ideal gas with P = 1atm and molar mass M = 28 g/mol. Use an external air temperature of 298K.
Using that the buoyant force on the envelope needs to support the
weight of the balloon plus the weight of the air in the envelope, determine the
minimum temperature that the air in the envelope must be to lift the balloon.
Homework Equations
Density: [itex]\rho=MP/RT[/itex] (derived from the Ideal Gas Law)
The Attempt at a Solution
Ok, so I know from Wikipedia that buoyancy can be defined as:
[itex]\frac{density of object}{density of fluid}=\frac{weight (of object)}{weight of fluid}[/itex]
and I've gotten to here:
[itex]\frac{density of air envelope}{density of air environmental}=\frac{weight of balloon and air envelope}{weight of air displaced by balloon}[/itex]
Just from thinking about the problem this is where I am at but I don't know where to go from here. Any ideas/suggestions?
Thanks