High altitude balloon gas expansion

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Homework Help Overview

The discussion revolves around calculating the rate of expansion of gas in a balloon at various altitudes, specifically focusing on helium or hydrogen. The problem involves understanding how temperature and atmospheric pressure affect the balloon's size and buoyancy at altitudes of 30,000, 60,000, and 90,000 feet, with a constant temperature of -30°F.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore how the balloon's size changes with altitude and question whether the balloon rises at a constant speed or is simply released to rise freely. There is also discussion about the effects of atmospheric pressure on gas expansion and the need to calculate the required volume for buoyancy at different altitudes.

Discussion Status

Participants are actively questioning the assumptions regarding the balloon's behavior at different altitudes and the relationship between pressure, volume, and buoyancy. Some guidance has been offered regarding the need to consider the weight of displaced air and the gas used, but no consensus has been reached on a specific method or solution.

Contextual Notes

There is a reference to a chart for air pressure at different altitudes, which may be relevant for calculations. Participants are reminded to be careful with units in their calculations.

Gmanme
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Homework Statement



Could someone help me calculate the rate of expansion of gas (helium or hydrogen) in a balloon at different altitudes.

temperature is -30f at all altitudes

http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html <- chart for air pressure

Homework Equations



What would the diameter of a balloon filled with helium OR hydrogen be at 30k 60k and 90k feet have to lift 500lbs total.

The Attempt at a Solution



around 23 ft at sea level
 
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I'm having trouble understanding. Is the balloon rising up at a constant speed? Is it just let go and free to rise? If you suddenly change a balloon's altitude, it would expand or contract because the atmospheric pressure is now different, but the expansion would stop once an equilibrium is reached.
 
Take the pressures from 30k, 60k and 90k, and find out how big the balloon would have to be to lift a total wieght of 500 lbs at these altitudes.
 
Gmanme said:
Take the pressures from 30k, 60k and 90k, and find out how big the balloon would have to be to lift a total wieght of 500 lbs at these altitudes.

Well you know the buoyancy required is 500 lbs. You will want to know at each of those pressures how big a volume is needed to supply the difference in weight of the air displaced and helium or hydrogen (choose one) at the same pressure.

Careful of your units.
 

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