# High altitude balloon gas expansion

1. Jun 28, 2009

### Gmanme

1. The problem statement, all variables and given/known data

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

temperature is -30f at all altitudes

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

2. Relevant 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.

3. The attempt at a solution

around 23 ft at sea level

2. Jun 28, 2009

### ideasrule

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.

3. Jun 28, 2009

### Gmanme

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.

4. Jun 28, 2009

### LowlyPion

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.