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Some think that when gas (propane-butane mixture for cooking) in a gas tank is almost used (only remainings are left inside and the flame is hardly noticeable) and you turn it upside down it will improve gas burning. Is it true?propane butane in a gas tank

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  • $\begingroup$ Are you asking about propane or butane? IIRC, tanks tend to contain one or the other, rather than a mixture of both, and they have sufficiently different properties to change the answer to a certain extent. $\endgroup$ – NotEvans. Jan 27 '16 at 0:12
  • $\begingroup$ Question updated. $\endgroup$ – Marian Paździoch Jan 27 '16 at 8:24
  • $\begingroup$ Can you hear any liquid inside? $\endgroup$ – sadljkfhalskdjfh Mar 26 '16 at 5:27
  • $\begingroup$ Yes, and if I leave the tank long enough without using I can burn flame for a few seconds in normal position. $\endgroup$ – Marian Paździoch Mar 29 '16 at 6:20
  • $\begingroup$ I was using a propane fed heater to dry drywall mud. I noticed that the tank was starting to get low, so I turned the tank upside down. Immediately the flame went back up to high. After a few minutes, I noticed a bulge form in the hose. I turned the tank upright and shut it off. The heater burned for 10 more minutes after I turned it off. I imagine that I was probably seconds away from the hose blowing up and burning down the house. Don't do it. It scared the crap out of me and I consider myself lucky. $\endgroup$ – user29846 May 7 '16 at 22:35
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In principle it won't make any difference, but in practice it sometimes can.

Since what you want to emerge from the tank is gas, in principle nothing you do will make more gas come out. The liquid inside will vaporise until there is no gas left and the pressure won't change while there is still liquid in the vessel (both gases liquefy easily under pressure and the pressure will be relatively constant while there is still liquid.) All this is true at equilibrium and constant temperature.

However, in practice the assumption that the inside of the vessel is in equilibrium and constant temperature is not always true. If you use a lot of gas, the vessel will cool as the liquid evaporates (and you sometimes see a ring of frost on the outside of the vessel corresponding to the level of the liquid). If this happens then shaking the vessel may have the effect of warming the liquid and increasing the pressure of the gas. So shaking it might help a little.

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