Calculating the escape velocity of a pressurised gas

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Discussion Overview

The discussion revolves around calculating the escape velocity of a pressurized gas from a container, considering parameters such as volume, diameter of the hole, pressure, temperature, and mass. The scope includes theoretical considerations and practical applications related to gas dynamics and thermodynamics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant inquires about the method to calculate the escape velocity of gas from a container, specifying parameters like volume and pressure.
  • Another participant asserts that the escape velocity for gas molecules is fundamentally the same as for any object.
  • A clarification is made regarding the context, specifying that the discussion pertains to gas escaping from a container, such as a gas canister.
  • One participant suggests using energy conservation principles, noting that if the diameter of the hole is small compared to the container, the pressure difference can be used to determine energy density and acceleration of the gas.
  • Another participant proposes considering the process as isenthalpic rather than purely adiabatic, arguing that it may be more applicable for steady flow conditions, while also noting the importance of pressure difference and specific enthalpy in the calculations.
  • There is a suggestion that adiabatic processes might be more relevant in scenarios where gas is released in a burst.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate thermodynamic processes to consider (adiabatic vs. isenthalpic) and the implications of the geometry of the nozzle on the escape velocity. No consensus is reached on a singular method for calculation.

Contextual Notes

The discussion highlights the dependence on specific assumptions regarding the flow conditions and thermodynamic processes, as well as the need for precise definitions of terms like energy density and enthalpy.

sadben
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Well this question I've had since high school (first year mech), how would i calculate escape velocity of a gas if i know volume, diameter of the hole, pressure, temprature and mass.
 
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Same as the escape velocity of anything... gas molecules are no different.
 
no i meant from a container like a gas canister or something something like this : http://www.sz-wholesaler.com/userimg/1068/1074sw1/co2-cylinder-for-lifejacket-799.jpg
 
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If the diameter of the hole is small compared to the container (=> the gas in the container does not move in a significant way), you can look at a small volume of gas and use energy conservation: The pressure difference inside<->outside gives an energy density*, this energy gets released to accelerate the gas.

*to be more precise, I think you should use adiabatic expansion and calculate the released energy
 
At first I thought he meant gas escaping by rupturing the pressure vessel :)
My next thought was - adiabatic process... but it may be easier to treat it as isenthalpic for similar reasons: the gas is flowing at a steady rate and we assume no exchange of heat with the surroundings - and we are only interested in the speed right outside the nozzle.

Adiabatic would be more in the case where most of the gas is released in a burst wouldn't it?

The calculation still depends on the pressure difference, but also the specific enthalpy of the fluid. This speed can be further modified by the geometry of the nozzle.
 

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