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Condensation of gas using bernoulli's principle

  1. Oct 28, 2011 #1
    hi experts

    This ought to be obvious but it sounds wrong.

    If I have a pipe carrying butane at a constant flow rate at room temperature fed from a liquid gas bottle without a restrictor so that the gas is almost condensing, then have a constriction in the pipe to accelerate the gas, will the drop in pressure caused by acceleration cause the gas to condense ?

    This is a purely theoretical question so no actual gases will be used. Just interested to see if gases can be condensed this way.

    Many Thanks


    Read an earlier thread on this forum re carburettor icing but it wasn't clear if this was the reason.
  2. jcsd
  3. Oct 28, 2011 #2
    Yes. The constriction conserves total enthalpy. If the kinetic energy of the fluid goes up, its sensible enthalpy goes down. Condensation is certainly possible under appropriate conditions. Of course, coming of of the constriction, the velocity drops again, and the sensible enthalpy rises, so the condensate could evaporate again....

  4. Oct 28, 2011 #3


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    For water around its triple point (I guess for any other such substances too), it can actually not only condense but freeze.

    This is why in aeroplanes there is a 'carburettor heater' so that you can make sure the venturi is warm. As you come in to land on closed throttle when the manifold pressure is low, the additional venturi pressure drop is enough to cause condensation and freezing. Not what you want just at landing, in case you need to go around, so you get a little lever to push up as you come in on finals to heat the carb.
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