Le 19/11/2014 11:33, Stephen a écrit :
> On 19/11/2014 09:01, scott wrote:
>>> As Scott pointed out vapour
>>> pressure might have something to do with it as well.
>>
>> The vapour pressure of butane will determine the pressure of the refill
>> can. When you fill a totally empty can with butane the pressure will
>> build until it reaches the vapour pressure (about 2 bar absolute
>> pressure at room temperature for butane), at this point any more butane
>> you push in will condense out as liquid and the pressure will not
>> increase any further.
>>
>> The reverse happens if you were to slowly release the butane gas, this
>> causes the pressure to momentarily drop in the can which allows some of
>> the liquid to evaporate to restore the vapour pressure.
>>
> 
> So far so good.
> 
>> What you are doing in the refill situation though is to use the pressure
>> in the can to force the liquid up into an "empty" lighter (due to the
>> dip tube inside the refill can).
>>
>> When you connect the lighter and refill can together the pressure in the
>> can will force the liquid up the dip tube and into the lighter.
> 
> Oops! Are you using the photograph that Bald Eagle posted to work this
> out? That is a disposable non-refillable lighter. Refillable lighters
> have a different construction. The refill valve is on the bottom of the
> lighter in the section opposite to the dip tube and the internal wall is
> the other way round. So that the gap is at the bottom near the inlet valve.
> 
>> Initially the pressure in the lighter is below the vapour pressure so
>> the liquid will evaporate rapidly as it enters the lighter (the same as
>> if you just sprayed it into the atmosphere). This will continue until
>> the pressure is equalised and both the lighter and the refill can are at
>> the vapour pressure of butane.
>>
>> Based on that simple explanation there should never be any liquid
>> flowing into the lighter. If the pressure in the lighter is below the
>> vapour pressure then any liquid coming in will evaporate, and once it's
>> at the vapour pressure then no more liquid will flow in due to the
>> pressures being equal. But what I think happens is that when the first
>> bit of liquid evaporates inside the lighter it reduces the temperature
>> (eg it drops to 1.5 bar after a 10 degress C drop in temperature). What
>> this means is that once the pressure in the lighter has reached 1.5 bar,
>> the liquid entering it will no longer evaporate and will remain liquid.
>> At this point liquid will continue to flow until the pressures (and
>> temperatures?) have equalised.
> 
> I am not sure that I follow your logic. Are you saying that initially
> only gas flows then liquid?
> 

So far so good... but we can add a bit of complexity:

The pressure to liquify the butane is the partial pressure, not the
global pressure, whereas the flow to equilibrate pressure is about
global pressure.

In the empty lighter, global pressure is 1.0 bar (btw, it's now illegal,
should be in Pascal), and no partial pressure of butane.

In a filled lighter, all the pressure is from the butane, 2 bar when
unused. (but lower when lighted, as butane is going out)

In a refilling lighter, if any pressure is not from butane it is cooled
by the expensing butane and that system is not equilibrated, so it is a
bit difficult to know the global pressure, but it should be less than
1+butane.

In the refilling can, we have butane in liquid form pushed through a
pipe by: saturated butane gas and we can add some compressed nitrogen as
initial filling, for a global pressure that will be greater than the one
in the refilling lighter.

-- 
Just because nobody complains does not mean all parachutes are perfect.

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