> 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.

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. 
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.

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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?

-- 

Regards
     Stephen

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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.

Post a reply to this message

>>> 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.

I meant the dip tube inside the refill can, not the lighter.

>> I am not sure that I follow your logic. Are you saying that initially
>> only gas flows then liquid?

I am saying that initially the liquid butane evaporates as it enters the 
empty lighter, only after a certain pressure has built up in the lighter 
will the liquid from the refill can remain a liquid as it enters the 
lighter.

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

Correct, I had assumed only butane in the system in my working...

> 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.

...wouldn't an "empty" lighter actually be full of butane gas at very 
slightly above 1 bar (often you can hear the gas escaping but it's not 
enough to make a flame)? Or should we assume some amount of air in there?

BTW I call it "total pressure" not "global pressure", so still legal 
here :-)

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On 19/11/2014 13:49, scott wrote:
> BTW I call it "total pressure" not "global pressure", so still legal
> here :-)

While I model it.
I prefer my pressure in "psi gauge".

As in 3-15 PSI ~ zero to full scale.

-- 

Regards
     Stephen

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I'm sorry, but Mr Stacey doesn't know the current location of Brains.

Are you SURE this is a job for International Rescue?

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On 20/11/2014 11:44, Orchid Win7 v1 wrote:
> I'm sorry, but Mr Stacey doesn't know the current location of Brains.
>

LOL
I said Big Brains not Wee Brains. ;-)

> Are you SURE this is a job for International Rescue?

Maybe not now you mention it. It is a job without any strings. :-)

-- 

Regards
     Stephen

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