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PICList Thread
'HOW TO MEASURE BOILING POINT'
1998\03\21@105957 by PHXSYS

picon face
Hello everyone,

I have a challenge!

I need some ideas for measuring the boiling point of various fluids. The
specific gravity of one fluid is approx 1.03, very close to water. The
accuracy I am looking for is +/- 3 %. I am looking for creative options, the
simplier the better.

The boiling points may be as high as 500 degress F. A very small sample of
fluid will be tested 3-10 ml. I believe I will use a small electric heating
probe (hot wire) to quickly raise the temperature. The tesing time should be
between 30-60 seconds. The higher the boiling point the longer the test.

Can I look for the presence of vapor is a closed system; measure the current
of the probe and watch for reaction at boiling point, measure pressure changes
or pulsations as the fluid boils?

I would appreciate any code snippits that help. Thanks in advance.

Jon

1998\03\21@111854 by Chris Eddy

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face
Well now, I cannot claim that I paid very close attention in Chemistry (and it
is
going on ten years now <gulp>).  But any liquid will heat to the boiling point
and
then the temperature will stay absolutely flat until all of the liquid is vapor
(gone).  At that point the temperature will shoot through the roof (assuming
that
your temp probe is somehow coupled to the element when the liquid is gone).  If
memory serves me, an impure liquid, such as salt water, will not flatten off
perfectly but will have a gentle slope during the boiling process.  You may have
to prepare for boiling phases that are simply less sharp than the heating phase.
You may have to make some pretty intuitive software.  Wait! I know! use fuzzy
logic and just say 'look for the flat spot'.  Then you're problem is solved.
Why
didn't we think of that sooner.

Chris Eddy
Pioneer Microsystems, Inc.

PHXSYS wrote:

{Quote hidden}

1998\03\21@141932 by Leo van Loon

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face
Hi Jon,

In chemistry, the boiling point is measured in the vapour phase. When there
is liquid present on a thermometer in the vapour, you measure the boiling
point of the liquid. When you try to measure the boiling point in the liquid
phase you have to cope with problems as 'boiling delay' (i don't know the
exact english word for it). Clean liquids tend not to boil at temperatures
far above boiling point. A little disturbance causis the start of boiling
with a little explosion.  (try the experiment with a little bit of water in
a clean glass in the microwave....)
Boiling the liquid and measuring the vapour temperature above until it
stabilises must be easy to automate?!

Leo van Loon
SBB simpeltronics
Netherlands
tel +31 (0481) 450034
fax+31 (0481) 450051
mail spam_OUTsbb.simpeltronTakeThisOuTspamtip.nl
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secondary education.


-----Oorspronkelijk bericht-----
Van: PHXSYS <.....PHXSYSKILLspamspam@spam@AOL.COM>
Aan: PICLISTspamKILLspamMITVMA.MIT.EDU <.....PICLISTKILLspamspam.....MITVMA.MIT.EDU>
Datum: zaterdag 21 maart 1998 17:04
Onderwerp: HOW TO MEASURE BOILING POINT


>Hello everyone,
>
>I have a challenge!
>
>I need some ideas for measuring the boiling point of various fluids. The
>specific gravity of one fluid is approx 1.03, very close to water. The
>accuracy I am looking for is +/- 3 %. I am looking for creative options,
the
>simplier the better.
>
>The boiling points may be as high as 500 degress F. A very small sample of
>fluid will be tested 3-10 ml. I believe I will use a small electric heating
>probe (hot wire) to quickly raise the temperature. The tesing time should
be
>between 30-60 seconds. The higher the boiling point the longer the test.
>
>Can I look for the presence of vapor is a closed system; measure the
current
>of the probe and watch for reaction at boiling point, measure pressure
changes
>or pulsations as the fluid boils?
>
>I would appreciate any code snippits that help. Thanks in advance.
>
>Jon
>
>

1998\03\21@160119 by Nicholas Irias

flavicon
face
A couple of mechanical solutions that may or not be applicable,
depending on your application:

1) put an inverted funnel in the solution, to make a float switch.
when rising vapor bubbles begin to accumulate under the
funnel, the switch is activated

2) in a quiet, vibration free environment, listen.  When boiling
is about to occurr, you will hear high frequency noise ~1000hz
for water.  A rolling boil is louder, and at a lower frequency


----------
> From: Leo van Loon <EraseMEsbb.simpeltronspam_OUTspamTakeThisOuTTIP.NL>
> To: PICLISTspamspam_OUTMITVMA.MIT.EDU
> Subject: Re: HOW TO MEASURE BOILING POINT
> Date: Saturday, March 21, 1998 11:14 AM
>
> Hi Jon,
>
> In chemistry, the boiling point is measured in the vapour phase. When
there
> is liquid present on a thermometer in the vapour, you measure the boiling
> point of the liquid. When you try to measure the boiling point in the
liquid
> phase you have to cope with problems as 'boiling delay' (i don't know the
> exact english word for it). Clean liquids tend not to boil at
temperatures
> far above boiling point. A little disturbance causis the start of boiling
> with a little explosion.  (try the experiment with a little bit of water
in
{Quote hidden}

of
> >fluid will be tested 3-10 ml. I believe I will use a small electric
heating
> >probe (hot wire) to quickly raise the temperature. The tesing time
should
{Quote hidden}

1998\03\22@041553 by Russell McMahon

picon face
You can use a thermistor to both heat the solution sample
and test the temperature. Or use a separate heater and still
use a thermistor sensor. Heat the fluid while monitoring
temperature. As you approach boiling the rate of temperature
rise will slow and then stop at the boiling point. You
should be able to determine the boiling point to under 1
degree C this way (depending on how you measure the (sensor)
and this has the added advantage of being able to stop the
heating as soon as boiling point is reached. If the
non-linear change of resistance is too hard to handle you
can use a platinum PT100 resistor which has a very
standardised linear change of resistance with temperature.
You could also cheat by using one of the digital temperature
measuring ic's that are available.

When heating you want to keep the sample small so the heater
can bring it to boiling essentially all at once.

I have seen brake fluid boiling point testers which seem to
work much along the above lines.


From: PHXSYS <TakeThisOuTPHXSYSEraseMEspamspam_OUTAOL.COM>
Subject: HOW TO MEASURE BOILING POINT


>I need some ideas for measuring the boiling point of
various fluids. The
>specific gravity of one fluid is approx 1.03, very close to
water. The
>accuracy I am looking for is +/- 3 %. I am looking for
creative options, the
>simplier the better.

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