[APD] Re: transporting CO2 tanks

["Douglas Guynn" <d_guynn at sbcglobal.net>]

SunflwrgrlS at aol dot com asked:

"In terms of leaving the tanks in the back of a trunk on a hot day --
exactly what temp is dangerous? "

First, here is a quote from a post I made that I did not proof very well.

"The critical temperature of CO2 is 87.8 F (31 C). At this temperature, and
above, it is impossible to liquefy the gas by increasing the pressure. At
the critical pressure of 1066 PSIA (7281 kPa gage), and above, it is
impossible to liquefy the gas by decreasing the temperature."

The first two statements are correct. The second part of the third statement
is not (That's what happens when I switch focus too quickly). It is possible
to liquefy CO2 at pressures above 1066 psia.

Critical pressure as it applies to phase change is defined as "the least
applied pressure required at the critical temperature to liquefy a gas." So,
at 87.8 degF, it takes 1066 psia to liquefy CO2. At higher temperatures, it
will not liquefy, regardless of pressure. CO2 is considered supercritical
when both the temperature and pressure are above the critical values
(Imagine that). In this state the fluid has properties of both a liquid and
a gas.

In answer to your question, here is a Mollier chart
(http://www.chemicalogic.com/download/co2_mollier_chart_eng.pdf) for CO2. If
you follow the 30lbs./cu.ft.density line from the critical
temperature/critical pressure point, you find the following approximate
relationships;

1100 psig at 100 deg F
1300 psig at 120 deg F
1900 psig at 140 deg F
3000 psig at 220 deg F

As the rupture disc on your cylinder is probably 3000 psig, I don't think
you have anything to worry about as far as the cylinder and valve are
concerned, however the regulator may not be rated for the higher pressures.
I suppose that it would be possible to get to the 140 or 150 degree range if
the cylinder was in direct sunlight on a hot day, especially if it were
painted a dark color.

I wouldn't worry too much about it setting on your porch, unless it right
next to a hot barbeque grill.

Here (http://www.chemicalogic.com/download/co2_phase_diagram.pdf) is another
interesting CO2 chart, although it still needs some work I think.


Douglas Guynn
        432.368.5411
        d.guynn at sbcglobal.net
Not everyone who says to Me, 'Lord, Lord,' will enter the kingdom of heaven;
but he who does the will of My Father who is in heaven. Matt 7:21

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