Is flash powder consider a high or low order explosive?
dmo...@my-deja.com
amounts it doesn't seem to detonate unless heavily confined.Does any
one know at what point an explosives goes from low order to high.Just
curious
dmo777
Sent via Deja.com http://www.deja.com/
Share what you know. Learn what you don't.
C.Beglin
wave propogation) - high order. Flash deflagrates, although when well
confined it certainly is quite potent.
Chris
On Wed, 09 Jun 1999 07:59:54 GMT, dmo...@my-deja.com offered the
following:
Chris
(Chris Beglin B.Eng (Hons) Systems - Mid Devon UK)
ch...@acbsystems.demon.co.uk
Broad Spectrum R&D and IT services.)
ICQ# - 35245971
C.Beglin
usefully been corrected by my friend Kaboomn - who noticed I was a bit
economical and incorrect with what I wrote! - probably didn't stop to
give it enough thought!
So - to add to this - I quote, courtesy of Kaboomn --
-----------------
I'm writing to correct a error you made on a
post a minute ago. You want to use the terms Low Explosive and High
Explosive not "Order" . Detonation may be either High-Order or
Low-Order and it is not deflagrating. The pressure time curve is the
same,but the amplitude against time is lower, both curves are bimodal
( two peaks, one high and one low, a double wave) Low Explosives
deflagrate and there is no bimodal curve, but a monomial one ( one
peak only, a single wave ) Low Order Detonation is a no-no in the
explosive world 99 % of the time. Shock tubing is one of the 1%, where
it is OK.
------------------
My thanks for his vigilance and apolagies for my inaccuracies.
Tm490
It blows out windows just like high explosives do if in a fair quantity. It
burns, but inside a tube, burns as fast as primary explosive--at least close
KaboomMn
--
Boomer
Kabo...@Gateway.Net
If you see me running you better catch up
Tm490 <tm...@aol.com> wrote in message
news:19990616215422...@ng-cq1.aol.com...
Arctic
KaboomMn wrote:
--
H. Beijeman
ICQ #14256779
My mind is incapable of conceiving such a thing as a soul. I may
be in error, and man may have a soul; but I simply do not believe it.
Thomas Edison, "Do We Live Again?"
An individual who should survive his physical death is also beyond my
comprehension, nor do I wish it otherwise; such notions are for the
fears or absurd egoism of feeble souls.
The World as I See It
KaboomMn
Nice to see you back .
--
Boomer
Kabo...@Gateway.Net
If you see me running you better catch up
Arctic <dobro...@hotmail.com> wrote in message
news:376897E3...@hotmail.com...
Jim
is a high explosive.
In English. An explosion is just a burn of a fuel. (rapid one.) If the
fuel is in a line (det cord) and set off, it has a burn rate. If the burn
rate is over 5280 feet in one second it is a high explosive. Common gun
powder is a low explosive. Prill is a usually a low explosive. These are
great for moving things...bullets or earth. Plastique on the other hand are
high explosives...great for breaking things...like you know.
<dmo...@my-deja.com> wrote in message news:7jl6tm$djb$1...@nnrp1.deja.com...
Hans
<e4Afs2Qu#GA.292@cpmsnbbsa05>...
> In English. An explosion is just a burn of a fuel. (rapid one.) If the
There are different types of explosions. They can be caused by mechanical,
explosive, thermal, chemical, or electrical means.
An explosion is a rapid expansion from a point.
> fuel is in a line (det cord) and set off, it has a burn rate. If the
burn
> rate is over 5280 feet in one second it is a high explosive. Common gun
> <dmo...@my-deja.com> wrote in message news:7jl6tm$djb$1...@nnrp1.deja.com...
> > I think the BATF considers flash powder a high explosive but in small
> > amounts it doesn't seem to detonate unless heavily confined.Does any
> > one know at what point an explosives goes from low order to high.Just
> > curious
When the speed of sound IN the explosive is exceeded it is a high
explosive. No absolute figure excists.
Hans
<376897E3...@hotmail.com>...
> Very true. However, some people claim it detonates, but it doesn't.
>
> KaboomMn wrote:
>
> > It Is a Low Explosive, it deflagrates and does not detonate
According to some litterature there are flash powders that do detonate.
With the fairly new technology of producing extremely small metal particle
sizes the detonation speed for high explosives is increased as well. People
used to say that that was impossible to achieve with a metal powder
additive.
Arctic
'detonating' explosives, man, it doesn't even come close!
Hans wrote:
--
KaboomMn
Typo-errro I hope 3280 and not 5280
--
Boomer
Kabo...@Gateway.Net
If you see me running you better catch up
Jim <West...@email.msn.com> wrote in message
news:e4Afs2Qu#GA.292@cpmsnbbsa05...
> If the lenier explosive component of the mixer exceeds the speed of sound
it
> is a high explosive.
>
> In English. An explosion is just a burn of a fuel. (rapid one.) If the
> fuel is in a line (det cord) and set off, it has a burn rate. If the burn
> rate is over 5280 feet in one second it is a high explosive. Common gun
> powder is a low explosive. Prill is a usually a low explosive. These are
> great for moving things...bullets or earth. Plastique on the other hand
are
> high explosives...great for breaking things...like you know.
> <dmo...@my-deja.com> wrote in message news:7jl6tm$djb$1...@nnrp1.deja.com...
> > I think the BATF considers flash powder a high explosive but in small
> > amounts it doesn't seem to detonate unless heavily confined.Does any
> > one know at what point an explosives goes from low order to high.Just
> > curious
KaboomMn
1. Detonation
2. Deflagration or fast burning
3. Pressurized container bursting
4. Rapid heating of air, as in lightning ( thunder ) or arch welding
--
Boomer
Kabo...@Gateway.Net
If you see me running you better catch up
Hans <HansN...@post.utfors.se> wrote in message
news:01beb980$8b3aedc0$d50969d4@default...
> Jim <West...@email.msn.com> skrev i inlägg
> <e4Afs2Qu#GA.292@cpmsnbbsa05>...
> > In English. An explosion is just a burn of a fuel. (rapid one.) If
the
>
> There are different types of explosions. They can be caused by mechanical,
> explosive, thermal, chemical, or electrical means.
>
> An explosion is a rapid expansion from a point.
>
> > fuel is in a line (det cord) and set off, it has a burn rate. If the
> burn
> > rate is over 5280 feet in one second it is a high explosive. Common gun
>
> > <dmo...@my-deja.com> wrote in message
news:7jl6tm$djb$1...@nnrp1.deja.com...
> > > I think the BATF considers flash powder a high explosive but in small
> > > amounts it doesn't seem to detonate unless heavily confined.Does any
> > > one know at what point an explosives goes from low order to high.Just
> > > curious
>
> When the speed of sound IN the explosive is exceeded it is a high
> explosive. No absolute figure excists.
>
Lindsay H. Greene, esq.
>'detonating' explosives, man, it doesn't even come close!
When ignited by FLAME, maybe, but many chlorate flashes have
been known to detonate (so we're clear here, that's DETONATE) when
initiated with a blasting cap.
Stay greene,
Lindsay G.
----
Visit Short Fuse Pyrotechnics:
http://www.angelfire.com/al/pyrotech/
Email me at: he...@western.wave.ca
My ICQ # is 24221175
Sometimes I think the surest sign that
intelligent life exists elsewhere in the universe is
that none of it has tried to contact us.
-Bill Watterson
Arctic
initiating explosive?? I consider a explosive compound/mixture, only when the
main ingredient can oxidize itself on a molecular level. I know this is a bit
controverse with the literature, since a detonating explosive would also be
considered something that a produces a shockwave, and a shockwave is only a
medium (gas mainly) wich moves faster than the speed of sound. Yet, thunder
produces a shockwave, but thunder isn't considered as a 'detonating explosive'
is it? So I think you failed to strengthen your point that flash can be a
detonating explosive. It is not by my definition. Flash is way different in its
behaviour than even the lowest detonating explosive, the chlorates. By the way,
I thought flash goes with 150m/s instead of approching the 1200 (mach 1) limit.
--
George Herbert
>haha, how can you be sure the detonation shockwave isn't the one from the
>initiating explosive?? I consider a explosive compound/mixture, only when the
>main ingredient can oxidize itself on a molecular level. I know this is a bit
>controverse with the literature, since a detonating explosive would also be
>considered something that a produces a shockwave, and a shockwave is only a
>medium (gas mainly) wich moves faster than the speed of sound. Yet, thunder
>produces a shockwave, but thunder isn't considered as a 'detonating explosive'
>is it? So I think you failed to strengthen your point that flash can be a
>detonating explosive. It is not by my definition. Flash is way different in its
>behaviour than even the lowest detonating explosive, the chlorates. By the way,
>I thought flash goes with 150m/s instead of approching the 1200 (mach 1) limit.
Your definition is *not* the industry standard definition.
You appear to know that.
Lightning produces a sonic-velocity thunder sound wave.
It's not supersonic.
Where a shockwave comes from is immaterial. If an explosive material
sustains supersonic propogation of that shockwave, it's detonatable.
Some chlorate powders are detonatable. Flash deflagrates under normal
conditions at subsonic velocities, but some flash powders can shift
into detonation if initiated by a detonator (supersonic shockwave)
or in large enough quantities. Same problem with pure ammonium nitrate;
by itself, it usually deflagrates, but if you put enough tons in one
place and light it it usually kicks over into detonation at some point.
A small discontinuity building up a sharp local pressure rise instead
of cleanly burning, and the reaction can run away into detonation.
By the way, the speed of sound in air is around 330 m/s, not 1200.
The speed of sound within the materials in question is what meets
the definition of detonation, though, which is usually not at all
the speed of sound in air...
-george william herbert
gher...@crl.com
Hans
<7kfe45$c9v$1...@news.laserlink.net>...
> and those types are
>
> 1. Detonation
>
> 2. Deflagration or fast burning
>
> 3. Pressurized container bursting
>
> 4. Rapid heating of air, as in lightning ( thunder ) or arch welding
...and gaseless explosives products heating ambient air
5. Rapid non-combustion chemical reaction producing gas(es) or mear heat
(polymerisation)
6. Mixing of two liquids, one with a lower boiling point then the other
7. More?
full...@aspi.net
>
> KaboomMn <kabo...@gateway.net> skrev i inlägg
> <7kfe45$c9v$1...@news.laserlink.net>...
> > and those types are
> >
> > 1. Detonation
> >
> > 2. Deflagration or fast burning
> >
> > 3. Pressurized container bursting
> >
> > 4. Rapid heating of air, as in lightning ( thunder ) or arch welding
>
> ...and gaseless explosives products heating ambient air
>
> 5. Rapid non-combustion chemical reaction producing gas(es) or mear heat
> (polymerisation)
>
> 6. Mixing of two liquids, one with a lower boiling point then the other
>
> 7. More?
BLEVE? (may overlap #6). Boiling Liquid Expanding Vapor Explosion. By
lowering the pressure, injecting vaporization nuclei, or by careful
heating you can create a super heated condition in a liquid. The liquid
exists and is (semi) stable at several degrees above boiling. Once
vaporization starts it propogates though the bulk material rapidly and a
fraction of the material changes phase. The resulting foam carries
considerable destructive power because the vapor carries the bulk liquid
along with it as it expands.
The easiest way to do this is heat water in a microwave without getting
it to a rolling boil. Then drop a tea bag into it (which lowers the
boiling point suddenly). The boiling water will splatter the kitchen
(and you) with water at over 200oF
The natural form of this is a geyser.
Allan
>The easiest way to do this is heat water in a microwave without getting
>it to a rolling boil. Then drop a tea bag into it (which lowers the
>boiling point suddenly). The boiling water will splatter the kitchen
>(and you) with water at over 200oF
Happened to me when I superheated a cold cup of coffee in a microwave. I
put the spoon in and whoosh--- out came the coffee. Funny thing was that
it was stone cold by the time it hit my skin.
I have heard tales from the old steam locomotive days of drivers and
firemen uninjured when a boiler went up because of the same phenomenon.
I attributed it to the rapid sudden expansion of the liquid causing
thermal energy loss.
The most dangerous substance we are involved with as far as bleves are
concerned is liquid propane. Nasty stuff if it gets out of control, but
not nearly in the same league as some of the chemicals you guys deal
with.
--
Allan
UK Amateur Radio Operator G7UZW
Remove NOSPAM in the return address
al...@rdodds.demon.co.uk
George Herbert
>[...]
>BLEVE? (may overlap #6). Boiling Liquid Expanding Vapor Explosion.
I thought BLEVE was Burning Liquid Expanding Vapor Explosion, not Boiling.
I don't regularly read the firefighter magazines, but I recall seeing some
discussion of it in the late 80s early 90s timeframe after a few incidents.
Superheated water isn't technically a BLEVE, it's just superheated liquid
flash vaporizing, which is unpleasant but not nearly as bad as say,
superheated propane flash vaporizing while burning and resulting in
a near-instantaneous combustion of the whole load.
There's another nifty effect which isn't quite in any of the
categories under discussion... if you have a tank full of
flammable liquid which floats, and a bit of contaminate water
at the bottom of the tank, the tank is highly dangerous if the
top starts on fire. The flammable liquid will get heated in a
zone moving down the tank, convecting some but generally with
a hot top zone and a cooler bottom zone, until the hot oil/gas/whatever
hits the bottom and flash vaporizes the water at the bottom,
which blows all the oil/gas/whatever out the top at once.
Major pain for firefighting in oil production and storage
facilities, because it makes it very dangerous to approach
tanks on fire.
-george william herbert
gher...@crl.com
donald haarmann
<full...@aspi.net> wrote in message news:377050A2...@aspi.net...
>
> BLEVE? (may overlap #6). Boiling Liquid Expanding Vapor Explosion. By
> lowering the pressure, injecting vaporization nuclei, or by careful
> heating you can create a super heated condition in a liquid.
Also -
HEALTH AND SAFETY EXECUTIVE
A study of the Causes of Molten Metal and Water Explosions
Joint Standing Committee on Health Safety and Welfare in Foundries
Fourth Report of the sub-committee on Continuous Casting and High
Speed Melting
LONDON: HER MAJESTY'S STATIONERY OFFICE 1977
In Part. Scanned and you know what that means!
Take good notes there will be a test.
The test will not be curved and "race normalizing" will not be applied. Sorry.
Introduction
1 During the process of continuous casting the molten metal may escape
from the mould', or from the section being cast, to flow into cooling water
and an explosion may occur. The explosion may result only in a
'sputtering' of metal; it may cause damage to plant; or very occasionally it
may wreck a plant. All these explosions may result in injury to persons
and all are undesirable, but the occasional catastrophic explosion is
clearly a source of much concern. A considerable amount of work has
already been done in different parts of the world and published on this
matter, but no fully satisfactory explanation has yet been found to account
for the sequence of events which leads to major explosions.
Explosions
2 The word explosion is commonly used in metallurgical practice to cover
rapid events which result in eruptions of molten metal which may or may
not be associated with damage to plant.
3 Explosions vary greatly in violence, but they also vary in nature and at
least three types can be distinguished. A 'chemical' explosion results from
the rapid interaction of two substances after ignition. What is often called
a 'steam' explosion results from the rapid vapourisation of water which
gives a correspondingly rapid and very considerable expansion as the
water changes from the liquid phase to the vapour phase. This expansion
exerts a pressure which disrupts the bolus of liquid metal and ejects it
from the vessel which contains it. In this case there is no chemical
reaction and no ignition. More recently a third type of explosion has been
recognised which is sometimes designated by the term 'vapour' explosion.
Vapour explosions may occur when two liquids of dissimilar temperature
come into contact with each other. The interaction appears to be physical,
not chemical, resulting, so far as is known, from a rapid generation of
vapour in the cold liquid as heat is transferred to it without ignition from
the hot one. Physical explosions may in some circumstances be followed
by chemical explosions. In semicontinuous or continuous casting plants
the cold liquid is the cooling water and the hot one is the molten metal.
These vapour explosions may release large quantities of energy with a
consequent violent and dangerous destruction of plant.
4 The sub-committee is engaged in a study of the causes of these
explosions, and also of the measures *A 'mould' may be called a 'die' and
for the purpose of this report either word will be used to include any
meaning which may be attributed to the other,that might be taken to
prevent them. Causation and prevention are two different matters,
although both are of the utmost importance. It is evident that if the precise
causation were known steps could be taken to Prevent the incident. On
the other hand if it were possible to guarantee that molten metal and
water were never allowed to mix no explosion would result, and in these
circumstances the explosions could be Prevented without ever knowing
the causes which instigated them. Both lines of approach are therefore
being examined simultaneously.
Empirical work on explosions
5 The early empirical work done by Long, on aluminium, was continued by
Hess and Brondyke, on the same metal. In this work relatively large
quantities of molten aluminium (about 22 kg or 50 [b) were dropped into
water in an effort to determine the conditions in which an explosion
occurred; and the work resulted in the postulation of a series of pre-
cautions to reduce the possibility of an explosion when liquid metal and
water were mixed. These experiments and subsequent practical
experience formed the basis of the sub-committee's first report3 entitled
Operational Safety during Vertical Semicontinuous and Continuous
Casting of Aluminium. This report is still valid and represents an important
contribution to safety, even though it offers no explanation of the
explosions.
Causes and prevention of break-out
6 A second approach to the problem would be to prevent liquid metal from
running into water. In practice this happens when the molten metal flows
from the mould or breaks out of the solid shell of the casting being made.
There are many reasons for this break-out of molten metal and it can
often be prevented by good design of the plant, and by careful
maintenance and by good casting practice. The second report of the
sub-committee I entitled Causes and Prevention of Break-out during
Vertical Semicontinuous and Continuous Casting of Aluminium Alloys
deals with this aspect of the matter and discusses the avoidance of failure
in the mould, the design and operation of cooling systems, the use of
lubricants, casting procedures and some metallurgical considerations.
Like the first report it has important things to say about safety in the
casting of aluminium alloys.
A warning and control system
7 There can be no doubt as to the desirability of a system which will
continuously monitor the process and give warning about the possibility of
a break-out of molten metal before it occurs; and such a system
would be still more valuable if it could be set to control the plant
automatically in the event of a break-out. Such a warning and control
system has been designed and operated successfully for some years on
vertical and horizontal single or multistranded plants casting copper based
alloys in submerged graphite dies. The third report of the subcommittee I
entitled A Warning and Control System for Continuous Casting (as applied
to copper alloys) describes this system. There would seem to be no good
reason why systems should not be devised for use on other plants casting
other metals and alloys, and it is hoped that the industry will not fail to
examine this most useful safeguard in continuous casting.
Causes of explosions
8 None of the work previously published by the sub-committee has been
concerned with the elucidation of the criteria which give rise to explosions
when liquid metal and cooling water are mixed, but this aspect of the
matter has been under examination for some years. The present report
contains a first discussion of results of a Research project which was
done at the University of Aston in Birmingham. This project was
sponsored by the Joint Standing Committee on Health Safety and Welfare
in Foundries and financed by the Department of Employment. It is
primarily directed to a determination of the mechanism which initiates
explosions when liquid metal and water mix in continuous casting plants,
but a successful conclusion of the work would doubtless assist in
preventing metal water explosions in other contexts within the
metallurgical industries.
9 It is well known that explosive interactions may occur when two liquids
are mixed, if one of them is at a temperature in excess of the boiling point
of the other. Examples could be quoted from many branlches of science
and technology ranging from the domestic frying pan to a volcano. A
considerable amount of work has been carried out in an effort to discover
the causes of this type of explosion, but though most research workers
are agreed that explosions occur through some unusual form of mixing of
hot and cold liquids, there is considerably less agreement on the origin of
this condition. This is probably due largely to the difficulty of obtaining
quantitative and reproducible results. In the present work therefore an
effort has been made to obtain this kind of data and to relate the
observations to the occurrence of explosions in normal working
conditions. It is for these reasons that the small scale experimental work,
which used quantities of metal of less than 1 gm was undertaken and has
been supplemented by series of pilot scale experiments in which quanties
of a variety of metals and alloys up to about 9 kg. (20 lb) were used.
Other aspects of safety in continuous
10 There are other theoretical cons which, although they have no bearing
o mediate cause of an explosion once the liquid and water have been
mixed, nevertheless considerable influence on the prevention of
admixture; a prevention which would in it all explosions impossible. These
theoretical considerations have therefore received the at the
sub-committee.
11 A continuously cast section consists of formed solid skin or shell which
surround liquid central core of metal. Before the section the mould the
solid shell or skin should enough and strong enough to hold the liqui metal
in order that it cannot escape into the water. In practice the whole cross
section billet being cast may be solid before it le mould or die, or
alternatively the section may the mould with a still liquid core. The pro
safe working conditions would be greatly facilitated if it were possible to
calculate the thickness shell at any position in the emerging cast this
reason a variety of mathematical mod been devised in an effort to
determine the( the solidus, which might be considered, in t to represent
the internal curved surface w casting beyond which all the metal is solid.
the solutions from these mathematical m precise or easily applied to the
variety of n the range of plants which are in use. They al the use of heat
transfer coefficients, and these constants are not always precisely k high
temperatures the mathematical model best only estimates.
12 The stability of the shell as it is formed with the mechanical properties
of the metal being cast. These properties are generally well at those
temperatures about which the r casting will be used in engineering
practice, are by no means so well known at temperature its melting point.
Much further information i fore necessary in order to support precise
calculations as to the strength of the shell or skin of the immediately after
solidification.
13 Similar considerations apply to the calculation of frictional forces which
might be set up betw emerging casting and the internal wall of the In
consequence precise calculation of frictional effects in the mould awaits
the accurate determination of the necessary co-efficients within the
temperature range which exists at the interface between mould wall and
metal shell.
14 Much work is proceeding on these and associated matters but in view
of its other pressing commitments the sub-committee has, so far,
restricted its activities in these aspects of the work to a search of the
literature and an examination of the validity of some mathematical models.
The results of the search of the literature together with some brief
comments are however available to other research workers in the field
(Appendix 5).
Melting practice
15 Continuous casting plants include melting or holding furnaces and
explosions may occur when charging scrap into the furnaces. These
explosions are outside the scope of the present work but because of their
frequency some work was done to determine the amount of condensed
moisture that may be carried in bales of scrap which are thought to have
been completely dried (Appendix 6).
Other considerations
16 It is not possible at present to draft a comprehensive report covering all
aspects of safety in respect of every metal or alloy cast in all types of
plant. Work is still proceeding, and this report must remain both interim
and to some extent tentative in character. It should be read in conjunction
with the first three reports already published. Together, the four reports
contain much important information on many aspects of safety in
continuous casting, and even where they do not directly concern particular
metals or plants they carry important implications which should be
construed in the context of the processes with which they do not
specifically deal.
Explosive liquid-liquid interactions
Disintegration of metal drops in water
17 The laboratory work was done to investigate the criteria which lead to
major explosions in industrial plant. It is evident that an explosion may
result from either physical or chemical reactions and both have been
suggested at various times. It appears however that the preliminary
causes are physical even though a secondary chemical reaction may
occur. If this is the case the chemical reaction would not take place if it
were not triggered by the initiating physical action, and the main
requirement is therefore to understand the physical criteria which initiate
the explosion.
18 An apparatus was constructed (Appendix 1) such that small separate
drops of molten metal of a relatively constant size could be dropped into
water, with both metal and water at varying temperatures. The progress of
each drop was recorded on film by a high speed cinernatograph camera.
The history of each drop could thus be observed. Each observation
recorded a series of drops, thereby representing something of the order of
a hundred single experiments. The results were, in consequence,
statistical in nature, while at the same time they offered the possibility of
individual examination of the fate of each drop.
19 Some drops solidified intact at the bottom of the water container, but
some exploded as they moved through the water. The effectiveness of
these explosions was measured by the 'percentage disintegration'. This
latter term was obtained by multiplying by 100 the ratio of drops
disintegrating to the total number of drops.
20 Tin, aluminium, bismuth, indium, gallium, thallium and lead were
studied. The coolant was normally water, when explosions often resulted;
but liquid nitrogen, acetone, alcohol, carbon tetrachloride and an
acetone/water mixture were also used, when no explosions resulted.
21 Experiments were also made with water after its surface tension had
been either raised or lowered by suitable additives.
22 The work on small drops is discussed in detail in Appendix 1, but it
may be said here that (1) disintegration is not normal behaviour; (2)
disintegration’s are not caused by vortex mixture at the surface of the
water; (3) there is no evidence of turbulent mixing of metal and water as
the metal falls through the water; (4) there is distinct evidence of two
regimes of disintegration, one at low temperature and one at high
temperature and (5) these regimes are clearly separated by a strong
minimum in percentage disintegration.
The path of a failing drop
23 The high speed photographs showed the path of the drops as they fell
through the coolant. In general, cool liquids fell vertically through the water
under the influence of gravity. Hot liquids (e.g. molten tin) fell vertically
until the moment of disintegration when the drops showed considerable
deviation from the vertical path, and in some cases the impulse caused
them to spin.
24 This aspect of the work which is discussed in detail in Appendix 2
provided a quantitative insight into the mode of disintegration of the metal
drop. It appears that the steam envelope or bubble which surrounded the
drop as it moved vertically downwards through the water collapsed at the
moment of transition from stable film boiling to pulsation boiling thereby
imparting sufficient energy to the drop to divert it from its vertical path or to
cause it to spin.
Heat transfer from metal surfaces during boiling
25 That there is a close connection between the different regimes of
boiling of the water and the occurrence of an explosion has been
generally recognized, and so a series of measurements of the rate of heat
transfer from solid steel spheres and from liquid tin were made during the
course of the studies on failing drops. This work is discussed in Appendix
3 where it is suggested that explosions occur when a critical rate of heat
transfer coincides with unstable or transition boiling.
Pilot scale tests
26 Towards the end of the experimental and theoretical work described in
Appendices 1 to 3 some preliminary tests, on a much larger scale than
was possible in laboratory conditions, were completed, largely to ascertain
how far the criteria for safety put forward by Long were valid for metals
other than aluminium. There can be no doubt that some sections of the
industry hold the view that the violent explosions which have occurred on
aluminium plants were caused by explosive chemical reaction which
would not occur consequentially with other much less 'sensitive' metals. It
is however now generally acknowledged that explosions are initiated by
physical causes and not chemical reactions; that chemical reactions often
play no part and that even if they occur they are secondary to, and are
triggered by the initiating physical processes. In this case it might be
expected that any molten metal failing into water would in suitable
conditions provide a violent explosion. If this could be shown
experimentally it would then become necessary to determine the validity
of Long's aluminium precautions for all the metals which would explode on
mixing with cooling water.
27 This series of tests, which is not yet completed, is described in
Appendix 4 which gives the results to date. Copper, brass, lead, zinc, iron
and magnesium were all tested, and it was found that all, except
magnesium, could give explosions. It may therefore be said that the first
five of these metals represent industrial risk which may not always have
recognized.
28 Copper was examined in more detail than yet been possible with the
other metals and it appears that the results in Table 1 of Appendix 4
indicate need for a modification of Long's criteria if they be used as safety
measures for copper. In part it may be noted that Long found with alum
that there was a maximum depth of water which explosions did not occur
and that there was also a minimum depth below which they did not occur.
The present corresponding work with c however showed that there was
no such minimum depth since even with the shallowest of water an
explosion occurred.
29 No explosion has yet been obtained i conditions of the experiments
with magnesium although some of the magnesium burned. It appears that
this result is due to the fact that molten magnesium, owing to its low
density, forms a layer surface of the water before slowly penetrating the
surface. Very little magnesium reached the bottom of the water tank.
However an alloy of lead and magnesium with a much higher density did
penetrate water and produced an explosion.
30 More work remains to be done with magnesium alloys and
experiments will shortly be commenced some higher melting point metals
which have not yet been tested. It appears however in the p state of the
work that the specific heat, the d and the temperature of the molten metal
are significant factors.
General discussion
31 The whole of the work on explosive I liquid interactions described in
Appendices 1 and done both in a laboratory and on a large test site has
served to underline how great an a still needed before any complete
explanation of liquid-liquid explosions is reached.
32 The use of defined and reproducible systems has produced data from
which the dy of an explosion can be deduced. Both the time scale
involved and the magnitude of energies deter disagree with the cyclic
model of Buchana Dullforce, and are closer to the pulsation model of
Witte.
33 Experiments on heat transfer from metal surfaces suggest that Witte's
model n refined, and the prerequisite for an explosive action is that a state
of pulsation boiling exist metal/water interface and that the heat transfer
rate, which depends on the temperature difference between the boiling
point of the coolant (water) and its actual temperature, rises to a critical
value. It is a reasonable postulate that bubbles can then be formed of a
sufficient size to produce interactions of the measured impulse on
collapse.
34 Interactions may occur on the coolant surface, probably according to
the vortex theory of Buchanan and Dullforce; or in the body of the coolant
as studied in Appendices 1 to 3; or on the bottom of the vessel containing
the coolant as suggested by Long. There is no reason to suppose that the
critical conditions differ in these situations, though they may be brought
about in differing ways.
35 Large scale tests have shown that interactions on the bottom of the
tank containing the coolant are of major importance.
36 If the metal surface at which boiling occurs is large compared to the
bubbles formed, an initial event, whether due to the collapsing bubble or
to external causes, will itself act as a cause to further events and the
disturbance will propagate across the extended surface at high speed.
Since initiation has been shown to be a chance event there is a probability
that near simultaneous initiation may occur at several places and the
meeting of the propagation disturbances will amplify their effect.
37 It is to be expected that large and irregular masses of metal will
disintegrate as readily as small regular drops, and that the greater energy
available will produce the major effects which have been observed.
38 With the exception of magnesium all the metals used in the pilot scale
tests have produced explosions. This work therefore, so far as it has been
completed, indicates that any molten metal which falls into water in
suitable conditions will produce an explosion. Even as a tentative
conclusion this bears important implications for industrial plants.
Moisture condensation on cold metal
39 This subject is not perhaps directly related to the main considerations
discussed in this report nor is it strictly part of the main work at present in
hand. However the incidence of explosions resulting from the charging of
aluminium into furnaces which may or may not be connected to
continuous casting plants induced the sub-committee to engage in a short
term experimental project in an effort to determine the amount of
condensation that may form on scrap bales, which, although thought to be
dry, are cold enough to cause the air in which they stand to pass through
the dew point.
40 The results are set out in detail in Appendix 6 which warrants careful
consideration by the industry. They indicate that unfavourable storage
conditions can give rise to serious hazards due to condensed water which
is difficult to drive off, and that commercial bales of scrap compacted at a
pressure of 0-21 t/in 2 might contain up to 30 lb of water per ton of scrap.
Conclusions
41 The following tentative conclusions have been reached although they
may need modification in the light of continuing experimental and
theoretical work.
(a) It is to be expected that any molten metal falling into water would in
suitable conditions produce a violent explosion.
(b) Large scale tests have shown that interactions on the bottom of the
tank containing the cooling water are of considerable importance.
/c/ Conditions such as height of metal fall, depth of water, water
temperature, surface state of walls of water container, metal temperature
and quantity are all important criteria in determining the occurrence of an
explosion.
(d) It is also to be expected that (in suitable conditions) when water is
mixed with and trapped in a bath of molten metal a similar violent
explosion may occur.
(e) Work has not progressed far enough to determine precisely either the
criteria or the reasons for the rare catastrophic explosion. All the
precautions which have so far been suggested, either in the 1st, 2nd
and 3rd reports or implied in this report, to prevent or mitigate the
violence of an explosion from the mixing of liquid metal and water are
therefore empirical, and it cannot yet be claimed that they will prevent
every explosion. For this reason further research work is now in
progress.
(
Conclusions from Appendices: explosive liquid-liquid interaction
42 Appendix 1 Disintegration of a falling drop of molten metal
Disintegration of the hot liquid or metal on hitting water is not normal
behaviour. Disintegrations are
not caused by vortex mixing at the surfaces. With molten metal falling into
water there is no evidence of hydrodynamic or turbulent mixing,
Disintegration of the metal bolus did occur at a low temperature and again
at a high temperature of the molten metal.
All features of the results are consistent with the transition boiling theory
advanced by Witte 14.
43 Appendix 2 The path of a falling drop
The transition from stable film boiling to pulsation boiling leads to a high
frequency instability of the surface film and to steam bubble collapse.
Such a collapse produces an impulse sufficient to displace the vertical fall
of the drop or cause it to spin.
Disintegration of one bubble may induce film collapse in a second one.
44 Appendix 3 Heat transfer from metal surfaces during boiling
The occurrence of explosions or disintegration appears to be closely
associated with the heat transfer reaching a critical rate under conditions
of unstable or pulsation boiling.
45 Appendix 5 Mathematical models
A literature survey was made of:
(a) heat flow calculations in continuous casting,
(b) the mechanical properties of metals in the region of their melting
points,
(c) friction in the mould and consequent billet rupture,
(d) stress patterns within the shell in the region of the mould,
(e) equipment for monitoring shell thickness and temperature below the
mould.
46 Appendix 6 Condensation of moisture onto cold baled scrap
The dominant mode of heat transfer to the bale is convection, but
significant heating by radiation occurs in the initial stages. The convected
air condenses water from the water vapour onto the surface of the bale,
whence it penetrates into the bale by distillation and condensation. It is
calculated that large metal bales will take several hours to be warmed
through, sufficiently to drive off all the trapped moisture.
Acknowledgements
47 It is evident that all this work could not have been done without the
assistance of many people and we gladly acknowledge this assistance.
The sub-committee has visited large numbers of plants [snip]
Appendix 4 Explosive liquid-liquid interactions: pilot scale tests
(Professor WO Alexander and Professor F M Page)
Introduction
1 Work carried out by dropping gram quantities of molten metal into water
in the laboratory has shown that explosive interactions between low
melting point metals and water can be obtained under conditions which
depend on the type of boiling phenomenon taking place at the interface
between the molten metal and water. It was considered desirable to
produce large scale explosions by dropping kilogram quantities of molten
metal into water. Experiments on this scale would bear a closer
resemblance to possible foundry accidents.
2 Dangerous physical explosions have been obtained in quite clearly
defined conditions with lead, zinc, leaded-brass, copper and a
magnesium-lead alloy, and preliminary experiments have shown that
explosions also occur with iron. These explosions were sufficiently violent
to blow the mild steel water containers apart and to expel a powdered
metal to a distance of several metres. In the experiments one condition
found to be necessary for explosions to occur was that molten metal
should hit the b the tank, the surface of which was rusty. In depth of water
and painting of the tank surface found to prevent explosions.
Experimental method
3 The experiments were carried out at an site, well away from buildings
(Fig 21a). sided bunker of concrete blocks reinforced with steel rods was
constructed having walls of thickness and a height of 4 m. The interior of
the bunker and the immediate vicinity were floored with concrete and the
bunker and adjacent service area were p from inclement weather by
tarpaulins. The (Fig 21 b) was situated within the concrete and consisted
of a rectangular steel frame supported in a horizontal position by a steel
leg at each corner. Each leg was firmly connected to a steel bas into the
floor. Various leg heights could be used.
4 Between the two longer sides of the frame an annular support could be
pivoted about a horizontal diameter. This steel ring held a crucible of
Capacity about 2 x 10-3 m3 (i.e. about 9 kg or 20 lb of aluminium)
containing the molten metal. The ring was kept locked in a horizontal
position before an experiment. A retaining catch could then be released
electrically thereby enabling a counterweight to rotate the pivot through
180' and empty the contents of the crucible into a tank of water positioned
below the rectangular frame. The tanks used were cubic in shape and of
two sizes, one with sides of 30-5 cm (1 ft) and the other of 61 cm (2 ft).
They were made of 6 mm and 8 mm thick mild steel respectively. Four
surface finishes were used: lanolin coated (the condition in which steel
tanks arrived), clean sandblasted, rusty, and covered with two coats of
Rustoleum paint (Ref. No. 769080). Mains water was used, taken from the
fire hydrant.
5 Mains electricity was used to run two 5 kW furnaces situated in the
service area adjacent to the bunker. The metal was heated in the type of
crucible mentioned previously and when at the required temperature was
transferred to the test rig. A protective steel plate covered the water tank
at this stage of the procedure to prevent spillage of molten metal into the
water. Also a bolt was inserted to prevent premature electrical release of
the counterweight. When all but one of the personnel were at a safe
distance from the bunker the remaining person removed the bolt and steel
plate by means of a wire threaded through the concrete wall. With this
done, the last person could join his colleagues at a safe distance and
inform the control room situated about 100 m from the bunker that the
metal could be poured.
6 A high speed camera suitably protected against flying debris was placed
about 20 m in front of the bunker and was started by remote control one
second before the counterweight was released by the control room. The
time between removing the crucible from the furnace and the release of
the counterweight was kept as short as possible, consistent with the
safety of personnel, to minimise the fall in temperature of the molten
metal. For most experiments this time was less than sixty seconds.
7 The explosions were characterised by a loud noise heard at least 200 to
300 metres away, by damage to the water tank and rig, by movement of
the tank and by explusion of most of the water from the tank. Debris from
explosions was in a finely divided form of characteristic dimensions less
than 2 mm. Experiments which did not result in an explosion produced no
noise, no damage and left the water volume virtually unchanged. The
poured metal remained undivided in a single compact mass. For purposes
of record after each explosion still photographs were also taken of the rig
and its surroundings (Figs 22 and 23). Debris was also removed and
photographed (Fig 24).
Development of experimental work
8 It must be emphasised that this is early experimental work and that in
consequence even qualitative conclusions which may be drawn from
these experiments can be no more than tentative because of the limited
number of experiments which it has yet been possible to complete.
9 The aim of the first series of experiments was to determine whether or
not an explosion would be obtained with molten copper by disregarding
every one of Long's experimentally-determined safety recommendations
for aluminium. After two 'dry runs' to test the apparatus, the third test
produced the most violent explosion that has been obtained with the
apparatus to date (Fig 22). Experimental details for this and all other tests
are given in full in Table 1. The metal temperature of 1430oC in the
furnace was the highest achieved by the furnaces, and since some
furnace elements had to be replaced as a result of it these high
temperatures have not been used since. In this test 9-1 kg of copper were
poured into 30 cm of water in a 30 cm rusty tank. The steel tank was torn
apart by the explosion which projected on of the tank to a distance of at
least 40 m remaining three sides were flattened into one plane. Copper
powder covered the walls bunker, the floor and tarpaulin, and its m colour
was still apparent. Llewelyn (20) has an debris from an explosion by
vacuum fusion and about 750 ppm oxygen compared to 75 ppm fo debris
when no explosion occurred. Slight sup oxidation could have occurred,
but to less than in 1000. The rig was damaged to such an extent that it
had to be replaced. In the light of this experiment later work with copper
was restricted to an amount 4.5 kg.
10 The second series of experiments cove range of metals; lead, zinc,
leaded-brass and copper. Two 'dry-runs' were first carried out to test t
after which each metal was dropped at a temperature approximately
100oC above its melting point 30 cm tank containing 30 cm of water. For
Tests6, 7 and 8, 9.1 kg of lead, zinc and leaded-brass used and caused
an audible explosion in each The three explosions all produced granular
debris. This was of a sponge-like nature for lead an gritty powder for
leaded-brass. The zinc debris was intermediate in nature between those
of lea brass. While the lead debris mostly remained tank, some zinc
debris was distributed onto the surrounding floor area, and the brass was
found on the walls and floor indicating that the explosions appeared to
become more violent with increcresing metal melting point. The last two
experiments (Tests 9 and 10) in this series were to determine whether
masses of copper smaller than the 9-1 kg (20 lb) used in Test 3 would
cause explosions. It was found that while 2.3 kg (5 lb) did explode, 0-9 kg
(2 lb) did not. Both metals were transferred to the rig at a furnace
temperature of about 1175oC. Dropping conditions were identical. The
larger amount of copper caused an explosion which ripped the overhead
tarpaulin and caused the tank to move and distorted it. Powdered debris
was again seen on the floor, walls and tarpaulin. In contrast to this the
smaller quantity of copper produced no audible explosion, left the tank
intact and most of the water still present. At the bottom of the tank was
found a compact mass of copper in the form of a thick I pancake which
appeared to have been formed as the molten metal solidified on the
bottom of the tank. No powdered or granular copper was present.
11 For the third series of experiments copper was the only metal
considered and the high speed camera was now in use. Long's work with
aluminium suggested that a sufficient depth of water might prevent
explosions. Consequently for Tests 11 and 12 a depth of 61 cm was used
in a large 61 cm rusty tank. Quantities of 2-3 kg and 4-5 kg of copper were
used. Neither of these experiments produced an explosion. After each
one the tank was still in position and had lost only a small amount of
water. In both cases an irregularly shaped mass of globular copper was
found at the bottom of the tank. This copper appeared to be an
agglomeration formed by copper droplets which had not quite solidified,
each globular droplet being of the order of 1 cm in diameter. The greater
depth of water in these experiments had cooled the molten copper to such
an extent that solidification was almost complete by the time the bottom of
the tank had been reached. In Test 13 by lowering the depth of water by
15 cm with conditions otherwise remaining as in Test 12 an explosion was
obtained which produced powdered copper, buckled the steel tank and
(as was seen on the cinernalograph film) propelled the tank upwards at a
velocity of 2-5 m/s. The tank could be seen striking the rectangular frame
and falling again, and since the tank and contents weighed approximately
300 kg the kinetic energy exhibited was equal to at least 2% of the
available sensible heat*.
12 Test 14 was with a sand-blasted clean 30 cm tank containing 30 cm of
water. Apart from this, conditions were identical with Test 13. No
explosion occurred in Test 14 despite the fact that a smaller depth of
water was being used. This was attributed to the cleanness of the bottom
of the tank. To ensure that the result of Test 10 had not been due to an
insufficiently rusty tank, Test 15 consisted of a repeat of Test 10 with a
rustier tank. No explosion occurred confirming the result of Test 10.
13 The fourth series of tests again considered copper. Tests 16 a nd 17
were both repeats of Test 14 using for 16 a sand-blasted tank which had
been allowed to rust slightly and for 17 a tank built from lanolin coated
steel which had been exposed to the weather for sufficient time for rust to
have developed. Both tests produced explosions which shifted the tanks
and left them in a distorted condition. A gritty powdered debris was again
scattered around the rig. On watching the cinernatograph films of these
two tests a movement of gases at speeds close to that of sound could be
seen, and this suggested that the damage was caused by shock waves.
The remaining test in this series, number 18, demonstrated that by using
water at a higher temperature (77 'C) than the ambient temperature used
in all the other tests, an explosion could be prevented. Conditions were
the same in Test 16 except for the water temperature. No explosion
resulted, supporting the suggestion that the more persistent nature of film
boiling, with water at a comparatively high temperature, may help in
preventing explosions. The copper was found at the bottom of the tank in
the now familiar pancake shape. As had been observed in previous cases
the impressions of vapour bubbles could be seen on the lower surface of
the copper pancake indicating that water had been trapped beneath the
molten metal.
14 For the fifth series of tests 4-5 kg of copper and the 61 cm tank were
used. The same tank was use
for all four tests (19-22) in this series, and although at the outset it was
covered with a thin lanolin layer which it is believed prevented explosions
up to Test 21, by the fourth test, number 22, with the metal temperature
1290oC before transfer, an explosion was obtained with 30 cm of water.
In this test copper was found to be welded to the bottom of the tank at one
point, indicating perhaps that at this point the protective coating had been
removed so allowing the initiation of an explosion. This may, however, a
associated with the 100oC higher metal temperature used.
15 Magnesium and copper were used for the sixth series of experiments
which consisted of four tests. A “Rustoleum” painted tank was used for
two tests to determine its effect on an explosion. With magnesium,
however, no explosion could be obtained even with a rusty tank. 2.3 kg of
magnesium at al: 100'C above the melting point were dropped 30 cm of
water in a 30 cm tank. Some of magnesium burned, but no explosion
occurred. 4 both the magnesium tests 23 and 24 a single cell metallic
structure was recovered from the tanks
25). It contained large connected cavities characteristic dimensions 5 cm.
The molten magnesium appeared to have formed a layer on surface of
the water before slowly penetrating surface in long pendulous forms, and
very I molten magnesium had reached the bottom of tank. The two other
experiments in this series involved the pouring of 4-5 kg of copper at a
furnace temperature of 1190oC into 30 cm of water. In test 25 a
“Rustoleum” painted 30 cm tank was u whereas in 26 a similar rusty tank
was used explosion occurred only in Test 26, indicating that paint had
prevented some triggering process f taking place. The typical pancake of
solidified coper was found after Test 25 with vapour bubble impression on
its lower surface. It would seem that paint did not prevent water
entrapment beneath molten metal, but due to surface tension effects it
had altered the likelihood of a potentially dangerous form of boiling.
16 Since the magnesium in Tests 23 and 24 had not reached the bottom
of the tank in any great quantity, it was decided (a) to use a smaller depth
of water and also (b) to alloy the magnesium with a much denser metal,
since either of these alternatives might result in the metal penetrating the
water to the bottom of the tank. In Tests 27 and 30 of the seventh series
of experiments the first of these proposals was tested. 2.3 kg of
magnesium were poured into 23 cm and 10 cm depths of water in rusty 30
cm tanks. Furnace temperatures of 750oC were used as in previous
magnesium drops, to give a pouring temperature about 100oC above the
melting point. Results were similar to those obtained with 30 cm of water,
No explosions occurred and the magnesium burned as before on the
surface of the water. Magnesium was then alloyed with lead in a 50%-
50% alloy in Test 28 but no explosion resulted on pouring 3-6 kg of this
alloy into 30 cm of water. An alloy of greater density was used for Test 30
and this did result in an explosion. 4.1 kg of an alloy of 33% magnesium
and 67% lead were poured into 15 cm of water. The tank broke at its weld
leaving one side detached. Gritty debris was blown over the floor of the
bunker.
17 It would appear from the copper experiments that for one copper
temperature explosions would not occur if the molten metal was poured
into water with a depth exceeding 60 cm. Copper has been used at three
temperatures (i.e. 1150oC, 1250oC and 1350oC). More experimental
work remains to be done, but it appears that copper at a temperature of
11 50'C will not produce an explosion if the depth of the water into which it
falls exceeds 60 cm.
18 Long' found for aluminium that not only did there exist a maximum
depth above which explosions did not take place, but also a minimum
depth below which they also did not take place. The final series of tests to
date was to determine whether such a minimum depth existed for copper.
The four experiments numbered 31 to 34 imply that no such minimum
depth exists. Depths of 1 -3 cm, 2 -5 cm, and 5 -1 cm were used in the 30
cm tank. In each case 4-5 kg of copper at a furnace temperature of
1180'C were dropped and each experiment resulted in an explosion.
These explosions were not as violent as those with greater water depths,
but were still potentially dangerous. Gritty debris resulted in all three
together with a small solidified pancake of copper. The tanks were not
damaged but had been moved by the explosion which produced a loud
bang. A small amount of gritty debris was scattered on the floor in each
case. This was blackened by oxide to a greater extent than the debris in
previous experiments. This might have been due to relatively high
temperatures of the debris as it entered the air and steam above the water
surface after its comparatively short passage through the shallow water.
However, on analysis of the debris it was found that the oxide was less
than 3% of the metal weight. It may be that the contrast between these
results with copper and shallow water, and Long's results with aluminium
and shallow water, could be explained in terms of the greater density of
copper. Clearly a given mass of molten copper would submerge more
readily than a similar mass of molten aluminium.
--
donald j haarmann - independently dubious
----------------------------
donald haarmann
<full...@aspi.net> wrote in message news:377050A2...@aspi.net...
>
> BLEVE? (may overlap #6). Boiling Liquid Expanding Vapor Explosion. By
> lowering the pressure, injecting vaporization nuclei, or by careful
> heating you can create a super heated condition in a liquid.
[pruned]
From a patent:
A phenomena of considerable industrial importance in recent years and
one that may have significant military application is so called vapor
explosion, often referred to as thermal explosion or steam explosion. This
phenomena results from the extremely rapid heat transfer from hot liquid
(e.g., molten metal) when introduced into cold liquid (e.g., water).
Sporadic explosions resulting from this phenomena have-been
responsible for loss of life and property in industry for a number of years
and efforts have been made to understand the extreme violence of these
interactions. It is not presently known if these explosions are a result of
liquid entrapment, flash of superheated liquid, collapse of vapor cavities,
metal-water chemical reaction, hydrogen-oxygen reactions, or a
combination of these things. However, resultant effects of these
interactions are drastic, and substantial amounts of energy are released
during such explosions. It would be desirable to provide moderate sized,
high energy explosive devices based on vapor explosions. Such devices
would have to be compact, self -contained, and have a relatively short
initiation to explosion time.
full...@aspi.net
>
> <full...@aspi.net> wrote:
> >[...]
> >BLEVE? (may overlap #6). Boiling Liquid Expanding Vapor Explosion.
>
> I thought BLEVE was Burning Liquid Expanding Vapor Explosion, not Boiling.
I'm pretty sure the original interpretation is Boiling. I first ran
into it during fractional vacuum distillation. You've got this nice
distillation column going with good separation and you get a slight
pressure reduction. Blam, the solution erupts through the column
disrupting everything. In glassware this can be excessively exciting.
> I don't regularly read the firefighter magazines, but I recall seeing some
> discussion of it in the late 80s early 90s timeframe after a few incidents.
> Superheated water isn't technically a BLEVE, it's just superheated liquid
> flash vaporizing, which is unpleasant but not nearly as bad as say,
> superheated propane flash vaporizing while burning and resulting in
> a near-instantaneous combustion of the whole load.
>
> There's another nifty effect which isn't quite in any of the
> categories under discussion... if you have a tank full of
> flammable liquid which floats, and a bit of contaminate water
> at the bottom of the tank, the tank is highly dangerous if the
> top starts on fire. The flammable liquid will get heated in a
> zone moving down the tank, convecting some but generally with
> a hot top zone and a cooler bottom zone, until the hot oil/gas/whatever
> hits the bottom and flash vaporizes the water at the bottom,
> which blows all the oil/gas/whatever out the top at once.
> Major pain for firefighting in oil production and storage
> facilities, because it makes it very dangerous to approach
> tanks on fire.
The term you are using, "flash vaporization", seems to mean the same as
BLEVE. It's a phase change powered by energy in the bulk material.
Because the phase change can be triggered by slight pressure waves, like
triggering the outgassing of carbonated water; and because the phase
change creates more pressure waves; you can get a wave of phase change
that moves throught the material at tke speed of sound. That's an
explosion without confinement.
The potential for this is controlled by the specific heat and heat of
vaproization of the fluid. If the super heated condition moves the
material to the point that the energy difference between the boiling
point and the supher heat temp is larger than the heat of vaporization
all of the fluid can transition to vapor. For water that means an
instant change in volume of 1800x. Ugly.
Hendrik Beijeman
but seemed to be close. And, in materials, it's higher I know, but I usually (myself)
think I have to give a point at wich it isn't a detonating explosive, or so. I mean,
I don't wrap myself into sharp corners finding ways in wich flash can detonate, or
nitroglycerine deflagerate. I strictly say, 0.1mol, normal pressure, and density,
standard methode of ignition, for any compound (or 0.1 m oxidizer in mixtures). And
then, flash deflagerates, so does gunpowder, and all the other millitary explosives
detonate. And, maybe it would be possible if we stack 1000 kg of gunpowder, it
results in a detonation, and so on... I'm talking here about chemical reactions,
involving=>resulting a detonation. Not physical examples.
Allan
>> I thought BLEVE was Burning Liquid Expanding Vapor Explosion, not Boiling.
>
>I'm pretty sure the original interpretation is Boiling.
Me too, because the liquid doesn't burn. It's the vapor that burns. And
if it's confined, pressure builds up .... (we all know the rest)
KaboomMn
. "Detonation may be either High-Order or Low-Order and
it is not deflagrating. The pressure time curve is the same,but the
amplitude against time is lower, both curves are bimodal ( two peaks, one
high and one low, a double wave) Low Explosives deflagrate and there is no
bimodal curve, but a monomial one ( one peak only, a single wave ) "
--
Boomer
Kabo...@Gateway.Net
If you see me running you better catch up
Hendrik Beijeman <beij...@wxs.nl> wrote in message
news:37732E30...@wxs.nl...
donald haarmann
An explosion occurred during a chemical demonstration at the University
of Illinois, Urbana-Champaign, earlier this month. The widely used
demonstration of the thermite reaction-which involves the reaction of iron
oxide and powdered aluminum to form iron and aluminum oxide-was part
of the university's annual Engineering Open House for local high school
and grade school students. There were 200 to 300 people in the
chemistry lecture hall at the time of the explosion. Four teachers and 23
students were taken to the hospital, where they were treated and
released. The injured suffered first- and second-degree burns and minor
cuts. Chemistry professor Steven S. Zumdahl, who was conducting the
demonstration, says it had just been run successfully using sand as a
receptacle for the molten iron. But when the sand was replaced with
water, something went wrong. Jiri Jonas, head of the department of
chemical sciences, says a committee, including university and local safety
experts, has been appointed not only to determine what went wrong with
the thermite demonstration, but also to review all safety issues
surrounding the open house.
March 12, 1990 C&EN23
John
how the reaction would go
comments?
donald haarmann <donald-...@worldnet.att.net> wrote in message
news:7kuo4d$36u$1...@bgtnsc02.worldnet.att.net...