Message Board Thread - "Emissivity Values for Exploding or Burning Ordnance "

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Emissivity Values for Exploding or Burning Ordnance DPG Jim Yale 1/8/2004
I have an unusual and somewhat complicated task to measure surface temperatures of exploding and/or burning ordnance items that are located within a shrapnel containment field. I have already worked out the design, approach and logistics I will use to record these data for further post analysis using the FLIR 2001 Researcher software. I will be using an SC500 camera calibrated out to the extended temp range 350-1500 C. Were I am stuck is deciding on a solid technique to measure the emissivity of these exploding ordnance flashes and long burns from the test items. I used both aluminum foil and black electrical tape targets, having a known emissivity, in the target area to measure the background Tamb and to determine emissivity of objects within the field of view of the camera, the same area near the exploding ordnance. I need some help in determining the correct emissivity for the exploding and/or burning ordnance. I do have a list of materials that make up these ordnance to include the burning materials inside the ordnance. Any help from any of my colleques out there doing similar high temperature work to calculate or measure unknown emissivity from specific or unknown materials would be helpful. appreciated.
 
Emmisity check of exploding ordnance Marv 1/14/2004
I suggest that you take the exploding particles from an ordnance that is exploded and do an Emissivity test on them throughout the expected temperature range. then feed the emissivity values into the camera to obtain an accurate temperature profile of the particles. The reason for doing a broad range of temperatures is that the emissivity may change with the higher temperatures.
 
Flame and Ignition Source Analysis Equine Bandit 1/14/2004
Due to the fact that the flames are much hotter than the range of the camera, I would suggest that you investigate the materials of combustion and determine the flah temperatures for each component.

If this is not available, then placing a flat black surface next to the ignition source (make sure it is blocking the flash) and analyzing the surface of the material. This is all rough due to the fact that the ignition is usually short and the heat transfer to the surface and the dissipation rate of the matewrial may grosely minimize the actual flash temperature.
 
PdM Analyst madmax 1/14/2004
Check out this link. Hope it helps. An instrument developed for your problem

http://www.quantumlogic.com/
 
Emissivity Values for Exploding or Burning Ordnance O'Neill 1/14/2004
The task you have is one that would require you to make your measurements during the actual explosion. The plasma generated will have a varying emissivity depending on the temperature of the explosive mixture of hot gases, shrapnel, dust and dirt debris in the cloud you are trying to measure. If I have this correct, I suggest the following method.

Know target material and explosive yield:

Within the target area, at various radii away from the epicenter of the blast, mount metal strips with different melting points and heat capacities. During the blast development, record your hi-speed IR images and digital images. After the test, collect the remaining partially melted foils to determine the level of heat energy at each radius from the blast center. From these the temperature and heat transfer rates may be calculated. Once this is known, you may work backward to obtain the correct temperatures on your IR images by adjusting the emissivity to get the measured temperatures. I suspect you might get a distribution of emissivities from blast initiation to blast exhaust.

You may have to perform this a number of times to get the measurements needed to determine the heat energy by using the IR imager and then it may only apply to a specific type of explosive in a particular configuration. It will depend on how accurate your measurement must be, i.e., if you must be able to tell by the heat signature that you have an FA explosive vs. TNT, more data will be needed during your experiments.

Hope this helps.

O'Neill
 
Emissivity values for exploding ordinance DJ 1/14/2004
Could you elaborate some on the procedure you used for determining emissivity of the objects in the explosion area using the black tape method. How did you create a difference in temperature between your black tape targets and the background? Do all of the exploding particles burn or char? In any case, you will need to measure particles at different temperatures due to the fact that emissivity values change with temperature.
 
Explosives uri 1/14/2004
Hi Yale,
I would definitely try to implement narrow band filters, but will require knowledge regarding the chemistry and tempertures of the materials in question.
Also, IR specroscopy is used in poison gas detection applications.
Using this instrument might help you determine the materials and elements inthe flame.
this can help you narrow the selection of gases to the one/s that the emissivity may be readily avalable at high or can be calculted?
thanks
uri
 
Emissivity Values for Exploding or Burning Ordnance Jim T. 1/14/2004
I am not familiar with the thermal-kinetic behaviour of explosions. I imagine it is somewhat similar to that of simple combustion, except on a very short time scale. The main problem with determining emissivities when combustion is involved is the fact that the IR emission is from a gas, not a solid. Gases do not behave anything like solids in that they emit in specific spectral bands instead of a continuous curve (ie. grey body). The particular bands of emission are well defined by the molecular make-up of the gas. However, each band changes in width (spectral) and magnitude with temperature.

So to answer your question you need to know what that spectral emittance of your explosion is to be able to back out the temperature from the IR imagery. Things will be further complicated by the fact that the atmosphere will attenuate the explosion's emission spectrally (due to absorption by the different molecules in the air), and the camera's spectral response must also be accounted for. With all this in mind, I think I like that other fellow's idea of measuring the impact of the explosion's heat on something else within the blast area.
 
Emissivity of Exhaust Gases tjp 1/14/2004
The Handbook of Military Infrared Technology has a graph that shows the emissivity of exhaust stream from a solid propellant rocket.
Particle size emissivity
5 micron 0.6
10 micron 0.87
15 micron 0.9
20 micron 0.95
25 micron 0.98
30 micron and above 1.

Another source (copied 30 years ago so do not have the reference) indicates the emissivity of engine exhaust gases (600 - 700 C) as unity. We did work with ordnance and the residual left on the test piece generally had a emissivity of unity because of the rough surface.
 
May be good... Dr.Fil 1/15/2004
Hi, some time we have same problem and one of solution that we use, is next: we place near flame under study cold metal mirror and than obtain two image of target in same time. After that we place two different interferrometric IR filters and obtain by one IR camera in one frame two same images in different spectral range. After that we can "corectly" calculate temperature of flame - so called temperature of spectral correlation. Spectral range of IR filters can be select from typical information of IR spectrum of gases (product of burning target)- CO or NOx or other (you also can study chemical reaction and gas distribution in space or temperature of different gases in flame). We use some time more than two filters, and good idea is use additional high speed optical (VIS or UV) channel for sinhronization and additional information...
 
About the determination of emmisivities of high temperature materials Rafael Royo 1/15/2004
I think it could be more convenient to try to apply an indirect methodology, with previous measurements on samples of material at high temperature controled with pirometers or another type of thermometers for high temperatures. If temperatures are so high that it could be impossible, you could even try to apply energy balances inside isolated calorimeters. If it is possible to measure temperature and emission from the surface, you could obtain an accurated value of emissivity, but the key is by the use of these controled experiments.
 
More information pgargano 1/15/2004
Jim, I'd like to get more information on the materials or matter that you are trying to measure. I would need the object shape, surface appearance and more information of exactly what you are trying to measure. Your description, although decriptive, isn't real clear to me what you are actually trying to measure. Is it the explosion itself is it the shrapnel, if so, is it in motion? What type of software are you using? There are a lot of questions that are unanswered. I may be able to help you out if the right information is given. You could Email me at garganopm@corning.com. Hope to hear from you soon.
 
Emissivity Values for Exploding or Burning Ordnance Junpei 1/15/2004
If I was given this assignment, I would take following approach.
(1) Explosion is a transient event. I would use a high speed
camera, such as S60, or SCs (SW camera might work also). Two cameras might be needed in order to record the full temperature range, from room temp to 350C and then from 350C to 1,500C. Depending on the types of explosive, temperature could be higher than 2,000C for some materials.
(2) As a first trial, I will use the adiabatic combustion to
calculate gaseous chemical composition after explosion (assume you know the chemical formula of the explosive). Based the concentration of CO2,NO2, and H2O, and assume there is dust (carbon soot) and an estimated optical thickness (the radius of blast); you should be able to calculate the gas mixture emissivity.
(3) The calculated emissivity at a certain temperature could be
verified by the thermocouple measurement of a controlled explosion. This will give you a semi-empirical correlation of the gaseous emissivity verse temperature. You can use this correlation to process the IR images with FLIR's research software.
(4) If there was metal debris involved in the experiment, the
thermal signature could be dominated by the solid temperature; then the life could be a little bit easier.
I am curios about the purpose of your application: is to determine the gas emissivity or to measure the temperature profile?
Junpei Zhou
Galaton International Inc.
Phone: (815)608-0741
email: galaton@insightbb.com
 
Emissivity for exploding or burning ordnance. Josh 1/16/2004
Both topics are chemical combustion related. The thermal image camera captures is the emission energy given out from the combusting chemicals, not from the material being burned or exploded. Since the burning and exploding are extreme chemical reaction, which gives out energy mainly through radiation, so I guess the emissivity parameter should be very high if not one. If the measuring target is the ordnance items, we have to check if the burning ordnance items are covered around by the burning chemicals or not. If they are covered, the thermal image doesn’t reflect their thermal status. If not, we can discuss about their surface emissivities. If something is in the between, most probably, it is very hard to guess. Since the emissivity parameter is also temperature dependant, it is safe to use thermo-couples to detect the real temperature and obtain the surface emissivity parameter from there. After gaining more experimental data, we will have a better guess what the thermal image can give us.

So, the question here leads to, is it a controllable experiment? Can we install and place the thermo-couples at location where we are interested in? If the answers are positive, we can do a lot to reach the goal we want. However, one more point we shouldn’t forget, usually at the exploding, burning ordnance and combusting engine the temperature can easily reach over 1500ÂșC that is your current camera limit. So, we can only analyze where the temperature sits in the range.

Another thinking is, can we measure the temperature of ordnance items immediately after explosion or burning? From there, we can have a good indirectly estimation of the temperature as it is burning, if the burning is very short. At the explosion case, I think we can because the explosion is so short. Of course, it is also depends on what the time interval we are looking for. The measurement methods for the instant temperature during 0.01 second and the instant temperature during 1 second are huge different.

Hope this penny thinking helps.
 
Emissivity measurements with laser Kim H.A. 1/19/2004
Hi Jim

Have you considered measuring emissivity with laser. Laser measurements are extremely quick, fraction of a second, and the reliability seems to be very good. I dont know the details of your application but it may be worth to check it out.
 
Re:Emissivity Values for Exploding or Burning Ordnance DPG Jim Yale 1/20/2004
To All

I have been out of the loop as I have been working overseas on specific projects. I responded to the ITC questions asked off the web page in response to my original ordance question this morning or at least I thought I did as I have not seen it posted yet on the web.

I used a emissivity table I found in a reference from "Handbook on Military Infrared Technology". We are following the particle size emission measurements to determine an emissivity or start point. More work needs to be done in using specific techniques for these measurements. As Piotr Pregowski has pointed out the measurements of metallic surface of ordnance versus second phase ie. mixture of gases, aerosols and solid parts after explosion is our challenge. Primarily we are after the temperatures after a homogeneous mixture state. This alone is difficult to measure but we are making some use of the data that has been presented. I plan to post a response on the web again this morning.

Thanks, to all who responded to our question on "Emissivity values for exploding ordance". Due to the nature of the materials used in the ordance, I can not discuss the project but I can tell you that the emissions of the particles generated from the explosions are between 10-30 micron and these are unity in nature. We are pursuing the particle emissivity values to determine our start points.

I do apologize for not responding sooner.

Thanks for all of your help

DPG Jim Yale

 
Re:Emissivity Values for Exploding or Burning Ordnance neonleon50 1/20/2004
Try using a camera cacoon and get your background temperature off of your crinkled foil while flashes occur. Take your average as your background temp. Get your ambient temperature off of cardboard close to the explosion. Put some black tape on a pole/stand in frot of the explosions. After three explosions in a row, measure the temp Tt of the tape. Remove the tape, explode the same material and measure the temp of the explosion Te. Vary Temp(e)Te -> Tt and the camera will show the approximate emissivity of the explosion.
 
Re:Emissivity Values for Exploding or Burning Ordnance DPG Jim Yale 1/20/2004
To NeonLeon50

Your idea works great! Tried this technique and we have some useful data. Thanks for your help.

"NeonLeon50 technique"

Try using a camera cacoon and get your background temperature off of your crinkled foil while flashes occur. Take your average as your background temp. Get your ambient temperature off of cardboard close to the explosion. Put some black tape on a pole/stand in frot of the explosions. After three explosions in a row, measure the temp Tt of the tape. Remove the tape, explode the same material and measure the temp of the explosion Te. Vary Temp(e)Te -> Tt and the camera will show the approximate emissivity of the explosion.

Thanks Again for your help

DPG Jim Yale
jyale@dpg.army.mil
435-831-5060
 
Re:Emissivity Values for Exploding or Burning Ordnance Colin at UKTA 1/29/2004
I know somebody who has done a considerable amount of research on explosions using infrared imaging. There was a brief report of some of his work in UKTA newsletter No.11, November 2000, http://www.ukta.org/newslt11.htm

You can contact him Stuart Hawksworth, Health and Safety Laboratory Harpur Hill, Buxton, Derbyshire, SK17 9JN UK
stuart.hawksworth@hsl.gov.uk
www.hsl.gov.uk

 


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