Aluminum Composite Panel
Jabir Jamal
I am learning about conduction features in FDS for a project and having some difficulty in modelling an aluminium sandwich panel (ACP).
Rough details of the panel are given in the attached figure.
Initially, I used the line of codes given section 8.3.5. However, I am interested in specifying an ignition temperature for Polyurethane material provided between the aluminium panels. Can this be achieved using FDS?
(I read a couple of comments in forums that conduction between obstruction is not achieved using FDS. Does that mean this arrangement cannot be modelled using FDS)
Jabir Jamal
o...@aquacoustics.biz
FDS will model the thermal properties of Aluminium Composite Panel (ACP) quite nicely using layered obstructions, at least for modest temperature increases.
However modelling thermal behaviour, ignition and flame spread in ACP will be challenging and should be considered research. You might refer to ‘Flammability testing of materials used in construction, transport and mining’, Apte, V.B (Ed.), CRC Press, 2006, and particularly those sections that discuss composite panel materials. There are many aspects to this complexity.
The large scale fire performance of ACP is highly dependant of the cladding system.
Extrapolation from bench scale tests to full scale fire performance is not well developed for these materials.
There are a large number of polyurethanes that vary in chemical composition, MW, density, additives, … Each has unique and quite variable thermophysical properties.
In practise the ignition of ACP involves macro effects such as deflections, delamination, exfoliation, melting and flow of some core materials (polyethylene in particular), thermal decomposition, physical orientation and, in the case of aluminium cladding, eventual melting of the outer layer.
This becomes even more complex as ACP often incorporates multiple aesthetic and protective films layers on the exterior surface (UV, oxidation protection, tinting etc) which significantly alter the radiative and convective heat transfer properties of the composite as a function of temperature.
You might try modelling ACP ignition and flame spread by ‘inventing’ an equivalent material with conservative properties of interest. As a contrived example:
a HRRPUA equivalent to the combustible content.
thermal properties of the composite until around 200°C at which point PE can be considered molten and PUR will have softened with a reduction in adhesion. Above 200°C the panel assumes the thermal properties of the core (delamination and/or exfoliation assumed to have occurred).
ignition as either piloted above the flash point (say 310 to 340°C) or otherwise at auto-ignition temperature (say 380 to 415°C ).
In the case of a severe thermal insult (for example flame venting from an unprotected opening in a compartment) you might simplify the model by assuming that the well insulated and very thin exposed aluminium heats to melting (say 660°C) at which point the ACP burns as exposed combustible core.
Any such model would need to be validated for your fire scenario by comparison with appropriate fire test data and agreed by stakeholders as appropriate for the intended purpose.
Tim O'Brien
I'd need to see your model before I can comment on what is going on.
Be aware of the 1D conduction limitation of FDS and the importance of having obstructions aligned with the computational domain in certain circumstances. This is explained in the FDS Users Manual.
t.
From: fds...@googlegroups.com [mailto:fds...@googlegroups.com] On Behalf Of Jabir Jamal
Sent: Tuesday, 19 June 2018 2:31 p.m.
To: FDS and Smokeview Discussions
Subject: [fds-smv] Re: Aluminum Composite Panel
Thank you for your response.
I have a very basic question regarding the first sentence in your response - When I used three obstructions forming a panel with SURF properties on 6 faces, it does not appear to conduct the heat through the panel. Should I be using a single OBST with a SURF line as provided in Section 8.3.5 (Page 75) and provide ignition properties to this SURF?
Thanks!
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Tim O'Brien
Oops, I may have missed the crux of your question. See Section 8.3 of the FDS Users Manual for a description of objects using layered materials.
t.
From: fds...@googlegroups.com [mailto:fds...@googlegroups.com] On Behalf Of Jabir Jamal
Sent: Tuesday, 19 June 2018 2:31 p.m.
To: FDS and Smokeview Discussions
Subject: [fds-smv] Re: Aluminum Composite Panel
Thank you for your response.
I have a very basic question regarding the first sentence in your response - When I used three obstructions forming a panel with SURF properties on 6 faces, it does not appear to conduct the heat through the panel. Should I be using a single OBST with a SURF line as provided in Section 8.3.5 (Page 75) and provide ignition properties to this SURF?
Thanks!
On Monday, June 18, 2018 at 7:43:31 PM UTC+10, o...@aquacoustics.biz wrote:
--
Tim O'Brien
Okay, I have made some time to look at your model. You are using a layered obstruction with appropriate mesh alignment. That's good.
In the first instance you have a syntax error on line 57. EXPOSED should be 'EXPOSED' - yes those apostrophises are important.
Your model conducts heat just fine (in fact far too well). Look at the Z temperature slice in SmokeView after a few hundred seconds of simulation time.
The 'INSIDE WALL TEMPERATURE' IOR and depth are sensible for the defined ACP obstruction, but note that using negative offsets from the origin is a common source of error for IOR.
If you look at your internal obstruction temperatures they are all the same, but we expect a temperature gradient through the composite layers. This is a direct consequence of using inappropriate material properties. PE is not an ultra-light super conductor, while aluminium is a relatively good heat conductor.
Try some realistic values from a reputable reference (and comment your reference in the FDS source code). For HDPE a specific heat of 2.4 kJ/(kg K), density of 925 kg/m3, and a conductivity of 0.5 W/(m K) are in the ball park, and are at least representative of polymers found on Earth.
We aren't burning the aluminium or PE at 200°C so drop the heat of combustion for now. In fact in real ACP fires most of the aluminium either falls from the element of construction, melts, or oxidises in slow time. Slow time oxidization such as occurs in the rusting of steel isn't flaming combustion. Bulk aluminium shouldn't burn at ordinary combustible fire temperatures (say less than 1,000°C). Its ignition temperature is greater that that of steel! When aluminium does burn it will flare brilliant white (similar to magnesium).
If you use realistic material properties then suddenly your internal temperatures will have a sensible gradient.
As a final comment, your device labels should correspond with the actual depth to assist with reviewing the device.cvs output.
t.
From: fds...@googlegroups.com [mailto:fds...@googlegroups.com] On Behalf Of Jabir Jamal
Sent: Tuesday, 19 June 2018 2:31 p.m.
To: FDS and Smokeview Discussions
Subject: [fds-smv] Re: Aluminum Composite Panel
Thank you for your response.
I have a very basic question regarding the first sentence in your response - When I used three obstructions forming a panel with SURF properties on 6 faces, it does not appear to conduct the heat through the panel. Should I be using a single OBST with a SURF line as provided in Section 8.3.5 (Page 75) and provide ignition properties to this SURF?
Thanks!
On Monday, June 18, 2018 at 7:43:31 PM UTC+10, o...@aquacoustics.biz wrote:
--
Jabir Jamal
Tim O'Brien
You need to study Section 8.3.5 of the FDS Users Manual, and in particular the last two paragraphs on page 75. Yes, you can specify combustion of inner layers, but note the need to establish permeability of the non-combustible outer layer.
In reality, the combustible core cannot burn until the fuel vapour and/or pyrolysis products are exposed to air, either by melting and flowing from the core, or by deflection, delamination, exfoliation or melting of the exposed aluminium face. A classic example of this is what occurs when wood is destructively distilled in an inert atmosphere. While it decomposes it does not burn. Results from cone calorimeter tests (ISO 5660 Part 1 Reaction to Fire) of ACP with the aluminium in place show that ignition does not occur, even with severe thermal insult over a protracted time. Note that this is a horizontal specimen bench scale test. The aluminium cannot fall from the specimen and it will not show representative deflections because it is not mechanically secured.
While PIR softens it doesn't actually melt and flow. So for modelling purposes you might do better to assume that between say 200 and 660°C the aluminium is no longer bound to the surface, the core is exposed to the incident heat from the fire source and any combustion occurring below. In full scale vertical fire tests of PE cored ACP cladding systems there is virtually no aluminium left on the exposed face of the specimen. Real fires indicate similar ACP performance.
It is worth while thinking again about what you are trying to do and the limitations of FDS. In my opinion you would do better to develop a model with comparable macro ignition and combustion characteristics as opposed to actually trying to model the dynamic ignition and combustion behaviour of ACP. I reiterate that modelling ignition, combustion and fire spread of composite materials are in the realm of research.
t.
T.G. O'Brien, PG Cert. Eng. (Fire), BE(Hons.), MSFPE, MNFPA, MIPENZ, CMEngNZ, Int. PE
Consulting Fire Engineer
FireNZE (a trading division of Aquacoustics Limited)
http://www.fire.aquacoustics.biz
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From: fds...@googlegroups.com [mailto:fds...@googlegroups.com] On Behalf Of Jabir Jamal
Sent: Monday, 25 June 2018 11:27 a.m.
To: FDS and Smokeview Discussions
Subject: Re: [fds-smv] Re: Aluminum Composite Panel
Thanks for all the replies.
I have been making some changes in the model and I came across an issue with LAYER_DIVIDE.
For a material with MATL_ID(1:3,1)='A','B','A', How do I only specify ignition properties to MATL_ID = B?
Thanks
On Tuesday, June 19, 2018 at 10:32:30 PM UTC+10, Tim O'Brien wrote:
To view this discussion on the web visit https://groups.google.com/d/msgid/fds-smv/a0052e1e-22e6-455d-af2b-8400013b012d%40googlegroups.com.