Properties of Plastics

Steve

Some help please guys. I’m building a scrubber and am having difficulty in tracking down some technical information on plastics. Specifically I am interested in various plastic’s;

• Thermal Conductivity
• Thermal Capacity
• Thermal Diffusivity
• Reactivity (off gassing into loop)

I'm happy with the various numbers for suitable metals but am failing on the plastics front.

Can anyone help please?

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Duncan Price

Do you have specific plastics in mind? The heat capacity (around 1 J/g/°C) and thermal conductivity (300-400 mW/m2/K) of most polymers is very similar and the thermal diffusivity is related to the other two by the density.

Reactivity (off gassing) is going to depend on what polymer - avoid plasticised materials. Most other stuff is OK though moisture uptake is going to be an issue with regards to dimensional stability.

(Dr) Duncan Price
Insititute of Polymer Technology & Materials Engineering
Loughborough University, UK

EBT

You'll need to register;

http://x5.ides.com/datasheet.aspx?&E=5726

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Steve

Thanks guys, (some green for both of you)

I'm still in the formative stages of material selection and just wanted to ensure that I wasn't assuming that what was popular was necessarily the best choice. I’m designing a large capacity radial for the Meg (4.5kg) and kicking around the topic of materials. A scrubber of this capacity is being considered due to its suitability for long dives (+8 hours) and the old axiom (in some circles) of plastic being best is looking shakey. If the scrubber is designed for a task, namely +8 hour dives, then surely the early energy wastage of heating the scrubber (versus sorb) early on will be off set by the latent heat capacity of the materials the scrubber is made from later on. Having said that, this angle may be a whole heap of toss.

Anodised aluminium anyone?

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plazma

PVC-U
Thermal Conductivity 0.14W/(m*K)
Specific weight 1.38g/cm3

PP-H
Thermal Conductivity 0.22W/(m*K)
Specific weight 0.92g/cm3

PE
Thermal Conductivity about 0.40W/(m*K)
Specific weight about 0.94g/cm3

POM-C
Thermal Conductivity 0.31W/(m*K)
Specific weight 1.41g/cm3

I would go with PVC-U with thick (about 8mm) walls. Good thermal properties and easy glue with Tangit.

-Pasi

Mistral Gagnant

Once time, it's in French, but you have some interresting info about stell, alu, and PLASTICS...

http://www.lesnonferreux.com/

enjoy your surf...and translating...

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Devil Dolby Digital

A Deep Devil Diver

http://www.deepdevildivers.com

Duncan Price

Its a heap of toss. Heat flow in polymers is my day job.

If you are making a radial scrubber you may want to exploit the higher thermal conductivity of aluminium compared to plastic to act as a condensation trap. Which way does the gas flow? - if outside>in then this is not a bad idea. With a radial scrubber the bed is insulated from the walls of the outside of the scrubber by an air gap. I guess its not a short fat radial scrubber like the 'borus.