Hi Joe, Bill, Tony and Phil,
Thanks for all the useful comments. I think that heat transfer will be
dominated by convectivity and I do not know how to extract thermal
conductivity from it. All I am trying to do is to see whether
existence of these solid particles have any effect on the thermal
conductivity or may be heat transfer properties of this gas. I am
trying to determine this as well.
I got hold of a CTA system today as someone assured me that it would do
what I need i.e. thermal conductivity but I now realise that it
measures the velocity. I got hold of a book on hot-wire anemometry but
how one would extract thermal conductivity from those equations set, I
have no idea at present as there are so many parameters.
This is actually a pretty complicated problem, and depending on what
the particle is, it could drastically effect thermal conductivity. Do
you absolutely need k, or are you looking for some general measure of
heat transfer ability? Will the overall heat transfer coefficient be
good enough? To keep the particles suspended (how small are they?),
you will have to introduce convection in the form of flow to prevent
them from settling. This introduces coupled fluxes, which can truly
make things nasty if you don't know a lot about your system already.
And you also get into the mess mentioned by the previous poster about
laminar vs. turbulent flow, you'd probably witness a drastic increase
in heat transfer transitioning from laminar to turbulent, which may
allow you to decouple heat convection from conduction? This is why you
*always* run a heat exchanger in turbulent regime - convection
dominates but you also don't want to introduce a series resistance with
a low-conductivity material for the transfer surface walls.
Without thinking about this more unnecessarily, why don't you do a
literature search. This is exactly the sort of thing that fluid
dynamicists spend their entire lives making models for and correlating
back to real measurements. It's a shame to spend so much time
developing a model and then not use it when a real-world problem comes
along (this seems to be what usually happens). Heat transfer
experiments in "fluidized bed reactors" will be directly applicable to
what you're doing, a solid in gas analysis will be fundamentally the
same as solid in liquid if not quite a lot easier (inviscid), just with
different parameters - they're all fluids.
If all you need is a general measure of heat transfer, say comparing
the gas with and without added particles, the overall heat transfer
coefficient can easily be measured by designing a crude heat exchanger
with insulation and thermocouples. It could be measured for a wide
range of flow rates.