[Gasification] Fw: Biomass heated ethanol plants

[Peter Singfield]

Hey Mike -- great urls you sent!! Thanks!!

Certainly in real time there is a point where to much insulation is a
throw-away.

Now -- lets look at this from another "view"

Copper condensers -- tubes.

The formulas you mention tell us the thicker the walls the more heat loss.

and make a very reasonable math model to support that.

In real time -- in condensers -- the thinner the tube wall -- the better
that condenser works.

That is all bout heat flow -- how many BTU's can be passed in a given time
period.

They have a fine finned tube example -- and prove that once the fins get to
long -- the cooling effect stops working.

Yet fins are simply wall thickens extensions

Mind you -- copper is a conductor -- not an insulator.

They give a fine example of a thermos bottle -- silvered glass -- vacuum.

They can also say that there will come a point that if the vacuum chamber
is to large diameter that even this style insulation effect reverses.

Bottom line -- it all depends on the heat transfer rates -- conductivity --
and the Delta T factors -- and the heat conductivity of the central
material -- and the heat conductivity of the external medium.

Now why condenser tubes work best when thinnest??

By the rules established for insulation -- the condensing effect -- the
moving of heat out -- the thicker the condenser tube wall -- the more heat
can be passed through -- which is the same as lost -- no??

Explain why finned tubes reach a "limit" --when according to the first
example -- the thicker they are -- the more distance from the central heat
-- the more heat "loss" possible from the core to outer surface??

There might be more to this problem than meets the slide-rule??

Refs:

http://ocw.mit.edu/NR/rdonlyres/Aeronautics-and-Astronautics/16-050Thermal-E
nergyFall2002/C923FE1C-0C8B-4BAF-9C8E-E3581C9CC560/0/10_part3.pdf




Peter




At 05:31 AM 8/15/2006 -0700, Michael Redler wrote:
>
>Look at the graph at:
>
http://www.eng.fsu.edu/~shih/eml3016/lecture-notes/thermal%20bubble%20jet/sl
d011.htm
>  
>A picture speaks a thousand words.
>
>At the far right, it actually shows better conduction with "lots of"
insulation than with none at all.
>   
>  Mike
>
>Mark Ludlow <mark at ludlow.com> wrote:
>  The issue is that, plus, depending on the heat transmitivity of the
>insulation, at some point the losses from convection and radiation can
>actually be increased. A pipe insulated with poor insulation has increased
>area from which to radiate energy. As the diameter is increased with
>insulation, the Grashof Number increases (to D^3; D is a characteristic
>diameter) and convective heat transfer also increases.
>
>A poor insulation with a low resistance to conduction will actually increase
>heat loss because it has a larger characteristic diameter and more surface
>from which to radiate energy. Past the critical thickness this is not an
>issue; economics is, however.
>
>Mark 
>
>-----Original Message-----
>From: gasification-bounces at listserv.repp.org
>[mailto:gasification-bounces at listserv.repp.org] On Behalf Of Ken Basterfield
>Sent: Sunday, August 13, 2006 1:52 PM
>To: 'Peter Singfield'; gasification at listserv.repp.org
>Subject: Re: [Gasification] Fw: Biomass heated ethanol plants
>
>
>Hello Mike & Peter,
>Ok,
>is it simply that the cost of extra layers of insulation can never be
>recovered at such lowering heat losses?
>ken
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