Re: Natural Convection in a Vertical Column

Russ wrote:
> 
> I am currently analyzing a problem involving a long vertical column
> with a relatively small conduit along the length column containing a
> group of power cables. There is a significant amount of heat
> generation in the cable due to a large current. I'm primarily
> interested in the temperature of the conductors and surrounding
> insulation.
> 
> It is fairly straightforward to take a control volume and perform a
> simple conservation of energy calculation to obtain component
> temperatures. This assumes that the temperature of the surrounding air
> is determined exclusively by that of the components.
> 
> In reality, since there is heat generation along the entire cable,
> natural convection will carry the heat upward and result in a higher
> air temperature at the top of the column. My problem is to quantify
> what "higher" is. I can do a parametric study to examine the component
> temperatures as the surrounding air temperature increases but I need
> some qualitative means of determining where we're really at along this
> parametric curve. The simplified analysis yields temperatures that are
> close to the specified limit for the insulation, even a modest
> increase in temperature could potentially push the insulation over the
> limit.
> 
> I've been considering a CFD analysis of the entire system but I have
> some concerns about the viability of CFD for natural convection
> modeling.  Also, CFD modeling, even for this relatively simple
> geometry may be a massive undertaking. I have done some work in CFD
> for forced flow without any temperature considerations but I'm afraid
> that introducing this additional level of complexity will make CFD
> unreasonable for this application. Any thoughts on that?
> 
> I'm looking for any suggestions or reference information that you may
> have. Although CFD is an option I'm considering I'd be interested in
> any potential analytical approach.

Isn't it slightly worse or at least different than that real world?  A
lot of the pullable cable I've seen has a marbled surface to lessen
friction during pulling.  Pullable cable is often dipped in goop to
lubricate its passage.  Pulled cable is often tortuous not nicely
linear in packing.  It's a pisser.

--
Uncle Al
http://www.mazepath.com/uncleal/eotvos.htm
 (Do something naughty to physics)