Urgent Help - Heat flux received and View Factors 1

[LossPEngg]

Hi everyone,

I have been given a problem at work where I have been told to evaluate the amount of heat/radiation received by a worker at the bottom of a exchanger. If the exchanger is at a certain temperature then we can evaluate the heat flux emitted by the body using stephen boltzamn law (correct me if I am wrong). From some publications I have managed to get an equation for incident received flux which is I= t x VF x SEP. kW/m2
Where t is the atmospheric transmissivity, VF is the view factor and SEP is the surface emissive power. SEP we can calculate using the boltzman law, t is transmissivty which I think certain values can be assumed but lastly I am having problems calculating the view factor. The typical view factor equation avalilible on wikipedia seems a difficult task if I am to make it an excel version as I would need to evaluate the flux at different distances and locations from the exchanger, furthermore the person could be standing between 2 different bundles emitting heat. Once we evaluate the heat from one bindle, assmuming that the person is standing between the 2, can we just add the flux received by 2 sources? Can someone please advise on the problem?

Thanks

 

[ione]

Maybe you can find useful info in the link below

http://www.ibpsa.org/proceedings/BS2003/BS03_0681_688.pdf

 

[IRstuff]

If the subject is able to receive energy from two sources, then they add.

Seems to me that the wki artical is pretty clear, particularly:

http://en.wikipedia.org/wiki/View_factor#View_factors_of_differential_areas

You can basically take all viewable area and divide into small, differential areas, say ~1 sq. in., and crank the equation for each one of the squares. You could treat the viewable area of the person from each differential area as a flat plate or a group of flat plates. There are probably programs for doing this sort of thing, though.

TTFN

FAQ731-376
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[davefitz]

For 2 dimensional problems , the easiest menas of developing a view factor is the "hottel's crossed string method".

 

[LossPEngg]

Many thanks guys. I have been able to solve the problem by assuming a value which has given me reasonable answers.
I did look at all the links that everyone provided and it was all very useful

Thanks again.

Regards