I am working on thermal analysis of a model consisting of 14 parts (including some heat generation components) in its assembly which is exposed to ambient conditions and solar radiation. So it will be having all modes of heat transfer. I want to find out Richardson number to see whether natural convection is significant compared to forced convection or not.
For a primitive geometry like cylinder we can decide the characteristic length easily by examining the flow pattern whether its happening along axial or radial direction. For an assembly like this with inclination towards the flow, how to find out the characteristic length to use in analytical predictions....?
Thanks in advance.
The answer is that any lenght could be used to define a Re number value. But the key is that if you want to characterize the problem by means of non-dimensional numbers you have to choice the characteristic length entering in the flow. For example the lenght of the device producing heat flux.
Could you show the sketch of the geometry of your problem and the BCs?
I agree with Ahmad... like the hydraulic diameter (flow area/wetted perimeter)
thank you for the replies Ahmad K. Sleiti, Filippo Maria Denaro and Dudley J Benton
Filippo Maria Denaro this is a PCB kind of model with internal heat generated inside and will be conducted to outer bodies. I thought of taking the inclined length of the model shown in pics as the air flow happens over the will . You said " I have to choice the characteristic length entering in the flow", do u mean the same ....?
can you please elaborate it?
for BC, iam using velocity inlet with atmospheric conditions with flow of 1.5 m/s, outflow for outlet and rest of the domain sides as walls with free slip condition.
its completely an external flow and there is infiltration of air into the model.
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