# FLOW SIMULATION INTERPRETATION OF DIFFERENT HEAT RATES OR FLUXES

Question asked by MAXIM FRAYER on Nov 10, 2014
Latest reply on Nov 21, 2014 by Jared Conway

My questions are from 2 streams.  In the first stage, I am running a study with all the modes of heat transfer turned on (radiative surface BC + natural convection, including gravity, etc.) and let's say there is one heat source (net Watts, uniform distribution) applied to an 'internal' component's surface, where there is only conduction.  I then apply a an equation goal, EG, to achieve the heat rate as surface goal SG heat flux * SG area.  Furthermore, the EG is exported onto the goal parameter (i.e., plot) list.   I expect this EG to match the input heat source at conclusion.  Upon running the solver, the initial value of the EG is exactly matching the input value, but at conclusion there is an error of 5-10%:

Q1. Is this normal performance for integral parameter estimates that coincide, exactly, with the input BC?

Now in the post-processing or Results interpretation mode, what is meant by the following available surface parameters (I include my interpretation for a point of agreement/disagreement)?

Q2.  surface parameter Heat transfer rate.  If I select a complete component or body, then should this = 0 net for steady state analysis?  I have a discrepancy error (referred to the input BC value) of 10-20%

Q3. Net versus leaving radiation rate, there appears to be an error in net.  In the model setup, this is supposed to be, effectively, an n=2 gray body system, where the extent of the computational domain is the large area body and the solid(s) of interest are the small area body.  I expect, therefore, net radiation rate = leaving rate?   I am seeing a large error then

Q4.  I see that there is a heat transfer coefficient but no actual convection heat rate or flux.  The problem with heat transfer or thin-film convection (apparently?) coefficient is I cannot, properly, account for, its distribution compared to the temperature (temperature potential with respect to the fluid at infinity) distribution.  In other words, I can only can get a rough estimate if I use the product of the average temperature potential and the average heat transfer coefficient!  Is there an actual convection heat rate or flux surface parameter?  I realize, with enough patience, if I select key faces only and not the whole component, which is what I rather do and have used as the implied work flow, then I may use the surface heat flux - net radiation flux to get a the convective heat flux.

Thanks for your consideration of the above questions.