# Question regarding whether flow simulation is the best tool for a problem

Question asked by Tyler Chapman on Jul 11, 2016

Hello all,

I apologize in advance for the somewhat long-winded question.

I have a small component that needs to be kept within a specific temperature range in order to operate correctly. This component is surrounded by insulation and an electronic heater to bring the component to operational temperature over a range of possible environmental temperatures. This assembly in situated within an enclosure that will be incorporated into a larger aerospace product and flown at significant speed. Due to the forced convective cooling on the larger product during flight, the external temperature of the enclosure that holds the component assembly will be held at very close to ambient air temperature. Therefore, the component in question will be heated via conduction by the electronic heater and cooled via convection by the still air inside its enclosure (again, whose outer surface will be held close to ambient temperature, which is well below the desired operating temperature of the component). Thus when conducting thermal analysis on the capabilities of this heater, I have simplified the analysis to just the component, heater, and insulation, running a convectional thermal analysis in the Simulations package with only two loads: one for the heater and one for the convective cooling of the still air inside the enclosure. For the convective cooling, I have a constant temperature equal to that of the bulk ambient air during flight, and a small convection coefficient to represent the natural convection inside the small enclosure. It is here where I am having trouble. Since I am defining static parameters for the convective phenomenon, the value of the convective coefficient greatly affects the results of the simulation. Furthermore, I am really out in the woods as far as what the actual value of the coefficient should be (currently I am using approx. 5 w/ m^2.K, which I understand may be a bit high, although I have no intuition for the number). In order to address these issues, I am considering running a thermal analysis using the Flow Simulation package. If my goal is to accurately model the above situation with a focus on determining the capabilities of the heater versus natural convective cooling in a small space, is the Flow Simulation thermal analysis the way to go? Or am I approaching the problem in the wrong way (in other words, is it possible to produce accurate results using the Flow Simulation software; I am very unfamiliar with the capabilities/limitations of the software). Secondarily, for those of you that are experienced with similar tasks, what are some reasonable convection coefficients for such a case?

Any and all input is greatly appreciated.

Thank you,

Tyler