What is the optimum time interval after each increment in heat flux? Should we wait till steady state for taking readings?
Is time constant concept applicable on these type of problems?
It depends on exactly what you want to determinate and which accuracy you want to reach. Every system has its own time for reaching steady state when there is a heat flow variation, but also has its own fluctuations due to their construction and inevitable external factors.
You can estimate statistically fluctuations related to your system taking data without heat flux increment. So, when you begin to take data with heat flux increments, you can determinate the time when fluctuations reduce to those only due to your system construction and inevitable fluctuations. Hope this will help you
Criterion of thermal equilibrium is the dimensionless Fourier number Fo = thermal diffusivity x time / squared thickness >>1, or at least >1
So, the minimum time to reach thermal equilibrium can be estimated as squared thickness divided by thermal diffusivity.
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