# Biot and fourier numbers

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 August 2, 2007, 04:12 Biot and fourier numbers #1 selim Guest   Posts: n/a Hi, I have a conjugate heat transfer problem in a oscillating laminar flow.I know the material properites and wonder how can I compute Biot and Fourier numbers? Fluid properties are temprature dependent? How can I obtain heat transfer coeffeienct? and what will be the time for the Fourier number calculation? Thanks, Selim

 August 2, 2007, 10:30 Re: Biot and fourier numbers #2 blaca Guest   Posts: n/a The Biot number is basically a ratio of thermal conductivities and can be obtained by ((Surface Temperature of metal not exposed to fluid - Surface Temperature of Metal exposed to fluid)/(Surface Temperature of Metal exposed to fluid - Temperature of fluid)) i.e. if Biot is a lot less than 1 then the resistance to thermal conduction within the solid is much less than that of the fluid. As far as Fourier goes, what time are you interested in?

 August 2, 2007, 17:00 Re: Biot and fourier numbers #3 Bart Weisser Guest   Posts: n/a Selim: The definitions are ... Bi = (h*l)/k (l is the characteristic length scale, e.g., thickness of your solid plate) Fo = (alpha*t)/l^2 (where l and t are the corresponding length and time scales) Since your problem is oscillatory, you will get different ranges of Biot and Fourier numbers depending on the frequency of your oscillation. I would use the period of oscillation as your time scale. I assume that you'd be using the Biot number to justify lumped capacitance modelling of your solid. Given the oscillatory nature of your problem, I am also uncertain whether the magnitude of this number alone would be an accurate representation in the steady state case. (For one, I think at higher frequency, heat conduction will dominate). I think, a more instructive approach would be to write out your governing equation of the plate, and approximate h as a function of the flow velocity (which is oscillatory). Then normalize your equation to obtain a reasonable set of dimensionless parameters, which you can use for your analysis.

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