CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

Biot and fourier numbers

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Display Modes
Old   August 2, 2007, 04:12
Default Biot and fourier numbers
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
  Reply With Quote

Old   August 2, 2007, 10:30
Default Re: Biot and fourier numbers
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?
  Reply With Quote

Old   August 2, 2007, 17:00
Default Re: Biot and fourier numbers
Bart Weisser
Posts: n/a

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.
  Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 21:41.