Talk:Biot number

Bond Number

what is bond number

• see Bond number

Biot number vs Nusselt number

Could someone explain what the difference between the Biot number and the Nusselt number is? They have very similar expressions.

I'm not an expert but obvious difference is: Biot number uses thermal conductivity of the body k_b (not fluid), whereas Nusselt number uses thermal conductivity of the fluid k_f. - Marsian / talk 15:52, 1 January 2006 (UTC)

Nusselt number correlations are useful for determining the convective heat transfer coefficient, h. In a steady-state problem this can then be used to find the heat flux from Newton's law of cooling, Q=hAdT. The Biot number, as the article states, is helpful for determining the applicability of certain transient heat transfer models.

Biot number characterizes the relative importance of heat transfer through a body (k_b) versus the heat transfer out of the body and into the coolant (h, the Heat transfer coefficient, time the body's surface-to-volume ratio). This could be important either in transient or steady-state heat transfer problems. For example, how steep is the temperature gradient from the center to the outside of the sample? Proportional to Bi.

Now, once the heat has been transfered to the coolant, the Nusselt number will tell you the relative importance of conductive versus convective heat transfer through the coolant (away from the sample). For example, how steep is the temperature gradient in the coolant as you move away from the sample? Proportional to Nu.

Analogy for Biot number for heat flux?

Is there an analogy to the Biot number for a situation with a heat flux boundary condition? In this case h goes to infinity (correct?). However, if the heat flux is very small compared to the conductivity a lumped capacity analysis ought to work. So is there something like the biot number to check this? — Preceding unsigned comment added by Aritglanor (talk • contribs) 12:38, 2 March 2012 (UTC)