Fins Flashcards
What is the requirement for executing a 1-D analysis of a thermal fin?
The Biot number normal to the xaxis (transverse direction) must be much less than one.
(mL)^2 is what? when is it useful?
(mL)^2 =( internal resistance in x-dircetion)/(gross external resistance). It is thus a hybrid Biot # and when it is big, (when theta(squiggly=1) approaches 0) we can then neglect tip convection.
When do you need to use a root temperature?
If the base temperature is not given and a fin is made up of the same material as its supporting structure.
If the Biot # hr/k is large, and the fin constant m is small, then what happens to the root temperature and flow of heat into the fin?
the heat transfer into the fin AND the root temperature are both reduced.
Fin efficiency is a measure of what?
(actual heat transferred by fin)/(heat that would be transferred if the entire fin were at T=To) = (tanh(mL)/(mL)
Do we typically want to design to a specified fin efficiency? Why or why not?
No, because as L increases, the fin efficiency decreases, so if we are looking to cool something off with a fin, then this isn’t the most useful parameter.
What is the effectiveness of a fin? Can we find it using fin efficiency?
= (heat flux from wall with the fin)/(heat flux from the wall without the fin)= fin efficiecy* (surface area of fin)/(cross-sectianl area of the fin)
Give six factors effecting the optimization of fin design.
The weight of material added by the fin as a cost factor and mas factor, the possible dependence of H on (T-Tf) & flow velocity past the fin, the incluence of the fin on the heat transfer coefficient h as the fluid moves around it, the geometric configuration of the channel that the fin lies in , the cost complexity of manufacturing fins, the pressure drop introduved by the fins.
What is Fo?
Fourier #= (thermal diffusivity)*t/(L^2)
