Conceptual Flashcards
1
Q
Explain the difference between Biot and Nusselt numbers
A
Biot number is the ratio of internal resistance to surface resistance
Nusselt number is the ratio of total heat transfer (cond + conv) to conductive heat transfer across a boundary
2
Q
In a shell and tube heat exchanger, how is the heat flow in the shell related to the heat flow in the tubes? Why?
A
Each q is identical but with opposite signs. This is because heat flows from one into the other
3
Q
If the overall heat transfer coefficient for a fluid in a heat exchanger increased, how would you expect that to change the necessary surface area of interaction between your hotter colder fluids? Why?
A
q = (UA)(deltaT)
A = q/(U)(deltaT)
If U increases, A decreases
