Lecture 10 : Heat exchange II

Question 1

What are the 2 different equations to calculate heat transfer rate, q?

Answer 1

1. q = mcΔT
2. q = UAΔT_lm, where U = overall heat transfer coefficient, a : surface area , ΔT_lm ; logarithmic mean temp difference

Question 2

For the energy balance method (q = mcΔT), what kind of problems is it used to solve?

Answer 2

to determine the inlet or outlet temperature / mass flow rate of one of the streams, given all other conditions

Question 3

For the Logarithmic Mean Temperature Difference (LMTD) method, what kind of problems is it used to solve?

Answer 3

1. To determine size of heat exchanger (in terms of heat transfer area (A), length (L) and diameter (D) of the pipe)
2. To determine overall resistance (U) in heat transfer