LMTD

Question 1

Draw parallel flow heat exchanger.

Answer 1

Th, in and Tc, in on left side
Tc, out and Th,out on right side

Question 2

Draw counter flow heat exchanger.

Answer 2

Th,in & Tc,out on left side
Tc,in & Th,out on right side

Question 3

Parallel flow: How do you calculate ΔT1 & ΔT2

hint: helps to draw!

Answer 3

T1 = Th,in - Tc,in
T2 = Th,out - Tc, out

we want a positive so do big - small

Question 4

If given:
Th,in
Tc, in
Tc,out
cc & ch
How do you calculate the length required to achieve heat.

Answer 4

• calculate Q for cold fluid
• calculate Th, out
• calculate ΔΤ1 & ΔΤ2
• calculate ΔT(Lm)
• calculate L using Q & A eq. (Q=UAs ΔT(Lm). - - A = pi *D * L

Question 5

What is overall heat transfer coefficient?

Answer 5

U

Question 6

Heat Transfer Rate Equation

Answer 6

Q = m* c(p) ( big - small)
cold: Q = m(c) * c(pc) (Tc,out - Tc, in)
hot: Q = m(h) * c(ph) (Th,in - Th,out)

Question 7

Heat Capacity Rate Equation

Answer 7

C = m(dot) * c(p)

m = mass flow rate
c(p) - specific hate rate

Question 8

Counter Flow: Equation for ΔΤ1 & ΔΤ2

Answer 8

ΔΤ1 - Th,in - Tc,out

ΔΤ2 - Th,out - Tc,in

Question 9

If the COLD OUTLET temperature is higher than the HOT OUTLET temperature, what flow is a heat exchanger in?

Answer 9

• counter flow.
• cold out temperature being higher than hot outlet temperature is not possible in parallel flow.