LMTD METHOD

1. NAME - RONIT KUMAR
ROLL NO - 2100290409013
BRANCH - MECHANICAL ENGINEERING
YEAR - 3RD YEAR / 5TH SEMESTER
SECTION - A
SUBJECT - HEAT AND MASS TRANSFER
KIET GROUP OF INSTITUTIONS
GHAZIABAD
TOPIC : LMTD METHOD OF HEAT EXCHANGERS

2. LOGARITHMIC
MEAN
TEMPERATURE
DIFFERENCE
(LMTD)
 During heat exchange between two fluids, the temperature
of the fluids, change in the direction of flow and
consequently there occurs a change in the thermal head
causing the flow of heat.
 In a parallel flow system, the thermal head (temperature
potential) causing the flow of heat is maximum at inlet and it
goes on diminishing along the flow path and becomes
minimum at the outlet.
 In a counter flow system, both the fluids are in their coldest
state at the exit.
 To calculate the rate of heat transfer by the expression, 𝑄 =
𝑈𝐴∆𝑇, an average value of the temperature difference ( i.e.
LMTD) between the fluids has to be determined.

3. • The overall heat transfer coefficient is uniform throughout the exchanger.
• The potential and kinetic energy changes are negligible.
• The specific heat of the fluids are constant.
• The heat exchange takes place between the two fluids.
• The temperature of both the fluids are constant over a given cross section and
may be represented by their bulk temperature.
ASSUMPTIONS

4. Logarithmic mean temperature difference for
'' counter-flow''

5. LMTD for Counter Flow Heat Exchanger

9. Logarithmic mean temperature difference for
"parallel-flow"

10. LMTD for Parallel Flow Heat Exchanger

14. THANK YOU