Shell & Tube Heat Exchanger LMTD Calculator
Calculate Log Mean Temperature Difference (LMTD), multipass F-correction factors, overall heat duty (Q), and required tube surface area per TEMA standards.
Hot & Cold Fluid Temperatures
Heat Duty & Flow Pass Geometry
Exchanger Area & LMTD Sizing
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Frequently Asked Questions
What is the Log Mean Temperature Difference (LMTD) and the F-correction factor?
LMTD is the logarithmic average temperature driving force between the hot and cold streams in a pure countercurrent heat exchanger. In multipass shell-and-tube heat exchangers, flow is a mixture of countercurrent and cocurrent passes; an empirical correction factor F (ranging from 0 to 1.0) multiplies LMTD to reflect the reduced driving force.
Why must the F-correction factor strictly exceed 0.80 in TEMA designs?
When F drops below 0.80, the mathematical curve of F versus thermal effectiveness P becomes extremely steep. A tiny fluctuation in cooling water temperature or flow rate causes F to collapse toward zero, rendering the heat exchanger incapable of satisfying its process duty.
What is a "temperature cross" in a shell and tube exchanger?
A temperature cross occurs when the cold fluid exit temperature is heated to a higher temperature than the hot fluid exit temperature (Tc,out > Th,out). This is impossible in parallel co-current flow and requires pure counterflow or multiple shell-passes in series.