Parallel or counterflow

Heat-exchanger ΔTlm

Inputs

Flow arrangementChoose parallel or counterflow for the displayed terminal-temperature relationship.

Hot-side inletTh,iHot-stream temperature at its inlet.

Hot-side outletTh,oHot-stream temperature at its outlet.

Cold-side inletTc,iCold-stream temperature at its inlet.

Cold-side outletTc,oCold-stream temperature at its outlet.

Declared overall coefficientUW/(m²·K)User-entered overall heat-transfer coefficient for the stated exchanger condition; it is not derived here.

Declared transfer areaAUser-entered effective transfer area; no geometry or fouling factor is inferred.

Log mean temperature difference

37.444

Declared-UA heat-transfer rate

67.4

Required area per 1 kW at declared U

0.059347

m²/kW

First terminal difference

Second terminal difference

ΔTlm = (ΔT1 − ΔT2) / ln(ΔT1/ΔT2); Q = UAΔTlm, counterflow

A first-pass number, not a code check, certification, or approval. Read the method and its limits below. What this is and is not.

Calculation snapshot

Formula version 1.0.0

Flow arrangement	counter
Hot-side inlet	80
Hot-side outlet	60
Cold-side inlet	20
Cold-side outlet	45
Declared overall coefficient	450
Declared transfer area	4

Log mean temperature difference	37.444 K or °C
Declared-UA heat-transfer rate	67.4 kW
Required area per 1 kW at declared U	0.059347 m²/kW
First terminal difference	35 K or °C
Second terminal difference	40 K or °C

ΔTlm = (ΔT1 − ΔT2) / ln(ΔT1/ΔT2) · Q = UAΔTlm, counterflow

Incropera & DeWitt, Fundamentals of Heat and Mass Transfer:

This printout is a record of displayed inputs and deterministic formula output. It is not an approval, certification, or engineering conclusion.

Method

Resolve the logarithmic mean temperature difference from four terminal temperatures and one selected flow arrangement.

ΔTlm = (ΔT1 − ΔT2) / ln(ΔT1/ΔT2); Q = UAΔTlm, counterflow

When

Don’t

This evaluates only ideal parallel or counterflow LMTD and user-entered UA arithmetic. It excludes correction factors, phase change, heat capacity rates, fouling, heat-transfer-coefficient derivation, pressure drop, transient behavior, materials, exchanger design/selection/rating, safety, and approval.

Incropera & DeWitt, Fundamentals of Heat and Mass Transfer