Heat Transfer Rate Calculator

Calculate heat-transfer rate from overall coefficient, area and temperature difference.

Live concept view — geometry scales with the entered design condition.

PRELIMINARY RESULT

Heat-transfer rate30.00 kW

Calculation detail

Formula: Q = U × A × ΔT

Heat-transfer rate uses the specified overall coefficient, surface area and temperature difference.

Heat Transfer Rate Calculator: operating questions

May inlet-to-inlet temperature difference be used?

Only if it is a justified representative mean difference for the physical arrangement. Heat exchangers generally require LMTD or an effectiveness-NTU treatment and sometimes a correction factor.

Does U remain constant?

The calculator assumes it does. In practice film coefficients, fouling, wall properties, phase and flow regime may change with operating condition.

Why can duty be correct while outlet temperatures are wrong?

The UA relation alone does not enforce both stream energy balances or heat-capacity rates. A complete exchanger model must satisfy those constraints.

Illustrative input values and units
Parameter	Unit	Example
Overall coefficient U	W/m²·K	250
Transfer area	m²	4
Temperature difference	K	30

Technical verification

Equation checked: 2026-09-15 · Units checked: 2026-09-15 · Independent numerical case: Pass

Source basis: TEXTBOOK — Lienhard, A Heat Transfer Textbook, mean temperature difference in heat exchangers

Unit basis: W/(m²·K) × m² × K = W

Independent example: 250 W/(m²·K) × 4 m² × 30 K = 30000 W = 30 kW.

Scope: Thermal duty is a rate, not stored energy. Appropriate driving ΔT, LMTD and correction factors must be supplied; transient and stream energy balances are excluded.

Technical verification is not professional engineering certification and does not approve a specific real-world design.