Engineering
Heat Exchanger Load Calculator
Calculate hot-side duty, required cold flow, counter-current LMTD, clean area, fouling allowance, and design heat flux.
Hot-side temperature drop (K)-
Process thermal duty (kW)-
Cold-side temperature rise (K)-
Required cold-side mass flow (kg/s)-
Hot-in/cold-out terminal difference (K)-
Hot-out/cold-in terminal difference (K)-
Counter-current LMTD (K)-
Clean required area (m²)-
Area including fouling allowance (m²)-
Design heat flux (kW/m²)-
Decision view
Counter-current temperature profile and UA duty block
Counter-current temperature profile and UA duty blockHot and cold temperature lines expose terminal approach while the transfer block reconciles duty, LMTD, U, and design area.
Exact scenario comparisonHot outlet temperature (°C) changes while all other entered assumptions remain constant.
| Hot outlet temperature (°C) | Hot-side temperature drop (K) | Process thermal duty (kW) | Cold-side temperature rise (K) | Required cold-side mass flow (kg/s) | Hot-in/cold-out terminal difference (K) | Hot-out/cold-in terminal difference (K) | Counter-current LMTD (K) | Clean required area (m²) | Area including fouling allowance (m²) | Design heat flux (kW/m²) |
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How to use Heat Exchanger Load Calculator
- Use mass flow and specific heat in consistent kW units.
- Enter physically ordered counter-current terminal temperatures.
- Select U from a comparable exchanger and service.
Calculator guide
Understanding Heat Exchanger Load Calculator
Heat-exchanger duty comes from an energy balance; area comes from duty divided by U times the logarithmic mean temperature difference. Keeping those steps visible prevents a temperature target from being mistaken for a complete design.
Detailed calculation process
Detailed heat-exchanger duty and area calculation
The default counter-current case cools 2.5 kg/s of water-like fluid from 120°C to 75°C while heating the cold side from 20°C to 60°C.
General formula: Q=m_h*cp_h*(T_hi-T_ho)m_c=Q/(cp_c*(T_co-T_ci))DT_1=T_hi-T_coDT_2=T_ho-T_ciLMTD=(DT_1-DT_2)/ln(DT_1/DT_2)A_c=Q/(U*LMTD)A=A_c*(1+f) Duty is closed on the hot side. Cold flow follows from the same duty, and area follows from the counter-current mean temperature driving force.
What each symbol means
Worked substitution with the default inputs
The default duty is 470.25 kW and the modeled design area is about 13.85 m².
Worked situations
Practical examples
- The default hot stream releases 470.25 kW.
- Terminal differences of 60 K and 55 K yield an LMTD near 57.46 K and about 13.85 m² design area.
Better inputs
Useful tips
- Use temperature-dependent properties for large ranges.
- Separate fouling resistance from area margin when detailed data are available.
- Check pressure drop and phase change outside this model.
Before relying on the result
Limitations and common mistakes
- Specific heats and U are constant.
- No phase change, correction factor, heat loss, pressure drop, or shell/tube arrangement is modeled.
- The LMTD expression requires positive terminal differences.
Reference
Key terms
- Thermal duty
- Heat transferred per unit time, in kW.
- LMTD
- Logarithmic mean of the two terminal temperature differences.
- Overall U
- Entered aggregate heat-transfer coefficient.
Important note
Final exchanger design requires qualified thermal/mechanical engineering, property data, pressure-drop and phase checks, materials, codes, fouling, and vendor rating.
Frequently asked questions
Why use a logarithmic mean?
Temperature driving force changes along the exchanger and is not generally represented exactly by an arithmetic average.
What if the terminal differences are equal?
The LMTD limit equals that common difference; use a nearby scenario or a detailed tool that handles the equality limit explicitly.
Does area identify a standard exchanger?
No. Geometry, passes, pressure drop, materials, fouling, and correction factors still control selection.