Calculator Inputs
This page uses one stacked workflow, while the form fields adapt to large, medium, and mobile screens.
Example Data Table
| Case | Hot Flow | Hot Cp | Hot In | Hot Out | Cold Flow | Cold Cp | Cold In | Cold Out | UA | F | Approx. Duty |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Balanced Example | 2.00 kg/s | 4.20 kJ/kg·K | 120 °C | 90 °C | 3.00 kg/s | 4.00 kJ/kg·K | 30 °C | 51 °C | 3.92 kW/K | 1.00 | 252 kW |
| Process Heater | 1.50 kg/s | 2.80 kJ/kg·K | 180 °C | 130 °C | 2.20 kg/s | 3.90 kJ/kg·K | 25 °C | 49.5 °C | 2.65 kW/K | 0.95 | 210 kW |
| Cooling Service | 4.00 kg/s | 3.60 kJ/kg·K | 95 °C | 65 °C | 5.00 kg/s | 4.18 kJ/kg·K | 22 °C | 42.7 °C | 6.00 kW/K | 0.92 | 432 kW |
Formula Used
1) Stream energy balance: Q = m × Cp × ΔT
Here, m is mass flow rate, Cp is specific heat capacity, and ΔT is the stream temperature change.
Hot-side duty: Qhot = mh × Cph × (Th,in − Th,out)
Cold-side duty: Qcold = mc × Cpc × (Tc,out − Tc,in)
2) LMTD method: Q = UA × F × LMTD
Terminal differences: ΔT1 = Th,in − Tc,out and ΔT2 = Th,out − Tc,in
LMTD: LMTD = (ΔT1 − ΔT2) / ln(ΔT1 / ΔT2)
3) Capacity rate: C = m × Cp
4) Maximum possible duty: Qmax = Cmin × (Th,in − Tc,in)
5) Effectiveness: ε = Qselected / Qmax
The tool compares hot-side duty, cold-side duty, and UA-LMTD duty. It also reports imbalance, effectiveness, and thermal driving force.
How to Use This Calculator
- Enter hot-stream mass flow, Cp, inlet temperature, and outlet temperature.
- Enter cold-stream mass flow, Cp, inlet temperature, and outlet temperature.
- Provide overall UA and a correction factor F.
- Choose the duty basis you want reported.
- Select the final output unit.
- Press the calculation button.
- Review the summary cards, detailed table, and Plotly charts.
- Download CSV or PDF for documentation or reporting.
FAQs
1) What does heat exchanger duty mean?
Heat exchanger duty is the thermal power transferred between hot and cold streams. It is commonly reported in watts, kilowatts, megawatts, or Btu per hour.
2) Why can hot-side and cold-side duty differ?
Differences usually come from measurement error, heat loss, uncertain Cp values, unit mistakes, or transient operation. A small mismatch is normal, but large gaps need review.
3) When should I trust the UA-LMTD result?
Use UA-LMTD when overall conductance, correction factor, and terminal temperatures are known. It is especially useful for design checks and exchanger rating calculations.
4) What is the correction factor F?
F adjusts the ideal counterflow LMTD for real exchanger arrangements, such as multipass or crossflow designs. Values are often below 1.0.
5) Why does the calculator show effectiveness?
Effectiveness compares the chosen duty with the maximum thermodynamically possible duty. It helps judge exchanger performance relative to available temperature driving force.
6) Can I use different engineering units?
Yes. The calculator converts flow, Cp, UA, and output units internally, then reports the final duty in the selected unit.
7) What if one terminal temperature difference is negative?
A negative or zero terminal difference means the entered temperature profile is physically inconsistent for standard LMTD evaluation. Recheck inlet and outlet values.
8) Is this calculator useful for quick process checks?
Yes. It is suitable for screening, reporting, teaching, and preliminary design review. Final process design should still use verified plant or vendor data.