Calculator Inputs
Example Data Table
| Flow | U (W/m²·K) | Area (m²) | Ch (W/K) | Cc (W/K) | Thi (°C) | Tci (°C) | UA (W/K) | NTU | Cr | ε | Q (W) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Counterflow | 650 | 12 | 4200 | 3200 | 95 | 25 | 7800 | 2.4375 | 0.7619 | 0.7677 | 171155.89 |
This sample illustrates a typical engineering case for validating your own entries.
Formula Used
The NTU method links exchanger size and thermal performance without requiring outlet temperatures in advance. First compute the minimum and maximum heat capacity rates:
Cmin = min(Ch, Cc)
Cmax = max(Ch, Cc)
Cr = Cmin / Cmax
NTU = UA / Cmin
Effectiveness relations
Counterflow: ε = [1 − exp(−NTU(1 − Cr))] / [1 − Cr exp(−NTU(1 − Cr))]
Counterflow when Cr = 1: ε = NTU / (1 + NTU)
Parallel flow: ε = [1 − exp(−NTU(1 + Cr))] / (1 + Cr)
Crossflow, both fluids unmixed: a standard engineering correlation is used.
Crossflow, Cmax mixed: ε = (1 / Cr) [1 − exp(−Cr(1 − exp(−NTU)))]
Crossflow, Cmin mixed: ε = 1 − exp[−(1 / Cr)(1 − exp(−Cr·NTU))]
Heat transfer and outlet temperatures
Qmax = Cmin (Thi − Tci)
Q = ε × Qmax
Tho = Thi − Q / Ch
Tco = Tci + Q / Cc
LMTD = (ΔT1 − ΔT2) / ln(ΔT1 / ΔT2)
Crossflow correlations are engineering approximations commonly used in design screening and educational analysis.
How to Use This Calculator
- Select the exchanger flow arrangement that matches your design.
- Choose whether to enter direct UA or enter overall U and area separately.
- Provide hot-side and cold-side heat capacity rates in W/K.
- Enter hot and cold inlet temperatures in °C.
- Submit the form to calculate NTU, effectiveness, heat duty, and outlet temperatures.
- Review the results panel above the form, then inspect the Plotly curve.
- Download CSV for spreadsheets or PDF for reports and documentation.
FAQs
1. What does the NTU effectiveness method do?
It predicts heat exchanger performance using UA, heat capacity rates, and inlet temperatures. This method is especially useful when outlet temperatures are unknown during design or quick performance checks.
2. Why are Cmin and Cmax important?
They define the capacity ratio Cr and the maximum possible heat transfer. The stream with Cmin limits thermal exchange and strongly influences effectiveness and outlet temperature changes.
3. Which arrangement usually gives better effectiveness?
For the same NTU and capacity ratio, counterflow usually performs best. Parallel flow is typically lower, while crossflow depends on whether each stream is mixed or unmixed.
4. Can I use U and area instead of UA?
Yes. This calculator supports both methods. If you know the overall coefficient and transfer area, it multiplies them to create UA automatically before solving the NTU equations.
5. What does a higher NTU mean?
A higher NTU generally means greater exchanger capability relative to the limiting heat capacity rate. That usually increases effectiveness, though the improvement becomes less dramatic at high NTU values.
6. Why might LMTD be unavailable?
LMTD needs positive terminal temperature differences. If your calculated temperatures create an invalid log term or a nonphysical crossover, the calculator flags LMTD as unavailable instead of showing a misleading number.
7. Are the crossflow formulas exact?
Some crossflow cases use well-known engineering correlations rather than exact closed forms. They are widely accepted for preliminary design, comparison work, and educational evaluation.
8. When should I export CSV or PDF?
Use CSV for further calculations, spreadsheet analysis, or archiving datasets. Use PDF when you need a clean report with computed results and the performance graph for presentations or documentation.