Heat Exchanger Design Lab (LMTD & Effectiveness-NTU)
Switch between counter-flow and parallel-flow, size a real heat exchanger, and watch the hot and cold temperature profiles run the length of the unit while effectiveness-NTU and LMTD agree on the same heat duty.
Choose counter-flow or parallel-flow, set the inlet temperatures, flow rates and heat-transfer size, and watch the hot and cold temperature profiles run the length of the exchanger.
NTU = UA/Cmin, Cr = Cmin/Cmax, ε from flow arrangement, q = εCmin(Th,in-Tc,in). Cross-check via LMTD: q = UA·ΔTlmAbout the Heat Exchanger Design Lab (LMTD & Effectiveness-NTU)
Free heat exchanger design lab (lmtd & effectiveness-ntu). Switch between counter-flow and parallel-flow, size a real heat exchanger, and watch the hot and cold temperature profiles run the length of the unit while effectiveness-NTU and LMTD agree on the same heat duty. Drag, change the sliders and see the result live. No sign-up, works on phone and computer. Built for engineering, the heat exchanger design lab (lmtd & effectiveness-ntu) runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Switch between counter-flow and parallel-flow, size a real heat exchanger, and watch the hot and cold temperature profiles run the length of the unit while effectiveness-NTU and LMTD agree on the same heat duty. Use it to explore engineering ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Heat Exchanger Design Lab (LMTD & Effectiveness-NTU)
- Use the controls to change Hot inlet Th,in (°C), Cold inlet Tc,in (°C), Hot mass flow (kg/s), Cold mass flow (kg/s), Overall U (W/m²K), and more. The simulation reacts instantly.
- Pick an option such as Counter-flow, Parallel-flow to switch modes or load an example.
- Press "Reset to defaults", "Lab report" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Try the counter-flow effectiveness-above-0.80 challenge.
- Switch to parallel-flow, push U and A to maximum, and watch effectiveness plateau at the 1/(1+Cr) ceiling.
- Compare the same U, A and flow rates between counter-flow and parallel-flow and see the heat duty difference.
- Watch the hot and cold temperature curves on the chart - see them stay apart in parallel-flow but nearly cross in counter-flow.
Key ideas you can learn
- The effectiveness-NTU method rates a heat exchanger by NTU = UA/Cmin and the capacity-rate ratio Cr = Cmin/Cmax, giving an effectiveness that directly yields the actual heat duty without needing to guess outlet temperatures first.
- For the same NTU and Cr, a counter-flow exchanger always reaches a higher effectiveness than a parallel-flow exchanger of identical size.
- Parallel-flow effectiveness is capped at 1/(1+Cr) no matter how large NTU gets, because the two fluids' temperatures can only approach each other, never cross, as they travel the same direction; counter-flow has no such hard ceiling.
- The log-mean temperature difference (LMTD) method gives the same heat duty as effectiveness-NTU when both are done correctly - q = UA times LMTD equals q from epsilon times Cmin times the maximum possible temperature difference.
Where this is used in the real world
Process, chemical and HVAC engineers use exactly this effectiveness-NTU and LMTD cross-check when sizing shell-and-tube or plate heat exchangers for power plants, chillers, radiators and industrial process cooling, since choosing counter-flow over parallel-flow can meaningfully shrink the exchanger needed for the same duty.
Who is this simulation for?
Engineering and technology students, makers, robotics clubs and teachers of design and technology. It gives a hands-on feel for how machines behave before you build a real one.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why does counter-flow always transfer more heat than parallel-flow for the same size and flow rates?
In parallel-flow both fluids move the same direction, so their temperature difference is largest at the inlet end and shrinks steadily, capping how close the outlet temperatures can get; in counter-flow the fluids move opposite directions, keeping a more even temperature difference along the whole length, which lets the cold outlet temperature actually exceed the hot outlet temperature in some cases - something parallel-flow can never achieve.
Why does parallel-flow effectiveness plateau instead of climbing toward 1 as NTU increases?
As NTU grows, both fluids approach a common temperature at the outlet since they can never cross paths (same direction of travel), and that common-temperature limit fixes the maximum possible heat duty at a fraction 1/(1+Cr) of the theoretical maximum - adding more area beyond that point does not transfer any additional heat.
Is the Heat Exchanger Design Lab (LMTD & Effectiveness-NTU) free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Heat Exchanger Design Lab (LMTD & Effectiveness-NTU) work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.