How it works
- the duty — Start with what the process needs: mass flow times specific heat times the temperature change. That is the duty, in kilowatts, and it is fixed by the process — no amount of clever exchanger design changes it.
- counter-current — Run the streams in opposite directions and the temperature difference stays roughly constant along the whole length. Run them in parallel and it collapses at the outlet end. Counter-current is why the cold stream can leave hotter than the hot stream does.
- LMTD and area — The driving force is the log-mean temperature difference. Area follows as duty over U times LMTD. Halve the approach temperature and you roughly double the area — the last few degrees are the expensive ones.
- the temperature cross — Push the hot outlet below the cold outlet and, in a single counter-current pass, you have asked for heat to flow uphill. LMTD goes imaginary, area goes infinite, and no exchanger exists. Drag the hot outlet down and watch the design fail.
- what governs it — Duty, U and approach. U you mostly inherit from the equipment type; duty the process gives you; approach is the only real design choice, and it trades capital area against operating temperature every time.
Design parameters
The panel opposite runs the same correlations as the E-800 design sheet, so the animation and the calculator cannot disagree. Drag any of them and the picture responds.
- Hot flow — m³/h
- Hot inlet — °C
- Cold flow — m³/h
- Cold inlet — °C
- Hot outlet target — °C
- Overall U — W/m²·K
Open the full E-800 design sheet for the governing equations, the accepted design envelopes and the worked calculation.