1. Set the exchanger and fluid properties
Area = UA/U. Use an overall coefficient based on the same heat-transfer area. This does not add a thermal constraint.
Inlet temperatures and both specific heats are always inputs. cp = 4.18 kJ/(kg·K) is an approximate water example; enter appropriate mean-temperature properties for each fluid. No property database or phase-change model is used.
2. Choose exactly three independent known values
Check Known input for a value you want to specify. Uncheck it to let the calculator solve for it. A dashed field is an output. Start with a preset, then adjust values or switches.
Solve for
Solve for
Solve for
Solve for
Solve for
Solve for
An unchecked value is not used in the equations. More than three known values blocks the solve; compare additional measured values with the outputs separately.
3. Calculated results
| Variable | Value | Role |
|---|
Model and equations
Q = ṁcold cp,cold (Tc,out − Tc,in)
Q = UA × LMTD
LMTD = (ΔT₁ − ΔT₂) / ln(ΔT₁ / ΔT₂)
If ΔT₁ = ΔT₂, LMTD = ΔT₁
Counterflow: ΔT₁ = Th,in − Tc,out and ΔT₂ = Th,out − Tc,in. Parallel flow: ΔT₁ = Th,in − Tc,in and ΔT₂ = Th,out − Tc,out. Every terminal difference must stay positive. A counterflow cold outlet may exceed the hot outlet without a local temperature crossover.
Six selectable variables and three equations require three independent known values once inlet temperatures and heat capacities are fixed. Duty, flow, and outlet temperature on the same stream provide only two independent conditions. The model-status message detects that case separately from simple input counting.
Steady, single-phase sensible heat exchange with constant mean cp and overall U, no external heat loss, no phase change, and ideal single-pass counterflow or parallel flow. It does not model pressure drop, geometry-dependent U, multipass correction factors, crossflow, fouling growth, or fluid properties. Positive flow, positive duty, distinct inlet temperatures, and finite positive terminal approaches are required. Use the resulting area for preliminary sizing only.
References: MIT heat exchanger notes; F-Chart effectiveness–NTU documentation. Interaction concept inspired by TLK Energy’s heat exchanger calculator; this implementation uses an independent constant-property model.