How to use this calculator
Enter the flow rate, specific heat and inlet temperature of each fluid and the exchanger size as UA (or U and A). Pick the flow arrangement. The calculator finds Cmin, NTU and the effectiveness, then Q and the outlets.
Formulas
Capacity ratesC = ṁcp, Cr = Cmin/Cmax, NTU = UA/Cmin
Counterflowε = [1 − e−NTU(1−Cr)] / [1 − Cre−NTU(1−Cr)]
Heat rateQ = εCmin(Th,in − Tc,in)
Worked example
Oil 2 kg/s (2100 J/kg·K) at 150 °C cooled by water 1.5 kg/s (4180 J/kg·K) at 20 °C, counterflow, UA = 4000 W/K (the default)
- Ch = 4200 W/K = Cmin, Cc = 6270 W/K, Cr = 0.670, NTU = 4000/4200 = 0.952.
- ε = (1 − e−0.3144)/(1 − 0.670e−0.3144) = 0.528.
- Q = 0.528 × 4200 × 130 = 288.3 kW; Th,out = 81.4 °C, Tc,out = 66.0 °C.
Frequently asked questions
ε–NTU or LMTD?
Use LMTD when all four temperatures are known and you need the size. Use ε–NTU when the exchanger is known and the outlets are not, which would make LMTD iterative.
What if one fluid boils or condenses?
Its capacity rate is effectively infinite, so Cr = 0 and ε = 1 − e−NTU for every arrangement.