Heat exchanger effectiveness–NTU rating
Duty and outlet temperatures of an existing exchanger from its area and U — counter-current, shell-and-tube, cross flow and phase change.
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The Shell and Tube Heat Exchanger Performance and Fouling Excel tool does everything here and more: actual U, fouling resistance and cleanliness from plant readings — with the duty lost to fouling, its yearly cost and the best cleaning interval. Print-ready report, any units, visible formulas, no macros.
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How this calculator works
The effectiveness–NTU method predicts how an existing exchanger performs when you know its area and U but not the outlet temperatures — for example at a new flow, a different inlet temperature or after fouling. The heat capacity rates C = ṁ·cp of the two streams give Cmin and the ratio Cr = Cmin/Cmax; NTU = UA/Cmin; the effectiveness ε follows from NTU, Cr and the flow arrangement; then the duty Q = ε·Cmin·(Thot,in − Tcold,in) and both outlet temperatures follow by heat balance.
Example: 20,000 kg/h of oil (cp 2.3 kJ/kg·K) at 150 °C cooled by 30,000 kg/h of water at 30 °C in a one-shell-pass exchanger of 60 m² with U = 350 W/m²·K: NTU = 1.64, Cr = 0.367, ε = 0.695, duty 1,065 kW, oil out at 66.7 °C and water out at 60.6 °C. The same area in true counter-flow would give 1,139 kW. The ε–NTU relations (Kays and London, as tabulated by Incropera) were checked against the open-source ht library for all seven arrangements at 88 points, agreeing to better than 0.0001 %.
The table shows how duty and outlet temperatures change with area at the same U — a quick way to see what an extra shell or a cleaning would give. To work out U and fouling from plant readings, use the LMTD calculator and the fouling calculator. References: Incropera and DeWitt, Fundamentals of Heat and Mass Transfer, Table 11.3; Kays and London, Compact Heat Exchangers; Perry's Chemical Engineers' Handbook §11.