Heat Exchanger Sizing Calculator (Liquid-to-Air)

📖 New to Effectiveness-NTU? Read the guide: Heat Exchanger Sizing: The Effectiveness-NTU Method — a plain-language explainer of the standard behind this calculator.

Method: effectiveness-NTU, crossflow with both fluids unmixed — the standard closed-form method for a single-pass finned-tube/microchannel core. Convection treatment — a deliberate, disclosed simplification: the industry-standard approach for detailed finned-tube design (Zukauskas tube-bank correlation plus Kays & London empirical fin-surface data) depends on large surface-specific empirical tables; rather than reproduce those without a verifiable source, this calculator models both the air-side fin channels and the coolant-side tubes/ports as simple ducts — Dittus-Boelter (Nu = 0.023·Re⁰·⁸·Prⁿ) above Re ≈ 2300, fixed fully-developed laminar constants below it (Nu = 3.66 circular duct/port, 7.54 wide parallel-plate fin channel). The free-flow area fraction σ is a geometrically-motivated approximation from the entered pitch/blockage dimensions, not a cited published formula. Fin efficiency uses the standard adiabatic-tip straight-fin formula with an equivalent length of half the inter-row gap (a simplification of the true annular/sector fin around a round tube). Tube/fin wall conduction is neglected (thin metal, well below either film resistance). The louvered-fin core type applies a literature-typical air-side enhancement factor (published comparisons report roughly 2–3× vs. plain fin) rather than the full multi-parameter Chang & Wang louver correlation. Scope: single tube row in the airflow direction — multi-row-deep cores reject substantially more heat for the same frontal footprint than this model predicts. First-pass screening tool — verify a final design against surface-specific correlation data, CFD, or wind-tunnel/calorimetric test.

Validated: the effectiveness-NTU formula's Cr=0 special case matches its exact closed-form identity (1−e^(−NTU)) to machine precision; effectiveness stays within (0,1), increases monotonically with NTU, and converges toward 1 (checked out to NTU=10,000 — the Cr=1 case is the physically slowest-converging). Dittus-Boelter output matches independent hand substitution at chosen Re/Pr for both exponents, with the laminar/turbulent switch landing exactly at Re=2300. The free-flow fraction σ matches a hand-derived case, and a two-way continuity check (mass flow computed from face velocity × frontal area vs. channel velocity × free-flow area) agrees to machine precision. The imported fin-efficiency function was re-verified against its exact tanh(x)/x identity. The full solve was checked on all three core types for energy-balance closure — Q from the ε-NTU calculation exactly matches independent mdot·cp·ΔT recomputation on both the air and coolant sides — plus monotonic Q trends with face velocity and coolant flow rate, correct Cmin side-selection in both directions, and the louver factor applying exactly as a multiplier on the plain-fin air-side h.