Heat Exchanger — validation & limitations

What it calculates

Engineering estimate — this tool uses an accepted simplified model rather than one citable governing standard. Use it for preliminary sizing and verify the final design against manufacturer data or a qualified engineer.

• LMTD method with TEMA / Bowman F-correction for shell-and-tube (1-2 pass) and effectiveness-NTU cross-flow (both fluids unmixed) — no constant-F shortcuts
• NTU-effectiveness method with ε-NTU charts across five heat exchanger types (counterflow, parallel, 1-2 shell-and-tube, cross-flow, condensing/evaporating C* = 0)
• Quick HX sizing by application type (water-water, air-water, oil-water, steam condensing, air-air) with a category U and the analytical arrangement F — capped at the category rule-of-thumb value, and refused outright when the arrangement cannot achieve the program
• Fouling resistance analysis: cleanliness factor, fouled overall U and the extra area the fouling allowance requires, to TEMA fouling tables
• Tube sheet layout: Kern/TEMA tube count, baffle spacing and cross-flow area for triangular, square and rotated-square pitch
• Tube-side heat-transfer enhancement using the Dittus-Boelter correlation (Re, Nu, h_plain vs h_enhanced) for four enhancement types

Standards this tool applies

• TEMA — Thermal rating: LMTD area sizing with Bowman/TEMA F-correction, NTU-effectiveness rating, fouling analysis with user-entered resistances, and an estimated tube count (baffle spacing fixed at 40 % of shell diameter). TEMA mechanical rules are not checked.

Validation evidence — independent reference cases (2)

Each case runs the tool's engine on a worked example whose values come from a published source or a hand derivation from the cited equations, and an automated regression test asserts the engine against those values within the stated tolerance. "Conservative" means the engine is known to sit on the safe side of the reference and the test asserts that side. Sources are cited; their text is not reproduced.

• Counterflow LMTD and required area (oil cooler)

  Agrees

  Source: Incropera, DeWitt, Bergman & Lavine, Fundamentals of Heat and Mass Transfer, 6th/7th ed., Ch. 11, Example 11.1; hand recomputation

  Inputs: Oil 0.1 kg/s cp 2131, 100->60 C; water 0.2 kg/s cp 4178 at 30 C; hi 2250, ho 38.8 W/m2K; Di 25 mm

  Quantity	Reference value	Tolerance
  log-mean temperature difference	43.20 K (book 43.2)	1e-9 relative vs hand; 0.1 % vs book
  required area	5.1731 m2	1e-9 relative
  tube length	65.87 m (book 65.9)	0.2 % vs book

  tests/golden/REF-heatex-lmtd-area.golden.test.ts

• Counterflow epsilon-NTU rating of the sized exchanger

  Agrees

  Source: Incropera, DeWitt, Bergman & Lavine, Fundamentals of Heat and Mass Transfer, 6th/7th ed., Example 11.1 and Sec. 11.4, Table 11.3 (counterflow effectiveness relation)

  Inputs: Oil 0.1 kg/s cp 2131 at 100 C; water 0.2 kg/s cp 4178 at 30 C; U 38.142 W/m2K; A 5.1758 m2 (L 65.9 m, D 25 mm)

  Quantity	Reference value	Tolerance
  NTU	0.92640	1e-9 relative
  effectiveness	0.57160 (book 40/70 = 0.5714)	1e-9 vs hand; 0.1 % vs book
  heat duty	8526.6 W (book 8524 W)	1e-9 vs hand; 0.1 % vs book
  outlet temperatures	hot 59.99 C, cold 40.20 C	0.05 K vs book

  tests/golden/REF-heatex-ntu-effectiveness.golden.test.ts

Limitations

Not checked by this tool

• Shell-side and tube-side pressure drop — Not computed (only an enhancement factor); compute the pressure drops or use the vendor's rating
• Flow-induced tube vibration (TEMA section V) — Only a baffle-spacing warning; check vibration for the actual spans and velocities per TEMA
• Mechanical design: tubesheet, shell and channel thickness — Thermal rating only; use /pressure for the shell and the vendor (TEMA / ASME VIII) for the tubesheet
• Differential thermal expansion between shell and tubes — Not checked; for fixed-tubesheet units decide on an expansion joint with the vendor
• Shell-side film coefficient — Only tube-side coefficients are computed; get the shell side from a Kern or Bell-Delaware rating
• Condensing or boiling coefficients and two-phase pressure drop — Single-phase rating; a phase-change stream needs its own correlations