HyFlux HX

✅ HyFlux HX — Validation Report

17-point physics cross-check for cryogenic heat exchanger design validation.

Correlations Used

Fluid Properties — NIST Validated

Helium (40–300 K): Ideal gas EOS (R=2077.1 J/kg·K), Cp=5193 J/kg·K. Viscosity and conductivity via ln-polynomial fits validated against CoolProp/REFPROP within 2–5%.

Para-Hydrogen (20–31 K liquid, 31–300 K gas): CoolProp 7.2.0 ParaHydrogen HEOS. LH₂ is >99.8% para-H₂ at 20K. T_sat(P) = quadratic in ln(P), error <0.07K across 1–12 bar. h_fg(P) pressure-dependent: 446→237→143 kJ/kg from 1→10→12 bar. Gas cp includes ortho→para conversion peak (~16 kJ/kgK at 150K). 4-segment Simpson integration for enthalpy accuracy.

Validation Checks (17 points)

• Reynolds numbers in turbulent range (Re > 4000) for both streams
• Prandtl numbers physical (0.1 < Pr < 1000)
• Nusselt numbers match Gnielinski ±5% vs Dittus-Boelter cross-check
• Energy balance to machine precision (|Q_hot − Q_cold|/Q_avg < 1e−10)
• Effectiveness bounded (0 < ε < 1)
• Second law satisfied (no temperature crossover)
• Subcooling margin ≥ 5 K (LH₂ stays liquid at inlet and outlet)
• Pressure drop < 10% of stream pressure
• NTU in reasonable range (0.1 < NTU < 10)
• Joule-Thomson coefficient sign check (He warms on expansion above inversion T)
• LMTD positive and finite
• Wall thermal resistance physically reasonable
• Capacity ratio bounded (0 ≤ C_r ≤ 1)
• Dean number check for spiral (De > 11.6 for enhancement)
• Curvature ratio check for spiral (δ = d/D_coil < 0.1)
• Surface density within AM limits
• Build volume fit verification for selected printer

Property Backend Priority

1. ctREFPROP (NIST license) → 2. CoolProp + REFPROP → 3. CoolProp HEOS → 4. Built-in polynomial correlations

Test Coverage

78 tests passing: helium properties (μ, k, ρ, Cp) at multiple temperatures, LH₂ properties, Gnielinski/Dittus-Boelter Nusselt correlations, Petukhov friction factor, ε-NTU solver (energy balance, effectiveness bounds, second law), API endpoints, phase safety, property backend detection.

References

• Gnielinski, V. (1976). New equations for heat and mass transfer in turbulent pipe and channel flow. Int. Chem. Eng., 16(2), 359-368.
• Petukhov, B. S. (1970). Heat transfer and friction in turbulent pipe flow. Advances in Heat Transfer, 6, 503-564.
• Lemmon, E.W., et al. NIST Standard Reference Database 23: REFPROP v10.0.
• Bell, I.H., et al. (2014). Pure and pseudo-pure fluid thermophysical property evaluation: CoolProp. Ind. Eng. Chem. Res., 53(6), 2498-2508.
• Mishra, P. & Gupta, S. N. (1979). Momentum transfer in curved pipes. Ind. Eng. Chem. Process Des. Dev., 18, 130-137.
• Žukauskas, A. (1987). Heat transfer from tubes in crossflow. Advances in Heat Transfer, 18, 87-159.