🔥 Flow Boiling Critical Heat Flux & DNB

Size flow boiling Critical Heat Flux (q_CHF), Minimum Departure from Nucleate Boiling Ratio (MDNBR safety margin), and dryout vapor quality using Bowring and Katto-Ohno models.

⚡ Fortran 90 Engine Double Precision (IEEE 754) ✓ ISO / ASME Validated

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👁️ Consultations 27

⚡ Calculs faits 21

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📅 Mise en service Jun 2026

⏱️ Latence < 1 ms

🔥 Vertical Flow Boiling Regimes & DNB / Dryout Front

Real-time visual simulation: Single-Phase → Bubbly Flow → Slug/Annular → Critical Heat Flux Dryout Hotspot

📝 Configuration & Presets

☢️ PWR Fuel Core DNB ⚡ BWR Channel Dryout 🏭 Boiler Evaporator Tube 🚀 Rocket Cooling Jacket

📐 Channel Dimensions

Tube Inside Diameter D [mm]:

Heated Channel Length L [m]:

⚡ Operating Hydraulics & Pressure

Mass Flux G [kg/(m²·s)]:

System Pressure P [bar]:

🌡️ Inlet Thermal Conditions & Heat Flux

Inlet Subcooling ΔT_sub [°C]:

Actual Applied Heat Flux q″ [kW/m²]:

Bowring / Katto Flow Boiling CHF Formulation:
• Critical Heat Flux: q″_CHF = [ A′ + ¼ D G Δh_sub ] / (C′ + L) [kW/m²]
• Minimum DNB Ratio: MDNBR = q″_CHF / q″_actual (Safety Margin > 1.3)
• Critical Power: Q_crit = q″_CHF · (π D L) [kW]
• Critical Exit Quality: x_crit = (Q_crit − G A_flow Δh_sub) / (G A_flow h_fg)

📊 CHF & DNB Margin Results

📊 Output Summary
💾 Fortran Source

Critical Heat Flux (q″_CHF)

q″_CHF = 100 kW/m²

Applied Flux: 450 kW/m² | MDNBR Margin: 0.22

BURNOUT RISK (MDNBR < 1.3)

Safety Ratio (MDNBR) 0.22 Requires heat reduction

Critical Channel Power (Q_crit) 117.8 kW Dryout thermal limit

Saturation Temp (T_sat) 357.3 °C h_fg = 600 kJ/kg

Critical Exit Quality (x_crit) 0.047 Subcooled/DNB departure

📈 Critical Heat Flux q″_CHF vs Mass Flux G [kg/(m²·s)]

📉 MDNBR Safety Ratio vs Applied Heat Flux q″ [kW/m²]

=================================================================
 THERMOFLUIDCALC — FLOW BOILING CRITICAL HEAT FLUX (CHF/DNB) REPORT
=================================================================
Case Title                 : Subcritical / Supercritical Utility Boiler Waterwall Tube
Channel Dimensions         : Inside Diameter D = 25.00 mm, Heated Length L = 15.00 m
Operating Parameters       : Mass Flux G = 1800.0 kg/(m2.s), Pressure P = 180.0 bar (Tsat = 357.3 C)
Inlet Subcooling           : 25.0 C (Delta h_sub = 105.0 kJ/kg)
Applied Actual Heat Flux   : 450.0 kW/m2
-----------------------------------------------------------------
CRITICAL HEAT FLUX (q_CHF) : 100.0 kW/m2
MINIMUM DNB RATIO (MDNBR)  : 0.222 [UNSAFE / DNB RISK]
CRITICAL CHANNEL POWER     : 117.81 kW
Critical Exit Vapor Quality: 0.0472
=================================================================

📘 Calculation Methodology & Critical Heat Flux Standards

Bowring & Katto-Ohno Correlation

Calculates the peak convective heat flux before bubble overcrowding prevents liquid wall replenishment:

                    q″CHF = [ A′ + ¼ D G Δhsub ] / (C′ + L)
                

DNB vs Annular Liquid Dryout

At high subcooling and high mass flux, CHF occurs by Departure from Nucleate Boiling (DNB). At higher qualities, it occurs by dryout of the annular liquid film.

Key Engineering Assumptions

Uniform axial heat flux profile in vertical round tubes.
Saturated and subcooled water-steam flow regimes.
Design criteria: $MDNBR \ge 1.30$ margin against thermal burnout.

ThermoFluidCalc Engineering Report