Critical Heat Flux Calculator

Enter the Zuber correlation coefficient, latent heat of vaporization, liquid density, vapor density, surface tension, and gravity into the calculator to determine the critical heat flux (CHF) for saturated pool boiling (a commonly used estimate).

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Critical Heat Flux Formula

A commonly used estimate for the critical heat flux in saturated pool boiling on a large horizontal surface is given by the Zuber correlation:

CHF = C \, h_{fg} \, \rho_v \left(\frac{\sigma \, g \, (\rho_l - \rho_v)}{\rho_v^2}\right)^{1/4}

Variables:

• CHF is the critical heat flux (heat flux at burnout), typically in W/m²
• C is a dimensionless correlation coefficient (often taken as about 0.131 in the classic Zuber correlation)
• h_fg is the latent heat of vaporization (J/kg)
• ρ_l is the density of the liquid (kg/m³)
• ρ_v is the density of the vapor (kg/m³)
• σ is the surface tension (N/m)
• g is gravitational acceleration (m/s²)

To calculate CHF with this correlation: compute the term (σ · g · (ρ_l − ρ_v)) / ρ_v², take the fourth root, then multiply by C · h_fg · ρ_v.

What is Critical Heat Flux?

Critical heat flux (CHF) is the maximum heat flux that can be applied to a surface before a transition occurs from nucleate boiling to film boiling. This transition is characterized by a sudden drop in heat transfer efficiency, leading to a rapid increase in surface temperature. CHF is an important parameter in the design and safety analysis of heat exchangers, nuclear reactors, and other systems involving boiling heat transfer. Understanding and predicting CHF is crucial to prevent overheating and potential failure of equipment.

How to Calculate Critical Heat Flux?

The following steps outline how to calculate the Critical Heat Flux (using the Zuber correlation shown above).

1. Determine the dimensionless coefficient (C) (commonly ~0.131 for the classic Zuber correlation).
2. Determine the latent heat of vaporization (h_fg).
3. Determine the density of the liquid (ρ_l).
4. Determine the density of the vapor (ρ_v).
5. Determine the surface tension (σ) and gravity (g).
6. Calculate CHF using: CHF = C · h_fg · ρ_v · ((σ · g · (ρ_l − ρ_v)) / ρ_v²)^1/4.
7. After inserting the values and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge (approximate saturated water properties near 100 °C and 1 atm):

Zuber Coefficient (C) = 0.131

Latent Heat of Vaporization (h_fg) = 2,257,000 J/kg

Density of Liquid (ρ_l) = 958.4 kg/m³

Density of Vapor (ρ_v) = 0.597 kg/m³

Surface Tension (σ) = 0.0589 N/m

Gravity (g) = 9.80665 m/s²

Result (using the formula above): CHF ≈ 1.1 × 10⁶ W/m² (about 1.1 MW/m²).