Jakob Number Calculator
Enter specific heat, temperature difference and latent heat to compute the Jakob number Ja = c_p·ΔT/h_fg.
Input Data
Results
At a glance:The Jakob number Ja = c_p·ΔT/h_fg is a dimensionless group in phase-change heat transfer (boiling/condensation). It is the ratio of sensible heat (energy to raise the liquid temperature by ΔT, per unit mass) to the latent heat of vaporization h_fg (energy to change phase). Small Ja means only a tiny fraction of the liquid must be heated through ΔT to supply the phase change, so most energy goes into latent heat (typical of water boiling: Ja ≪ 1). Large Ja indicates sensible heating dominates. It appears in correlations for bubble growth and condensation film thickness.
Formula
Jakob number: Ja = c_p·ΔT/h_fg
$$\mathrm{Ja} = \dfrac{c_p\,\Delta T}{h_{fg}}$$How to Use
- Enter specific heat c_p (J/(kg·K)).
- Enter the temperature difference ΔT (K) and latent heat h_fg (J/kg).
- The calculator returns Ja.
Case Studies
Water boiling
c_p = 4186 J/(kg·K), ΔT = 10 K, h_fg = 2.26e6 J/kg.
Ja = 41860/2.26e6 ≈ 0.0185.
Sensible heating is ~2% of latent — boiling dominated by phase change.
FAQ
What does a small Jakob number mean?
Sensible heat c_p·ΔT is tiny compared with latent heat, so phase change is the dominant energy sink — typical for water boiling (Ja ~ 0.01–0.1).
Where else is it used?
In bubble dynamics (bubble growth rate depends on Ja) and condensation film analysis; it separates thermally-thick from thermally-thin liquid layers.
Related Tools
References
Content review: Calculatorism Editorial Team. Results are for reference only; please refer to the relevant authorities for the official figures.