# Jakob Number

on . Posted in Dimensionless Numbers

Jakob number, abbreviated as Ja, a dimensionless number, is the ratio of sensible latent heat absorbed or released during liquid vapor phase change.  It represents the dominance of convection over conduction in heat transfer processes.

The Jakob number is commonly used in the analysis and design of heat exchangers, cooling systems, and other applications involving convective heat transfer.  It helps engineers and researchers understand and optimize heat transfer processes by considering the relative importance of convection and conduction.

## Jakob Number formula

$$\large{ Ja = \frac{ c_p \; \left( T_s \;-\; T_{sat} \right) }{ \Delta h_f } }$$     (Jakob Number)

$$\large{ c_p = \frac{ Ja \; \Delta h_f }{ T_s \;-\; T_{sat} } }$$

$$\large{ T_s = \frac{ Ja \; \Delta h_f }{ c_p } + T_{sat} }$$

$$\large{ T_{sat} = T_c - \frac{ Ja \; \Delta h_f }{ c_p } }$$

$$\large{ \Delta h_f = \frac{ c_p \; \left( T_s \;-\; T_{sat} \right) }{ Ja } }$$

Symbol English Metric
$$\large{ Ja }$$ = Jakob number $$\large{ dimensionless }$$
$$\large{ c_p }$$ = constant pressure at specific heat $$\large{\frac{lbf}{in^2}}$$ $$\large{Pa}$$
$$\large{ T_s }$$ = total stagnation temperature $$\large{F }$$ $$\large{ K }$$
$$\large{ T_{sat} }$$ = temperature saturation point $$\large{F }$$ $$\large{ K }$$
$$\large{ \Delta h_f }$$  = evaporation enthalpy change $$\large{\frac{Btu}{lbm}}$$  $$\large{\frac{kJ}{kg}}$$

Tags: Heat Transfer Vapor