# Hatta number

The Hatta number (Ha) was developed by Shirôji Hatta, who taught at Tohoku University.[1] It is a dimensionless parameter that compares the rate of reaction in a liquid film to the rate of diffusion through the film.[2] For a second order reaction (rA = k2CBCA), the maximum rate of reaction assumes that the liquid film is saturated with gas at the interfacial concentration (CA,i); thus, the maximum rate of reaction is k2CB,bulkCA,iδL.

${\displaystyle Ha^{2}={{k_{2}C_{A,i}C_{B,bulk}\delta _{L}} \over {{\frac {D_{A}}{\delta _{L}}}\ C_{A,i}}}={{k_{2}C_{B,bulk}D_{A}} \over ({\frac {D_{A}}{\delta _{L}}})^{2}}={{k_{2}C_{B,bulk}D_{A}} \over {{k_{L}}^{2}}}}$

For a reaction mth order in A and nth order in B:

${\displaystyle Ha={{\sqrt {{\frac {2}{{m}+1}}k_{m,n}{C_{A,i}}^{m-1}C_{B,bulk}^{n}{D}_{A}}} \over {{k}_{L}}}}$

It is an important parameter used in Chemical Reaction Engineering.

## References

1. ^ S. Hatta, Technological Reports of Tôhoku University, 10, 613-622 (1932).
2. ^ R.B. Bird, W.E. Stewart, E.N. Lightfoot, Transport Phenomena, 2nd ed. John Wiley & Sons, 2002