AbstractA dimensionless equation has been derived for the mass transfer coefficient in the liquid phase (k1) both for physical and chemical absorption.The equation can be written:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm Sh} = {\rm c}\,{\rm Re}^{2/3} {\rm Sc}^{1/3} {\rm Ha} $$\end{document}where the dimensionless groups2) have the following significance:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rl} {{\rm Sh} = } & {\frac{{{\rm k}_1 }}{{\rm D}}\left( {\frac{{\eta ^2 }}{{{\rm g}\varrho ^2 }}} \right)^{1/3} \quad {\rm Re} = \frac{{I'}}{\eta }} \\ {{\rm Sc} = \frac{\eta }{{\varrho {\rm D}}}\quad {\rm Ha} = } & {\frac{{\left( {\frac{{\eta ^2 }}{{{\rm g}\varrho ^2 }}} \right)^{1/3} \left( {\frac{{{\rm k}_{11} {\rm c}_{\rm R} }}{{\rm D}}} \right)^{1/2} }}{{{\rm th}\left[ {\left( {\frac{{\eta ^2 }}{{{\rm g}\varrho ^2 }}} \right)^{1/3} \left( {\frac{{{\rm k}_{11} {\rm c}_{\rm R} }}{{\rm D}}} \right)^{1/2} } \right]}}} \\ \end{array} $$\end{document}When the absorption is purely physical the group Ha has the value of 1. The equation is checked with the available data in the literature and those from experiments by the authors.The “constant” c seems to depend on the relation:\documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{{\rm diameter}\,{\rm of}\,{\rm packing}}}{{{\rm height}\,{\rm of}\,{\rm scrubber}}} $\end{document}; the function can be approximated by the formula:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm c} = 0.05\left( {\frac{{\rm d}}{{\rm h}}} \right)^{1/3} . $$\end{document}The equation derived resembles the non‐dimensionless equation ofSherwoodandHolloway3) (for physical absorp