Determination of column packed height commonly involves the overall gas-phase coefficient,
because most often the liquid has a strong affinity for the solute, so resistance to mass transfer is mostly in the gas phase. This is analogous to a trayed tower, where the tray-efficiency analysis is commonly based on A or B. In the counter-current-flow absorption column in P for a dilute system, a differential material balance for a solute being absorbed in a differential height of packing dl