original liquor the consistencies of the samples of fiber pads leaving the washer were measured these results are also shown in table a there is no statistically significant difference between the consistencies of pad samples taken before and after the addition of polymer it is concluded that in this case the polymer did not affect drainage through the pad on the washer in a drum washer both displacement and 34 dilution and thickening 34 are used to separate pulp and spent cooking chemicals consequently to predict the overall efficiency of a drum washer it is necessary to consider both of the washing mechanisms and their interaction however once the displacement process is characterized all of the pulp and liquor flows around a drum washer can be deduced from simple mass balances the steady state compositions and volumes of all flows around the washer can be deduced for a particular dilution factor using the empirical description of the displacement process together with a comprehensive series of simultaneous equations which describe the mass balances for each of the elemental processes of mixing dilution and thickening for example the data presented in fig4 can be used to deduce the steady state composition of all the streams around the number one washer it should be noted that this level of analysis does not consider the interaction between washers it does however enable the overall operation of a washer to be characterized a nordeen efficiency factor e may be used to characterize washing efficiency e is defined as the number of countercurrent ideal mixing stages in series that is required.