Abstract
A perturbation method is applied to obtain an approximate analytical solution to the non-linear differential equation which describes the steady state concentration profile of the liquid flowing on a distillation plate. This method proved effective in producing results with reasonable deviations from the exact solution of the differential equation and a considerable reduction in computing time. However, it sometimes requires the solution of a single first order differential equation. Thus, a further approximation was adopted, giving a method which does not involve the solution of any differential equation. Although the deviation in the exit liquid composition is somewhat higher, yet the computing time is less.