In our previous paper a possible theoretical framework was proposed for the structure based modelling of the conservational processes with lumped parameters. The direct mapping of the studied conservational processes onto a descriptive computer programme eliminates the many-fold transformation of individual model building, from the cognitive model via the mathematical construct and the numerical algorithm to the computer programme. Recently the transformation of the continuous models of distributed parameters to an approximate discrete one has been studied. In the derivation of the lumped model from the distributed one the most interesting problem is the clear distinction between the adequacy and the accuracy. The refinement of the discrete model (i.e. the increase of the cell number) should be accompanied by the adjustment of the model parameter expressing the prescribed degree of mixing. As a possible solution the measure theoretical foundation of the discretization has been combined with a degree of mixing [10]. It follows that the cell model with convective mixing is an adequate representation of the flows, as well as of the mixing in the new modelling methodology. The theoretical issues and the methodology of direct mapping are illustrated by a simple example of a tubular reactor with consecutive reactions.