and the steam channels and copper content for the same b value calculated for a given plant as 2400 days for example is presented to illustrate the changes that occur as presented in fig2 the top line 1 represents tortuosity of the path for the escape of steam from the deposit steam channels line 2 presents the porosity of the material present on the heating surface line 3 presents the copper fraction of the materials deposited on the heating surface line 4 presents the k parameter as provided in fig2 the k parameter and tortuosity of the deposited material increases over time the porosity however decreases over time indicating an increasingly dense structure over the period of evaluation the tortuosity is defined as the amount of length of the path through a steam chimney in the deposit divided by the overall thickness of the deposit the above values may be obtained from a reduced number of measured deposit thickness porosity copper content heat transfer resistance and or tortuosity values fitted to the formulas below or derived analytically from the model using the equations below deposit inventory mass and operating plant thermodynamic data or through a combination of both approaches individual model parameters evolve as a function of the b parameter as follows a t tube bundle outside diameter surface area affected by deposition t the.