A study on the accuracy and precision of external mass transfer and diffusion coefficients jointly estimated from pseudo-experimental simulated data

Optimal experimental designs for maximum precision in the estimation of dif fusivities (D) and mass transfer coefficients (K-c) for solute transport fr om/to a solid immersed in a fluid were determined. Diffusion in the solid w as considered to take place according to Fick's second law. It was found th at the optimal design was dependent on the Blot number. In the range of Blo t numbers tested (0.1-200), the first sampling time corresponded to values of fractional loss/uptake between 0.10 and 0.32, and the second sampling ti me corresponded to values of fractional loss/uptake between 0.67 and 0.82. Pseudo-experimental data were simulated by applying randomly generated sets of errors, taken from a normal distribution with 5% standard deviation, to data calculated using given values of the model parameters. Both optimal a nd heuristic designs (for which the sampling times corresponded to values o f fractional loss/uptake from 0.30 to 0.95) were analyzed. The accuracy and precision of the estimates obtained by non-linear regression were compared . It was confirmed that optimal designs yield best results in terms of prec ision, although it was concluded that the joint estimation of D and K-c sho uld, in general, be avoided. For intermediate values of the Blot number, re asonably precise and accurate estimates can however be obtained if the expe rimental error is small. (C) 1998 IMACS/Elsevier Science B.V.