The study was devoted to test the effect of the process variables on the desublimator
(cold trap) efficiency under vacuum technique. Since several intermediate process
parameters could not be measured or inspected, then it was necessary to predict them by
the gray model. Although the novel approach (tendency model) for the desublimator was
less accurate than the detailed one, but it showed agreement results when compared with
the experimental data. The accuracy of model could be increased by increasing the
process variable monitors. The tendency model was more effective to deal with the lack
of knowledge about the process when implemented with the optimal control system.