Among the inputs, inlet air temperature gave more significant effect on outlet air temperature and powder moisture compared to feed flow rate and feed concentration. Thus, this parameter was selected as manipulated variable in order to control the outlet air temperature and also indirectly to control moisture content. Two empirical models of spray drying of non sticky and sticky products were determined based on process reaction curve. These models had similar dynamic behavior and can be represented as first order plus time delay (FOPTD) models. However, the process response of non sticky product was slower compared to sticky product. Both models were valid (R20.6) not only for experiment data that used in calculating its parameter, but also for the additional data that are not used in the parameter estimation.
Acknowledgments
The authors gratefully acknowledge the Department of Process and Food Engineering, Faculty of Engineering, Universiti Putra Malaysia and the Ministry of Science, Technology and Innovation (MOSTI) for the financial support under FRGS grant (5523399).