Abstract
Dynamic Operating Window is an unique and effective approach to improve chemical reaction speed, which is the function of chemical reactions. The concept is simple and easily understood. The main reaction speed is treated as the larger-the-better type SN ratio and the side reaction speed is treated as the smaller-the-better type SN ratio. Another distinctive feature is that there is no necessity to provide noise factors for the study because the main reaction and side reactions behave as noise factors. In this study, dynamic operating window was applied to the granulation process of herbal medicines. Both the movement of fine particles in a granulation process and the generic function of a chemical reaction follow the exponential form. Therefore, the dynamic operating window approach was applied to the granulations process. In the granulation process, powder is fed into a chamber while the heated air is blown upward and the binder solution is sprayed from the top. The particle size increases as particles come in contact. Similar to chemical reactions, the oversize and the undersize are considered as over-reaction and under-reaction respectively. The reducing speed of under-reacted portion (β1) is treated as larger-the-better characteristic and the increasing speed of over-reacted portion (β2) is treated as smaler-the-better characteristic and their SN ratios are denoted by η1 and η2 respectively. Time is treated as the signal factor. The total of the two SN ratios is called the dynamic operating window. After the optimization, the yield was improved by 20 db compared to the initial condition.
