One problem facing many processors today is accurately predicting how a major structural modification will affect a process machine's performance. With the cost of high-speed computers dropping and software becoming more powerful, it is more practical and cost effective than ever to use computer modeling to solve such complex industrial problems. Using the example of a spray dryer that will be modified to produce an improved powder, this two-part article describes how you can use computational fluid dynamics modeling to predict the performance of modified equipment before you make hardware changes. This and similar computer modeling methods can be applied to predicting the performance of various bulk solids processing equipment.