Five models of a spray dryer design for a whey protein process were analyzed in this study. These models include first principle approaches and empirical correlations. From a large set of given design specifications (inlet and outlet moisture contents, inlet air conditions and residence time), the physical size of the spray drying system was determined from their correlations. Then, the designs were compared to both industry heuristics for size ratios and dryer performance (when possible) to assess the validity of these models. Specific consideration was given to the correlation between the systems that met design heuristics and those that produced a usable product.