Scale-up, experimentation, and data evaluation

Abstract This chapter discusses the approach to solve the problem of scaling up food extruders. This includes an approach to ensuring that the extruded product properties are maintained across different scales (diameter) of the extruder. Ensuring the quality of the product across product scales generally require testing across two small-scale extruders, before proceeding to the design of the full-scale (commercial) process. This allows one to determine the criteria that will result in the product's qualities being independent of scale. The type of experiments and data evaluation required to accomplish this task are described. This exercise requires experiments wherein the screw speed, die open area, and (in general) extruder feed rate are varied. Once the criteria that control the product's quality are established, the full-scale extruder must be engineered. It requires establishing the relationship between the extruder's performance characteristics, such a capacity, power consumption, and heat transfer (which is a function of operating conditions and extruder diameter). The analysis of operational characteristics using dimensional analysis is described. The required experimentation and data analysis required to apply dimensional analysis are also described. Considerable discussion of heat transfer in extruders is included. The scale-up of heat transfer in extruders has been shown to be a very critical issue in the scale-up of the extrusion process. Finally, a brief discussion of the scale-up of preconditioners is included. Preconditioners have become a frequent addition to the basic extrusion process and are an important part of the entire process.