Therefore, using dimensionless parameters for the correlation of data has advantages not only for the consistency ofunits, but also for the scale-up purposes However, it is difficult, if not impossible, to satisfy the ynamIc similarity when more than one dimensionless group is involved in a system, which creates the needs of scale-up criteria. The following example addresses this problem Example 9.1 The power consumption by an agitator in an unbaffled vessel can be expressed as no PNDZ N2DI DNDTherefore, using dimensionless parameters for the correlation of data has advantages not only for the consistency of units, but also for the scale-up purposes. However, it is difficult, if not impossible, to satisfy the dynamic similarity when more than one dimensionless group is involved in a system, which creates the needs of scale-up criteria. The following example addresses this problem. ------------------------------------------------------ Example 9.1 The power consumption by an agitator in an unbaffled vessel can be expressed as = 3 5 I mo N D P  ( , ) 2 2 g ND N D f I I  