Table 3.

Factors and Levels for the Box-Behnken Design

Variable	Process Parameter	Unit	Levels
			Low (−1)	Mid (0)	High (+1)
X1	Feed concentration	g/mL	0.2	0.3	0.4
X3	Atomization pressure	MPa	0.1	0.2	0.3
X4	Inlet air temperature	°C	160	200	240