Table 1 Independent variables, and their coded and actual values used for analysis

Symbol1)	Independent variable	Coded level
		-1	0	1
		X1	Inlet temperature (℃)	90	105	120
X2	Air flow rate (mL/min)	30	45	60
X3	Feed flow rate (mL/min)	7	12	17

X₁, Inlet temperature (℃); X₂, Air flow rate (mL/min); X₃, Feed flow rate (mL/min).