. The range of Vgs1 and Vgs2, as key operating
parameters,were 0.0005–0.0069 m/s (central value = 0.0037 m/s)
and 0.0040–0.0238 m/s (central value = 0.0139 m/s), respectively.
The experimental design for X1 (Vgs1) and X2 (Vgs2) is shown in
Table 2. This table also lists the results of all responses under thedifferent operating conditions. A stepwise regression analysis was
conducted by generating a second-order polynomial equation:
Y = ˛0 + ˛1 · X1 + ˛2 · X2 + ˛11 · X2 1 + ˛22 · X2 2 + ˛12 · X1 · X2 (6)
in which Y is the expected response value predicted by RSM; ˛i, ˛j
and ˛ij are the parameters estimated from the regression results
(i = 1,2; and j = 1,2). Ten performance indices were used to assess
the influence of these variants on hydrodynamic and mass transfer
properties.