were designated for the variables as 1, 0, and −1, respectively. The coded and actual levels of the independent variables in the BBD experimental design matrix are listed in Table 1.Statistical analysis of variance (ANOVA) and regression model analysis were performed, and two-dimensional contour plots were drawn. It can be seen from pareto chart (Fig. 5), that two interaction coefficients (X3X4) and (X2X3) and one linear term coefficient(X2) were significant. Data analysis at 95% confidence level, permitted to obtain the following
semi empirical expression in terms of significant coded factors:Y