Table 4.

Combined effect of temperature and oil concentration on the apparent viscosity at 50 s⁻¹

	Equations for combined effect					Statistical test parameters
	iη i	j	D j	E a a [kJ mol−1]	R 2b	MPE	MBE	RMSE	EF	χ 2
η 50 = η 3exp [D 1 C + E a/R (T + 273.2)]	η 3 [Pa s]		D 1 [%]−1
	1.81 × 10−4	1	0.089	7.140 ± 0.41	0.979	0.690	−0.006	0.021	0.999	0.001
η 50 = η 4 ${\mathit{C}}^{{\mathit{D}}_2}$ exp [E a/R (T + 273.2)]	η 4 [Pa s]		D 2
	2.17 × 10−4	2	1.518	4.591 ± 0.24	0.713	−0.980	−0.002	0.071	0.987	0.007

^a E _a is the activation energy

^b R ² is determination coefficient for the equations

MPE, mean percentage error; MBE, mean bias error; RMSE, root mean square error; EF, modeling efficiency and χ ², chi-square