A Theoretical and Experimental Study of Oil Wicking Mechanism of Kapok Fibrous Powder Assembly

Figures & data

Figure 1. Schematic diagram of two-scale wicking model.

Table 1. Structural parameters of kapok fiber.

Outer diameter $d_e$ (μm)	Inner diameter $d_i$ (μm)	$\mathrm{D}\mathrm{e}\mathrm{n}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{y}{\rho }_f$ (g/cm^3)	Lumen wall density ${\rho }_{fw}$ (g/cm^3)
16.29	14.29	0.305	1.35

Figure 2. SEM of (a) KFP, (b) cross-section of single kapok fiber.

Table 2. Basic properties of test oils at 20°C.

Type of oil	Density (g/cm^3)	Viscosity (mPa · s)
Mineral oil	0.85	74.73
PAO synthetic oil	0.82	29.55

Figure 3. Schematic diagram of Tensiometer device. 1 – electronic balance, 2 – sample holder, 3 – sample tube, 4 – oil, 5 – liquid reservoir, 6 – lifting platform.

Figure 4. Relationship between the square of oil sorption mass and time (a) mineral oil, and (b) PAO synthetic oil. Solid line represents the linear fitting at the initial stage.

Figure 5. The relationship between (a) saturated oil sorption, and (b) sorption coefficient of KFP to test oils with packing density.

Table 3. Experimental and theoretical values of sorption coefficient (mineral oil).

Packing density (g/cm^3)	Experimental value		Theoretical value			Deviation
	$D_0$	R^2	$D_{\mathrm{e}}$	$D_{\mathrm{i}}$	$D_{\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{o}\mathrm{r}\mathrm{y}}$	$\text{{{rm{(}}{D\_{{rm{theory}}}} - {D\_0})}}/\text{{{D\_0}}}100$
0.08	12.7	0.9959	11.86	0.28	12.14	4.41
0.10	8.09	0.9939	7.17	0.44	7.61	5.93
0.12	6.07	0.9971	4.39	0.63	5.02	17.30
0.14	4.38	0.9949	2.67	0.86	3.53	19.41

The unit of sorption coefficient in the table is 10⁻³ g²/s.

Figure 6. Theoretical and experimental values of sorption coefficient (a) mineral oil, and (b) PAO synthetic oil.

Figure 7. Oil sorption in lumens and interfibrous pores of KFP, $M_{\mathrm{i}}$ represents oil sorption in lumens, and $M_{\mathrm{e}}$ represents oil sorption in interfibrous pores.

Table 4. Experimental and theoretical values of sorption coefficient (PAO synthetic oil).

Packing density (g/cm^3)	Experimental value		Theoretical value			Deviation
	$D_0$	R^2	$D_{\mathrm{e}}$	$D_{\mathrm{i}}$	$D_{\mathrm{t}\mathrm{h}\mathrm{e}\mathrm{o}\mathrm{r}\mathrm{y}}$	$\text{{left({{D\_{{rm{theory}}}} - {D\_0}} right)}}/\text{{{D\_0}}}100$
0.08	29.03	0.9944	28.03	0.69	28.72	1.07
0.10	19.72	0.9956	17.57	1.07	18.64	5.48
0.12	14.56	0.9960	10.76	1.54	12.30	15.52
0.14	10.42	0.9962	6.54	2.10	8.64	17.08

The unit of sorption coefficient in the table is 10⁻³ g²/s.

Table 5. Theoretical values of oil sorption by interfibrous pores of KFP and kapok lumens.

Packing density (g/cm^3)	Mineral oil			PAO synthetic oil
	$M_{\mathrm{e}}$ (g/g)	$M_{\mathrm{i}}$(g/g)	$M_{\mathrm{e}}/M_{\mathrm{i}}$	$M_{\mathrm{e}}$ (g/g)	$M_{\mathrm{i}}$ (g/g)	$M_{\mathrm{e}}/M_{\mathrm{i}}$
0.08	10.79	1.66	6.50	10.24	1.61	6.63
0.10	7.71	1.91	4.04	7.49	1.85	3.89