Thermophysical Properties of Okara During Drying

Figures & data

Figure 1 Spray-dryer adapted: fixed bed dryer. (Color figure available online.)

Table 1  Centesimal composition of okara

Component	Composition w.b. (%)	Composition d.b. (%)
Water	76.49 ± 1.09	—
Carbohydrates	13.30 ± 0.49	56.56 ± 2.10
Fats	0.58 ± 0.04	2.48 ± 0.18
Proteins	9.15 ± 0.70	38.93 ± 2.98
Ashes	0.48 ± 0.06	2.03 ± 0.26

Table 2  Drying air relative humidity and velocity in function of its temperature

Temperature (°C)	Relative humidity (%)	Velocity (m/s)
130	1.17	0.044
150	0.77	0.051
170	0.38	0.073

Figure 2 Profiles of moisture content versus time during okara drying in fixed bed dryer.

Figure 3 Okara water activity in function of its moisture content.

Figure 4 Okara density during drying versus (a) time (min) and (b) moisture content (kg/kg).

Figure 5 Okara specific heat during drying versus (a) time (min) and (b) moisture content (kg/kg).

Figure 6 Okara thermal conductivity during drying versus (a) time (min) and (b) moisture content (kg/kg).

Figure 7 Okara thermal diffusivity during drying versus (a) time (min) and (b) moisture content (kg/kg).

Table 3  Okara thermophysical properties

Property	Equation
Specific heat (J/kg·°C)	cp (x) = –44.93x ^4 + 382.13x ^3 – 1246.30x ^2 + 2123.60x + 1678.10
Thermal conductivity (W/m·°C)	k(x) = −4.70 × 10^−3 x ^4 + 3.94 × 10^−3 x ^3 − 1.25 × 10^−2 x ^2 + 0.21x + 0.16
Thermal diffusivity (m²/s)	α(x) = −8 × 10^−10 x ^4 + 7 × 10^−9 x ^3 − 2 × 10^−8 x ^2 + 4 × 10^−8 + 9 × 10^−8

Table 4  Air velocity, Re, and Nu for okara during drying at different temperatures

Air temperature (°C)	Air velocity (m/s)	Re	Nu
130	0.044	8.320	1.319
150	0.051	9.279	1.408
170	0.073	11.874	1.633

Table 5  Okara drying parameters

Temperature (°C)	Xe d.b. (kg/kg)	h (W/m^2·K)	hm  × 10^5 (kg/m^2s)	Dap  × 10^9 (m^2/s)
130	0.0078	8.93	1.26	4.1
150	0.0059	9.97	1.50	6.2
170	0.0032	11.72	1.63	7.4