Experimental investigation on the comparison of fenugreek drying in an indirect solar dryer and under open sun

Abstract

The convective heat transfer coefficient is an essential parameter for designing of any solar drying system. In this paper heat transfer modeling in term of convective heat transfer coefficient is performed and compared with open sun drying. The data obtained from experimentation under open sun and indirect solar drying conditions have been used to find values of the experimental constant ‘C’ and exponent ‘n’ by regression analysis and, consequently, convective heat transfer coefficient. From this study it is concluded that the convective heat transfer coefficient is decreasing with drying time it is due to decrease in moisture content. Results also showed that convective heat transfer coefficients are more in indirect solar dryer system than under open sun drying.

Appendix

The physical property of humid air such as specific heat (C), thermal conductivity (K_h), dynamic viscosity, density (ρ), Kinematic viscosity (ν) and expansion factor (β) is obtained by using mean value of crop temperature (T_M) and air temperature just above the crop (T_e) [14, 21]

$$C = 999.2 + 0.1434T_{i} + 1.101 \times 10^{ - 4} + 1.101 \times 10^{ - 4} T_{i}^{2} - 6.7581 \times 10^{ - 8} T_{i}^{3}$$

(15)

$$K_{h} = 0.0244 + 0.7673 \times 10^{ - 4} T_{i}$$

(16)

$$\mu = 1.718 \times 10^{ - 5} + 4.620 \times 10^{ - 8} T_{i}$$

(17)

$$\rho = 353.44/\left( {T_{i} + 273.15pr} \right)$$

(18)

$$\nu = \frac{\mu }{\rho }$$

(19)

$$\beta = 1/(T_{i} + 273)$$

(20)