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Simulation of Moisture Changes During Storage of Paddy in Traditional Storage Systems

B. K. Bala
Department of Farm Power and Machinery, Bangaladesh Agricultural University, Mymensingh 2202, Bangladesh.

M. A. Zaman
Department of Farm Power and Machinery, Bangaladesh Agricultural University, Mymensingh 2202, Bangladesh.

Abstract/ Executive Summary:

Experimental studies on storage of paddy in traditional storage systems indicate that the moisture movement during storage is mainly due to the changes in the moisture of the ambient air. A two dimensional time dependent mathematical mod el was developed to predict the moisture changes during storage of paddy and the simulated results agree well with the experimental data at least qualitatively.

Keywords: Moisture changes, Traditional storage system, Seasonal changes, Humidity of the ambient air.

Location: Bangaladesh Agricultural University, Mymensingh 2202, Bangladesh

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Rice

Objectives:

To develop a two-dimensional time dependent diffusion model to simulate the moisture changes in traditional storage system such as berh due to the seasonal changes in the humidity of the ambient air.

Methodology:

When paddy is stored in traditional storage system such as berh, large vapour pressure gradients are produced in the storage systems because of the variations in ambient humidity. These vapour pressure gradients lead to the moisture movement by diffusion through porous walls, bottom and lid of the bins into grains. Hygroscopic equilibrium is assumed and the water vapour pressure P may be, therefore, calculated from an appropriate sorption isotherm. We have the following expression for equilibrium moisture content of rough rice [9], − ln(rh) =co T_ab^c1 exp (c2 T_ab^c3 M_e) where, c₀ = 3.88368E9 ; c₁ = − 3.52486, c₂ = −1.1205E-2 ; c₃ = 1.30047, and P = P_s rh; The saturated vapour pressure P_s is given by Chambell as Ps = Exp[52.576−(6790.5/(Ta + 273) − 5.0281 ln(Ta + 273)]; and the diffusion coefficient is given by Thorpe. Dv = 9.1 × 10-9 Tab2.5 / (Tab + 245.18). P(R,z,t) and P(r,H/2,t) are computed from changing ambient dry bulb and wet bulb temperatures using the following equations: P_ambient = P_s (T_w) − y (T_d – T_w); Where y = 0.063; The saturated vapour pressure P_s (T_w^₎at wet bulb temperature T_w is given by eqn. Equation was transferred into finite difference form by employing forward difference approximations for the time derivative and central difference approximations for spatial derivatives. Equation was solved using alternating direction implicit method.

Source of Information: Journal of Energy, Heat and Mass Transfer Vol. 14,9-14 (1992)

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

A two dimensional time dependent model is developed to predict the moisture changes during storage of paddy in traditional storage systems. The model was simulated using alternating direction implicit method and programmed in BASIC suitable for microcomputer. The model developed can simulate the moisture changes during storage of paddy due to changes in the ambient air humidity in porous storage systems and it agrees well with the experimental results at least qualitatively.

Knowledge Management: Journal