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Physical and Mechanical Properties of Some Selected Paddy Varieties at Different Moisture Levels

M. Z. Abedin
Associate Professor
Department of Farm Structure, Bangladesh Agricultural University, Mymensingh-2202. Bangladesh.

M. O. Hossain
Lecturer
Department of Farm Structure, Bangladesh Agricultural University, Mymensingh-2202. Bangladesh.

M. Z. Rahman
Graduate students.
Department of Farm Structure, Bangladesh Agricultural University, Mymensingh-2202. Bangladesh.

M. F. Akhtar
Lecturer
Department of Farm Structure, Bangladesh Agricultural University, Mymensingh-2202. Bangladesh.

Abstract/ Executive Summary:

Attempts were made to determine the physical and mechanical properties of paddy varieties BRI 1, IR20 and Pajam at five different levels of moisture contents ranging from about 12 to 25 per cent (wet basis). Among the varieties, BRI 1 was the coarse, IR20 was the medium and Pajam was the fine paddy. The experimental results revealed that both the physical and mechanical properties of paddy kernels were higher for the coarser variety indicating a linear relationship with the dimensions of paddy grains. The maximum kernel density was found in. the coarser BRI 1 due to heavier kernels and higher void ratio (or higher porosity). The frictional coefficients increased with contact area that related closely to the surface area of grains in addition to the roughness degree of sliding surfaces. The static coefficient. irrespective of the sizes of paddy grains and roughness of sliding surfaces. was always greater than the dynamic coefficient of friction. But their values are almost indifferent and independent of grain sizes when sliding on the smooth surface (glass plate).

Keywords: Physical and Mechanical Properties, Different Moisture levels, Paddy varieties

Location: Local market under Mymensingh District.

Start Date:

End Date:

Program Area: Variety and Species

Commodity: Rice

Objectives:

To determine the design related physical and mechanical properties of three locally available paddy varieties BRI1, IR20 and Pajam at different moisture levels ranging from about 12 to 25 per cent (wet basis).

Methodology:

The uniform and healthy paddy kernels of BRIt. IR20 and Pajam harvested about two months prior to the study were collected from local market under Mymensingh District. They were thoroughly cleaned and sun dried to obtain the suitable moisture content. A certain amounts of paddy kernels from each variety were moistened with a predetermined amount of distilled water. The treated paddy kernels were then kept into an airtight plastic bag and stirred periodically and left overnight in order to ensure uniform absorption of water. After 24 hours. the treated paddy kernels from plastic bag were used for determining all physical and mechanical properties. The same procedure was adopted every time for each variety after treating with the predetermined amount of water.

Moisture content The Air-oven Method of drying at 130°C for a period of 16 hours as proposed by Bala et (II. (1987) was followed for measuring the moisture content of paddy kernels. The value of moisture content (u) on wet basis (wb) was calculated from the weight of moist (W) and dry (W d) paddy using the following formula and taking mean of three reading for the same paddy grains. % w (wb) = 100 (W - W_d )/W

Linear dimensions: The Overhead Projection Method was followed to determine the length and breadth of paddy grain. Firstly. a line of length Li was drawn on a transparent paper placed on the surface of overhead projector (OHP). The OHP was focused on a magnified screen. The magnified length L_s on the screen was marked and measured carefully and the magnification factor. M_fwas calculated as the ratio of magnified to drawn lengths was calculated by M_f= L_s/L_i Secondly, the sample paddy grain placing on the OHP was focused and its magnified length and breadth were carefully marked and measured. Actual dimensions of paddy kernel were obtained dividing the magnified length by M_f. A micrometer with the least- count of 0.01 mm was used to measure thickness of the paddy kernel. The mean of 10 grains was taken as the length L breadth B and thickness T of the paddy variety.

Density, porosity and angle of repose: The bulk density P_b of paddy grains was obtained dividing the weight by volume. The kernel density P_k was determined by the Toluene Displacement Method as proposed.

Frictional coefficients The frictional coefficients may be static and dynamic based on the kinetic states of paddy kernels and their values largely depend upon the surface roughness over which the grain slides. The concrete slab, polished wooden plank and glass plate were used as sliding surfaces in this study. experimental set-up has been. The empty box was calibrated initially. The hollow box. filled with paddy grains. was pulled horizontally with added weight on the loading pan. The dynamic coefficient of friction 11 was determined with the same kernels from the force that at an additional gentle push towards movement makes the grain-filled box mobile continuously and was calculated by where, F is the force that at gentle push makes the grain-rilled box mobile. It is worth to mention here µ_o should always be greater than µ due to energy potentials.

Source of Information: Journal of the Institution of Engineers. Bangladesh Agricultural Engineering Division. Vol. 28/ AE. No. I. Dec. 2001

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

From the experiment conducted on paddy grains on three varieties of rice at five moisture levels the following conclusions can be drawn:

1. The linear dimension of selected varieties of paddy is directly related to moisture contents. and the surface area. volume. porosity. void ratio and angle of repose differ with each other at different moisture content.

2. No significant difference in porosity has been found between IR20 and Pajam varieties at the same moisture content.

3. The static and dynamic coefficient of frictions for all the varieties increase with increase in moisture contents. and the BR 11 has the higher static and kinetic coefficient of friction compared to IR20 and Pajam varieties. The static and kinetic coefficients of friction for all the varieties on the glass surface do not change at the same moisture content.

Knowledge Management: Journal