Moisture dependent physical properties of rough rice grain
Introduction The knowledge of various physical properties is essential to facilitate and improve the design of equipment for handling, harvesting, processing, and storing the agricultural material such as grains. Some physical properties of the grain particles are principal dimensions, equivalent diameter, sphericity, surface area, volume, bulk density, true density, porosity, angle of repose, friction coefficient, and specific heat capacity. Principal dimensions namely, length, width, and thickness are important in sizing, sorting, and other processes. They can also be used to calculate equivalent diameter, sphericity, surface area, and volume of the grain particles. Bulk density and true density are useful in storing, handling, separating, and processing operations. Porosity data is required in modeling of the heat and mass transfer process operations. The angle of repose has practical applications in the design of processing, storage, and conveying systems of the grain material. The static coefficient of friction plays an important role in transport and storage of the grains. The specific heat capacity is necessary for the design of a new unit operation or analysis of the present process e.g. drying, cooling, and storage (Mohsenin, 1986; Sahay and Singh, 1996) Several studies have been conducted to investigate the physical properties or the influence of moisture content on physical properties of different agricultural material such as sunflower seed (Gupta and Das, 1997) millet (Baryehe, 2002) almond nuts and kernels (Aydin, 2003) jatropha seed (Garnayak et al. 2008) niger seed (Solomon and Zewdu, 2009) shelled and kernel walnuts (Altuntas and Erkol, 2010) and tung seed (Sharma et al. 2011) Some physical properties of some specific varieties of the rough rice have been determined and reported by various research workers (Morita and Singh, 1979; Iguaz et al. 2003; Reddy and Chakraverty, 2004; Ghasemi Varnamkhasti et al. 2008; Kibar et al. 2010) However, there is a dearth of information on some physical properties of rough rice for a wide range of moisture content. The aim of this study was to determine the moisture dependent physical properties of the rough rice, namely: length, width, thickness, equivalent diameter, sphericity, thousand grain mass, grain volume, surface area, bulk density, true density, porosity, angle of repose, static coefficient of friction, and specific heat capacity. Materials and Methods Dried long grain rough rice of the Fajr variety was used in this study. The moisture content of the cleaned grain was determined using the ASAE standard method (ASAE, 1984) Samples of the grains were conditioned to moisture content levels of 10.29, 15.37, 20.5, 25.4, and 30.6% d.b. (dry basis, kilograms of water per kilogram of dry solid) Samples of the rough rice with desired moisture content levels prepared as reported by Selvi et al. (2006) The length, width, and thickness of the grain were measured by a digital caliper with an accuracy of 0.01 mm. The equivalent diameter considering a prolate spheroid shape for the grain particle was determined using the following equation (Mohsenin, 1986) (1)