determination of the angle of repose and internal friction coefficient in common wheat varieties

the friction properties of granular materials play an important role in the determination of specifications for designing hoppers, transporting passages, dryers, silos and machines through which grain flows. in this study, the angle of repose and internal friction coefficient were determined for three common wheat varieties (sardary, gaspard and saysoter) at four moisture contents (12, 15, 18, 21 w.b.%). four contact surfaces (black, mild, aluminum and galvanized sheets) were used to measure the angle of repose. the tests were done in five replications. analysis of variance was used to analyze the data and duncan’s multiple range test was used to compare the effect of the means (p < 5%). the results showed that the effects of moisture content, variety and contact surface were significant for the angle of repose. the effects of grain moisture content and variety were significant for the internal friction coefficient (p < 1%). when moisture content of the grain increased, the angle of repose and internal friction coefficient increased significantly. only where grain moisture level changed from 18 to 21% w.b. the internal friction coefficient did not change significantly. the highest and lowest internal friction coefficients belonged to the sardary and saysoter varieties, respectively. the highest and lowest the angles of repose belonged to the gaspard and sardary varieties, respectively.