Analytical study of friction coefficients of pomegranate seed as essential parameters in design of post-harvest equipment

Friction coefficients (static friction coefficient (SFC) and dynamic friction coefficient (DFC)) of pomegranate seed on different structural surfaces (glass, aluminum, plywood, galvanized steel and rubber) as affected by moisture content (4–21.9% (d. b.)) and sliding velocity (1.4–16 (cm/s)) were investigated. Analysis of variance (ANOVA) was performed to determine the effect of main treatments and their interactions on SFC and DFC. Significance of single or multiple effect of the main treatments with five levels was assessed using Duncan’s multiple range test (DMRT). To predict SFC and DFC, multiple linear regression (MLR) modeling technique was applied for each type of structural surface. The goodness of fit of each MLR model was evaluated using statistical parameters: coefficient of determination, root mean square error and mean relative deviation modulus. Results showed that the minimum and maximum SFC or DFC were in minimum and maximum moisture content on glass and rubber surface, respectively. ANOVA table indicated the significant effect of main treatments and their interactions on SFC and DFC at significance level of 1% (P < 0.01). According to DMRT results, SFC linearly increased as moisture content increased and DFC increased also linearly as individual or simultaneous increment of moisture content and sliding velocity occurred, for all experimental conditions. According to the obtained statistical parameters, both SFC and DFC were properly predicted by means of MLR modeling technique.