91C-14 |
Friction of food powders: A new flowability index |
P. JULIANO1, B. Muhunthan2, and G. V. Barbosa-Cánovas1. (1) Biological Systems Engineering, Washington State University, Pullman, WA 99164, (2) Department of Civil and Environmental Engineering Food powders represent a wide range of particulate materials utilized in the food industry. They differ in their chemical composition and physical characteristics. Many food powders present problems with flow in food production and storage operations. Flowability is the ease at which a powder flows through a chute or hopper. It can be expressed by indices such as the flow factor and cohesiveness determined with shear tests. Accurate measurement of flowability indices has, however, remained a problem. The objective of this research is to propose a new method to determine flowability index of powders with different composition and to relate it with conventional flowability parameters. The method recognizes that the total shear strength of a particulate material during shearing is composed of friction and interlocking. The interlocking strength results for the volumetric changes during shearing. The frictional strength of powders can hence be determined by accounting for interlocking. A shear cell was used in order to determine the friction values in cocoa powder, powdered cheese, sugar and salt at different consolidation stresses. Salt, sugar, and cheese were restricted to specific particle size ranges in order to provide homogenous voidage. Friction in cohesive powder cheese and cocoa was lower than in crystalline and less cohesive dry materials salt and sugar. Sugar and salt provided similar friction and cohesion values. The flow factors of these materials were, however, different. In general, higher friction values indicated higher flowability. Friction coefficient could be easily and directly calculated. The proposed method can be used to find flowability of food powders with different compositions. It avoids the ambiguity in the selection normal stress at which powders flow freely.
Session 91C, Food Engineering: Food process engineering
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