Journal on Processing and Energy in Agriculture 18 (2014) 3 111 Biblid: 1821-4487 (2014) 18; 3; p 111-114 Original Scientific Paper UDK: 621.86 Originalni naučni rad UTILIZATION OF SCREW CONVEYOR AS PRE-MIXER: DISCRETE ELEMENT MODEL KORIŠĆENJE PUŽNOG TRANSPORTERA KAO PREDMEŠAČA: MODEL DISKRETNIH ELEMENATA Aca JOVANOVIĆ * , Milada PEZO ** , Lato PEZO * , Sanja STANOJLOVIĆ * , Biljana LONČAR *** , Milica NIĆETIN *** , Ljubinko LEVIĆ *** * University of Belgrade, Institute of General and Physical Chemistry, 11000 Belgrade,Studentski trg 12/V, Serbia ** University of Belgrade, Institute of Nuclear Sciences Vinča, Laboratory for Thermal Engineering and Energy, 11001 Belgrade, P. O. Box 522, Serbia *** University of Novi Sad, Faculty of Technology, 21000 Novi Sad, Bulevar Cara Lazara 1, Serbia e-mail: akiyov@gmail.com ABSTRACT Single pitch screw conveyors are commonly used equipment in industry, used for transport of bulk materials. In this paper, sever- al horizontal single-pitch screw conveyors with modifications in helices geometry were investigated for mixing action during trans- port, using Discrete Element Method. The influence of geometry variations on the performance of screw conveyor was examined, dif- ferent designs were compared, and their effects on mixing performances were investigated. During the transport, the particle tumbles down from the top of the helix to the next free surface and that segment of the path was used for auxiliary mixing action. According to results, the addition of three complementary helices or blades, oriented in the same, or the opposite direction of screw helix, enlarges the particle path within the screw conveyor 3 - 5 times. Key words: Screw conveyor, Transport, Pre-mixer, Discrete Element Model. REZIME Pužni transporteri su dobro poznata procesna oprema, koja se veoma intenzivno koristi u različitim granama industrije, uglav- nom za podizanje i/ili transport rasutih materijala na kratkim i srednjim rastojanjima. Pužni transporteri se koriste u proizvodnji i preradi hrane, u industriji plastike, preradi mineralnih sirovina, u poljoprivrednoj proizvodnji kao i u prerađivačkoj industriji. Upr- kos veoma jednostavnoj konstrukciji, sam transport materijala pužnim transporterom je veoma složen za razumevanje i optimizaciju (korišćenjem matematičkih modela) i konstruktori se veoma često oslanjaju na iskustvene podatke pri konstruisanju i izradi. U ovom radu je opisano nekoliko horizontalnih puževa, konstantne dužine koraka puža, sa izvesnim izmenama u geometriji pužnih spirala, kod kojih su testirane mogućnosti mešanja tokom transporta materijala, korišćenjem „Metode diskretnih elemenata“.Ispitivani su uticaji ovih izmena u geometriji na transportne performanse pužnog transportera, različit a konstrukciona rešenja su međusobno poređena, kao i efekti ovih izmena u geometriji na mešanje u toku transporta.Tokom transporta u pužnom transporteru, čestice padaju sa vrha pužne spirale na prvu sledeću slobodnu površinu pužne spirale i taj segment putanje čestice može da bude iskorišćen za dopunsko mešanje materijala tokom transporta. Putanja čestice se drastično povećava ugradnjom tri dodatne zavojne površine usmerene u isom pravcu kao i pužna spirala. Skraćivanjem dodatnih zavojnica, koje su usmerene u istom smeru kao i pužna spirala, unekoliko se smanjuje putanja čestice (usled prekidanja zavojnice na sredini pužnog transportera). Putanja čestice se produžava, kada se ugrade dodatne zavojne površine koje su usmerene u suprotnom pravcu od pravca pužne spirale. Ugradnjom tri dodatna pravolinijske letve, dobijena je najduža putanja čestice. Ključne reči: pužni transporter, transport, predmešač, model diskretnih elemenata. INTRODUCTION Screw conveyors are widely used for process equipment, uti- lized for transport and/or elevate particles continuously, at con- trolled rates. A summary of current design methods and prob- lems experienced for screw conveyors can be found in Bortola- masi and Fottner (2001). The description of the theoretical be- havior of screw conveyors can be found in articles by Yu and Arnold (1997), and Roberts (1999). Screw conveyors are also used for metering (measuring the flow rate) from storage bins and adding small controlled amounts of trace materials (dosing) such as pigments to granular materials or powders, (Roberts and Willis, 1962, Cleary, 1998a, Cleary, 1998b). Discrete element modeling (DEM), of particulate flow in a screw conveyor was first reported by Shimizu and Cundall (2001). They examined the performance of horizontal and ver- tical screw conveyors and compared their results with previous work and empirical equations. Owen et al. (2003) introduced the use of a periodic slice model to explore the performance of a long screw conveyor. Cleary (2004) used DEM to study draw down patterns from a hopper by a 45° inclined screw conveyor. This work was extended by Cleary (2007) to examine the effect of particle shape on the draw down flow from the hopper and on the transport characteristics of the screw conveyor. Screw transporters are frequently used to remove powder or grain material from silos, and transport it to the mixer. Before the mixing process is performed, it is often practice that some premixing action is done, using some type of the auxiliary mix- er. The main aim of this paper is to consider the possibility of prolonging particle transport path from the moment of entering to the moment of leaving the screw conveyor, with addition of new elements welded on the helix of screw conveyor, in order to increase the effect of auxiliary mixing along with the transport of particles. In this way a screw transporter could be considered as