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Mechanisms causing wear in a homogenizer gap
2010 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Homogenization is the process used to disrupt fat globules in diary products and beverages. This is done to reduce the creation of cream layer (separation) and to enhance the viscosity of certain products. This process takes place in a narrow gap in the homogenizer machine. The process causes wear in the homogenization gap and after an amount of wear time the machine loses its homogenization effect. This thesis aim is to identify the mechanisms causing wear in the homogenization gap and to find a measurement method so that experiments can be carried out. The wear is analyzed by measurement of the weight loss, i.e. the worn off material. To measure the weight loss a balance and an optical 3D-profiler is used. The structure of the worn surface is also analyzed using the microscope pictures from the optical 3D-profiler. Two experimental rigs were used to study the differences between wear during operating conditions with and without particles. For the tests without added particles the influence of cavitation-erosion phenomena was studied. For the tests with added particles the influence of particle properties and the effect of cavitating and non-caviting conditions were studied. The trajectories of the particles are simulated without the influence of cavitation using a CFD-code, to see if the particles could be a possible cause of wear. The gap has been simulated for a worn geometry in order to see how the particle trajectories change. The results show that added particles accelerate the wear compared to that in tests without added particles. The most important parameters affecting the wear are the particle hardness and mass. When cavitation and particles are combined they create a synergetic effect on the wear amount. This can be explained by the fact that cavitation can accelerate particles in random directions by the action of the implosion of the cavity. According to the theory of erosion wear a changed impact angle, from low to medium and increased velocity will increase the wear amount significantly. CFD-simulations and calculations show that the particles do not follow the streamlines well and therefore creates wear on the gap surfaces. The simulations of the particle trajectories show that the changed geometry due to wear changes the velocities and impact angles of the particles thus creating more wear.

Place, publisher, year, edition, pages
Keyword [en]
Technology, Homogenization, erosive wear, cfd, simulation, cavitation, cavitation-erosion, stokes number, finnie, diary product, processing
Keyword [sv]
URN: urn:nbn:se:ltu:diva-50837ISRN: LTU-EX--10/018--SELocal ID: 80f25309-ac4b-4d6a-a5ef-15626b4c78dbOAI: diva2:1024200
Subject / course
Student thesis, at least 30 credits
Educational program
Mechanical Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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