Temperature distribution in a high shear mixer during heating

Abstract

High shear mixer is used in various kinds of processing industries, such as chemical, cosmetic, food, pharmaceutical industries for emulsification and dispersion. In this project, the high shear mixer works as a batch pasteurizer. Although pasteurization time for different types of food products has been investigated by many scientists, the heating time required from the initial food temperature to the targeted pasteurization temperature is unknown. Besides, the temperature distribution and the coldest region of the fluid during heating process in the mixer remains to be studied. Since the geometry and the flow motion inside the double-agitator high shear mixer are complicated, Ansys® Fluent™ is used in this project to help understand the flow field behavior and temperature distribution.
Both the experimental measurement and theoretical calculation are required for the understanding of the heating system and investigation of thermal boundary conditions performed in CFD. There are totally three ways to implement the thermal boundary conditions in Fluent: A) Temperature, B) Heat flux, C) Convection – heat transfer coefficient. The theoretical calculation results indicate that the steam temperature (method A) and steam heat transfer coefficient (method C) are suitable for viscous products, i.e. sweet chili sauce, because heat transfer coefficient on the product side is the main limiting factor. While method A and C are not suitable for water, because both water and steam heat transfer coefficient have great impact on the heat transfer. Heat flux (method B) relies on experimental data.
Based on CFD simulation results, the cold region in products (water and sweet chili sauce) locates around the corner of the rotor. The temperature of both products distributes evenly during heating process, which proves that 29 rpm is a good enough rotational speed for heating. Therefore, cold region should not be an issue during heating inside the high shear mixer.

Popular Abstract

High shear mixer is a powerful processing equipment that is mainly used in creating emulsions, suspensions, Iyosols, and granular products in industries. There are different types of mixers, such as batch high shear mixer, inline high shear mixer, inline powder induction, high shear granulator and ultra-high-shear inline mixer. The one used in this project is a batch high shear mixer, which is able to process a given volume of material approximately twice as fast as an inline rotor–stator mixer of the same power rating. (Wikipedia, 2020) For some type of products, for instance, sweet chili sauce, mayonnaise and curry mango sauce, the high shear mixer works as a batch pasteurizer as well. During the heating process, the rotor is normally kept still, while the agitators rotates to help speed up the heating process. The equipment at Tetra Pak Product Development Centers is a 500 L double-agitator high shear mixer. Due to the complexity of the machine geometry, it is very difficult to find out the coldest region of the fluid through experimental measurement. In this situation, whether the whole domain of the fluid is heated to the targeted temperature with the given heating time is hard to know. This question could be answered through computational fluid dynamics (CFD) simulation and the result shows that temperature distributes quite evenly in the high shear mixer for both water and sweet chili sauce products.

• author: Qu, Ruohong
• supervisor: Fredrik Innings
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLTM01 20201
• year: 2020
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: food engineering, high shear mixer, heat transfer, cold region, livsmedelsteknik
• language: English
• id: 9021415
• date added to LUP: 2020-06-25 13:43:45
• date last changed: 2020-06-25 13:43:45