Cavitation in High-Pressure Homogenizers - Investigation of an Experimental Method Based on Free Radical Formation

Abstract

High-pressure homogenizers (HPHs) are widely used in the food industry for breaking down droplets and particles to improve product stability and mouthfeel. HPHs are prone to cavitation, characterized by the formation and collapse of vapor bubbles, leading to wear and reduction in efficiency. This study evaluates the potassium iodide (KI) oxidation method as a tool for measuring cavitation. The method is based on the principle that oxidation of KI to triiodide ions only occurs in the homogenizer if the solution is subjected to cavitation.

The project aims to critically evaluate the effectiveness of the KI method and use it to investigate the correlation between cavitation and homogenizing pressure. The aim is also to investigate the potential suppression of cavitation by the application of back pressure. In addition, the KI method is validated using ultrasonication due to its controlled cavitation conditions.

The results indicate that the KI method is effective for ultrasonication, as there is a linear increase in triiodide formation with sonication time, suggesting cavitation. However, the results also suggest that the method may not be as effective to detect cavitation in hydrodynamic environments as in acoustic environments. No correlation between homogenizing pressure and triiodide formation was observed for HPHs, contrary to theoretical models and previous studies. In addition, the effect of back pressure gave inconclusive results, possibly because of low triiodide formation.

While the KI method shows potential for ultrasonication, the results suggest that it is unsuitable for HPH. Future research should focus on alternative experimental methods to measure cavitation in HPHs.

Popular Abstract

Imagine having a machine making products like milk smoother and more stable by breaking down fat globules into tiny fat droplets. This is why high-pressure homogenizers (HPH) are essential in industries like food, biotechnology, and pharmaceuticals. However, there is a challenge: HPHs face a phenomenon called cavitation, in which vapour bubbles form and violently collapse, causing mechanical wear and reduced efficiency. This thesis project investigated a way to measure cavitation in HPHs using a chemical reaction, in order to measure and study cavitation more easily.

High-pressure homogenizers work by forcing a liquid under high pressure through a narrow gap. By increasing the homogenizing pressure of the machine, the gap gets tightened, creating smaller droplets and particles. When the fluid passes through the narrow gap, high velocities are created, causing a decrease in pressure. When the pressure drops, tiny pockets of vapor start to form and start to implode when the pressure rises again. These implosions lead to shockwaves that destroy the internal parts of the machine. Previous studies have investigated suppression of cavitation with the application of back pressure. Back pressure is created by passing the liquid through a second narrow valve.


Understanding the behavior of cavitation is essential to start tackling it. Previous studies researched that cavitation generates free radicals, highly reactive molecules, which can be detected with potassium iodide (KI). The free radicals can oxidize the KI and form triiodide, and the amount of formed triiodide can be measured in a spectrophotometer. This thesis project investigated if the KI method could be used as a reliable indicator for cavitation in HPHs.

Experiments with the KI method were performed on two different HPHs and the result was compared to an ultrasonicator, a machine which has controlled cavitation. While the results showed to be promising for the ultrasonicator, they are more uncertain for the HPH. The findings showed no link between homogenizing pressure and cavitation. The application of back pressure gave inconsistent results and no conclusions could be drawn about the potential suppression of cavitation. Besides, the KI method had some sources of error as the storage time and temperature of the samples affected the results. Therefore, it is concluded that the KI method is unsuitable for measuring cavitation in HPHs, and other experimental methods should be explored.

• author: Sevrell, Fanny and Beekwilder, Pim Emilius
• supervisor: Andreas Håkansson
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLTM06 20242
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: High-Pressure Homogenization, Cavitation, Hydrodynamic Cavitation, Cavitation Number, Thoma Number, Potassium Iodide, Free Radical Formation, Triiodide Formation, Ultrasonication, Spectrophotometry, Food Engineering Nutrition and Food Chemistry
• language: English
• additional info: Degree Project in courses: KLTM02 – Degree Project in Food Engineering, Nutrition and Food Chemistry – Masterexamensarbete i livsmedelsteknik, nutrition och livsmedelskemi; KLTM06 – Degree Project in Food Engineering, Nutrition and Food Chemistry – Examensarbete i livsmedelsteknik, nutrition och livsmedelskemi
• id: 9185786
• date added to LUP: 2025-03-13 13:05:52
• date last changed: 2025-03-13 13:05:52