## 3 Results and Discussion
### Continuous LBI Measurement  
#### 3.2.1 Sesame Oil Sedimentation Dynamics  
During the sedimentation process of crude sesame oil, the oil and the sediment were divided, with an increasingly distinct interface (Figure 4). After 720 h of sedimentation, 493 mm of clear oil was obtained from the initial height of the crude oil layer of 592 mm. The change in interface height and sedimentation velocity over time are illustrated in Figure 5. The sedimentation velocity remained close to \(-7\) mm/h until about 25 h of the sedimentation. Afterwards, the velocity decreased to \(-2\) mm/h within about 15 h, then  
Figure 3: Backscattering images of oil samples under (**a**) the 635 nm laser and (**b**) the 405 nm laser. The crosses in the images indicate the incident points where the laser light entered the surface of the oil. Note that the light from the 635 nm laser transmitted from left to right, reaching the bottom of the container as the oil became cleaner. The 405 nm laser transmitted light from right to left.  
gradually dropped to a value close to 0. Linear and exponential regressions were performed to fit the curves within 0-39 h and 39-720 h, respectively. The timepoint 39 h was fitted as the turning point, since the R\({}^{2}\) of the linear regression remained above 0.999 between 0 and 39 h and dropped below 0.999 after 40 h. Both regressions showed an R\({}^{2}\) value close to 1.  
At 24 h, the interface was still blurred. This is likely because, as sedimentation continued, particles within the sample mainly settled individually at varying speeds due to differences in particle size or shape within the crude oil, resulting in a slightly spatial difference for the particles and a blurred interface. As the particles approached each other, their settling patterns became increasingly influenced by their proximity, leading them to settle more collectively as a whole. This resulted in a clearer interface and a sedimentation velocity smaller than \(-2\,\mathrm{mm/h}\) at 48 h. As the sedimentation process persisted, the particles were increasingly compacted, thereby causing a continual decrease in the sedimentation velocity. According to the features of different sedimentation stages, we could confirm that at least diluted sedimentation and hindered sedimentation exist for the sesame oil sedimentation process.  
The sedimentation velocity of diluted sedimentation is not related to the sedimentation tank's cross-section area. [PERSON] and [PERSON] also found that both horizontal and vertical sedimentation system had the same sedimentation speed at the beginning of their sedimentation process [15]. Further, it is interesting that oil sedimentation velocity is at a magnitude millimeter per hour, while for wastewater it is millimeter per minute [39]--this could be  
Figure 4: Images of the entire tank during the sedimentation process.  
explained by the much higher viscosity of edible oil compared with water. In practice, when combining sedimentation with other oil-refining techniques, the rapid sedimentation velocity changing period could be a possible option to switch from sedimentation to other techniques. Additionally, for unrefined sesame oil producers (who typically only filter the oil after pressing), due to the nature of diluted sedimentation, it is possible for them to predict and control the time when an obvious sediment could be seen by customers.