High‐Pressure Homogenization: Simplified Drop Deformation Estimate during Transition through Orifices

Walzel, Peter

doi:10.1002/ceat.201600364

Cited by 3 publications

(6 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This mismatch may cause differences when investigating the droplet deformation and breakup in detail at the 50-fold scale. Since it is assumed that the diffusion of the emulsifier in the original scale process is much slower than the breakup process [6,29,30], the influence of the emulsifier on the breakup is, however, expected to be moderate, which would still allow the comparison of the droplet breakup in all three scales.…”

Section: Discussionmentioning

confidence: 99%

“…Any results from this scaled experimental setup therefore need to be interpreted with caution. It is presumed, though, that the diffusion time of the emulsion to the newly created surface during droplet deformation is much higher than the breakup process itself [29,30]. Hence, the influence of the higher interfacial tension on the droplet may be moderate.…”

Section: Matching Of Orifice Dimensions and Materials Systemmentioning

confidence: 99%

See 1 more Smart Citation

Scaling of Droplet Breakup in High-Pressure Homogenizer Orifices. Part I: Comparison of Velocity Profiles in Scaled Coaxial Orifices

et al. 2021

View full text Add to dashboard Cite

Properties of emulsions such as stability, viscosity or color can be influenced by the droplet size distribution. High-pressure homogenization (HPH) is the method of choice for emulsions with a low to medium viscosity with a target mean droplet diameter of less than 1 µm. During HPH, the droplets of the emulsion are exposed to shear and extensional stresses, which cause them to break up. Ongoing work is focused on better understanding the mechanisms of droplet breakup and relevant parameters. Since the gap dimensions of the disruption unit (e.g., flat valve or orifice) are small (usually below 500 µm) and the droplet breakup also takes place on small spatial and time scales, the resolution limit of current measuring systems is reached. In addition, the high velocities impede time resolved measurements. Therefore, a five-fold and fifty-fold magnified optically accessible coaxial orifice were used in this study while maintaining the dimensionless numbers characteristic for the droplet breakup (Reynolds and Weber number, viscosity and density ratio). Three matching material systems are presented. In order to verify their similarity, the local velocity profiles of the emerging free jet were measured using both a microparticle image velocimetry (µ-PIV) and a particle image velocimetry (PIV) system. Furthermore, the influence of the outlet geometry on the velocity profiles is investigated. Similar relationships were found on all investigated scales. The areas with the highest velocity fluctuations were identified where droplets are exposed to the highest turbulent forces. The Reynolds number had no influence on the normalized velocity fluctuation field. The confinement of the jet started to influence the velocity field if the outlet channel diameter is smaller than 10 times the diameter of the orifice. In conclusion, the scaling approach offers advantages to study very fast processes on very small spatial scales in detail. The presented scaling approach also offers chances in the optimization of the geometry of the disruption unit. However, the results also show challenges of each size scale, which can come from the respective production, measurement technology or experimental design. Depending on the problem to be investigated, we recommend conducting experimental studies at different scales.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Matching Of Orifice Dimensions and Materials Systemmentioning

confidence: 99%

Scaling of Droplet Breakup in High-Pressure Homogenizer Orifices. Part I: Comparison of Velocity Profiles in Scaled Coaxial Orifices

et al. 2021

View full text Add to dashboard Cite

show abstract

“…The correlation was only proven for small constant stresses under laminar flow conditions. Simulations of Walzel [ 10 ] showed that this correlation may also be applicable to the droplet deformation behaviour during high‐pressure homogenization. The influence of the interfacial tension on the droplet deformation should increase with decreasing viscosity ratio.…”

Section: Resultsmentioning

confidence: 99%

“…Droplet deformation in an optically accessible step-type orifice was evaluated by Kelemen et al [9] They found that the droplets are supercritically Ca > Ca crit ð Þdeformed in the inlet and only break up downstream of the orifice exit. Walzel [10] simulated the droplet deformation inside a passage through an orifice on the centreline using an approach stated by Cox [6] and Kalb et al [11] These findings were later validated using experimental data from a scaled orifice setup whereby a good agreement was found between the simulation and the experiment at limited settings. [12] Among others, Feigl et al [13] and Hövekamp [14] used computational fluid dynamics (CFD) simulations to determine the stress history on the droplet streamline with changing stress loads and constant interfacial tension, which was subsequently correlated with the droplet deformation from simulations and experimental data.…”

Section: Introductionmentioning

confidence: 97%

“…Droplet deformation in an optically accessible step‐type orifice was evaluated by Kelemen et al [ 9 ] They found that the droplets are supercritically

((), italicCa > {Ca}_{crit})

deformed in the inlet and only break up downstream of the orifice exit. Walzel [ 10 ] simulated the droplet deformation inside a passage through an orifice on the centreline using an approach stated by Cox [ 6 ] and Kalb et al [ 11 ] These findings were later validated using experimental data from a scaled orifice setup whereby a good agreement was found between the simulation and the experiment at limited settings. [ 12 ]…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Influence of the droplet trajectory on the resulting droplet deformation and droplet size distribution in high‐pressure homogenizer orifices

et al. 2022

View full text Add to dashboard Cite

High‐pressure homogenization is a commonly used process to produce emulsions with a droplet size of less than 1 μm. During the process, a pre‐emulsion is pumped with a pressure of several mega Pascal through a disruption unit, where the droplets are deformed and subsequently broken up in the turbulent area of the disruption unit. The scope of this investigation is to determine the influence of the droplet trajectory on the droplet size distribution of emulsions of different viscosity ratios or interfacial tension. Measurements of the droplet deformation prior to the droplet breakup using image‐processing tools complemented the observations. In addition, computational fluid dynamics simulations were performed to determine the stress history on the droplet trajectories. It was found that droplets on a trajectory close to the wall are more deformed when leaving the disruption unit compared to droplets on the centreline. The deformation of droplets at the edge of the jet increases downstream the disruption unit until it is finally disrupted. The simulation results support the experimental data, as it can be shown that shear and strain stresses on the trajectories close to the wall significantly exceed the stresses on the trajectories on the centreline. For an emulsion with a viscosity ratio greater than 3, droplets on a trajectory close to the wall resulted in smaller droplets and narrower droplet size distribution, while no significant influence was found for smaller viscosity ratios. Lowering the interfacial tension results in a stronger deformation, which was more pronounced for lower viscosity ratios (λ ≈ 3).

show abstract

Comparison of Experimental and Numerical Transient Drop Deformation during Transition through Orifices in High-Pressure Homogenizers

2021

View full text Add to dashboard Cite

The droplet deformation in dispersing units of high-pressure homogenizers (HPH) is examined experimentally and numerically. Due to the small size of common homogenizer nozzles, the visual analysis of the transient droplet generation is usually not possible. Therefore, a scaled setup was used. The droplet deformation was determined quantitatively by using a shadow imaging technique. It is shown that the influence of transient stresses on the droplets caused by laminar extensional flow upstream the orifice is highly relevant for the droplet breakup behind the nozzle. Classical approaches based on an equilibrium assumption on the other side are not adequate to explain the observed droplet distributions. Based on the experimental results, a relationship from the literature with numerical simulations adopting different models are used to determine the transient droplet deformation during transition through orifices. It is shown that numerical and experimental results are in fairly good agreement at limited settings. It can be concluded that a scaled apparatus is well suited to estimate the transient droplet formation up to the outlet of the orifice.

show abstract

High‐Pressure Homogenization: Simplified Drop Deformation Estimate during Transition through Orifices

Cited by 3 publications

References 30 publications

Scaling of Droplet Breakup in High-Pressure Homogenizer Orifices. Part I: Comparison of Velocity Profiles in Scaled Coaxial Orifices

Scaling of Droplet Breakup in High-Pressure Homogenizer Orifices. Part I: Comparison of Velocity Profiles in Scaled Coaxial Orifices

Influence of the droplet trajectory on the resulting droplet deformation and droplet size distribution in high‐pressure homogenizer orifices

Comparison of Experimental and Numerical Transient Drop Deformation during Transition through Orifices in High-Pressure Homogenizers

Contact Info

Product

Resources

About