Piotr Synowiec

Biomaterials, like hydroxyapatite (HAp), are the subject of many scientific investigations. Their specific application, however, is determined by the form and some characteristic features of the resulting material. Synthesis methods and optimization procedures leading to a product of predetermined characteristics are therefore of great interest. To broaden the existing knowledge, sonoprecipitation was investigated as a potential method for the production of nanosized HAp particles. The research was carried out in a static mixer (STM) immersed in the ultrasonic bath. The influence of operating conditions, e.g., ultrasonic power P_US (ε_US), ultrasonic frequency (f_US), and unit mixing power (ε_mix), was investigated in terms of nucleation intensity, product quality, and characteristics (particle size distribution (PSD), mean size, shape, etc.). As a result, the optimal conditions for the HAp nanoparticles synthesis (mean size: d~150 nm; length: L₁~250 nm; width: L₂~80 nm) in the form of needles/whiskers/rods—similar to the shape of the HAp present in natural human bones, free from agglomerates, with negligible signs of particle destruction—were determined. The formation of HAp of smaller sizes (d ≤ 100 nm) and more compact shapes (L₁~155 nm, L₂~90 nm), useful in bone regeneration processes, was also discussed.

The use of materials requires adjusting their features to current applications/needs. In crystallization, the production methods leading directly to the product with pre-determined characteristics are being sought. The research focuses on the abilities of “shaping” the solid product (CSD, shape, form, etc.) and is based on experimental work carried out in the ultrasound (US)-assisted Koflo static mixer (STM). As the model reaction calcium fluoride precipitation has been used as a “common denominator” that complements the previous authors’ studies, providing comprehensive knowledge and a more general look at the mentioned problem. It has been shown that it is possible to obtain crystals with the desired characteristics; however, one should be aware of the used reactors’ limitations. The conscious selection of operating conditions, as well as US parameters (if they are used), is also essential. It has been revealed that the introduction of US to the STM only affects the turbulence intensity, but it doesn’t change the mixing profile. The kinetics of crystallization remain unchanged, but crystals are subjected to greater attrition. In the stirred tank reactors, one might significantly improve the homogeneity of the unit mixing distribution by the selection of the relative input power ε_rel and, thus, affect the kinetics of crystallization.

In the process industry the use of static mixers is constantly rising. Notwithstanding, due to the multitude of available types, the selection of a proper construction is not as simple and requires the knowledge of complete description of a device. In the performed research there was an attempt to present the complete fluid‐dynamic characteristics of two static mixers: Kenics, well known and commonly used, and Koflo, which has not yet been described in the relevant literature. The empty pipe was also studied as a background for comparison. However, according to the huge amount of gathered data, the report was divided into separate parts, dedicated to pressure drops, residence time distributions, and mixture homogeneity, respectively. The presented paper is focused on the pressure drop analysis which contains the experimental study, the validation of the obtained data on the basis of manufacturer's correlations, as well as computational values and the presentation of new pressure drop relations that enable the pressure drop predictions from Eu or Ne number. As a result of the accomplished study, a good accuracy between the values calculated form given equations and those achieved in the experimental manner was confirmed. It was also shown that due to smaller energy consumption Koflo static mixer can be successfully used instead of Kenics. What is more, the presented report clearly states that static mixers require a huge power demand which leads to the increased maintenance costs and that information should be considered during the system design.

The presented paper is part of the complete description of fluid‐dynamic conditions in the selected static mixers: Koflo and Kenics. The research was also performed for an empty pipe used as a reference state. The scope of work included the analysis of the residence time distribution in the mentioned devices for different Reynolds numbers for both laminar and turbulent flow regimes. The report contains a discussion about residence time distribution functionE(t), cumulative distribution functionF(t), as well as the parameters like the mean residence timet_mand the varianceσ². The main aim of the presented work was to show the applicability of static mixers as chemical reactors and to present their operation characteristics to evaluate the derogations distinguishing them from well known ideal states (i.e. plug flow or ideal mixing). As a result of the accomplished study it was proved that Reynolds number increase results in narrower RTD in all of the tested devices, however the fluid motion is far from plug flow due to axial and radial mixing and the considered equipment should be treated as non‐ideal reactors requiring some additional models for the right description. What is more, in the case of laminar flow, the Kenics static mixer showed the narrowest spread and was considered as the best solution among the studied devices. In the turbulent flow, the difference betweenE(t)functions for all of the mentioned equipment was so small that the suggestion of small impact of insert type on the RTD was made.