Modelling flow and mass transfer of thermal separation equipment constitutes one of the most challenging tasks in fluids process engineering. The difficulty of this task comes from the multiscale multiphase flow phenomena in rather complex geometries. Both analysis of flow and mass transfer on different scales as well as validation of models and simulation results require advanced experimental and measurement techniques. As a follow-up to intensive discussions during the 2019 Tutzing Symposium ''Separation Units 4.0'' a wide set of available modern experimental technologies is presented.
Solid lipid nanoparticles (SLN) as a new generation of drug carrier systems for pharmaceutical applications are currently under intensive investigation. They can be prepared by melt-homogenization of a matrix lipid in surfactant-containing aqueous media. In the corresponding production sequence, the crystallization of the resulting lipid droplets to solid nanoparticles is a crucial step for reproducible product properties. Hitherto, melt crystallization in these dispersions is usually performed in a batchwise process under poorly defined cooling conditions, without much regard to the well-known aspects of heat transfer, homogeneity in the product mixture, and precise process control. In addition, these setups often only allow the application of low cooling rates. The use of high, well-defined cooling rates would, however, offer very interesting new possibilities for the manufacturing of such drug carrier systems. Due to their small volumes and superior heat and mass transfer performance, microfluidic devices ensure a precise setting and control of the optimum process conditions. In this study, a microfluidic process for the continuous melt crystallization of SLN suspensions is established, allowing for high and well-defined cooling rates. For various cooling rates, the crystallized SLN were analyzed by differential scanning calorimetry, X-ray diffraction, laser diffraction, and photon correlation spectroscopy. The samples were also analyzed after well-defined storage times in order to investigate the stability of the suspensions.
This contribution presents results from entrainment measurements in a forced circulation flash evaporator which was designed to systematically investigate the droplet entrainment under real evaporating conditions. Operating pressures in a range of 100 to 800 mbar(a) and temperature differences between 5 and 55 K were conducted. Gas load factors up to f G = 4.0 Pa 0.5 were achieved with glycerol-water and water as evaporating liquids. A conductivity measurement was used to determine the absolute entrained liquid and entrainment ratios. The results show an exponential behavior between entrainment, gas load factor, and heat flux due to superimposing effects. Investigation on the pressure drop across the orifice plate showed no influence for operation at gas load factors of f G < 2.5 Pa 0.5 .
For the assessment of separation technologies from an ecological and economic perspective, a case study was performed to investigate the influence of entrainment on energy and resource demand of a single apparatus and on a single production process. Taking the example of the Rectisol process, the influence of droplet entrainment on individual separation equipment as well as on the process as a whole was identified via flowsheet simulation. Based on the calculated mass and energy balances, an LCA and LCC approach was used for the quantification of the entrainment influence.
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