Drop coalescence in technical liquid/liquid applications : a review on experimental techniques and modeling approaches

The coalescence phenomenon of drops in liquid/liquid systems is reviewed with particular focus on its technical relevance and application. Due to the complexity of coalescence, a comprehensive survey of the coalescence process and the numerous influencing factors is given. Subsequently, available experimental techniques with different levels of detail are summarized and compared. These techniques can be divided in simple settling tests for qualitative coalescence behavior investigations and gravity settler design, single-drop coalescence studies at flat interfaces as well as between droplets, and detailed film drainage analysis. To model the coalescence rate in liquid/liquid systems on a technical scale, the generic population balance framework is introduced. Additionally, different coalescence modeling approaches are reviewed with ascending level of detail from empirical correlations to comprehensive film drainage models and detailed computational fluid and particle dynamics

Computational Fluid Dynamics (CFD) Simulation of Mixing Tank at Milk Powder Factory to Reduce Material Losses

Industrial milk powder production applies the principle of a spray dryer. In the powdered milk industry using a spray dryer, there are still some problems in actual conditions such as fouling in the heat exchanger and losses. Losses are lost material or time so that result in losses for the company. The importance of finding material losses as soon as possible it is possible to make a solution so that initially unknown material is wasted in vain can be used as a finished good. Steps taken to resolve the problem material losses is to identify problems and data by making mapping losses according to actual conditions. After that, a CFD mixing tank simulation can be performed on Ansys with the aim of the simulation is to get the contour of the foaming phenomenon and find out the height the phenomenon of foaming (foam) with the properties set up begins at the beginning of making geometric designs with the size of the tank is 3.5 m and uses a marine propeller type,  then proceeds with meshing In geometry, meshing here uses the automatic meshing method due to the limited analysis students. after that the solving stage is carried out by inputting data such as density, viscosity and input multiphase (mixture), viscous (Large Eddy Simulation), as the boundary conditions of the geometry, after that by making a plane from the results of running to form a plane in geometry, then choose the results of the contour volume fraction to find out the phenomena that occur in mixing  tank so that conclusions and solutions can be drawn. Based on the results of data analysis and the field in the form of mapping and data on quantity losses, there are still some material losses in the form of wet and dry losses that have not been identified, initially the percentage ratio of material losses is 40.57% to 9%. One of the biggest contributors to material wet losses is mixing tanks which simulated until it is known that there is a foaming phenomenon. It interferes with the way it works level sensor which causes less maximum withdrawal of milk liquid by the pump. The best solution right way to reduce losses that occur in the mixing tank is to close the valve mixing tank output when showing 1.8% or can be rounded to 2% for safety pump. The liquid that is used as a product is 270 liters which is equivalent to 113 kg. If the calculation is carried out, the company can store 8,505 kg/month of powder

Numerical simulation of droplet formation in a microchannel device

The formation of droplets is a phenomenon with particular importance in the development of industrial emulsions. The quality of these compounds is associated with droplet size and stability over time. Anna et al. (2003) developed a methodology named ¨flow focusing¨ to improve droplet formation processes for engineering applications. In this work, Computational Fluid Dynamics (CFD) based techniques are used to assess the capacity of a pseudo-2D numerical model to reproduce water droplets formation within silicon oil, as obtained in Anna et al.’s experiments. Average time of droplet onset obtained via numerical analysis was 1.5 times larger than observed experimentally, whereas droplets convection velocity and diameter predictions differed by 40-45% and 60%, respectively. Nevertheless, calculated velocity profiles downstream the discharge slot reproduced the expected free-jet shear layer according to outer/inner flow ratio

Fluid Mechanics in Innovative Food Processing Technology

Generally, food industries employ traditional technologies and bulk devices for mixing, aeration, oxidation, emulsification and encapsulation. These processes are characterized by high energy consumption and result in high cost product, with limited diversity and usually with non-competitive quality. Moreover, the byproduct is also high. In recent years immense efforts have been dedicated to overcome these issues and major advances in food engineering have come from transfer and adaptation of knowledge from related fields such as chemical and mechanical engineering. It is well known that the majority of elements contribute to transport properties, physical and rheological behavior, texture and sensorial traits of foods are in micro-level. In this context invention at microscopic level is of critical importance to improve the existing foods quality while targeting also the development of new products. Therefore, microfluidics has a significant role in future design, preparation and characterization of food micro-structure. The diminutive scale of the flow channels in microfluidic systems increases the surface to volume ratio and is therefore advantageous for many applications. Furthermore, high quality food products can be manufactured by means of innovative microfluidic technology characterized by less energy consumption and a continuous process in substitution to the problematic batch one. To meet these challenges, this work is focused on main two tasks: (i) efficient micromixing, and (ii) production of microbubbles and microdroplets. Firstly, two novel 3D split and recombine (SAR) micromixers are designed on an extensive collection of established knowledge. Mixing characteristics of two species were elucidated via experimental and numerical studies associated with microchannels at various inlet flow-rate ratios for a wide range of Reynolds numbers (1-100); at the same time, results are compared with two well-known micromixers. It was found that performances of the mixers are significantly affected by their design, inlet flow-rate ratios and Reynolds numbers. The proposed micromixers show better efficiency (more than 90%) in all examined range of Reynolds numbers than the well-known basic mixers at each desired region; the required pressure-drop is also significantly less than that of the previous mixers. Furthermore, numerical residence time distribution (RTD) was also explored, which successfully predicts the experimental results. In a word, the presented new micromixers have advantages of high efficiency, low pressure-drop, simple fabrication, easy integration and ease for mass production. Secondly, four micro-devices are designed for the mono-dispersed droplets and bubbles generation. Two different experimental setups were used to create water droplet in silicone oil (W/O) and air bubble in silicone oil (A/O) for continuous flow rate from 10 ml/h to 230 ml/h. The mean size of droplet and bubble as well as frequency of generation can be controlled by dispersed and continuous flow rate. Besides, squeezing and dripping flow regimes are observed inside the four devices over a broad range of Capillary numbers: 0.01~0.18. Among the examined four devices, T-1 and T-2 provide smaller droplet (100 µm) and higher production rate. Furthermore, negative pressure setup provides more robust bubble generation but positive pressure yields better production rate. In addition, droplet and bubble diameter is about four times less than the microchannel dimension, therefore small droplet and bubble can be generated spending less energy. In summary, the investigation in this dissertation reflects that both SAR micromixers and micro-devices are very efficient and can be applied to meet the growing demands of food industries. The first part of the thesis, chapters 1 to 5, addresses state of art, design, experimental technique and results of micromixers. The second part, chapters 6 to 9, presents background, construction of devices, tests and results related to the production of microdroplets and microbubbles. Finally, chapter 10 summaries the whole presented work