The technology of emulsions is used in various industrial application such as cosmetics, foods and pharmaceutics. It is also well known that mono-dispersed distribution is required stability. We focused on emulsions preparation by Shirasu Porous Glass (SPG) membrane emulsification. Compared to conventional emulsification method, this emulsification method doesn't require strong shearing force to prepare emulsions. It is also noted that the emulsions prepared by SPG membrane has mono-dispersed droplet size distribution and the droplet size. SPG membrane emulsification method requires only less energy input when prepare the same droplet size.
In this study, Oil-in-water (O/W) microemulsions prepared using SPG membrane emulsification method. Soya oil and ion-exchanged water were used as dispersed and continuous phase respectively. Sodium dodecyl sulfate (SDS) was used as anionic surfactant, and it added to ion-exchanged water. Soya oil was forced into continuous phase through SPG membrane (membrane pore size is 5 or 20 μm, and its surface is hydrophilic) using syringe pump. To disperse the oil droplet, the continuous phase was stirred by magnetic bar.
The effect of volumetric flow rate, stirring speed, and concentration of surfactants were examined. In this abstract, only about changing volumetric flow rate is described. In the condition that volumetric flow rate was changed 4 steps from 0.8 ml h-1 to 6.4 ml h-1 average droplet size, average droplet size had no significant change on each condition. Interestingly, these droplet sizes were about 3-4 times as large as membrane pore size (5 μm). On the other hand, coefficient of variation (CV), which is index of mono-dispersed distribution, increased with increasing volumetric flow rate.
Microfluidics, the potentiality of generating monodisperse droplets, is an interesting tool in the encapsulation process due to its capability of microparticles fabrication. Droplet generation which occurs by two immiscible fluid is controlled by providing of flow- or pressure-driven approach. To combining the size of droplet in both physical and operating parameters, using the dimensionless number characterize the flow motions in different systems was studied. The dependence of the droplet size/channel size on the flow rate ratio (Qc/Qd), viscosity ratio (λc/λd), Reynolds number (Re) and Capillary number (Ca) was investigated for a wide range of fluid properties and flow conditions. The data was collected from the two-channel size of the 100 and 190 μm etch depth of microfluidic flow-focusing devices. An increase of the flow rate ratio resulted in a decrease of the droplet size. The viscosity ratio played an important role in droplet generation. This study also reveals that the droplet size and flow regime could be correlated with the Re and Ca of both phases. A diagram of a changing of flow regime was obtained. Moreover, the results indicated that the monodisperse droplet not only occurs in a dripping regime but also could be produced in a tip-streaming regime.
Magnetorheological fluid (MRF) attracts attention as a functional fluid of which viscosity can be controlled by magnetic field. Since MRF is a mixture of a base oil and magnetic particles, we often find particle sedimentation and/or oil separation due to the density difference and familiarity of the particles and the base oil. The objective of this study is to increase the sedimentation stability of MRF by using suitable stabilizing additives. Also, we consider the mechanism of stabilization with the connection of the network structure build by the additives and interaction with the magnetic particles.
We selected three stabilizing additives; a fumed silica, a styrene-based polymer, and an organogelator (PMDA-2C8/oleyl) and prepared MRF using such additives. We measured steady state flow characteristics and time-dependency of the viscosity of MRF by using a rheometer; Rheologia A-300, Elquest. Stability test was also conducted using a graduated cylinder. Morphological observation of the stabilizing additives was conducted by using a transmission electron microscope (TEM). From the experimental results, we found thixotropic behavior both for MFR prepared with the fumed silica and PMDA-2C8/oleyl. Particularly, PMDA-2C8/oleyl was expected to build internal structure due to the network formed by self-assembly of molecules. Although the viscosity of MRF increased with the addition of the styrene-based polymer, the MRF displayed no viscosity time-dependency. The styrene-based polymer can increase the yield stress of MRF, consequently prevent the sedimentation of particles. From TEM images, we can observe that fumed silica particles connected alternately, while the self-assembly of PMDA-2C8/oleyl formed network structure in the oil.
Magnetorheological fluid "MRF" is a slurry prepared with an oil and magnetic particles having the average particle diameter of several μm. Since the viscosity of MRF can be reversibly controlled by a magnetic field, MRF is classified as a functional fluid. The quick and large variation of the rheological property of MRF with respect to a magnetic field is convenient to the application such as dampers, brakes, and clutches of automobiles. In order to show good fluidity of MRF under no magnetic field conditions, suitable dispersant is generally added to prevent viscosity increase due to particle aggregation. Moreover, MRF has large difference of density between the oil and particles, consequently shows particle sedimentation and liquid separation of the upper layer. Therefore, the development of the technique to increase the stability of MRF is necessary.
In this study, we focused on the effect of fumed silica as a stabilizer, which is widely used for paint industries. We prepared MRF with oleic acid as a dispersant and several fumed silica additives <see table> with different surface characteristics. The rheological measurements and stability tests were conducted for thus obtained samples. From the results, we found that the degree of hydrophobization and the concentration of silanol groups of fumed silica affected to the rheological properties and stability of MRF. In addition, MRF prepared with hydrophilic fumed silica showed further reduction of viscosity by the addition of oleic acid as compared to hydrophobic fumed silica.
In this study, we numerically study and experimentally validate the flow resistivity of commercial nonwoven fabrics filters used for a bag filter system. A numerical method that coordinates the filter structure obtained by X-ray CT imaging with computational fluid dynamics using immersed boundary method is developed to represent a realistic flow field inside the filter during simulation. We investigated the effect of superficial velocity, porosity of the filter domain, and the type of filter then analyzed the results using Darcy's law. The results showed that the calculation results from our numerical method were quantitatively in good agreement with the experimental measurement. We also verify that the Kozeny constant can be estimated by utilizing the solid volume fraction defined by immersed boundary method. These results show that our simulation method can be used to clarify the effects of porosity, fiber arrangement, and fiber shape on the pressure drop. We will discuss the application of this method to coalescence of oil droplets in oil-water separation process.
There are lots of stuff, which is subject to the rheological issue, in a market. Typical examples are grease for mechanical industries, cream and hair gel for cosmetic industries, and gelatin for food industries.
On the other hand, there is few number of the research for mixing dealing with rheology due to complex factors, in spite of facing many of mixing problems in industries. One of the important factors is fluid viscosity. Therefore, as guided by N. Harnby et al. (Mixing in the Process Industries, 2nd edition issued 1997), in case of non-Newtonian fluid, mixing Reynolds number is modified with apparent viscosity, which is converted with coefficient of shearing rate (Kagakukogaku-Binran) proposed each type of impeller.
In this study, comparing with spinnability fluid and non-spinnability fluid (no 1st normal force difference fluid), as non-Newtonian fluid has been done, in terms of flow characteristics.
The mixing power has been measured with similar viscosity, the power for spinnability fluid is proportional to cubic of impeller speed for all type of impeller we have investigated. This is typical behavior in turbulence region. On the other hand, the mixing power for non-spinnability fluid perform differently. Exponent of impeller speed change from approximately 2 to 3, depending on impeller shape. However, flow is not observed, especially at the condition obtained exponent 2 of impeller speed.
