Interaction of a liquid jet with a co-current gas flow inside the nozzle and under ejection into vacuum

The structure of a gas-droplet flow arising under gas outflow with liquid jet injected into it from a supersonic nozzle into vacuum is studied experimentally. Possibility of the flow structure control in order to obtain droplets of a certain size, composition, and velocity, is considered. The liquid was injected into the co-current gas flow in the prechamber of the supersonic nozzle and then flowed out into the vacuum chamber in the form of a gas-droplet jet. Using the developed technique of droplet deposition on paper substrates, the effect of the Reynolds number of the gas and the pressure in the vacuum chamber on the angular distribution of droplet phase behind the nozzle exit is investigated.

Вплив технології виготовлення випаровуємих катодів на якість іонно-плазмових покриттів лопаток турбін

The article considers coatings deposited on turbine blades via plasma vapor deposition (PVD) method with Ni-Cr-Al-Y cathodes obtained using powder metallurgy (PM) and electron beam remelting process (EBMR). The study analyzes the effect of cathodes manufacturing techniques on surface roughness of rotor turbine blades. Task: to examine a microstructure and chemical composition of the considered cathodes; to quantify a droplet phase of a heat-resistant coating of turbine blades subdivided into size-fractions. Methods used optical microscopy, SEM-analysis. Next results were obtained. In the microstructure of two cathodes under study, it is revealed γ-solid solution with intermetallic Ni-Cr-Al and yttrium-based phases. Simultaneously, distribution of the yttrium phase in the PM-cathode more uniform in compare with EBMR-cathode. Metallographic studies showed that yttrium phase in the structure of the PM-cathode is highly-dispersed, with sizes up to 5 microns, and due to structural and dimensional heredity received during cathode hot isostatic pressing compaction. The structure of the cathode obtained using EBMR-process is a series of the conglomerates of intermetallic phases, with more than 50 microns long, which are branched out on volume. The compliance of the chemical composition of the cathodes under study to requirements of the specifications is established. After the coating deposition on turbine blades by a PVD-method with cathodes under study, were not observed any coating delamination, and their thickness corresponded to the specifications. With a distribution analysis of droplet phase on the turbine blade surface were established that coatings with PM-cathode have been characterized by complete absence of a 65 microns droplet phase, and has half less 25…45 microns droplet phase compared with the EBMR-cathode. Conclusions. The coating with PM-cathode has smaller droplet phase on the turbine blade surface and as a result improved their roughness and gas path surface state. The use of PM in the production of the cathodes for protective coatings provides stable performance of installation and provides long-term operation time of cathodes, compared with the EBMR-cathodes.

Study of non-Newtonian polymer blends using large amplitude oscillatory shearing flow

Large amplitude oscillatory shear (LAOS) was performed on non-Newtonian minor phase in Newtonian matrix phase polymer blends as a first step toward understating more complex immiscible polymer blends under high deformation condition. The blend consists polybutadiene (PBD) as the droplet phase and polydimethylsiloxane (PDMS) as the matrix phase. The PBD droplet phase was an elastic “Boger” fluid prepared by dissolving a high-molecular-weight PBD into a low-molecular-weight Newtonian PBD. Different percentages of the high-molecular-weight PBD were used to prepare different types of Boger fluids that resulted in blends with different viscosity ratios from lower than unity, to unity and higher than unity. Furthermore, the LAOS results of the blends were analyzed by using the Fourier Transform (FT) technique. From a theoretical point of view, the constrained volume model (CV-model) for Newtonian components is adapted to the case of a Newtonian matrix phase and non-Newtonian Boger fluid droplet phase by taking into account stresses that arise in the Boger fluids. The adapted model and the Newtonian CV-model were compared to the experimental results of FT-LAOS for checking the predictability of the model against the rheological properties. The adapted model shows some reasonable qualitative and quantitative agreements at high strain amplitude values.

Research on the phase transition process of sessile droplet on carbon fiber cold surface

The droplet phase transition process on the cold surface of a T300 carbon fiber substrate was studied by observing the droplet freezing process. Through the construction of visualized experimental device, the change in the droplet phase transition time under different experimental conditions, the progression of the solid-liquid interface during the phase transition process, the droplet deformation rate, and the ratio of growth of the interface height after the phase interface appears were experimentally obtained. The influence of different surface temperatures and different droplet volumes on the phase transition process was investigated. The experimental results show that the phase interface shows an irregular profile during the phase transition of the sessile droplet on the cold surface of the carbon fiber substrate, it presents a wave-shape early and smooth concave-shape later. The influence of droplet volume on the phase transition time is not a simple linear relationship. The height of the solid-liquid phase interface during the droplet phase transition process first grows rapidly, then slowly, and then fast once again. In other words, the growth rate of the phase interface is relatively fast when the phase transition has just occurred and the when the bulged tip is formed. At different cold surface temperatures, the droplet deformation rate with a volume of 10μL is basically the same, which is about 32.4%, within an uncertainty of about 1%. However, the influence of gravity factor is important in determining the droplet deformation rate for different droplet volumes.

Diamagnetic Manipulation of Cell-Encapsulating Droplets

In this thesis, a microfluidic method for label-free control of cell encapsulating droplets is developed using diamagnetic forces. To generate droplets in a microfluidic device, we use a symmetrical flow-focusing design, where two streams of a continuous phase shear a single stream of a droplet phase, resulting in droplet generation. First, it is shown that by adjusting only the droplet phase flow rate, precise control of empty droplets can be achieved. Human prostate cells are then introduced to the system and encapsulated by droplets. Control of the cell-encapsulated droplets and empty droplets is studied. It is shown that cell-encapsulated droplets and empty droplets deflect by different amounts when exposed to the magnetic field. By exploiting this difference, efficient sorting of empty droplets from cell-encapsulated droplets is achieved at a purity of 85% in a single pass. Following sorting, cells are analyzed and show 90% viability after a two-hour incubation period.

Diamagnetic Manipulation of Cell-Encapsulating Droplets

In this thesis, a microfluidic method for label-free control of cell encapsulating droplets is developed using diamagnetic forces. To generate droplets in a microfluidic device, we use a symmetrical flow-focusing design, where two streams of a continuous phase shear a single stream of a droplet phase, resulting in droplet generation. First, it is shown that by adjusting only the droplet phase flow rate, precise control of empty droplets can be achieved. Human prostate cells are then introduced to the system and encapsulated by droplets. Control of the cell-encapsulated droplets and empty droplets is studied. It is shown that cell-encapsulated droplets and empty droplets deflect by different amounts when exposed to the magnetic field. By exploiting this difference, efficient sorting of empty droplets from cell-encapsulated droplets is achieved at a purity of 85% in a single pass. Following sorting, cells are analyzed and show 90% viability after a two-hour incubation period.