Two-stage particle separation channel based on standing wave surface acoustic wave

Microfluidic technology has great advantages in the precise manipulation of micro and nano particles, and the collection method of micro and nano particles based on ultrasonic standing waves has attracted much attention for its high efficiency and simplicity of structure. This paper proposes a two-stage particle separation channel using ultrasound. In the microfluidic channel, two different sound pressure regions are used to achieve the separation of particles with positive acoustic contrast factors. Through numerical simulation, the performance of three common piezoelectric substrate materials was compared qualitatively and quantitatively, and it was found that the output sound pressure intensity of 128°YX-LiNbO3 was high and the output was stable. At the same time, the influence of the number of electrode pairs of the interdigital transducer and the electrode voltage on the output sound wave is studied. Finally, 15 pairs of electrode pairs are selected, and the electrode voltages of the two sound pressure regions are 2.0V and 3.0V respectively. After selecting the corresponding parameters, the separation process was numerically simulated, and the separation of three kinds of particles was successfully achieved. This work has laid a certain theoretical foundation for rapid disease diagnosis and real-time monitoring of the environment in practical applications.

MÉTODOS DE INJEÇÃO DA AMOSTRA EM MICROSSISTEMAS ELETROFORÉTICOS

SAMPLE INJECTION METHODS IN ELECTROPHORETIC MICROSYSTEMS. Electrophoresis is by far the most popular separation method implemented in microscale, most probably due to its instrumental simplicity, low cost and portability. Due to the increasing use of miniaturized electrophoretic systems, the study of fundamental aspects can improve the development of methodologies for several applications. One of the major challenges related to electrophoresis chips refers to the sample injection mode, in this way, this study presents a review on sample injection methods for microchip electrophoresis covering electrokinetic and hydrodynamic approaches, describing theoretic and instrumental aspects. Since the sample volume affects the analytical performance, the precise and reproducible control of the sample amount to be introduced into the separation channel is highly desirable to ensure reliable chemical analysis. Electrokinetic modes based on floating, pinched and gated protocols are presented and discussed providing an overview about the electrokinetic control of the sample through three methodologies. In the same way, hydrodynamic techniques including the use of microfabricated valves and pumps, syringe pumps, electronic micropipettes, rubber suction bulb and acupuncture needle are approached, thus expanding the view of hydrodynamic injectors based on classical and alternative methods.

Calculation of particle trajectories in the pneumatic separation channel using various methods

The article presents the comparison testing of particle trajectories in the pneumatic separation channel (PSC) of the pneumatic seed separator SP-2F and its bend, calculated using computer simulation method and two experimental-theoretical methods. They are based on taking into account the real airflow velocity field. In the first variant, the velocity field was measured in an idle mode, in the second at the nominal grain load. The studies were carried out in a vertical PSC with a supporting grid divided into two parts by a partition wall. In the variant with the theoretical velocity field the trajectories of light and grain impurities in the first part of the PSC are shifted closer to the outer wall. In the second part of the channel, particles with hovering speed of 8.0...10.0 m/s are carried upwards, and with hovering speed of 11.0 m/s they fall down into the purified material. In the variant of the experiment in an idle mode, particles with the hovering speed of 7.0...10.0 m/s rise up in the second part of the PSC. In the variant with grain load, particles with the hovering speed of 7.0...9.0 m/s rise upward and ricochet off the inner walls of the PSC and a bend wall, and particles with the hovering speed of more than 10.0 m/s fall down into the purified material. In the variant of the experiment with the grain load, the particle velocity with the hovering speed of 5.0...9.0 m/s at the exit of the PSC bend is more evened as compared to other options - 2.3...2.7 m/s, and the velocity vector of most particles is directed at a lower angle to the horizontal: from 4 up from the horizontal to 17 down from the horizontal. The most accurate is the calculation of particle trajectories using the velocity field in the PSC at the nominal grain load. The results of the study can be useful in the theoretical substantiation of the design parameters of pneumatic systems of grain cleaning machines.

Study of Performance Characteristics of the Gravitational Guide Curve of Feeder Unit

The rate of the feed velocity and specific load in the air separator are interrelated and require a rational approach to their choice, because reducing the rate of velocity increases grain flow thickness, which adversely affects the efficiency of grain separation in the separation zone, but limits separator performance. Based on the research of many authors, it was concluded that the feed velocity of grain material into the pneumatic separation channel should be in the range of 0.4… 0.6 m/s. Taking into account that using a feeder unit for multilevel grain input, the total thickness of grain flow is divided by the number of the involved levels of input. The main condition is to ensure a single layer of grain feed at the velocity at which the most intense release of light impurities. Therefore, the purpose of the study is to identify rational parameters of the guide gravitational surface of the feeder unit with the provision of appropriate performance characteristics of the grain flow during its multilevel feeding into the pneumatic separating channel. As a result of experimental research, the dependences of the modes of movement of grain material on the gravitational guide curve on its main parameters, namely, the length of the acceleration section Lp, its angle α and the radius of the arcuate section r. On the basis of the carried-out research parameters of a gravitational guide surface at which a single-layer mode of movement of grain material for a range of specific loadings is reached are established qB = 250 – 500 kg/hour. Accordingly, for the conditions of movement of grain material with a thickness of one grain with the velocity of feeding into the pneumatic separation channel vв = 0.5…0.6 m/s, the rational parameters of the guide gravity curve for cereals with the internal friction coefficient φтер = 0.47…0.73 there are: the length of the acceleration section Lp = 0.2 m, the angle of its inclination α = 33° and the radius of the arcuate section r = 0.15 m.

The technological aspect of soybean seed separation

The results of a study on the purification of soybean seeds by the combined use of a gravity column with a zigzag channel formed by a cascade of installed combs and a pneumatic separation channel with a vertically ascending air flow and with narrowing partitions installed in it are presented.

Increase of seeding material quality of agrarian crops by the pneumatic electric separator

A detailed analysis of technical means and methods of seeds separation, as well as the research results of domestic and foreign authors, have proved that one of the perspective methods for getting of high quality seed material is the pneumatic and electric separation.The analysis of research works and the modern technical level of pneumatic separators showed that insufficient attention was paid to the study of aerodynamic separation of small-seed crops, especially, cereal grasses. By the conditions of separation in a vertical pneumatic channel the cereal crops change the area of the midlength section as to the air flow forces, and the probability was increased of getting of seeds with germs to a biologically defective seed without germs. To increase the quality of pneumatic separation one can by the selective orientation of seeds in mixture with longer axis perpendicularly to the flow of air. It is possible to achieve these conditions by the additional force action on seeds (as particles). The response of this force action could be different for a healthy seeds (with germs) and for a non-viable (without embryo) or a weed seed. Such a force effect on the particles of small-seed crop mixtures can be realized by creating of a homogeneous electric field in a separation channel. This requires a theoretical and experimental study of force action on particles during the process of separation, also justification of parameters and operating modes of the pneumatic electric separator. This study is the preconditions for design improvement of the pneumatic electric separator.