Optimizing the separation characteristics of the waterinjection hydrocyclone using mathematical modelling

Purpose. Although the hydrocyclone separator has many advantages, it still has some limitations which decrease its separation efficiency in many mineral processing applications because of fine particles which are miss separated to the coarse product in the underflow. Water injection in the conical part of the cyclone was recently implemented to solve this problem. The water injection mechanism and the way in which the injected water affects the separation are still not clear and need to be more investigated. Methods. New design of water injection hydrocyclone was tried using a modified conical part with a water injection range consist of five equal distance injection openings open directly on the periphery of the cone part. Findings. This study presents a mechanical mathematical model that simulates the water injection to give a clear indication of the injection mechanism impact on the classification process. It could also predict the dependence of the basic characteristics of the classification on the amount of the injected water and the influence of different operating and design parameters of the hydrocyclone. Originality. The model accounts for the fluid flow, the particle motion, the turbulent particle diffusion, and particle settling. Particle interactions and fine particle entrainment by settling coarse particles are also included in the model. The model was found to predict well the injection effect and agrees with the experimental results. Practical implications. The results showed also that the increase in water injection velocity leads to an increase in both the cut size and the minimal value of the separation curve. It was found also that the hydrocyclone length has an important effect on the injection process, and the separation sharpness is directly proportional to it at higher values of water injection velocity.

A method based on circumferential strain distribution for roller path design in conventional spinning of thin-walled conical part with curved surface

Multi-pass conventional spinning is the preferable forming technology for the forming of thin-walled conical part with curved surface (TCPCS) in aerospace field. In multi-pass conventional spinning, the design of roller path is a critical problem due to its sensitive effect on the deformation mode and forming defect during spinning process. However, at present, the roller path is still mainly designed based on experience and trial-and-error, which seriously restricts the high-performance spinning of TCPCS. In this work, a new quantitative method based on circumferential strain distribution was developed for the roller path design in multi-pass conventional spinning of TCPCS. In this method, the total required circumferential strain for the forming of final TCPCS by conventional spinning was firstly determined. Then, the spinning passes number were obtained through dividing the total required circumferential strain by the ultimate circumferential strain producing the spinning instability ( ε θult ). As for the roller path profile in each pass, it is divided into two sections and determined respectively, i.e. the attaching mandrel section and the performing section. The attaching mandrel section presents the same profile of mandrel. The profile of preforming section is determined point-by-point by distributing the rest of circumferential strain { ε θni } to produce the final TCPCS. The point-by-point distributed circumferential strain is half of the { ε θni } at the initial stage until reaches the half of ε θult , then it will keep the half of ε θult to the end. The proposed new method of roller path design was validated by finite element simulation, where well spinning stability, wall thickness distribution and roundness were obtained. This method provides a quantitative, high-efficient and universal way for the roller path design in conventional spinning of TCPCS.

Study of the structure of gas flow іn a cyclone wіth іntermedіate dust removal

The works in which designs of the dust collectors, which are often used in the industry, are analyzed. It is shown that the efficiency of dust collectors largely depends on the structure of the gas flow in the apparatus. Based on the analysis of the current cyclone devices, a picture of the separation process is obtained, and the factors that negatively affect the operation of dust collectors are identified. It is established that forecasting the work of dust collecting devices in certain conditions is most effective to perform methods of numerical modeling and simulation of the separation process, which are widely used for the research of devices of this type. Using the methods of numerical simulation, the study of the cyclone with intermediate dust removal was carried out. In this cyclone, the change in the radius of the apparatus of the tangential, radial, and axial velocity components is investigated. In the course of the research, it is established that in the separation space the tangential component of velocity increases from 18–20 m/s in the upper part of the device to 22–25 m/s in the area of the lower end of the exhaust pipe, the radial component of velocity takes values from 0 to 2 m/s, and the axial component of the speed has a maximum value of 10–15 m/s. In the conical part of the apparatus the tangential component of velocity decreases from 27 m/s in the upper planes of the conical part of the apparatus to 10 m / s near the dust unloading pipe, the radial component of speed has centripetal character, the axial component of speed decreases as the gas flow to the dust unloading pipe decreases. It has been established that in the cylindrical part of the apparatus about 60 % of the gas flow volume is transferred from the downstream to the upstream by a secondary vortex, and in the conical part, about 40 % of the gas volume is transferred from the downstream to the upstream. It is shown that large values of the tangential component of velocity in the separation zone contribute to the ingress of dust particles into the annular space behind the dust unloading holes, and small values of the tangential component of velocity, axial and radial in the annular space behind the dust unloading holes has a positive effect on the operation of the dust collector.

Influence of the Undercut Anchor Head Angle on the Propagation of the Failure Zone of the Rock Medium—Part II

Problems concerning the influence of the geometric parameters of an undercutting anchor on the range of the failure zone of rock medium during the pulling out of the anchor constitute one of the aspects that arouse the interest of authors due to attempts to use undercutting anchors in the process of rock lump separation. This method is considered an alternative to the existing methods of separation, especially in special cases of mining technologies. This article presents the results of numerical investigations into the effect of changes in the head geometry that occur as a result of wear on the conical part of the undercutting anchor and the extent of failure of the rock medium during its pulling out. This is an extension of considerations presented in previous work, where special attention was paid to the influence of potential errors in anchor installation, leading to changes in head geometry and, consequently, to changes in the extent of the failure zone of the rock medium. As a result, significant changes in the volume of the detached rock masses are observed. This study shows that the increasing surface friction of the stripping anchor head leads to a decrease in the angle of the undercutting head. As a result, the extent of the failure zone measured on the free rock surface increases, the value of the angle of the failure cone at the initial stage of the stripping decreases, and the deformation of rock in the plane perpendicular to the anchor axis increases.

Law of Metal Flow of Thin-Walled Conical Part With Variable Section During Spinning

During the spinning process of the variable-section thin-walled conical parts, the metal flow law is relatively complicated and the flange is prone to be unstable, which resulting in wrinkling and other defects. In this paper, the variable-section conical part of superalloy GH1140 is taken as the research object. The spinning forming process is numerically simulated by using Simufact Finite Element software and the metal flow in each stage of the forming process is analyzed. The flow velocity shows an annular distribution as a whole. The metal near the center of the circle flows more slowly, and the metal far from the circular flange flows more quickly. In the direction of thickness, the velocity of metal flow decreases gradually. Under the feeding action of the roller, the metal in front of the roller is subjected to axial tensile stress, tangential and radial compressive stress, resulting in a strain state of one-way tension and two-way compression. The metal moves along the negative direction of the rotary wheel feed, resulting in the increase of the sheet wall thickness. The correctness of the model in this paper is further verified by spinning experiments. The research results provide a theoretical basis for analyzing the mechanism of forming defects and improving the quality of spinning forming of conical thin-walled parts with variable sections.

Modeling Tsunami-Induced Erosion of Bridge-Abutment Backfill

Tsunamis can seriously damage bridges in coastal areas. Studies of such damage have elucidated the action of tsunami-induced forces on girders. However, tsunami-induced erosion of bridge-abutment backfill has been largely neglected. This article investigates this little-studied topic using hydraulic model experiments and numerical analyses. The results show that a tsunami erodes the backfill close to the abutment; the scale of the erosion increases with the duration of the tsunami. By contrast, the backfill on the far side of the abutment remains relatively intact. This suggests that the presence of the abutment accelerates the erosion of the backfill in its vicinity. A numerical simulation shows that the tsunami erodes the oval conical part of the backfill on the landward side of the onshore wing. When the erosion reaches the lower end of the wing the backfill begins to flow out from underneath. Thus, an increase in the soil-cover depth of the onshore wing might help slow down the erosion.

Effects of the Geometric Parameters of Mixer on the Mixing Process of Foam Concrete Mixture and Its Energy Efficiency

The paper studies the influence of the geometric parameters of the mixer on the mixing process, the construction of the mixing body, its location in the mixer bulk, and the mixer shape and geometry. The technique of calculating the power spent on mixing the foam concrete mixture is described. The effects of the ratio of the mixture height to the mixer diameter, the number and width of reflective partitions, and the shape of the conical part of the mixer on the homogeneity of the foam concrete mixture and the power consumption are considered. The optimal ratios of the foam concrete mixture height to the mixer diameter have been determined. Moreover, the optimal range of the ratios of the partition width to the mixer diameter has been established, in order to obtain a homogeneous foam concrete mixture throughout the volume with lower energy consumption. The optimal values of the angle of the mixer conical part for the preparation of a foam concrete mixture have been determined.

SPINDLE-WHORLS FROM THE LATE TRYPILLIA SETTLEMENT TROIANIV

At the Troianiv settlement more than 200 ceramic whole and fragmened spindle-whorls (SW) have been found. The size of the SW from Troianiv can be roughly divided into large, medium and small, with a diameter of approximately 55, 40 and 30 mm respectively. The height of the SW is from 2.0 to 3.5 cm. The weight of the SW ranges from about 20 up to 45 g. The shape of the SW from Troianiv was not standardized. Their profiles are varied but they mostly come down to a conical or biconical shape. Most of the SW has no decoration, only 56 items are ornamented. Two basic techniques are used to decorate — crossed lines and small needles made by very fine needle-shape tool. Only conical part on the Troianiv SW was covered by decoration. There are two main schemes of ornamentation — the radial and the circular ones. Large number of the items has the pictographic images. Among them several types of drawings can be distinguished with the dominated sign that most likely acts as a symbol of vegetation. The plant symbols on the spears are in conjunction with the zigzag and cross signs. The analysis of Troianiv SW suggests that they were not only utilitarian objects but also used in cult practice. With the SW from the Late Trypillia and other Early Bronze Age (EBA) cultural groups Troianiv items is definite unity by morphological features and decoration. However, many ornamental elements are inherent in the decoration of the SW from the specific locally-chronological groups of Trypillya CII and may indicate the identity of particular social collectives with common traditions in the sacral sphere. The analogies to the Troianiv SW in different EBA cultural groups testify to the close intercultural links between Late Trypllia and neighboring cultures.