Investigation on Film Formation Characteristics of Pressure-Swirl Nozzle

The film formation during the spray/wall impingement has attracted more attention. The present study investigated the film formation characteristics of the pressure-swirl nozzle by applying the contact-free optical method. According to experimental results, the impingement distance had a slightly more significant effect on the actual spray angle than the mass flow rate, and the maximum changing value was 34.6°. The bulge at the center of the surface became insignificant with the impingement distance. The liquid film was divided into the raised zone, annular zone, and free flow zone. The maximum time-average thickness at the central position was 2.84 mm, and correlations for predicting the time-average thickness and surface roughness were fitted. The time-average thickness of the annular zone was 0.38–0.59 mm, relatively thinner than other zones. When the impingement distance was lower than 10 mm, the time-average film thickness and surface roughness in the annular zone and free flow zone decreased first and then increased with the impingement distance. However, effects of mass flow rates and impingement distance on the liquid film were negligible when the impingement distance was higher than 10 mm. The experimental findings are helpful to fundamentally understand the film formation during the spray/wall impingement.

Objective Assessment of Corneal Backscattered Light in Myopic, Hyperopic, and Emmetropic Children

Purpose: To determine the corneal densitometry values by using Scheimpflug imaging in myopic, and hyperopic children and to compare the results with emmetropic children.Methods: The corneal densitometry measurements of the subject were obtained with Pentacam Scheimpflug tomography. The values were automatically measured in standardized grayscale units (GSU) over an area 12 mm in diameter, which was subdivided into 4 annular concentric zones (0-2 mm, 2-6 mm, 6-10 mm, 10-12 mm) and 3 corneal depths (anterior layer: anterior 120 µm; central layer: from 120 µm to the last 60 µm; posterior layer: last 60 µm). In addition, we evaluated the correlation between spherical equivalence and anterior corneal morphological parameters and the corneal densitometry values.Results: A total of 216 participants were included in this prospective cross-sectional study. The eyes were divided into three groups related to their spherical equivalent (SE) refractive error values as follows: 89 (41.2%) hyperopic eyes, 66 (30.6%) myopic eyes, and 61 (28.2%) emmetropic control eyes. The hyperopic eyes were found to have lower corneal densitometry values in 4 annular zones and the total diameter of all depths except the central layer. However, only the 6-10 mm annular zone of the central and posterior layers of the myopic eyes had lower corneal densitometry values than emmetropic eyes. There was also a significant correlation between spherical equivalence and corneal densitometry values in some zones of the hyperopic eyes. Conclusion: Backward scattering of light was lower in hyperopic eyes and this could affect the visual quality.

TiC – Cr3C2 – WC – NiCr – Mo – C cermet plasma coatings

Two bulk cermets TiC – WC – Cr3C2 – Ni 20 % Cr – Mo – 2.8% C after liquid-phase sintering at 1400 °C for 1 hour were used to manufacture powders for plasma spraying of coatings. Cermets were obtained with limited time of mechanical alloying at the stage of mixing. Plasma coatings were sprayed on a setup with a nozzle attached to a plasmatron for local protection of the sprayed particles from the air atmosphere. The content of WC – Cr3C2 – C in the cermets provided compensation for carbon losses at all stages of coating production and the formation of an annular zone, the volume of which determines the increase in the TiC content in the coatings by 20 % and the formation of additional carbides in the matrix. The microhardness of cermet with an initial carbide content of 60% is 15.26 – 16.83 GPa with a load on the indenter of 200 G and 20.91 – 24.68 GPa with a load on the indenter of 20 G, the difference was explained by a scale factor. The contribution of the microhardness of carbides to the microhardness of cermet with an initial carbide content of 60% was estimated according to the rule of mixtures, proceeding from their volume fraction and microhardness of cermet under a load on the indenter of 20 G. In the initial powder for spraying, this contribution is high, 33.19 GPa, close to Hardness TiC. The contribution of microhardness of carbides in the coating is lower, 28.09 GPa.

Resonant excitation of rotating waves in annular zones

A method and a device are developed for exciting powerful resonant acoustic rotating waves in a gaseous or liquid flowing working medium located in the annular zone between the rotor and stator, for its vibration treatment. Keywords: vibration treatment, vibrations, natural frequency, vibration form, waves, acoustic vibrations, resonance. [email protected]

Impact of friction coefficient on particles circulation velocity calculated by euler-lagrange model in spouted bed apparatus for dry coating

This paper is a continuation of research concerning gas-solid flow modelling using the Euler-Lagrange approach in a spout-fluid bed apparatus. The major challenge in this case was to determine the friction coefficient for particles hitting against the walls of the apparatus. On the basis of the properties of similar materials the value of this quantity was estimated at 0.2. Therefore, it proved useful to check the model’s sensitivity to the value of this parameter. The study investigated the effect of friction coefficient on calculated values of particles velocity in the draft tube and the annular zone of the device for various volumes of the circulating bed. In the course of calculations, a relatively small influence of friction coefficient on particles velocity was observed in the tested zones of the apparatus. The changes were most visible for large volumes of the bed, which was connected with an increase in the number of collisions of particles with the walls.

An explanation of large-scale coal and gas outbursts in underground coal mines: the effect of low-permeability zones on abnormally abundant gas

Large-scale coal and gas outbursts pose a risk of fatal disasters in underground mines. Large-scale outbursts (outburst of coal and rock greater than 500 t) in recent years in China indicate that there is abundant gas in areas of outbursts containing large amounts of potential energy. The adequate sealing properties of the roof and floor of a coal seam are required for local abundant gas around the site of an outburst, but an annular low-permeability zone in a coal seam, which prevents the loss by gas migration through the coal seam itself, is also required. The distribution of coal gas with this annular zone of low permeability is described, and it is proposed that the annular zone of low permeability creates conditions for confining the coal gas. The effect of this low-permeability zone on the gas distribution is analyzed after allowing for simplifications in the model. The results show that the permeability and length of the low-permeability zone have a great impact on the gas distribution, and the permeability is required to be several orders of magnitude less than that of normal coal and enough length is also in demand. A steep gradient of gas pressure in the low-permeability zone and the high-pressure gas in the abundant zone of gas can promote coal mass failure and coal wall deformation, thereby accelerating the coal and gas outburst. The high-pressure gas in abundant zone of gas will lead to a large-scale outburst if an outburst occurs.

An explanation of large-scale coal and gas outbursts in underground coal mines: the effect of low-permeability zones on abnormally abundant gas

Large-scale coal and gas outbursts post a risk of fatal disasters in underground mines. Large-scale outbursts (outburst of coal and rock greater than 500 t) in recent years in China indicate that there is abundant gas in areas of outbursts containing large amounts of potential energy. The adequate sealing properties of the roof and floor of a coal seam are required for local abundant gas around the site of an outburst, but an annular low-permeability zone in a coal seam, which prevents the loss by gas migration through the coal seam itself, is also required. The distribution of coal gas with this annular zone of low permeability is described, and it is proposed that the annular zone of low permeability creates conditions for confining the coal gas. The effect of this low-permeability zone on the gas distribution is analyzed after allowing for simplifications in the model. The results show that the permeability and length of the low-permeability zone have a great impact on the gas distribution. A steep gradient of gas pressure in the low-permeability zone and the high gas pressure in the abundant zone of gas can promote coal mass failure and coal wall deformation, thereby accelerating the coal and gas outburst. The high pressure gas in abundant zone of gas will lead to a large-scale outburst if an outburst occurs.

A computer-aided specimen design to induce shearing strain around a hole

The local torsion process which involves an axisymmetric torsional loading around the design position of a hole in a structure has recently found important applications for grain refinement in tubes and fastener holes. The specimen design is a pre-requisite for any experimental investigation of the local torsion process. The purpose of this study is to investigate a number of potential designs which enable the implementation of the local torsion. These designs include a mandrel to twist the specimen and a range of connection configurations between the mandrel and the specimen including threaded, hexagonal and spline bindings. In order to understand the process requirements and for estimating the effect of design parameters, a coupled numerical analysis of the specimen is utilized, involving a non-linear finite element analysis using Abaqus. A sequence of computational steps with different boundary conditions at the interface is devised to simulate the coupled problem. The proposed configurations are compared for their abilities to perform the local torsion and produce the shearing strain within an annular zone around the hole. This allows investigation of the effectiveness of each design for the implementation of the local torsion. The distribution of strain accumulated around the hole in the radial direction is studied after carrying out the process. Finally, a specimen–mandrel assembly design is recommended to ensure that the process can be successfully implemented.