EFFECT OF MICROSTRUCTURE OF CARDBOARD ON ITS MECHANICAL PROPERTIES

The article is devoted to the prediction of mechanical properties on the study of the microstructure of the cross section of cardboard. The results of the work in the future can be used as an addition to standard methods for evaluating the mechanical properties of cardboard. On the basis of images of the microstructure of the cross sections of the two-layer test liner cardboard and their graphic processing using modern computer programs, the lengths of fiber contacts were determined. Guided by the fact that the most significant indicator of all geometric parameters of the microstructure is the length of fiber contacts, the main mechanical properties of cardboard were determined (bursting strength and compression resistance, breaking length, bending stiffness, interlayer strength)produced according to various technologies (conventional method of preparing recovered paper stock, dry defibration of recovered paper with aerodynamic formation of the top layer, dry defibration of recovered paper with subsequent supply of fibers to the stock and dry defibration of recovered paper with subsequent grinding in the stock). Each of the technologies allows to obtain cardboard with different mechanical parameters. It has been established that almost all mechanical indicators depend directly proportionally on the length of the fiber contact lines. The obtained dependencies can be used to predict the mechanical properties of cardboard in its production at industry enterprises.

Procedure for calculation of the admissible continuous power transmission currents of overhead wires and contact lines

The proposed methodology summarizes published and original domestic and foreign theoretical and experimental materials on heating and cooling of spiral and shaped wires of overhead power transmission lines and electric power systems and uses those of them that best meet the fundamental laws of heat transfer. Formulas for calculating the surface area for spiral and shaped wires are given. A generalized formula for the convective heat transfer coefficient taking into account the direction and speed of the wind, including for the anti-ice regime, is given. The parameters of this formula do not coincide with the existing ones, since they are based on the experimental data for spiral and shaped wires, and not for round pipes. The formula for calculating the power of heat transfer under solar radiation is given. A generalized formula is given for calculating the continuous allowable current, all components of which are described in detail in the article.

Topological heterogeneity and evaporation dynamics of irregular water droplets

Water droplets sitting between wires are ubiquitous in nature and industry, often showing irregular (non-spherical) droplet shapes. To understand their topological singularity and evaporation mechanism, measuring volume changes of irregular water droplets is essential but highly challenging for small-volume water droplets. Here we experimentally explore topological heterogeneity and evaporation dynamics for irregular water droplets between wires with four-dimensional X-ray microtomography that directly provides images in three spatial dimensions as a function of time, enabling us to get three-dimensional structural and geometric information changes with time. We find that the topological heterogeneity of an irregular droplet is due to the local contact lines and the evaporation dynamics of an irregular droplet is governed by the effective contact radius. This study may offer an opportunity to understand how the topological heterogeneity contributes to the evaporation dynamics of irregular water droplets.

Time Resolved PIV of the Flow Field Underneath an Accelerating Meniscus

We present an experimental analysis of the flow field near an accelerating contact line using time-resolved Particle Image Velocimetry (TR-PIV). Both advancing and receding contact lines are investigated. The analyzed configuration consists of a liquid column that moves along a vertical 2D channel, open to the atmosphere and driven by a controlled pressure head. Large counter-rotating vortices were observed and analyzed in terms of the maximum intensity of the Q-field. To compute smooth spatial derivatives and improve the measurement resolution in the post-processing stage, we propose a combination of Proper Orthogonal Decomposition (POD) and Radial Basis Functions (RBF). The RBFs are used to regress the spatial and temporal structures of the leading POD modes, so that “high-resolution” modes are obtained. These can then be combined to reconstruct high-resolution fields that are smooth and robust against measurement noise and amenable to analytic differentiation. The results show significant differences in the flow topology between the advancing and the receding cases despite velocity and acceleration of contact lines are comparable in absolute values. This suggests that the flow dynamics are tightly linked to the shape of the interface, which significantly differs in the two cases.

Individually Switchable InGaN/GaN Nano-LED Arrays as Highly Resolved Illumination Engines

GaN-based light emitting diodes (LEDs) have been shown to effectively operate down to nanoscale dimensions, which allows further downscaling the chip-based LED display technology from micro- to nanoscale. This brings up the question of what resolution limit of the illumination pattern can be obtained. We show two different approaches to achieve individually switchable nano-LED arrays. We evaluated both designs in terms of near-field spot size and optical crosstalk between neighboring pixels by using finite difference time domain (FDTD) simulations. The numerical results were compared with the performance data from a fabricated nano-LED array. The outcome underlines the influence of geometry of the LED array and materials used in contact lines on the final illumination spot size and shape.