Influence of Diffusion through a Porous Film under Electrode Surface in Chronoamperometry Problems

In the presented work on chronoamperometry, the Cottrell model has been generalized by taking into account a thin porosity layer covering the surface of the electrode and Tafel kinetics of an electrode reaction. The effective diffusion coefficient inside a porosity layer is calculated by Bruggeman’s law. It is shown that in the quasi-stationary approximation of diffusion inside a thin porous layer, the chronoamperometry problem can be solved analytically. The obtained solution has been compared with the results of direct numerical simulations and a good agreement is shown. Limiting cases of the solution related to low and high porosity are considered.

Квазистационарное приближение в задаче возбуждения низкочастотных электромагнитных полей в литосфере

The paper considers the excitation of a horizontal grounded antenna of the ELF-ELF electromagnetic field and a lower frequency range in a two-layer environment. Approximate analytical formulas are obtained that describe quite completely behavior of fields in the low-frequency range. The accuracy of using the quasi-stationary approximation is analyzed. The possibility of replacing the actual surface impedance with a plane wave impedance, normally falling on the interface. For a number of experiments carried out on the Kola Peninsula in the framework of the international cooperation (FENICS-2014, FENICS-2019), the frequency boundaries of the applicability of the approximate approach in assessing conductivity of the Earth.

Effect of temperature gradient on heavy quark anti-quark potential using gravity dual model

Thermal systems have traditionally been modeled via Euclideanized space by analytical continuation of time to an imaginary time. We extend the concept to static thermal gradients by recasting the temperature variation as a variation in the Euclidean metric. We apply this prescription to determine the Quark anti-Quark potential in a system with thermal gradient. A naturally occurring QCD medium with thermal gradients is a Quark Gluon Plasma (QGP). However, the QGP evolves in time. Hence, we use a quasi-stationary approximation, which is applicable only if the rate of time evolution is slow. Hence the application of our proposal to a Quark anti-Quark potential in QGP can be seen as a step towards a more exact theory which would incorporate time varying thermal gradients. The effect of a static temperature gradient on the Quark anti-Quark potential is analyzed using a gravity dual model. A non-uniform black string metric is developed, by perturbing the Schwarzchild metric, which allows to incorporate the temperature gradient in the dual AdS space. Finally, an expression for the Quark anti-Quark potential, in the presence of a static temperature gradient, is derived.

MODELING A CLINKER FURNACE MONITORING SYSTEM

Вращающиеся печи используются для преобразования кальцинированной сырьевой смеси в цементный клинкер. В этой статье рассматривается система контроля и управления клинкерной вращающейся печью посредством трехмерной модели для моделирования ключевых процессов, происходящих в твердом слое клинкерных печей. Эта система опирается на математическую модель, состоящую из пяти операционных уровней: три слоя для мониторинга состояния печи и два для ее системы управления. Изменение высоты слоя и образование расплава в горячей зоне внутри печи были учтены. Энергетический баланс (включая кондуктивный, конвективный и радиационный теплообмен) определялся на основе квазистационарного приближения. Численные эксперименты проводились с целью исследования влияния основных рабочих и проектных параметров на потребление энергии печи. Модель можно использовать для мониторинга температурного профиля внутри печи, для снижения потребления энергии на тонну клинкера. Модель и результаты, рассматриваемые в данной статье, обеспечивают настройку системы управления печи обжига клинкера. Rotary kilns are used to convert calcined raw materials into cement clinker. This article discusses a control and management system for a clinker rotary kiln through a 3D model to simulate key processes occurring in the solid bed of clinker kilns. This system is based on a mathematical model consisting of five operating levels: three layers for monitoring the state of the furnace and two for its control system. The change in the layer height and the formation of melt in the hot zone inside the furnace were taken into account. The energy balance (including conductive, convective and radiative heat transfer) was determined on the basis of a quasi-stationary approximation. Numerical experiments were carried out to investigate the influence of the main operating and design parameters on the energy consumption of the furnace. The model can be used to monitor the temperature profile inside the kiln to reduce energy consumption per tonne of clinker. The model and results discussed in this article provide tuning of the clinker kiln control system.

METHODOLOGY FOR DETERMINING SPEED COEFFICIENTS IN THE DESIGN OF RADIAL-AXIAL TURBINE

The article proposes a method for the interrelated determination of the speed coefficients and optimal geometry of a radial-axial centripetal turbine flow range. The method is based on a model of gas flow at an average diameter in a one-dimensional quasi-stationary approximation, supplemented with ratios to determine the optimal operating parameters of the turbine.

RECIPROCITY RELATIONS FOR A CONDUCTIVE SCATTERER WITH A CHIRAL CORE IN QUASI-STATIC FORM

We analyse a scattering problem of electromagnetic waves by a bounded chiral conductive obstacle, which is surrounded by a dielectric, via the quasi-stationary approximation for the Maxwell equations. We prove the reciprocity relations for incident plane and spherical electric waves upon the scatterer. Mixed reciprocity relations have also been proved for a plane wave and a spherical wave. In the case of spherical waves, the point sources are located either inside or outside the scatterer. These relations are used to study the inverse scattering problems.