Andris Jakovics

A Statistical Approach to Permeability of Clustered Fibre Reinforcements

The focus is set on mesoscale modelling of permeability of real fabrics used in composite manufacturing. Of particular interest is the effect of expected perturbations from perfect geometries, such as fibre bundle crimp, on the permeability. To start with, variational methods are used to calculate the permeability of individual gaps between fibre bundles. Based on this study a network of unit cells is formed enabling studies of two-and three-dimensional flow through the structure. From such an analysis the overall permeability of an arbitrary distribution of unit cell permeabilities can be calculated. Here random and controlled distributions are simulated. The former is an approximate representation of a continuous strand mat and the latter may describe Non-Crimp Fabrics. The result is that for random distributions, the permeability decreases with the maximum variation in unit cell while for a controlled permeability distribution the overall permeability can as well increase as decrease depending on the type of perturbation. In both cases the type of flow: one-, two-or three-dimensional strongly influence on the quantitative result. Hence, for the type of fabrics studied, it is necessary to model the full 3D-flow through to get a correct permeability value.

Numerical studies of the melting process in the induction furnace with cold crucible

Purpose – Aims to present recent activities in numerical modeling of cold crucible melting process.Design/methodology/approach – 3D numerical analysis was used for electromagnetic problem and 3D large eddy simulation (LES) method was applied for fluid flow modeling.Findings – The comparative modeling shows, that higher H/D ratio of the melt is more efficient when total power consumption is considered, but this advantage is held back by higher heat losses through the crucible walls. Also, calculations reveal that lower frequencies, which are energetically less effective, provide better mixing of the melt.Originality/value – 3D electromagnetic model, which allows to take into account non‐symmetrical distribution of Joule heat sources, together with transient LES fluid flow simulation gives the opportunity of accurate prediction of temperature distribution in the melt.

Experimental investigations and numerical modelling of the melting process in the cold crucible

Purpose – Aims to present recent activities in experimental investigations and numerical modelling of the induction cold crucible installation.Design/methodology/approach – Temperature and velocity measurements using thermocouples and electromagnetic velocity probes were performed in aluminium melt which was used as a model melt. Measured temperature field and flow pattern were compared with transient 3D calculations based on large eddy simulation (LES) turbulence modelling scheme. Numerical results are in good coincidence with the experimental data.Findings – The modelling results show that only 3D transient LES is able to model correctly these heat and mass transfer processes.Originality/value – It is revealed that transient 3D modelling provides a universal tool for simulating convective heat and mass transfer processes in the entire melt influenced by large scale instabilities in the recirculating flows, which contain several main vortexes of the mean flow.

Numerical Modeling of Free Surface Dynamics of Melt in an Alternate Electromagnetic Field: Part I. Implementation and Verification of Model

By means of ANSYS Classic and ANSYS CFX external coupling, a numerical model for free surface dynamics of electrically conductive fluid in an alternate electromagnetic field is developed. Volume of Fluid (VOF) numerical technique and k–ω SST turbulence model are applied for the high Reynolds number two-phase flow calculation. The model is extended on 3D and adjusted for the case of electromagnetic levitation. Results for the steady-state free surface shapes obtained with transient calculations are compared with other models and experimental measurements in induction furnaces, induction furnace with cold crucible, and electromagnetic levitation melting device. Numerical calculation results of free surface dynamics are compared with analytic estimation of free surface oscillation period. Parameter studies by means of developed approach and comparison between 3D simulations of free surface dynamics of electromagnetically induced flow with k–ω SST and large eddy simulation (LES) turbulence models are discussed in the second part of the article to follow.

The Numerical Model of Electrothermal Deformations of Carbides in Bearing Steel as the Possible Cause of White Etching Cracks Initiation

Despite the ongoing debates on influence of hydrogen uptake and penetration in the steel, pulsed and extraordinary fatigue on white etching cracks (WEC) formation in bearing steel SAE52100, the present paper proposes an alternative hypothesis on electrothermal initiation of the WEC. The hypothesis points to differences between electrical and thermal properties of elements of steel microstructure that lead sequentially to redistribution of current, resistivity heating, thermal expansion and deformations of the carbide particle. Appearance of a nano-void is also predicted by the model in the cases of the martensite and the bainite structures. The model also predicts higher probability of the WEC formation for the bainitic steel.

Statistical analysis of the influence of forces on particles in EM driven recirculated turbulent flows

The present paper contains an analysis of the statistical distribution of forces affecting non-conducting particles dispersed in an EM induced recirculated flow in induction furnaces. The simulation is conducted adopting the LES-based Euler-Lagrange approach in the limit of dilute conditions (one-way coupling). It is done by means of a development of OpenFOAM software code. The used Lagrange equation for particle tracking includes drag, EM, buoyancy, lift, acceleration and added mass forces. The relevant approximations for the forces are chosen on the basis of the statistical analysis of the non-dimensional parameters (particle Reynolds number, shear stress and acceleration parameter). The effect of force distribution on particle homogenization is described under different density ratios and particle sizes. The recommendations of the consistence of the Lagrange model for the simulation of the particle motion in the laboratory scale induction crucible furnace are given in conclusion.

Turbulent flow dynamics, heat transfer and mass exchange in the melt of induction furnaces

Experimental investigations of the turbulent flow velocities measured in the melt of experimental induction furnaces show, that beside the intensive local turbulence pulsations, macroscopic low‐frequency oscillations of the recirculated toroidal main flow eddies play an important role in the heat and mass exchange processes. Traditional numerical calculations of the flow and transfer processes, based on wide spread commercial codes using various modifications of the k‐e turbulence model show that these models do not take into account the low‐frequency oscillations of the melt flow and the calculated temperature and concentration distributions in the melt essentially differs from experimental results. Therefore, the melt flow dynamics in an induction crucible furnace was numerically simulated with help of transient three‐dimensional calculations using the large eddy simulation turbulence model. This leads to a good agreement between calculated and measured periods of low‐frequency oscillations and heat and mass transfer between the toroidal flow eddies.

Numerical Modeling of Free Surface Dynamics of Melt in an Alternate Electromagnetic Field. Part II: Conventional Electromagnetic Levitation

By means of external coupling between electromagnetic (EM) problem in ANSYS and hydrodynamic problem in FLUENT, a numerical model for the liquid metal free surface flow in an alternate EM field has been developed and verified in the first part of the article. Volume of Fluid (VOF) algorithm has been used for tracking of free surface. In this work, improved performance of the model is presented. General validation of the VOF algorithm is performed by comparison of the calculated free oscillations of the liquid column to its analytical solution. The 3D/VOF calculation of coupled EM field and free surface flow with Large Eddy Simulation turbulence description for the first time is applied for modeling of conventional EM levitation. Calculation results are compared with 2D/VOF and 3D/VOF models that use less precise k–ε and k–ω SST turbulence formulations. Obtained time-averaged droplet shapes are used for single-phase flow calculations with different turbulence models and free-slip/no-slip velocity conditions at the fixed free surface for validation of the flow. Meanwhile, series of levitation melting experiments are performed for verification of the simulated droplet shapes. In conclusion, parameter impact on the fully developed flow and the levitated droplet shape is discussed.

Performance Analysis of Air-to-Water Heat Pump in Latvian Climate Conditions

Abstract Strategy of the European Union in efficient energy usage demands to have a higher proportion of renewable energy in the energy market. Since heat pumps are considered to be one of the most efficient heating and cooling systems, they will play an important role in the energy consumption reduction in buildings aimed to meet the target of nearly zero energy buildings set out in the EU Directive 2010/31/EU. Unfortunately, the declared heat pump Coefficient of Performance (COP) corresponds to a certain outdoor temperature (+7 °C), therefore different climate conditions, building characteristics and settings result in different COP values during the year. The aim of this research is to investigate the Seasonal Performance factor (SPF) values of air-to-water heat pump which better characterize the effectiveness of heat pump in a longer selected period of time, especially during the winter season, in different types of residential buildings in Latvian climate conditions. Latvia has four pronounced seasons of near-equal length. Winter starts in mid-December and lasts until mid-March. Latvia is characterized by cold, maritime climate (duration of the average heating period being 203 days, the average outdoor air temperature during the heating period being 0.0 °C, the coldest five-day average temperature being −20.7 °C, the average annual air temperature being +6.2 °C, the daily average relative humidity being 79 %). The first part of this research consists of operational air-towater heat pump energy performance monitoring in different residential buildings during the winter season. The second part of the research takes place under natural conditions in an experimental construction stand which is located in an urban environment in Riga, Latvia. The inner area of this test stand, where air-to-water heat pump performance is analyzed, is 9 m2. The ceiling height is 3 m, all external wall constructions (U = 0.16 W/(m2K)) have ventilated facades. To calculate SPF, the experimental stand is equipped with sensors which provide measurements for electricity consumption and gained heat energy.

BURNER BACKFLOW REDUCTION IN REGENERATION FURNACE

Abstract In the present case from the steel industry, waste hydrochloric acid from the pickling process is regenerated using spray roasting. The process is driven by four burners placed symmetrically along the periphery of the cylindrical main section of the reactor. Severe problems with gas backflow and sintering of iron oxide inside the burner chamber have led to a complete shut down of the process 1–2 times every week, which is a frequency which significantly affects the productivity. In this study the influence of a kick-out on the gas flow in the vicinity of the burner chamber is investigated numerically. It is shown that the kick-out geometry creates a vortical low pressure region preventing the inflow of gas and hence the sintering of iron oxide. This has led to a significant increase in the productivity with no additional shut-downs than needed for the ordinary maintenance every 6–8 weeks.