Magazine et Edition

Volume 59 (2022): Edition 4 (August 2022)

Volume 59 (2022): Edition 3 (June 2022)

Volume 59 (2022): Edition s3 (June 2022)

Volume 59 (2022): Edition 2 (April 2022)

Volume 59 (2022): Edition 1 (February 2022)

Volume 58 (2021): Edition 6 (December 2021)

Volume 58 (2021): Edition 5 (October 2021)

Volume 58 (2021): Edition 4 (August 2021)

Volume 58 (2021): Edition 3 (June 2021)

Volume 58 (2021): Edition 2 (April 2021)

Volume 58 (2021): Edition 1 (February 2021)

Volume 57 (2020): Edition 6 (December 2020)

Volume 57 (2020): Edition 5 (October 2020)

Volume 57 (2020): Edition 4 (August 2020)

Volume 57 (2020): Edition 3 (June 2020)

Volume 57 (2020): Edition 1-2 (April 2020)

Volume 56 (2019): Edition 6 (December 2019)

Volume 56 (2019): Edition 5 (October 2019)

Volume 56 (2019): Edition 4 (August 2019)

Volume 56 (2019): Edition 3 (June 2019)

Volume 56 (2019): Edition 2 (April 2019)

Volume 56 (2019): Edition 1 (February 2019)

Volume 55 (2018): Edition 6 (December 2018)

Volume 55 (2018): Edition 5 (October 2018)

Volume 55 (2018): Edition 4 (August 2018)

Volume 55 (2018): Edition 3 (June 2018)

Volume 55 (2018): Edition 2 (April 2018)

Volume 55 (2018): Edition 1 (February 2018)

Volume 54 (2017): Edition 6 (December 2017)

Volume 54 (2017): Edition 5 (October 2017)

Volume 54 (2017): Edition 4 (August 2017)

Volume 54 (2017): Edition 3 (June 2017)

Volume 54 (2017): Edition 2 (April 2017)

Volume 54 (2017): Edition 1 (February 2017)

Volume 53 (2016): Edition 6 (December 2016)

Volume 53 (2016): Edition 5 (October 2016)

Volume 53 (2016): Edition 4 (August 2016)

Volume 53 (2016): Edition 3 (June 2016)

Volume 53 (2016): Edition 2 (April 2016)

Volume 53 (2016): Edition 1 (February 2016)

Volume 52 (2015): Edition 6 (December 2015)

Volume 52 (2015): Edition 5 (October 2015)

Volume 52 (2015): Edition 4 (August 2015)

Volume 52 (2015): Edition 3 (June 2015)

Volume 52 (2015): Edition 2 (April 2015)

Volume 52 (2015): Edition 1 (February 2015)

Volume 51 (2014): Edition 6 (December 2014)

Volume 51 (2014): Edition 5 (October 2014)

Volume 51 (2014): Edition 4 (August 2014)

Volume 51 (2014): Edition 3 (June 2014)

Volume 51 (2014): Edition 2 (April 2014)

Volume 51 (2014): Edition 1 (February 2014)

Volume 50 (2013): Edition 6 (December 2013)

Volume 50 (2013): Edition 5 (October 2013)

Volume 50 (2013): Edition 4 (August 2013)

Volume 50 (2013): Edition 3 (June 2013)

Volume 50 (2013): Edition 2 (April 2013)

Volume 50 (2013): Edition 1 (February 2013)

Volume 49 (2012): Edition 6-II (December 2012)

Volume 49 (2012): Edition 6-I (December 2012)

Volume 49 (2012): Edition 5 (October 2012)

Volume 49 (2012): Edition 4 (August 2012)

Volume 49 (2012): Edition 2 (April 2012)

Volume 49 (2012): Edition 1 (February 2012)

Volume 48 (2011): Edition 6 (December 2011)

Volume 48 (2011): Edition 5 (October 2011)

Volume 48 (2011): Edition 4 (August 2011)

Volume 48 (2011): Edition 3 (June 2011)

Volume 48 (2011): Edition 2 (April 2011)

Volume 48 (2011): Edition 1 (February 2011)

Volume 47 (2010): Edition 6 (December 2010)

Volume 47 (2010): Edition 5 (October 2010)

Volume 47 (2010): Edition 4 (August 2010)

Volume 47 (2010): Edition 3 (June 2010)

Volume 47 (2010): Edition 2 (April 2010)

Volume 47 (2010): Edition 1 (February 2010)

Volume 46 (2009): Edition 6 (December 2009)

Volume 46 (2009): Edition 5 (October 2009)

Volume 46 (2009): Edition 4 (August 2009)

Volume 46 (2009): Edition 3 (June 2009)

Volume 46 (2009): Edition 2 (April 2009)

Volume 46 (2009): Edition 1 (February 2009)

Volume 45 (2008): Edition 6 (December 2008)

Volume 45 (2008): Edition 5 (October 2008)

Volume 45 (2008): Edition 4 (August 2008)

Volume 45 (2008): Edition 3 (June 2008)

Volume 45 (2008): Edition 2 (April 2008)

Volume 45 (2008): Edition 1 (February 2008)

Détails du magazine
Format
Magazine
eISSN
2255-8896
Première publication
18 Mar 2008
Période de publication
6 fois par an
Langues
Anglais

Chercher

Volume 58 (2021): Edition 2 (April 2021)

Détails du magazine
Format
Magazine
eISSN
2255-8896
Première publication
18 Mar 2008
Période de publication
6 fois par an
Langues
Anglais

Chercher

6 Articles
Accès libre

Ab-Initio Calculations of Oxygen Vacancy in Ga2O3 Crystals

Publié en ligne: 30 Mar 2021
Pages: 3 - 10

Résumé

Abstract

Gallium oxide β-Ga2O3 is an important wide-band gap semiconductor. In this study, we have calculated the formation energy and transition levels of oxygen vacancies in β-Ga2O3 crystal using the B3LYP hybrid exchange-correlation functional within the LCAO-DFT approach. The obtained electronic charge redistribution in perfect Ga2O3 shows notable covalency of the Ga-O bonds. The formation of the neutral oxygen vacancy in β-Ga2O3 leads to the presence of deep donor defects with quite low concentration. This is a clear reason why oxygen vacancies can be hardly responsible for n-type conductivity in β-Ga2O3.

Mots clés

  • β-GaO
  • ab-initio calculations
  • band structure
  • DFT
  • oxygen vacancy
Accès libre

Benefits of Energy Storage Systems for Small-Scale Wind Farm Development in Latvia

Publié en ligne: 30 Mar 2021
Pages: 11 - 18

Résumé

Abstract

The paper covers the main aspects and restrictions on siting small-scale wind farms in Latvia and benefits of using energy storage systems with small-scale wind farms. The restrictions of siting have been analysed. Grid connection restrictions are addressed as the main issues for small-scale wind farm development in Latvia. Two small-scale wind farm models with similar properties have been made and analysed within the framework of the research. The paper proposes the idea for maximising the production of small-scale wind farm in a small area site with high wind potential.

Mots clés

  • Energy storage
  • wind energy
  • wind farm
Accès libre

Optimization of Energy Extraction Using Definite Geometry Prisms in Airflow

Publié en ligne: 30 Mar 2021
Pages: 19 - 31

Résumé

Abstract

An approximate method for analysis and synthesis of moving rigid bodies (prisms) in the airflow without using numerical methods of space-time programming techniques is described by applying a fluid (air)–rigid solid body interaction concept for engineering applications through a straightforward mathematical model. The interaction of rigid body (prism) and air is encountered in different cases: moving body (prism) in the air; stationary bodies (prism) in the airflow; moving body (prism) in the airflow. The complicated task of rigid body (prism) and air interaction is simplified by using superposition principles, i.e., by taking into account the upstream and downstream rigid body (prism) and air interaction phenomenon, which has been found to be different under varying speeds. Numerical results obtained for various forms of prisms are shown for constant air–speed, where the steady state Reynolds-averaged Navier–Stokes (RANS) equation is solved by using k-ε realizable turbulence model. A detailed explanation to support the proposed approximate method is given by using numerical results obtained in ANSYS computations. All equations are formed based on laws of classical mechanics; the interaction of viscous forces is neglected in forming the mathematical model. Numerical results for different model prisms are compared and the theoretical results discussed in detail. The mathematical model in the present paper is applicable only to bodies that undergo a rectilinear translation motion. In the final part of the present paper, the proposed method is used in the synthesis and optimization task of energy extraction by considering the motion of a variable parameter prism in the airflow.

Mots clés

  • Rigid body (prisms)
  • superposition principle
  • space-time programming
Accès libre

Potential of End-User Electricity Peak Load Shift in Latvia

Publié en ligne: 30 Mar 2021
Pages: 32 - 44

Résumé

Abstract

One of the main challenges in the world as well as in Latvia is the reduction of the fossil fuel consumption. Electricity generation, which is still mainly produced by fossil fuel or nuclear power, is one of the largest shares. Nowadays end-users can efficiently control their electricity consumption by shifting electrical loads and taking into account fluctuating electricity price at Nord Pool. The smart metering systems have been expanding, but for the time being, end-users do not use this possibility efficiently.

This study provides an analysis of Latvian electricity consumption specifics and evaluates a potential to shift electricity peak loads. The study includes households, industry and commercial/public sector. Based on the questionnaire distributed among end-users, the initial data on equipment and usage profile were collected. The most essential equipment was reviewed to estimate the potential for load shift. The obtained results show that that there is a positive effect of the load shift. In the household sector, the average electrical load shift can be 6 % (95 GWh/ year) during a period at a cheaper price; in the industry sector on average 37 % (36.58 GWh/ year) and in the commercial/public sector there is no potential due to its specifics (working hours, constant use of refrigerators, etc.).

Mots clés

  • Demand side management
  • electricity consumption of the energy sector
  • electricity peak
  • peak load shift
  • user behaviour
Accès libre

Liquefied Natural Gas Infrastructure and Prospects for the Use of LNG in the Baltic States and Finland

Publié en ligne: 30 Mar 2021
Pages: 45 - 63

Résumé

Abstract

In the early 2010s, only 23 countries had access to the liquefied natural gas (hereinafter – LNG). Import terminals, despite attractive short-term economics, took long time to build, and rigid supply contracts made truly global use of LNG rather complicated. Concerns about geo-political risks also stunted demand growth from existing supply sources, even when new LNG export routes and sources became available.

Current natural gas market is very different, both in terms of market participants and accessibility and diversity of services. In 2019, the number of LNG importing countries reached 43. Rising competition among suppliers and increasing liquidity of markets themselves created favourable conditions to diversify contract duration, size, and flexibility. In addition, development of floating storage and regasification unit (hereinafter – FSRU) technology provided LNG suppliers with a quick response option to sudden demand fluctuations in regional and local natural gas markets [1].

Moreover, LNG is one of the major options not only for bringing the natural gas to regions where its pipeline supply infrastructure is historically absent, limited or underdeveloped, but also for diversification of the natural gas supply routes and sources in regions with sufficient state of pipeline delivery possibilities. And it concerns smaller natural gas markets, like the Baltic States and Finland as well. Accordingly, prospects for use of LNG there in both mid and long-term perspective must be carefully evaluated, especially in regards to emerging bunkering business in the Baltic Sea aquatory and energy transition in Finland, replacing coal base-load generation with other, more sustainable and environmentally friendly alternatives.

Mots clés

  • Bunkering
  • Finland
  • LNG
  • LNG infrastructure
  • natural gas
  • the Baltic States
Accès libre

Corrosion and Electrochemical Impedance Spectroscopy of Thin TiALN and TiCN PVD Coatings for Protection of Ballast Water Screen Filters

Publié en ligne: 30 Mar 2021
Pages: 64 - 78

Résumé

Abstract

The electrochemical impedance spectroscopy (EIS) and corrosion behaviour of physical vapour deposited (PVD) TiAlN and TiCN coatings of 50 µm mesh shaped AISI 316 stainless steel were estimated under simulated marine conditions (3.5 wt. % NaCl solution). The coatings were prepared by creating adhesive Cr-CrN interlayer with the thickness of about 0.3 µm. The obtained thicknesses of produced coatings were measured to be in a range between 2 and 3.5 µm. The presence of protective coatings leads to corrosion potential (Ecorr) shifting to more positive values as compared to the bare stainless steel. This effect indicates higher protection efficiency of coated steel under marine conditions. The protective behaviour of produced coating leads to the decreased corrosion current density (jcorr) by indicating up to 40-fold higher polarization resistance as compared to resistance of the naturally formed oxide layer over the stainless steel. The Nyquist and Bode plots were obtained with the help of EIS measurements by applying alternating potential amplitude of 10 mV on observed Ecorr. The obtained plots were fitted by appropriate equivalent circuits to calculate pore resistance, charge transfer resistance and capacitance. The present study reveals that pore resistance was the highest in the case of TiCN coating (Rpore=3.22 kΩ·cm2). The increase in duration of the immersion up to 24 h leads to change in the capacitive behaviour of the coatings caused by the penetration of the aqueous solution into pore system of TiCN coating with low wettability and surface passivation of reactive TiAlN coating. The presence of defects was confirmed by examining the obtained samples with the help of the scanning electron microscope.

Mots clés

  • Coatings
  • corrosion
  • electrochemical impedance spectroscopy
  • marine conditions
  • protection
  • PVD
6 Articles
Accès libre

Ab-Initio Calculations of Oxygen Vacancy in Ga2O3 Crystals

Publié en ligne: 30 Mar 2021
Pages: 3 - 10

Résumé

Abstract

Gallium oxide β-Ga2O3 is an important wide-band gap semiconductor. In this study, we have calculated the formation energy and transition levels of oxygen vacancies in β-Ga2O3 crystal using the B3LYP hybrid exchange-correlation functional within the LCAO-DFT approach. The obtained electronic charge redistribution in perfect Ga2O3 shows notable covalency of the Ga-O bonds. The formation of the neutral oxygen vacancy in β-Ga2O3 leads to the presence of deep donor defects with quite low concentration. This is a clear reason why oxygen vacancies can be hardly responsible for n-type conductivity in β-Ga2O3.

Mots clés

  • β-GaO
  • ab-initio calculations
  • band structure
  • DFT
  • oxygen vacancy
Accès libre

Benefits of Energy Storage Systems for Small-Scale Wind Farm Development in Latvia

Publié en ligne: 30 Mar 2021
Pages: 11 - 18

Résumé

Abstract

The paper covers the main aspects and restrictions on siting small-scale wind farms in Latvia and benefits of using energy storage systems with small-scale wind farms. The restrictions of siting have been analysed. Grid connection restrictions are addressed as the main issues for small-scale wind farm development in Latvia. Two small-scale wind farm models with similar properties have been made and analysed within the framework of the research. The paper proposes the idea for maximising the production of small-scale wind farm in a small area site with high wind potential.

Mots clés

  • Energy storage
  • wind energy
  • wind farm
Accès libre

Optimization of Energy Extraction Using Definite Geometry Prisms in Airflow

Publié en ligne: 30 Mar 2021
Pages: 19 - 31

Résumé

Abstract

An approximate method for analysis and synthesis of moving rigid bodies (prisms) in the airflow without using numerical methods of space-time programming techniques is described by applying a fluid (air)–rigid solid body interaction concept for engineering applications through a straightforward mathematical model. The interaction of rigid body (prism) and air is encountered in different cases: moving body (prism) in the air; stationary bodies (prism) in the airflow; moving body (prism) in the airflow. The complicated task of rigid body (prism) and air interaction is simplified by using superposition principles, i.e., by taking into account the upstream and downstream rigid body (prism) and air interaction phenomenon, which has been found to be different under varying speeds. Numerical results obtained for various forms of prisms are shown for constant air–speed, where the steady state Reynolds-averaged Navier–Stokes (RANS) equation is solved by using k-ε realizable turbulence model. A detailed explanation to support the proposed approximate method is given by using numerical results obtained in ANSYS computations. All equations are formed based on laws of classical mechanics; the interaction of viscous forces is neglected in forming the mathematical model. Numerical results for different model prisms are compared and the theoretical results discussed in detail. The mathematical model in the present paper is applicable only to bodies that undergo a rectilinear translation motion. In the final part of the present paper, the proposed method is used in the synthesis and optimization task of energy extraction by considering the motion of a variable parameter prism in the airflow.

Mots clés

  • Rigid body (prisms)
  • superposition principle
  • space-time programming
Accès libre

Potential of End-User Electricity Peak Load Shift in Latvia

Publié en ligne: 30 Mar 2021
Pages: 32 - 44

Résumé

Abstract

One of the main challenges in the world as well as in Latvia is the reduction of the fossil fuel consumption. Electricity generation, which is still mainly produced by fossil fuel or nuclear power, is one of the largest shares. Nowadays end-users can efficiently control their electricity consumption by shifting electrical loads and taking into account fluctuating electricity price at Nord Pool. The smart metering systems have been expanding, but for the time being, end-users do not use this possibility efficiently.

This study provides an analysis of Latvian electricity consumption specifics and evaluates a potential to shift electricity peak loads. The study includes households, industry and commercial/public sector. Based on the questionnaire distributed among end-users, the initial data on equipment and usage profile were collected. The most essential equipment was reviewed to estimate the potential for load shift. The obtained results show that that there is a positive effect of the load shift. In the household sector, the average electrical load shift can be 6 % (95 GWh/ year) during a period at a cheaper price; in the industry sector on average 37 % (36.58 GWh/ year) and in the commercial/public sector there is no potential due to its specifics (working hours, constant use of refrigerators, etc.).

Mots clés

  • Demand side management
  • electricity consumption of the energy sector
  • electricity peak
  • peak load shift
  • user behaviour
Accès libre

Liquefied Natural Gas Infrastructure and Prospects for the Use of LNG in the Baltic States and Finland

Publié en ligne: 30 Mar 2021
Pages: 45 - 63

Résumé

Abstract

In the early 2010s, only 23 countries had access to the liquefied natural gas (hereinafter – LNG). Import terminals, despite attractive short-term economics, took long time to build, and rigid supply contracts made truly global use of LNG rather complicated. Concerns about geo-political risks also stunted demand growth from existing supply sources, even when new LNG export routes and sources became available.

Current natural gas market is very different, both in terms of market participants and accessibility and diversity of services. In 2019, the number of LNG importing countries reached 43. Rising competition among suppliers and increasing liquidity of markets themselves created favourable conditions to diversify contract duration, size, and flexibility. In addition, development of floating storage and regasification unit (hereinafter – FSRU) technology provided LNG suppliers with a quick response option to sudden demand fluctuations in regional and local natural gas markets [1].

Moreover, LNG is one of the major options not only for bringing the natural gas to regions where its pipeline supply infrastructure is historically absent, limited or underdeveloped, but also for diversification of the natural gas supply routes and sources in regions with sufficient state of pipeline delivery possibilities. And it concerns smaller natural gas markets, like the Baltic States and Finland as well. Accordingly, prospects for use of LNG there in both mid and long-term perspective must be carefully evaluated, especially in regards to emerging bunkering business in the Baltic Sea aquatory and energy transition in Finland, replacing coal base-load generation with other, more sustainable and environmentally friendly alternatives.

Mots clés

  • Bunkering
  • Finland
  • LNG
  • LNG infrastructure
  • natural gas
  • the Baltic States
Accès libre

Corrosion and Electrochemical Impedance Spectroscopy of Thin TiALN and TiCN PVD Coatings for Protection of Ballast Water Screen Filters

Publié en ligne: 30 Mar 2021
Pages: 64 - 78

Résumé

Abstract

The electrochemical impedance spectroscopy (EIS) and corrosion behaviour of physical vapour deposited (PVD) TiAlN and TiCN coatings of 50 µm mesh shaped AISI 316 stainless steel were estimated under simulated marine conditions (3.5 wt. % NaCl solution). The coatings were prepared by creating adhesive Cr-CrN interlayer with the thickness of about 0.3 µm. The obtained thicknesses of produced coatings were measured to be in a range between 2 and 3.5 µm. The presence of protective coatings leads to corrosion potential (Ecorr) shifting to more positive values as compared to the bare stainless steel. This effect indicates higher protection efficiency of coated steel under marine conditions. The protective behaviour of produced coating leads to the decreased corrosion current density (jcorr) by indicating up to 40-fold higher polarization resistance as compared to resistance of the naturally formed oxide layer over the stainless steel. The Nyquist and Bode plots were obtained with the help of EIS measurements by applying alternating potential amplitude of 10 mV on observed Ecorr. The obtained plots were fitted by appropriate equivalent circuits to calculate pore resistance, charge transfer resistance and capacitance. The present study reveals that pore resistance was the highest in the case of TiCN coating (Rpore=3.22 kΩ·cm2). The increase in duration of the immersion up to 24 h leads to change in the capacitive behaviour of the coatings caused by the penetration of the aqueous solution into pore system of TiCN coating with low wettability and surface passivation of reactive TiAlN coating. The presence of defects was confirmed by examining the obtained samples with the help of the scanning electron microscope.

Mots clés

  • Coatings
  • corrosion
  • electrochemical impedance spectroscopy
  • marine conditions
  • protection
  • PVD

Planifiez votre conférence à distance avec Sciendo