Energies

Editorial

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4 pages, 153 KiB

Open AccessEditorial

Electric Fields in Energy and Process Engineering

by Lars Zigan

Energies 2018, 11(9), 2246; https://doi.org/10.3390/en11092246 - 27 Aug 2018

Viewed by 2019

Abstract

This Editorial provides an introduction to and an overview of the special issue “Electric Fields in Energy and Process Engineering”. Full article

(This article belongs to the Special Issue Electric Fields in Energy & Process Engineering)

Research

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24 pages, 5529 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Plasma-Assisted Biomass Gasification with Focus on Carbon Conversion and Reaction Kinetics Compared to Thermal Gasification

by Yin Pang, Leo Bahr, Peter Fendt, Lars Zigan, Stefan Will, Thomas Hammer, Manfred Baldauf, Robert Fleck, Dominik Müller and Jürgen Karl

Energies 2018, 11(5), 1302; https://doi.org/10.3390/en11051302 - 20 May 2018

Cited by 25 | Viewed by 8650

Abstract

Compared to conventional allothermal gasification of solid fuels (e.g., biomass, charcoal, lignite, etc.), plasma-assisted gasification offers an efficient method for applying energy to the gasification process to increase the flexibility of operation conditions and to increase the reaction kinetics. In particular, non-thermal plasmas [...] Read more.

Compared to conventional allothermal gasification of solid fuels (e.g., biomass, charcoal, lignite, etc.), plasma-assisted gasification offers an efficient method for applying energy to the gasification process to increase the flexibility of operation conditions and to increase the reaction kinetics. In particular, non-thermal plasmas (NTP) are promising, in which thermal equilibrium is not reached and electrons have a substantially higher mean energy than gas molecules. Thus, it is generally assumed that in NTP the supplied energy is utilized more efficiently for generating free radicals initiating gasification reactions than thermal plasma processes. In order to investigate this hypothesis, we compared purely thermal to non-thermal plasma-assisted gasification of biomass in steam in a drop tube reactor at atmospheric pressure. The NTP was provided by means of gliding arcs between two electrodes aligned in the inlet steam flow with an electric power of about 1 kW. Reaction yields and rates were evaluated using measured gas temperatures by the optical technique. The first experimental results show that the non-thermal plasma not only promotes the carbon conversion of the fuel particles, but also accelerates the reaction kinetics. The carbon conversion is increased by nearly 10% using wood powder as the fuel. With charcoal powder, more than 3% are converted into syngas. Full article

(This article belongs to the Special Issue Electric Fields in Energy & Process Engineering)

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14 pages, 2066 KiB

Open AccessArticle

Degradation of Low Concentrated Perfluorinated Compounds (PFCs) from Water Samples Using Non-Thermal Atmospheric Plasma (NTAP)

by Vojislav Jovicic, Muhammad Jehanzaib Khan, Ana Zbogar-Rasic, Nataliia Fedorova, Alexander Poser, Peter Swoboda and Antonio Delgado

Energies 2018, 11(5), 1290; https://doi.org/10.3390/en11051290 - 18 May 2018

Cited by 54 | Viewed by 7098

Abstract

Perfluorinated compounds (PFCs) are manmade chemicals, containing the covalent C-F bond, which is among the strongest chemical bonds known to organic chemistry. Abundant use of these chemicals contaminates air, water, and soil around the world. Despite recent initiatives and legal regulations set to [...] Read more.

Perfluorinated compounds (PFCs) are manmade chemicals, containing the covalent C-F bond, which is among the strongest chemical bonds known to organic chemistry. Abundant use of these chemicals contaminates air, water, and soil around the world. Despite recent initiatives and legal regulations set to reduce their omnipresence, conventional water purification processes are either inefficient or very expensive, especially for low PFC contamination levels. This research is focused on the non-thermal atmospheric plasma (NTAP) decomposition of very low concentrations (<1 µg/L) of PFCs (especially perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS)), present in the wastewater produced during the process of PFCs removal from contaminated soil. The efficiency of the decomposition process was investigated for air, oxygen, and nitrogen plasma, with exposure times of 1–10 min and different plasma nozzle- and reactor sizes. Experiments demonstrated that the NTAP treatment is an efficient alternative method for degradation of more than 50% of the initial PFC concentration in the water samples, in less than 200 s. The final concentration of PFC showed strong dependency on the tested parameters. The treatment effect showed to be strongly non-linear with time, followed by the reduction of the pH-value of the treated sample, which might present a limiting factor for further PFC decomposition. Full article

(This article belongs to the Special Issue Electric Fields in Energy & Process Engineering)

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13 pages, 6429 KiB

Open AccessFeature PaperArticle

Electric Field Induced Changes of a Diffusion Flame and Heat Transfer near an Impinging Surface

by Yu-Chien Chien and Derek Dunn-Rankin

Energies 2018, 11(5), 1235; https://doi.org/10.3390/en11051235 - 12 May 2018

Cited by 15 | Viewed by 4146

Abstract

This research investigates heat transfer phenomena on a plate used with impinging electric field flames; i.e., flames burning in the presence of an electric field. Electric field effects on flames have been investigated in different applications but not when the flames are impinging [...] Read more.

This research investigates heat transfer phenomena on a plate used with impinging electric field flames; i.e., flames burning in the presence of an electric field. Electric field effects on flames have been investigated in different applications but not when the flames are impinging on nearby surfaces. Challenges to measurement methods when an electric field is applied in the system have limited the understanding of changes to the temperature distributions and species concentrations caused by the field. This study uses an infrared forward looking infrared (FLIR) camera with Schlieren visualization to examine the heat flux from flames over an impinging plate with different electric fields applied. In particular, we study the electric field effects on flames when those flames transfer heat to a nearby plate, and then how that transfer can be controlled using the electric field. The results show that electric fields affect substantially the heat flux distribution through the ion-driven wind, particularly when the plate location is just above the flame tip. Full article

(This article belongs to the Special Issue Electric Fields in Energy & Process Engineering)

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17 pages, 6209 KiB

Open AccessArticle

Fast and Precise Soft-Field Electromagnetic Tomography Systems for Multiphase Flow Imaging

by Malte Mallach, Martin Gevers, Patrik Gebhardt and Thomas Musch

Energies 2018, 11(5), 1199; https://doi.org/10.3390/en11051199 - 9 May 2018

Cited by 16 | Viewed by 4009

Abstract

In the process industry, measurement systems are required for process development and optimization, as well as for monitoring and control. The processes often involve multiphase mixtures or flows that can be analyzed using tomography systems, which visualize the spatial material distribution within a [...] Read more.

In the process industry, measurement systems are required for process development and optimization, as well as for monitoring and control. The processes often involve multiphase mixtures or flows that can be analyzed using tomography systems, which visualize the spatial material distribution within a certain measurement domain, e.g., a process pipe. In recent years, we studied the applicability of soft-field electromagnetic tomography methods for multiphase flow imaging, focusing on concepts for high-speed data acquisition and image reconstruction. Different non-intrusive electrical impedance and microwave tomography systems were developed at our institute, which are sensitive to the local contrasts of the electrical properties of the materials. These systems offer a very high measurement and image reconstruction rate of up to 1000 frames per second in conjunction with a dynamic range of up to 120 dB. This paper provides an overview of the underlying concepts and recent improvements in terms of sensor design, data acquisition and signal processing. We introduce a generalized description for modeling the electromagnetic behavior of the different sensors based on the finite element method (FEM) and for the reconstruction of the electrical property distribution using the Gauss–Newton method and Newton’s one-step error reconstructor (NOSER) algorithm. Finally, we exemplify the applicability of the systems for different measurement scenarios. They are suitable for the analysis of rapidly-changing inhomogeneous scenarios, where a relatively low spatial resolution is sufficient. Full article

(This article belongs to the Special Issue Electric Fields in Energy & Process Engineering)

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15 pages, 24683 KiB

Open AccessArticle

Experimental Investigation on Flow and Heat Transfer Characteristics of a Needle-Cylinder Type Ionic Wind Generator for LED Cooling

by Jingguo Qu, Lingjian Kong and Jianfei Zhang

Energies 2018, 11(5), 1149; https://doi.org/10.3390/en11051149 - 4 May 2018

Cited by 23 | Viewed by 5729

Abstract

Ionic wind cooling for electronic elements is a relevant research field. In order to study the cooling performance of ionic wind on a Light Emitting Diode (LED), an ionic wind generator with a needles-ring electrode configuration was set up. A cylindrical heat sink [...] Read more.

Ionic wind cooling for electronic elements is a relevant research field. In order to study the cooling performance of ionic wind on a Light Emitting Diode (LED), an ionic wind generator with a needles-ring electrode configuration was set up. A cylindrical heat sink for the heat dissipation of a heating film representing the LED chip was also manufactured. Following this, the effect of the needle number, the distance between the needles and the ring electrode, and the polarity of the corona discharge on the ionic wind velocity were studied. Finally, the optimal distance between the needles and the ring electrode was adopted to attain the maximum wind velocity with different numbers of needles. After this, the ionic wind device was used to cool the heating film at the working power of 10 watts. The surface temperature of the heating film was measured to evaluate the cooling performance of the ionic wind device. The experimental results indicate that the maximum temperature drop in the heating film center reaches 35.6 °C in the five needle-electrode case, which is very effective and can meet the demands of a 10 watts LED heat dissipation. Full article

(This article belongs to the Special Issue Electric Fields in Energy & Process Engineering)

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Review

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35 pages, 13477 KiB

Open AccessReview

Electrically Driven Supersonic Combustion

by Sergey B. Leonov

Energies 2018, 11(7), 1733; https://doi.org/10.3390/en11071733 - 2 Jul 2018

Cited by 50 | Viewed by 5278

Abstract

This manuscript reviews published works related to plasma assistance in supersonic combustion; focusing on mixing enhancement, ignition and flameholding. A special attention is paid for studies, which the author participated in person. The Introduction discusses general trends in plasma-assisted combustion and, specifically, work [...] Read more.

This manuscript reviews published works related to plasma assistance in supersonic combustion; focusing on mixing enhancement, ignition and flameholding. A special attention is paid for studies, which the author participated in person. The Introduction discusses general trends in plasma-assisted combustion and, specifically, work involving supersonic conditions. In Section 2, the emphasis is placed on different approaches to plasma application for fuel ignition and flame stabilization. Several schemes of plasma-based actuators for supersonic combustion have been tested for flameholding purposes at flow conditions where self-ignition of the fuel/air mixture is not realizable due to low air temperatures. Comparing schemes indicates an obvious benefit of plasma generation in-situ, in the mixing layer of air and fuel. In Section 3, the problem of mixing enhancement using a plasma-based technique is considered. The mechanisms of interaction are discussed from the viewpoint of triggering gasdynamic instabilities promoting the kinematic stretching of the fuel-air interface. Section 4 is related to the description of transitional processes and combustion instabilities observed in plasma-assisted high-speed combustion. The dynamics of ignition and flame extinction are explored. It is shown that the characteristic time for reignition can be as short as 10 ms. Two types of flame instability were described which are related to the evolution of a separation zone and thermoacoustic oscillations, with characteristic times 10 ms and 1 ms correspondingly. Full article

(This article belongs to the Special Issue Electric Fields in Energy & Process Engineering)

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33 pages, 2874 KiB

Open AccessReview

Overview of Electric Field Applications in Energy and Process Engineering

by Lars Zigan

Energies 2018, 11(6), 1361; https://doi.org/10.3390/en11061361 - 27 May 2018

Cited by 28 | Viewed by 12502

Abstract

Heat and mass transfer as well as chemical reactions in technical processes can be enhanced by using electric fields. This paper provides an overview of current fundamental and applied research as well as potential technical applications of electric fields in energy and process [...] Read more.

Heat and mass transfer as well as chemical reactions in technical processes can be enhanced by using electric fields. This paper provides an overview of current fundamental and applied research as well as potential technical applications of electric fields in energy and process engineering. This includes electrosprays, technical combustors as well as electrochemical reforming and plasma gasification of waste or biomass. Other emerging fields are plasma technologies for treatment of water, surfaces and gases including flue gases. In particle or aerosol-laden flows, plasmas are used to promote particle nucleation and surface growth for controlled nanomaterial synthesis. Furthermore, non-invasive diagnostics based on electromagnetic fields and electric fluid properties are relevant techniques for online control and optimization of technical processes. Finally, an overview of laser-based techniques is provided for studying electro-hydrodynamic effects, temperature, and species concentrations in plasma and electric-field enhanced processes. Full article

(This article belongs to the Special Issue Electric Fields in Energy & Process Engineering)

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