This document discusses the design of plasma torches, specifically addressing how a rotating magnetic field can extend the operational life of electrodes. A plasma torch uses an electric arc to generate very high temperatures by ionizing process gases. However, electrode erosion is a problem. A rotating magnetic field manipulates the arc's attachment point on the electrodes, exposing them to the arc for only short periods, allowing cooling and reducing erosion. The document examines heat transfer mechanisms affecting the cathode and anode, how arc mode and pressure influence erosion, and ionization processes within the torch. A rotating magnetic field enables effective arc control and positioning to minimize electrode damage through reduced current density and thermal gradients.
This document provides information about a High Voltage Engineering course, including:
- The examination scheme which includes marks for internal and end semester exams, as well as term work.
- An overview of the 6 course units which cover topics like breakdown in gases and liquids, generation of high voltages, measurement techniques, and testing of electrical apparatus.
- Detailed content on Unit 1 related to breakdown in gases, including Townsend's theory, ionization processes, and the limitations of Townsend's theory.
This document provides information on various optical detection devices including thermal detectors, thermoelectric detectors, bolometers, pyroelectric detectors, photomultipliers, and photodetectors. It describes the basic operating principles of each device, discussing how they absorb light and convert it to an electrical signal. Key aspects like sensitivity, response time, and frequency response are addressed for different detector types.
Detailed explanation of Plasma arc machining, equipment of plasma arc machining, working of plasma arc machining, construction of plasma arc machining , modes of plasma gun , appliaction of PAM, Advantages of PAM, Disadvantages of PAM and some Youtube Links of PAM
A Study on Liquid Dielectric Breakdown in Micro-EDM DischargeSantosh Verma
The growing interest in applications of micro-nano scale devices in many applications diversified the market demand towards batch production of multi material micro parts. Therefore, innovative integration and development of knowledge base for scaling up of production by precision manufacturing technologies to ensure effective industrial utilization has become the primary focused area of micro-nano scale manufacturing research. There is a huge demand in the production of microstructures by a non-traditional method which is known as Micro-EDM. Micro-EDM process is based on the thermoelectric energy between the work piece and an electrode. Micro-EDM is a newly developed method to produce micro-parts which are in the range of 50 µm -100 µm. Micro-EDM is an efficient machining process for the fabrication of a micro-metal hole with various advantages resulting from its characteristics of non-contact and thermal process.
This document provides a summary of key concepts regarding electrical breakdown and conduction in gases:
- Gases can act as insulating or conducting media depending on the applied voltage. Low voltages allow small currents, while higher voltages cause electrical breakdown through ionization processes.
- Breakdown occurs through the formation of a conductive spark between electrodes. It involves transitions from non-sustaining to self-sustaining discharges.
- Ionization processes like collisional ionization and photoionization generate free electrons and ions, leading to current growth. Secondary processes like positive ion bombardment and photon emission further sustain the discharge.
- The Townsend theory and streamer theory describe the mechanisms of breakdown under different conditions involving
Electric heating has several advantages over other heating systems, including cleanliness, ease of control, and higher efficiency. There are three main modes of heat transfer: conduction through solids, convection in liquids and gases, and radiation through empty space. Electric heating works through either direct resistance heating by passing current through a material, or indirect heating where a resistive element transfers heat via convection or radiation. Electric arc heating produces very high temperatures by generating an electric arc between electrodes, and is used in electric arc furnaces for melting metals.
This document discusses the mechanisms of breakdown in gases. It explains that at high electric fields, free electrons in gas can gain enough energy between collisions to cause ionization when striking other molecules. This leads to an electron avalanche effect where the number of electrons increases rapidly. The document outlines various types of ionization processes and theories of breakdown proposed by Townsend, including his first and second ionization coefficients. Townsend's theory of electron avalanches explains the exponential rise in current during breakdown. The document provides mathematical equations to describe current growth based on these coefficients.
This document discusses gas-filled tubes, which contain a small amount of inert gas at low pressure. There are two main types: cold-cathode tubes, which use natural electron emission, and hot-cathode tubes, which have a heated cathode. Gas-filled tubes can conduct more current than vacuum tubes because electron collisions ionize gas molecules, increasing the number of charge carriers. They also have less control over electron flow than vacuum tubes. Common applications include voltage regulation, rectification, switching, and radio frequency detection.
This document provides information about a High Voltage Engineering course, including:
- The examination scheme which includes marks for internal and end semester exams, as well as term work.
- An overview of the 6 course units which cover topics like breakdown in gases and liquids, generation of high voltages, measurement techniques, and testing of electrical apparatus.
- Detailed content on Unit 1 related to breakdown in gases, including Townsend's theory, ionization processes, and the limitations of Townsend's theory.
This document provides information on various optical detection devices including thermal detectors, thermoelectric detectors, bolometers, pyroelectric detectors, photomultipliers, and photodetectors. It describes the basic operating principles of each device, discussing how they absorb light and convert it to an electrical signal. Key aspects like sensitivity, response time, and frequency response are addressed for different detector types.
Detailed explanation of Plasma arc machining, equipment of plasma arc machining, working of plasma arc machining, construction of plasma arc machining , modes of plasma gun , appliaction of PAM, Advantages of PAM, Disadvantages of PAM and some Youtube Links of PAM
A Study on Liquid Dielectric Breakdown in Micro-EDM DischargeSantosh Verma
The growing interest in applications of micro-nano scale devices in many applications diversified the market demand towards batch production of multi material micro parts. Therefore, innovative integration and development of knowledge base for scaling up of production by precision manufacturing technologies to ensure effective industrial utilization has become the primary focused area of micro-nano scale manufacturing research. There is a huge demand in the production of microstructures by a non-traditional method which is known as Micro-EDM. Micro-EDM process is based on the thermoelectric energy between the work piece and an electrode. Micro-EDM is a newly developed method to produce micro-parts which are in the range of 50 µm -100 µm. Micro-EDM is an efficient machining process for the fabrication of a micro-metal hole with various advantages resulting from its characteristics of non-contact and thermal process.
This document provides a summary of key concepts regarding electrical breakdown and conduction in gases:
- Gases can act as insulating or conducting media depending on the applied voltage. Low voltages allow small currents, while higher voltages cause electrical breakdown through ionization processes.
- Breakdown occurs through the formation of a conductive spark between electrodes. It involves transitions from non-sustaining to self-sustaining discharges.
- Ionization processes like collisional ionization and photoionization generate free electrons and ions, leading to current growth. Secondary processes like positive ion bombardment and photon emission further sustain the discharge.
- The Townsend theory and streamer theory describe the mechanisms of breakdown under different conditions involving
Electric heating has several advantages over other heating systems, including cleanliness, ease of control, and higher efficiency. There are three main modes of heat transfer: conduction through solids, convection in liquids and gases, and radiation through empty space. Electric heating works through either direct resistance heating by passing current through a material, or indirect heating where a resistive element transfers heat via convection or radiation. Electric arc heating produces very high temperatures by generating an electric arc between electrodes, and is used in electric arc furnaces for melting metals.
This document discusses the mechanisms of breakdown in gases. It explains that at high electric fields, free electrons in gas can gain enough energy between collisions to cause ionization when striking other molecules. This leads to an electron avalanche effect where the number of electrons increases rapidly. The document outlines various types of ionization processes and theories of breakdown proposed by Townsend, including his first and second ionization coefficients. Townsend's theory of electron avalanches explains the exponential rise in current during breakdown. The document provides mathematical equations to describe current growth based on these coefficients.
This document discusses gas-filled tubes, which contain a small amount of inert gas at low pressure. There are two main types: cold-cathode tubes, which use natural electron emission, and hot-cathode tubes, which have a heated cathode. Gas-filled tubes can conduct more current than vacuum tubes because electron collisions ionize gas molecules, increasing the number of charge carriers. They also have less control over electron flow than vacuum tubes. Common applications include voltage regulation, rectification, switching, and radio frequency detection.
High Voltage engineering Unit-01 (As per AKTU)Mohammad Imran
It contains information about Breakdown mechanism of solids, liquids and gasses.
Also it covers the part of Paschen's Law, Corona Discharge and Breakdown in Vacuum.
Estimation of cooling requirement of magnets in the multi cusp plasma deviceeSAT Journals
Abstract The need for energy generation from clean sources like nuclear fusion has given rise to increased research in the Plasma and its characteristic properties. Multi-cusp Plasma Device installed at the IPR is one of the device used to study the plasma characteristics wherein quiescent plasma is generated. An optimized design of water cooling system is necessary to ensure the removal of heat losses and keep the electromagnets of the plasma device under the safe operating conditions of temperature and thermal stresses by passage of flow of water, thereby increasing the life cycle of the device. The project focuses on the fluid flow analysis for the heat transfer of generated heat in the magnet due to the continuous supply of electricity. The aim of this project is to determine the performance and working attributes of the cooling system used. The design and evaluation of the cooling system are executed on the basis of analytical calculations and actual experimentation work on the device. Key Words: Chiller requirement, cooling requirement, electromagnet cooling, fluid flow analysis, Multi-cusp plasma device, pressure drop, pump requirement, water cooling
1. This document summarizes an experiment on determining the heat of reaction using a calorimeter. Electrical energy was passed through a coil in the calorimeter, heating the water and increasing its temperature.
2. The experiment aimed to determine the equivalence between electrical/mechanical energy and heat energy. Measurements of voltage, current, water mass, and temperature changes were recorded over multiple trials.
3. The results showed that a larger voltage and current produced a greater increase in temperature over time. This supported the conclusion that a larger amount of electrical energy input leads to a larger amount of heat energy generated.
Thermal size effects in contact metal semiconductor structures are investigated. In thin diodes where the sample size is much smaller than the carrier cooling length, the electron temperature at the contact is much higher than the phonon temperature. Energy is transferred to the environment through electronic thermal conductivity. In thick diodes where the sample size is much larger than the cooling length, the electron and phonon temperatures equalize in the volume. At ohmic contacts in both thin and thick diodes, the temperatures equalize with the environment temperature under ideal heat transfer conditions. The temperatures depend on thermal boundary conditions and sample size, with thermal size effects more pronounced in barrier structures.
Utilization of electric power (17 ee742)9th septRanganathGaonkar
This lecture covers arc heating and its classification as direct or indirect arc heating. Direct arc heating involves current passing directly through the material being heated, allowing for inherent stirring. Indirect arc heating involves heat transfer by radiation only, with no current passing through the material. The equivalent circuit of an arc furnace is derived, showing the resistances of the electrodes, furnace, and load. An example calculation is provided to estimate the average power input, arc voltage, and total KVA required from the supply to melt 10 tonnes of steel in an arc furnace over 2 hours.
This document describes atomic absorption spectroscopy (AAS), a technique introduced in 1950 for quantitative elemental analysis. AAS uses atomic absorption of light to determine the concentration of gas-phase metal atoms. Samples are atomized in a flame or graphite furnace then irradiated to promote electron excitation. Absorption of characteristic wavelengths is measured using a detector. AAS can detect metals down to ppm levels and is used to analyze biological, environmental, food, and other samples for various elements.
This document discusses the history and development of high voltage engineering. It begins with early experiments with static electricity by ancient Greeks. Key figures who contributed include Franklin, Faraday, Tesla, and Edison. Faraday's law established that a magnetic field can induce current in a wire. Advances allowed longer distance power transmission. Challenges included developing high voltage insulation. Numerical methods like finite element analysis are now used to model electric field distributions in complex high voltage components.
The document discusses plasma processing in extractive metallurgy. It describes plasma as the fourth state of matter and its properties. Plasma is used as both a heat source and carrier medium in materials processing. Different types of plasma torches and furnace designs are presented, including DC plasma torches, AC plasma torches, and RF plasma torches. Applications of plasma include plasma reducing technologies like shaft furnaces and falling film plasma furnaces. Plasma melting technologies such as plasma arc melting, plasma induction furnaces, and plasma arc remelting are also discussed.
Study Some Parameters of Electrical Discharge in N2 and CO2 Without and With ...IOSRJECE
:We study the breakdown voltage under low pressure for N2, CO2 gases of with a magnetic field to the electrode of iron and aluminum with diameter (8.8cm) cm and distance separation between them is (3cm). by using Passion curve, we measur less effort collapsed, and we notice that less effort is linked to the collapse of a function held cities and when the magnetic field will be reduced to shed breakdown voltage. Since the breakdown voltage for CO2 is greater than breakdown voltage N2. Through curved Passion was calculated (훾) and when to shed the magnetic field will increase in value
Plasma arc machining uses a high-temperature plasma stream to cut metals. It melts and vaporizes metal using the concentrated heat of an electrical arc formed through an ionized gas jet. This allows it to cut materials like stainless steel and aluminum that are difficult to cut with oxyfuel. It provides rapid cutting speeds, can cut a wide range of materials and thicknesses, and is more economical than oxyfuel for many applications.
The document summarizes key aspects of superconductivity. It describes how superconductivity was discovered in 1911 when the electrical resistance of mercury suddenly dropped to zero at 4.2 K. Some key properties discussed include the Meissner effect where magnetic flux is expelled from the superconductor below the critical temperature, and the distinction between type I and type II superconductors based on their behavior in magnetic fields. The document also provides an overview of the BCS theory of superconductivity and discusses some industrial applications of superconductors such as in MRI machines, maglev trains, and electricity transmission.
Partial discharge is a discharge event that does not bridge the entire insulation system between electrodes. It occurs within cavities in insulation materials under high electric fields. During partial discharge, a plasma channel briefly forms within the cavity, conducting electricity from one side to the other without crossing the entire material. Measurement setups use coupling devices and detectors to monitor the short voltage pulses caused by partial discharge, in order to evaluate insulation condition and detect defects.
Physical and technical basics of induction heating technologiesLeonardo ENERGY
In this course the physical and technical basics of induction heating processes and technologies will be explained. During the introduction the author will demonstrate along typical features of induction heating, why today induction heating is used in many industrial processes. In the first part of this course the physical basics will be discussed by explaining the fundamental equations. The most important features of induction heating, like skin effect, penetration depth, proximity effect, Joule heat effect, induced current and power density distribution in the workpiece and the effect of electromagnet forces as well as the influence of electromagnetic field guiding systems will be discussed along selected examples. In the second part of this course the author explains, how the electrical efficiency of an induction heating process depends on the design of the induction heating system and how the frequency of the inductor current has to be chosen in order to get the desired temperature distribution in the workpiece but at the same time a high efficient induction heating process. In the following the physical principle of induction longitudinal and transverse flux heating of flat material we be shown. At the end of this course using an example of an induction through heating application, a typical energy flow diagram will be explained and potentials for improve-ments will be discussed. The recapitulation of the most important features of induction heating processes and technologies will conclude this course.
Thermal Simulations of an Electronic System using Ansys IcepakIJERA Editor
Present electronics industry component sizes are efficiently reducing to meet the product requirement with
compact size with greater performance in compact size products resulting in different problems from thermal
prospective to bring product better performance electrically and mechanically.
In this paper we will study how to overcome the thermal problem for a product which includes components
reliability and PCB performance by using CFD thermal simulation tool (Ansys Icepak).
The document discusses various theories related to breakdown in liquid dielectrics. It begins with an introduction to pure and commercial liquids, and different breakdown theories. Some of the key theories discussed include the suspended particle theory, cavitation and bubble theory, and stressed oil volume theory. The document also covers factors that affect breakdown strength such as impurities, gas content, liquid viscosity, and stressed volume. Thermal breakdown mechanisms are discussed as well. A variety of liquid dielectric materials and their typical breakdown strengths are also listed.
Induction Heating – Operation, Applications and Case Studies - Presentation S...Leonardo ENERGY
The industrial process heating applications that use electrotechnologies have been found to improve product quality, productivity, energy efficiency, reduce energy intensity and have many other non-energy benefits. Induction technology is another electrotechnology based heating method for heating electrical conductive materials. It involves sending an alternating current (AC) through a copper coil which surrounds the material to be heated or melted. When a metal is placed inside the coil and enters the magnetic field, circulating eddy currents are induced within the metal. The resistance of the metal to the flow of the eddy currents causes the metal to heat up. In this webcast, the operation principles of induction heating technology used for both heating and melting, its applications and EPRI case studies will be presented. The information of vendors as well as other links to reference materials will be presented at the end.
Superconductivity is the ability of certain materials to conduct electric current with practically zero resistance. This capacity produces interesting and potentially useful effects. For a material to behave as a superconductor, low temperatures are required.
This document describes the arc discharge method for synthesizing nanomaterials. It discusses how an arc discharge works by thermionic emission to vaporize electrode materials and form a plasma. The document provides details on the experimental setup, conditions for producing single-walled carbon nanotubes, and applications of the arc discharge method such as synthesizing carbon nanotubes, metal nanoparticles, and nanowires.
Plasma arc machining (PAM) uses a plasma torch to cut metals. It was initially developed to cut difficult metals like stainless steel and aluminum. Recent improvements allow it to cut mild steel with improved cut quality compared to earlier plasma cutting. The plasma is generated by heating gas with an electric arc until it ionizes, producing free electrons and ions that conduct electricity. PAM works by melting metal with the high temperature plasma jet and blowing away the molten metal. Key parameters that affect PAM performance include the plasma torch design, the physical setup configuration, and the operating environment.
High Voltage engineering Unit-01 (As per AKTU)Mohammad Imran
It contains information about Breakdown mechanism of solids, liquids and gasses.
Also it covers the part of Paschen's Law, Corona Discharge and Breakdown in Vacuum.
Estimation of cooling requirement of magnets in the multi cusp plasma deviceeSAT Journals
Abstract The need for energy generation from clean sources like nuclear fusion has given rise to increased research in the Plasma and its characteristic properties. Multi-cusp Plasma Device installed at the IPR is one of the device used to study the plasma characteristics wherein quiescent plasma is generated. An optimized design of water cooling system is necessary to ensure the removal of heat losses and keep the electromagnets of the plasma device under the safe operating conditions of temperature and thermal stresses by passage of flow of water, thereby increasing the life cycle of the device. The project focuses on the fluid flow analysis for the heat transfer of generated heat in the magnet due to the continuous supply of electricity. The aim of this project is to determine the performance and working attributes of the cooling system used. The design and evaluation of the cooling system are executed on the basis of analytical calculations and actual experimentation work on the device. Key Words: Chiller requirement, cooling requirement, electromagnet cooling, fluid flow analysis, Multi-cusp plasma device, pressure drop, pump requirement, water cooling
1. This document summarizes an experiment on determining the heat of reaction using a calorimeter. Electrical energy was passed through a coil in the calorimeter, heating the water and increasing its temperature.
2. The experiment aimed to determine the equivalence between electrical/mechanical energy and heat energy. Measurements of voltage, current, water mass, and temperature changes were recorded over multiple trials.
3. The results showed that a larger voltage and current produced a greater increase in temperature over time. This supported the conclusion that a larger amount of electrical energy input leads to a larger amount of heat energy generated.
Thermal size effects in contact metal semiconductor structures are investigated. In thin diodes where the sample size is much smaller than the carrier cooling length, the electron temperature at the contact is much higher than the phonon temperature. Energy is transferred to the environment through electronic thermal conductivity. In thick diodes where the sample size is much larger than the cooling length, the electron and phonon temperatures equalize in the volume. At ohmic contacts in both thin and thick diodes, the temperatures equalize with the environment temperature under ideal heat transfer conditions. The temperatures depend on thermal boundary conditions and sample size, with thermal size effects more pronounced in barrier structures.
Utilization of electric power (17 ee742)9th septRanganathGaonkar
This lecture covers arc heating and its classification as direct or indirect arc heating. Direct arc heating involves current passing directly through the material being heated, allowing for inherent stirring. Indirect arc heating involves heat transfer by radiation only, with no current passing through the material. The equivalent circuit of an arc furnace is derived, showing the resistances of the electrodes, furnace, and load. An example calculation is provided to estimate the average power input, arc voltage, and total KVA required from the supply to melt 10 tonnes of steel in an arc furnace over 2 hours.
This document describes atomic absorption spectroscopy (AAS), a technique introduced in 1950 for quantitative elemental analysis. AAS uses atomic absorption of light to determine the concentration of gas-phase metal atoms. Samples are atomized in a flame or graphite furnace then irradiated to promote electron excitation. Absorption of characteristic wavelengths is measured using a detector. AAS can detect metals down to ppm levels and is used to analyze biological, environmental, food, and other samples for various elements.
This document discusses the history and development of high voltage engineering. It begins with early experiments with static electricity by ancient Greeks. Key figures who contributed include Franklin, Faraday, Tesla, and Edison. Faraday's law established that a magnetic field can induce current in a wire. Advances allowed longer distance power transmission. Challenges included developing high voltage insulation. Numerical methods like finite element analysis are now used to model electric field distributions in complex high voltage components.
The document discusses plasma processing in extractive metallurgy. It describes plasma as the fourth state of matter and its properties. Plasma is used as both a heat source and carrier medium in materials processing. Different types of plasma torches and furnace designs are presented, including DC plasma torches, AC plasma torches, and RF plasma torches. Applications of plasma include plasma reducing technologies like shaft furnaces and falling film plasma furnaces. Plasma melting technologies such as plasma arc melting, plasma induction furnaces, and plasma arc remelting are also discussed.
Study Some Parameters of Electrical Discharge in N2 and CO2 Without and With ...IOSRJECE
:We study the breakdown voltage under low pressure for N2, CO2 gases of with a magnetic field to the electrode of iron and aluminum with diameter (8.8cm) cm and distance separation between them is (3cm). by using Passion curve, we measur less effort collapsed, and we notice that less effort is linked to the collapse of a function held cities and when the magnetic field will be reduced to shed breakdown voltage. Since the breakdown voltage for CO2 is greater than breakdown voltage N2. Through curved Passion was calculated (훾) and when to shed the magnetic field will increase in value
Plasma arc machining uses a high-temperature plasma stream to cut metals. It melts and vaporizes metal using the concentrated heat of an electrical arc formed through an ionized gas jet. This allows it to cut materials like stainless steel and aluminum that are difficult to cut with oxyfuel. It provides rapid cutting speeds, can cut a wide range of materials and thicknesses, and is more economical than oxyfuel for many applications.
The document summarizes key aspects of superconductivity. It describes how superconductivity was discovered in 1911 when the electrical resistance of mercury suddenly dropped to zero at 4.2 K. Some key properties discussed include the Meissner effect where magnetic flux is expelled from the superconductor below the critical temperature, and the distinction between type I and type II superconductors based on their behavior in magnetic fields. The document also provides an overview of the BCS theory of superconductivity and discusses some industrial applications of superconductors such as in MRI machines, maglev trains, and electricity transmission.
Partial discharge is a discharge event that does not bridge the entire insulation system between electrodes. It occurs within cavities in insulation materials under high electric fields. During partial discharge, a plasma channel briefly forms within the cavity, conducting electricity from one side to the other without crossing the entire material. Measurement setups use coupling devices and detectors to monitor the short voltage pulses caused by partial discharge, in order to evaluate insulation condition and detect defects.
Physical and technical basics of induction heating technologiesLeonardo ENERGY
In this course the physical and technical basics of induction heating processes and technologies will be explained. During the introduction the author will demonstrate along typical features of induction heating, why today induction heating is used in many industrial processes. In the first part of this course the physical basics will be discussed by explaining the fundamental equations. The most important features of induction heating, like skin effect, penetration depth, proximity effect, Joule heat effect, induced current and power density distribution in the workpiece and the effect of electromagnet forces as well as the influence of electromagnetic field guiding systems will be discussed along selected examples. In the second part of this course the author explains, how the electrical efficiency of an induction heating process depends on the design of the induction heating system and how the frequency of the inductor current has to be chosen in order to get the desired temperature distribution in the workpiece but at the same time a high efficient induction heating process. In the following the physical principle of induction longitudinal and transverse flux heating of flat material we be shown. At the end of this course using an example of an induction through heating application, a typical energy flow diagram will be explained and potentials for improve-ments will be discussed. The recapitulation of the most important features of induction heating processes and technologies will conclude this course.
Thermal Simulations of an Electronic System using Ansys IcepakIJERA Editor
Present electronics industry component sizes are efficiently reducing to meet the product requirement with
compact size with greater performance in compact size products resulting in different problems from thermal
prospective to bring product better performance electrically and mechanically.
In this paper we will study how to overcome the thermal problem for a product which includes components
reliability and PCB performance by using CFD thermal simulation tool (Ansys Icepak).
The document discusses various theories related to breakdown in liquid dielectrics. It begins with an introduction to pure and commercial liquids, and different breakdown theories. Some of the key theories discussed include the suspended particle theory, cavitation and bubble theory, and stressed oil volume theory. The document also covers factors that affect breakdown strength such as impurities, gas content, liquid viscosity, and stressed volume. Thermal breakdown mechanisms are discussed as well. A variety of liquid dielectric materials and their typical breakdown strengths are also listed.
Induction Heating – Operation, Applications and Case Studies - Presentation S...Leonardo ENERGY
The industrial process heating applications that use electrotechnologies have been found to improve product quality, productivity, energy efficiency, reduce energy intensity and have many other non-energy benefits. Induction technology is another electrotechnology based heating method for heating electrical conductive materials. It involves sending an alternating current (AC) through a copper coil which surrounds the material to be heated or melted. When a metal is placed inside the coil and enters the magnetic field, circulating eddy currents are induced within the metal. The resistance of the metal to the flow of the eddy currents causes the metal to heat up. In this webcast, the operation principles of induction heating technology used for both heating and melting, its applications and EPRI case studies will be presented. The information of vendors as well as other links to reference materials will be presented at the end.
Superconductivity is the ability of certain materials to conduct electric current with practically zero resistance. This capacity produces interesting and potentially useful effects. For a material to behave as a superconductor, low temperatures are required.
This document describes the arc discharge method for synthesizing nanomaterials. It discusses how an arc discharge works by thermionic emission to vaporize electrode materials and form a plasma. The document provides details on the experimental setup, conditions for producing single-walled carbon nanotubes, and applications of the arc discharge method such as synthesizing carbon nanotubes, metal nanoparticles, and nanowires.
Plasma arc machining (PAM) uses a plasma torch to cut metals. It was initially developed to cut difficult metals like stainless steel and aluminum. Recent improvements allow it to cut mild steel with improved cut quality compared to earlier plasma cutting. The plasma is generated by heating gas with an electric arc until it ionizes, producing free electrons and ions that conduct electricity. PAM works by melting metal with the high temperature plasma jet and blowing away the molten metal. Key parameters that affect PAM performance include the plasma torch design, the physical setup configuration, and the operating environment.
02_Heatflowinwelding and joining processSakib987640
This document discusses heat flow during welding. It covers topics such as heat sources in welding like arc, resistance, laser, and friction welding. It describes the welding arc and plasma formation. It also discusses parameters that affect heat flow like polarity, heat source efficiency, and methods to measure efficiency. The objectives are to provide information on heat flow during welding and how it influences microstructure and properties, and identify heat sources and power density in different welding methods.
Direct energy conversion involves transforming one form of energy directly into another without intermediate steps. This summary will discuss three methods of direct energy conversion:
1) Thermoelectric generators directly convert heat into electricity through the Seebeck effect using semiconductors. They have no moving parts and can operate with a simple design of p-type and n-type materials.
2) Fuel cells also directly produce electricity from chemical reactions without combustion, like the Grove fuel cell developed in 1839.
3) Thermoelectric photovoltaic cells directly convert sunlight into electricity through the photovoltaic effect in semiconductor junctions.
The document describes an experiment to determine the average surface heat transfer coefficient in natural convection. The apparatus consists of a vertically oriented brass tube heated by an electric element inside an enclosure. Thermocouples measure the tube temperature. Natural convection heat transfer from the tube to surrounding air is calculated using Newton's law of cooling. Correlations are used to compare the experimentally obtained heat transfer coefficient. The experiment aims to determine the heat transfer coefficient and compare it to values from correlations.
This document summarizes research into using laser excitation of cesium ions to enhance the performance of thermionic energy converters (TECs). The researchers have developed a particle-in-cell model of a planar diode discharge to simulate TEC operation and are using it to model the effects of laser excitation on current-voltage characteristics. They have also designed a laboratory test cell to experimentally validate the effects of laser excitation on TEC performance. Initial results suggest laser excitation could substantially improve TEC current density and efficiency over conventional ignited or triode configurations.
This document summarizes research into using laser excitation to enhance the production of cesium ions in thermionic energy converters (TECs). The researchers have developed a particle-in-cell model of a planar diode discharge to simulate TEC performance with and without laser ionization. They have also designed a laboratory test cell to experimentally validate the effect of laser excitation on TEC current-voltage characteristics. Future work will include refining the models, procuring parts for the test cell, and conducting experimental studies to analyze how laser excitation can increase TEC efficiency and be used in energy systems to reduce carbon emissions.
This document summarizes research into using laser excitation to enhance the production of cesium ions in thermionic energy converters (TECs). The researchers have developed a particle-in-cell model of a planar diode discharge to simulate TEC performance with and without laser ionization. They have also designed a laboratory test cell to experimentally validate the effect of laser excitation on TEC current-voltage characteristics. Future work will include refining the models, procuring parts for the test cell, and conducting experimental studies to characterize optimized TEC performance with optical modulation. The goal is to increase TEC efficiency for applications in solar and combustion energy systems to reduce greenhouse gas emissions.
This document summarizes research into using laser excitation of cesium ions to enhance the performance of thermionic energy converters (TECs). The researchers have developed a particle-in-cell model of a planar diode discharge to simulate TEC operation and are using it to model the effects of laser excitation on current-voltage characteristics. They have also designed a laboratory test cell to experimentally validate the effects of laser excitation on TEC performance. Initial results suggest laser excitation could substantially improve TEC current density and efficiency over conventional ignited or triode configurations.
Electron Beam Machining (Modern ManufacturingProcess)Dinesh Panchal
The document summarizes electron beam machining (EBM). EBM uses a focused beam of high-energy electrons to melt and vaporize metal, allowing for precise machining. There are two types - thermal EBM uses the beam's heat to selectively vaporize material, while non-thermal EBM causes surface chemical reactions. The document discusses the generation and control of electron beams, the physical processes involved in thermal EBM, and a phenomenological theory of non-thermal EBM film growth proposed by Christly.
The document discusses thermoelectric power generation. It describes how Seebeck discovered that a temperature difference across two dissimilar conductors produces a voltage (Seebeck effect), which is the operating principle of thermoelectric generators. A thermoelectric generator uses semiconductor materials like bismuth telluride that convert heat into electricity through the Seebeck effect. When heat is applied to one side of the semiconductor couple, electrons move from the hot side to the cold side, producing a current proportional to the temperature difference across the couple.
Plasma arc machining uses ionized gas (plasma) to cut metals. It can cut materials that are difficult to cut with traditional techniques due to high thermal conductivity and oxidation resistance. The process involves generating a pilot arc to ignite the plasma and transferring the arc to the workpiece to melt and vaporize the metal, which is removed by the high-velocity gas. Plasma arc machining produces high-quality cuts at maximum productivity and is suitable for automated cutting applications.
In 1821, Seebeck discovered that a temperature difference across two dissimilar conductors produces a voltage. Good thermoelectric materials have a large Seebeck coefficient and high electrical conductivity with low thermal conductivity, such as bismuth telluride. A thermoelectric generator uses p-type and n-type semiconductors packed between hot and cold side plates to produce electricity from a temperature difference based on the Seebeck effect. The proposed work will fabricate a thermoelectric generator module and test it using a heat source and measuring the voltage and current output at different temperatures.
The document discusses the principles and physics of welding. It covers topics such as fusion welding processes, characteristics of heat sources like welding arcs, arc structures, and potential drop characteristics. The key points are:
1) In fusion welding, material around the joint is melted to join two parts together. Important factors include the heat source, arc characteristics, filler material deposition, and heat flow.
2) A welding arc is a sustained electrical discharge through an ionized gas that produces heat. It is maintained by thermionic emission and ionization between the electrodes.
3) The voltage drop across a welding arc depends on factors like the electrode material, spacing and current. There is an optimal arc length that produces maximum power
Solar Energy based Refrigeration System using Peltier Device 18 ABHISHEK.pdfkeshavkumar403723
This document summarizes a research paper on a solar energy-based refrigeration system using Peltier devices. The system utilizes solar energy to power thermoelectric modules that provide refrigeration without the need for refrigerants or mechanical devices like compressors. The system is intended to provide refrigeration to remote areas without reliable power sources. It describes the construction of the refrigeration system, including the thermoelectric module, refrigeration chamber, battery, solar cells, and frame. It also provides background on thermoelectric effects like the Peltier effect that allow the system to operate.
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1. International Journal of Engineering Science Invention
ISSN (Online): 2319 – 6734, ISSN (Print): 2319 – 6726
www.ijesi.org ||Volume 3 Issue 12 || December 2014 || PP.43-49
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Rotating Magnetic Field in Plasma Torch
Anyaegbunam F. N. C.
(Ph.D.)
Department of Physics/Geology/Geophysics,
Federal University Ndufu-Alike Ikwo, Abakaliki, Ebonyi State, Nigeria.
ABSTRACT:A plasma torch is a device which provides hot plasma for high temperature thermal processes.
Plasma is a mixture of ions, electrons and neutral particles produced when stable molecules are dissociated by
an electric arc or high temperatures. The electric arc is formed between two electrodes - anode and cathode of
a plasma torch. Plasma is thus an electrically conductive gas in which an important fraction of the atoms are
ionized and capable of generating temperatures up to 10000'C with appropriate high tech plasma torch. The
energy generated by plasma arc has been recently used for hazardous waste control. An important problem in
plasma torch design is how to prolong the electrodes lives. Electrode erosion is usually the cause of hot molten
spots on the anode being flung off by the force of impact of the arc. By magnetically rotating the arc, portions of
the anode are exposed to the arc for very short periods of time and are allowed to cool. Again rotating magnetic
field enables effective control of the arc and its proper placement between the electrodes to minimize electrode
erosion. This paper presents the effects of rotating magnetic field in plasma torch design: enhance very high
temperatures and extend the operational lives of the electrodes.
KEY WORDS: plasma torch, rotating magnetic field, plasma arc, process gas.
I. INTRODUCTION
Plasma may be created in a variety of ways, including passing a gas between objects with large
differences in electrical potential, as in the case of lightning, or by exposing gases to high temperatures, as in the
case of arc welding or graphite electrode torches. Plasma arc torches utilize a combination of these techniques
[1], [2]; [3]. A relatively small quantity of ionized gas is produced by an “arc igniter” and introduced between
the electrodes contained in the body of the torch. The presence of this ionized gas allows the formation of an
electric arc between the electrodes, and the arc serves as a resistive heating element with the electric current
creating heat which creates additional plasma that allows the arc to be sustained. Interaction between the arc and
process gas introduced into the torch causes the gas to reach very high temperatures, often nearly as hot as the
sun’s surface. The ability to increase the temperature of the process gas to temperatures up to ten times higher
than those attainable by conventional combustion makes plasma arc technology ideally suited for high
temperature process applications such as gasification of waste[3]. The extremely intense energy produced by the
torch is powerful enough to disintegrate the MSW into its component elements. However, there is need for
improvement on the torch design to improve the operational life of the electrodes for optimal performance [4].
A major advantage of plasma arc torch design is that it takes advantage of the ability of plasma to respond to
magnetic fields by utilizing a rotating magnetic field to manipulate the attachment point of the arc on the
electrodes to provide extended electrode life and reduced maintenance costs [2].
II. PLASMA TORCH DESIGN
Plasma torches vary widely in design and use. They have been used for waste management, metal
cutters, flame stabilization, IC engine lean burn applications and exhaust emission control, among others.
Plasma torches vary widely in power rating as well. Depending on their application and design, torches have
been designed to operate with power consumption of a few hundred watts to several hundred kilowatts. Plasma
torch designs are as diverse as the applications they are used for. For waste destruction application, the plasma
torch must be designed to generate the very high temperatures necessary to disintegrate the waste into its
component elements.A schematic of a generic plasma torch is shown in Figure 1. The gas enters the torch body
through a tube, travels up the length of the cathode and out through the anode throat, meanwhile passing through
the generated arc and becoming plasma. Many different types of process gases have been used with plasma
torches;
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Figure 1: A Generic Plasma Torch Design
Air, O2, N2, H2, Ar, CH4, C2H4 and C3H6 [5] to name a few. Initially, a small quantity of process gas
is introduced between the electrodes to create the plasma arc. Then as the gas enters the torch, the first object it
encounters when entering is the cathode. Typically, cathodes are thin, pointed rods made of tungsten or copper,
although some are flat-ended depending on the application [5]. They are electrically connected to the negative
power supply of the torch, while the anode is connected to the positive terminal of the power source. After
travelling up along the cathode, the gas then encounters the electric plasma arc created by the ionization of a
small quantity of process gas earlier introduced between the electrodes, creates more plasma and passes out of
the torch through the anode throat. The anode is generally constructed from copper or tungsten, like the cathode.
It has a nozzle upstream of the throat to accelerate the flow, ejecting the gas-plasma mixture at high velocity out
of the torch at a very high temperature.
III. MATERIALS AND METHODS:
HEAT TRANSFER DESIGN CONSIDERATIONS : Perhaps the most difficult design consideration
one must contend with when designing a plasma torch is heat transfer [6]. Inadequate cooling of the electrodes
can severely limit the operational life of the torch. High thermal gradients can produce high rates of electrode
erosion, eventually leading to failure]7]. The heat transfer into an electrode is the net sum of radiation,
convection, conduction and electron heating. Both the anode and cathode exhibit different heating and cooling
characteristics due to the geometry of the torch and electron path, so each will be examined separately. The
following sections describe the heat transfer mechanisms to the cathode and the anode.
Cathode Heat Transfer : Heat transfer to the cathode can occur through convection, conduction, radiation and
electron interaction [5]. Throughout the course of the plasma torch operation, the cathode is heated by the
current passing through it (Joule heating). This is plainly seen in a common halogen bulb; as current increases,
so does the temperature and brightness of the filament. Cathode heating in this manner is purely a function of
cathode diameter and current. Another method of cathode heating is radiation. As the process gas passes through
the electric arc it is converted into plasma. This plasma radiates heat onto the electrodes and torch body, since
they are at much lower temperatures [8]. Radiation to the electrodes is known to increase as the current density
increases [5]. However, this radiation effect is rather small compared to the effect of Joule heating. Only 2-8
percent of the total heat transfer to the anode was due to radiation [9]. Likewise, the effect of radiation heating
to the cathode will be small compared to other heating modes. Radiation is also a method of cooling for the
cathode. Hot spots, especially the cathode tip, will radiate energy to the cooler gas surrounding it. Finally, the
cathode can be heated by positive ion bombardment. Since the cathode is negative, it attracts positive ions,
which collide with the cathode and convert their kinetic energy into thermal energy. Convection, conduction and
electron emission all serve to cool the cathode. Electron emission from the cathode occurs primarily at the tip.
Electron emission from the cathode in a high-pressure plasma torch is thought to occur in two ways; field
emission and thermionic emission [5]. Field emission is the extraction of an electron from a material due to a
large magnetic field. Thermionic emission is the emission of electrons from a material due to high temperatures
(similar to sweat evaporation, this type of electron emission cools the material). The Richardson-Schotky
equation predicts the current density at the cathode due to these two effects:
j = AT2
(1)
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From this equation (1) it is apparent that the current density, j, leaving the cathode is a strong function
of temperature, T. Concurrently, since the highest temperature of the cathode is located at the tip, one can
conclude that the current density is generally confined to that area. Convection is another main source of cooling
for the cathode. The flow geometry of the plasma torch is designed so that gas enters through the gas inlet ports,
travels up the cathode body, through the electric arc and out through the anode throat. As the gas travels along
the cathode body, it has not yet reached the electric arc and been converted into hot plasma. Therefore, it is still
at ambient temperature and provides convective cooling. Finally, conduction serves as another means of cooling
the cathode. Since the cathode is one of the hottest elements in the plasma torch, second only to the anode,
anything it is in contact with serves as a heat sink. A steel alignment sheath usually covers a majority of the
cathode. This sheath is an excellent heat sink. Heat transfer also occurs through various electric insulators.
However, electric insulators are usually good heat insulators as well (especially when compared to steel) and do
not contribute significantly to help cool the cathode. Curren (1985), studied the overall heat transfer to a cathode
in a low power DC arcjet. He discovered that only 1 to 5 percent of the total arc power was lost to the cathode.
In his experiments, as the power was increased, the percentage of power lost to the cathode actually decreased.
This is an important consideration when improvements are needed in torch design. Apparently, power losses to
the cathode are small when compared to the anode.
Anode Heat Transfer : The anode is the part of the plasma torch that receives the brunt of the thermal abuse. It
is exposed to high temperature plasma, radiation, Joule heating, ion bombardment and electric arc impact.
Unlike the cathode, which is cooled by convection, the anode is heated by convection. As the cool gases flow
past the cathode and into the electric arc, they become ionized and extremely hot. The gases then flow through
the anode throat, heating it by convection. This convection is a strong function of electrode geometry and
alignment. If the plasma jet leaving the cathode tip is misaligned, instead of flowing through the center of the
anode throat it may flow directly into the anode surface and severely increase the rate of convective heat
transfer. Also, the diameter of the anode throat is important.
As the diameter of the anode throat increases, convective heat transfer to the anode should decrease
because of the increased distance between the anode wall and the centerline of the plasma jet. In fact, as the
anode throat diameter and feedstock flow rate increases, a cool layer of gas may completely avoid the arc and
follow the anode throat wall providing a cooling effect. As with the cathode, the anode is both heated and cooled
by radiation. The high temperature plasma flowing through the anode heats the anode by radiation. However,
this radiation is generally quite small compared to other heating effects. Also, hot spots on the anode, especially
portions exposed to the atmosphere, can radiate heat to the cooler gases surrounding them. Joule heating is a
significant source of heating to the anode, although not as severe as the cathode because of its larger mass.
Current passing through any substance will tend to heat that substance proportionally to its electrical resistance.
The rate of heat transfer for the anode is a function of electrical resistance, anode mass and the amount of
current passing through it. Compared to the cathode, the anode has a lower electrical resistance because of its
larger size and also has greater mass with which to dissipate heat. Therefore, Joule heating, although important,
does not play as significant a role with the anode as it does with the cathode. Perhaps the most important sources
of heat transfer to the anode are ion bombardment and electric arc impact. Similar to the cathode, the anode
attracts ions, in this case negative, which collide with the anode and convert their kinetic energy into thermal
energy. The heat transfer to the anode is especially high at the point of arc attachment. Heat transfer occurs from
the arc to the anode in several ways. First, the electrons have thermal energy, which they release upon contact
with the anode. They also have kinetic energy, which partially gets converted to thermal energy as it passes
through the anode. The heat transfer at the point of arc attachment is described by:
qe = j[(5kTe/2e) + Ua + фa] (2)
This equation (2), demonstrates how the thermal energy (first term), kinetic energy gained by the
electron acceleration through the arc (second term) and the kinetic energy given up by the electrons on impact
(third term), relate to the heat transfer at the point of arc attachment, qe. It is important to note that each term is
multiplied by the current density, j. Therefore, the heat transfer to the anode due to the electric arc is largely
dominated by the current density. This conclusion was also reached by Curren (1985) cited by [5]. He
determined that the heat transfer to the anode increased as current increased and decreased as feedstock flowrate
increased. The anode is primarily cooled by conduction, although convection and radiation do play minor roles.
In most plasma torch designs, the anode is secured to the torch body by an anode cap, generally made of steel.
This cap provides an excellent large body heat sink. Without it, the anode would quickly overheat.
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This anode cap is also connected to the torch body, another excellent heat sink. In most torch designs,
the positive section of the torch comprises a majority of the torch mass. This is important in uncooled plasma
torches to provide enough material to act as an effective heat sink for the anode.
Arc Mode Design Considerations : An anode, which has a constrictor, or throat, can operate in two different
arc modes; high voltage and low voltage (also known as diffuse and constricted modes, respectively [5]. Both
modes are shown in Fig. 2. The high voltage mode is characterized by an arc that passes completely through the
anode throat and attaches on the downstream side of the constrictor. For the low voltage mode, the arc attaches
somewhere before the anode throat. Of the two modes, the low voltage mode is more damaging to the anode.
The high pressure upstream of the anode throat causes this high rate of electrode erosion. As pressure increases,
an electric arc will tend to constrict. Because of the geometry of the anode, the pressure upstream of the anode
throat is at a much higher pressure than the pressure downstream of the throat, which is roughly at atmospheric.
Recall that the heat transfer rate to the anode at the point of arc attachment is a strong function of current
density. Therefore, as pressure increases, current density increases and heat transfer at the point of arc
attachment increases. This causes large thermal gradients, which generally result in high rates of electrode
erosion. When designing a plasma torch anode, it is important to keep in mind in what arc mode the torch will
operate.
Figure 2: Arc Mode Operation
Regions of an Electric Arc : In addition to being able to operate in two different modes, there are also three
different regions within an arc, each with unique characteristics. These regions are: the cathode fall region,
positive column and anode fall region.
a) Cathode Fall Region: The cathode fall region is located on the surface of the cathode. It is only about 0.001
mm thick, but depends on the pressure of the gas. The electric field strength in this area is very strong. Only
electrons are found in this region, there is no plasma present. Also, the current density is highest in this section
of the arc because the arc is narrowest at the cathode.
b) Positive Column: The length of an arc largely falls within the description of a positive column. In contrast to
the cathode fall region, the electric field is very weak in the positive column. Also, this region is considered
electrically neutral, so it is classified as plasma.
c) Anode Fall Region: Like the cathode fall region, the anode fall region has a strong electric field and contains
only electrons, no plasma. However, it is much thicker than the cathode fall region by several orders of
magnitude and is located on the surface of the anode.
Ionization Processes : The goal of any plasma torch is to ionize and/or dissociate the feedstock gas passing
through it. The energy necessary for ionization can be provided by electron collision, positive ion impact,
absorption of radiant energy, or the gas may become so hot that ionization occurs thermally by the impact of
neutral atoms. All of these processes occur within a plasma torch, but the ionization processes in the region of
the arc column are largely dominated by the first and fourth cases. The ionization potential of electrons depends
largely on their velocity, which is largely determined by the voltage.
High Voltage Mode
Low Voltage Mode
Low Voltage Mode
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Slow moving electrons will not have sufficient kinetic energy to ionize an atom. Quickly moving
electrons will pass through the sphere of influence of an atom before being able to remove an electron. Each
particular element or compound has its own unique voltage at which ionization occurs most readily. As an
example, mercury is most easily ionized into Hg+ at 40 volts, past which, this ability decreases steadily.
Producing Hg+++ occurs most readily at just over 200 volts [5]. Two conclusions can be made from this. First,
it is possible to produce different species from the same gas using different ionization voltages and second,
producing known, desired specie will best occur at a certain voltage. Ionization occurring at extremely high
temperatures is known as thermal ionization. It is the principal source of ionization in electric arcs. As the
temperature of a gas increases, so do the velocities, increasing the likelihood that two or more neutral atoms will
collide and ionize. At high temperatures, polyatomic molecules are also likely to dissociate, from which their
simpler products can ionize.
Arc Stability : Arc stability is of utmost importance in maintaining smooth reliable operation of a plasma
torch. Unfortunately, many of the forces present in a plasma torch tend to work against arc stability. However,
several methods can be employed to increase the likelihood of stable arc operation. Increasing the arc diameter
is perhaps the easiest way to produce a more stable arc. This is accomplished simply by increasing the current,
or reducing the pressure. Aerodynamic stabilization can be accomplished through anode geometry or by
inducing vorticity into the flow.
Arc Diameter : The diameter of an electric arc is directly related to how stable it is; the wider it is, the more
stable it is. An arc with a wide cross-section is more likely to resist any sort of disturbances introduced by the
gas flow or other means. Disturbances will generally be confined to the outer edges of the arc leaving a large
straight path for current to travel through down the center. Thinner arcs do not have this type of buffer. Their
current carrying path is much narrower. Once they are disturbed, their current path is displaced, creating a
longer, unstable arc. Plasma torches operating with diatomic feedstock generally suffer from this type of
instability, because the arcs produced tend to be much narrower than arcs produced in monatomic gases. The
underlying principle is that, given the same amount of disturbance, a narrow arc will be broken before a wider
arc. Pressure also affects the arc diameter. Increasing pressure will tend to constrict the arc and make it
narrower. Another effect of increasing the pressure is to increase the temperature of the arc. Changing the flow-
rate of the feedstock, or changing the diameter of the anode throat can change the pressure. In order to reduce
the pressure in the torch body, the flow-rate can be decreased, or the anode throat can be increased. However,
decreasing the flow-rate will limit the amount of convective cooling available to cool the electrodes. Also,
increasing the diameter of the anode throat will reduce the amount of wall stabilization (discussed in the next
section). Therefore, there is a tradeoff between arc stability and electrode cooling.
Wall Stabilization : Arc stability can be improved using wall stabilization. In the case of a plasma torch anode,
wall stabilization occurs in the anode throat where the radial movement of the arc is constricted. Smaller throat
diameters produce better wall stabilization, but also increase the pressure in the torch body, which constricts the
arc. In this situation, a tradeoff occurs between which type of arc stabilization to use; low pressure or a small
diameter throat. Ideally, the arc column would fill the entire anode throat, but because the melting temperature
of every known solid material is much lower than the temperature of the plasma, a real arc will not completely
fill the constrictor. Regardless, an arc in a smaller diameter constrictor will be more stable than one in a larger
constrictor, given the same pressure. The length of the constrictor is also important. If the constrictor is longer
than the entry length of the arc column, the efficiency of the plasma torch suffers. The entry length of an arc
column is defined as the length for the arc to become asymptotic. At this point, all of the local power input is
lost to the constrictor walls. If the constrictor is longer than this length, more power is needed for the arc to pass
through, but with no added benefit.
Vortex Stabilization : Low power plasma torches operating at high pressures will generally have very thin arcs.
From a wall stabilization perspective, this would force the anode throat to be small, which has the previously
mentioned drawbacks. One way to overcome this drawback is to use vortex stabilization. Inducing swirl into the
flow forces for the arc to rotate about the anode, rather than remaining fixed in a single area. Arc rotation
frequency is important when considering the thermal loading of the electrodes, according to Chan [9]. Chan,
hypothesized that too slow a rotation rate would result in too high a temperature during the time of contact and
too fast a rotation rate would not allow for sufficient heat dissipation between rotations. Flow swirl can be
produced either by the use of a flow swirler, or tangential gas inlets into the torch body. A flow swirler is a
device that receives the incoming axial flow and forces it into a vortex, much like inlet guide vanes in a turbojet.
With tangential gas inlets, the gas enters the torch body with a tangential velocity component. Either method
produces roughly the same results with different disadvantages.
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Flow swirlers are changeable pieces, which can easily be replaced with new designs, but also have
large losses associated with them. Tangential injection does not suffer from these large losses, but in turn, once
the torch is constructed, the tangential component of the inlets is permanently fixed. For either method of vortex
stabilization, as the gas passes into the anode nozzle the diameter of the anode nozzle decreases and the rate of
tangential rotation of the flow must increase to maintain conservation of angular momentum. This produces two
benefits. First, as the flow rotates, denser cooler gases are forced to the anode walls. This provides convective
cooling for the anode. Also, the hot, less dense gases are kept towards the center of the anode throat. Recall that
the arc column tends to follow the path of least resistance, which is also where the gas temperature is highest.
This tends to make the arc column remain in the center of the anode throat. Another added benefit is the
variation of pressure with radius produced by the vortex in the anode throat. Mager (1961), cited by [5],
analytically studied isentropic flow through a nozzle with swirl. He concluded that for ideal, isentropic flow, the
pressure of the gas is zero at the centerline of the nozzle. This area of zero pressure increased as swirl strength
increased. Naturally, the flow in a plasma torch is not ideal, but this does provide a convenient model. Due to
the generated vortex, the pressure at the center of the anode throat is expected to be lower than at the walls. This
will allow the arc column to increase its diameter and become more stable.
Magnetic Arc Rotation : Although not truly a form of arc stability, magnetic arc rotation provides many of the
benefits of arc stability methods without many of the disadvantages. Magnetic arc rotation is accomplished by
rotating a permanent magnet or producing a rotating electric field around the axis of the plasma torch by some
other means [3]. This rotating electric field causes the arc to rotate about the axis of the torch and greatly
reduces the rate of electrode erosion, particularly on the anode. Electrode erosion is usually the cause of hot
molten spots on the anode being flung off by the force of impact of the arc. By magnetically rotating the arc,
portions of the anode are exposed to the arc for very short periods of time and are allowed to cool. One torch
design that utilizes magnetic arc rotation is described by [6] and [10]. Their torch design forces the arc to rotate
at 105
rpm by means of a field coil. The new magnetic arc rotation will, in addition to arc stability, also
manipulate the arc attachment point on the electrode thereby improving the efficiency of the arc operation and
prolong the electrodes lives.
There are some disadvantages to this type of system. A plasma torch that uses magnetic arc rotation
will be more complex than one that uses some form of vortex or wall stabilization, simply because of the
addition of parts. Also, magnetic arc rotation does not provide any convective cooling to the anode like vortex
stabilization does because it does not alter the characteristics of the flow, just the arc. However, even
considering these effects, magnetic arc rotation allows one to control and change the frequency of arc rotation,
unlike vortex or wall stabilization, which are basically hit-or-miss techniques. When designing a plasma torch,
the advantages and disadvantages of each arc stabilization technique must be weighed and chosen to fit the
particular type of plasma torch application.
IV. CONCLUSION
In plasma torch design, an important problem is how to prolong the life of the electrodes, and thus
operational live of the torch in any application. We have seen that arc stability is of utmost importance in
maintaining smooth reliable operation of a plasma torch since the impact of the plasma arc with the electrodes
causes electrode erosion. Various methods of arc stabilization to reduce electrode erosion have been presented
with necessary trade-offs to achieve efficiency. Thus control of gas flow-rate to reduce pressure and increase the
arc diameter achieve some advantages but with several drawbacks. The wall and vortex stabilizations addressed
some of these drawbacks but have their limitations. By magnetically rotating the plasma arc, portions of the
anode are exposed to the arc for very short periods of time and are allowed to cool. Again rotating magnetic
field enables effective control of the arc and its proper placement between the electrodes to minimize electrode
erosion and also to manipulate the arc attachment point on the electrode thereby improving the efficiency of the
arc operation and prolong the electrodes lives.
.
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