A model of the cathode of a thermionic arc

Abstract

A theoretical model of the cathode of a thermionic arc is presented. Attention is focused on the energy balance of the electrode, with the interplay between the cathode and the arc plasma being described by boundary conditions specified on the electrode surface. Physical processes included in the model are thermal conduction and Joule heating in the electrode, radiative energy exchange between the electrode and the arc plasma, thermionic emission, and ion flow in the cathode sheath. A model of the cathode of a 100 A arc burning on tungsten in argon at atmospheric pressure is described in detail. It is shown that the flow of electric current and heat close to the tip of the electrode is controlled by thermionic emission and arc radiation, while the ion current plays a dominant role in the outer parts of cathode spot.

Investigation on arc light intensity in gas metal arc welding. Part 1: Relationship between arc light intensity and arc length

“…A s surface area of arc cylinder F R radiative energy flux density h enthalpy of arc k 1 -k 4 constants relating to arc voltage k 5 , k 6 constants relating to electrode melting I a welding current L contact tip to workpiece distance L a arc length L e electrode extensioṅ m a mass flowrate of arċ Q joule joule heating in plasma S arc light intensity t time T a arc temperature T 0 ambient temperature U radiative power density v w wire feed rate V plasma volume V a arc voltage V A , V C , V p anode, cathode, plasma voltage drop a surface area ratio for convection d e effective length emissivity k thermal conductivity r density of arc…”

Time resolved characterization of a free-burning argon arc after ignition by optical emission spectroscopy

“…Over the past few decades, a large number of studies have been devoted to such arc plasmas in both experiment [3][4][5][6][7][8][9][10][11] and modeling. [12][13][14][15][16] Using optical emission methods, arc properties, including the cathode surface temperature, 3-8 the plasma temperature, [5][6][7][8][9] and so on, have been determined and the effects of different arc conditions, e.g., the operation parameters 3,8,9 and the cathode shapes and materials, [4][5][6] have been extensively investigated. On the other hand, the recent remarkable progress in arc theory enables the electrodes, the sheath regions, and the arc plasma to be included in arc models.…”

“…Both experiments and modeling have shown the important role of the cathode energy transfer on arc properties. 6,7,13,16 For example, the cathode cone angles effect the cathode surface temperature distribution and, consequently, effect the plasma temperature, 6,13 and different arc cathode modes and the transitions between them are considered due to the bifurcation of energy balance problem in the cathode region. 7,16 In spite of considerable research and development, the mechanisms in the arc cathode region are still not fully understood, due partly to the multiplicity and diversity of the processes involved and their interplay and partly to the extreme conditions in this region.…”

“…The arc cathode surface temperature is determined by the heat balance of processes, such as ohmic heating, thermal conduction in cathode bulk, thermionic cooling, and heat transfer from the plasma to the cathode. 6,13 After the arc was ignited, compared with the heat loss terms, the heat inputs, including ohmic heating and heat transfer from the plasma to the cathode, are the dominant factors, thus the cathode surface temperature increases with time. The increase in the cathode surface temperature enlarges the region that contributes to the arc current by thermionic emission.…”

Markownikoff's rule: What did he say and when did he say it?

“…One of the simplest and most fundamental rules in organic chemistry, Markownikoff's rule, appears in a number of different versions in just about every organic text (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) that has been published over the past three decades. Further intrigue is added by the varied spelling of Markownikoff's name and from the date that he initially proposed his rule which ranges from 1868 (1) to 1905 (11).…”