A two-temperature plasma model (electrons having a temperature T e and ions and gas atoms having a temperature T h ) together with relevant Maxwell's equations is used to simulate a microwave generated argon plasma jet at atmospheric pressure operating at 896 MHz and 2.45 GHz. Electromagnetic field propagating along the active zone feeds the energy into the plasma. A large proportion of the energy gained by electrons from the field is used to excite argon atoms and ions. Outside the active zone, power input is negligible and electrons and heavy particles rapidly attain a single temperature. Typical self-consistent computational results with representative values of microwave source power and flow rate are given and compared with the spectroscopic measurements of Yan et al (2002( J. Phys. D 35 2594.

In circuit breakers, high temperature arcing may lead to material erosion at the contacts. In this paper, numerical investigations have been performed in order to study the arc behaviours under the influence of copper vapours contamination in a simple Laval nozzle. The arc is assumed to be in local thermodynamic equilibrium. The erosion rate is estimated by considering the energy balance processes at the contact surface. Computations have been performed by a commercial computational fluids dynamics package (PHOENICS). The effects of contact polarity have also been investigated. It has been found that the presence of copper vapours cools down the arc temperature at the region close to the contacts. However, at current zero, the copper vapours concentration is very low. Post arc simulation has been performed in order to determine the critical rate of rise of recovery voltage (RRRV). Good agreement has been achieved with the experimental measurement of RRRV. It has been predicted that the contact erosion has a negligible effect on the interruption capability of the breaker.

In this study, the computation analysis of the arc behavior in a 245 kV class 40 kA rated hybrid gas circuit breaker model has been performed. The model includes radiation transport, poly(tetrafluoroethylene) (PTFE) nozzle ablation, contact movement and turbulence-enhanced momentum and energy transport processes. It has been found that the ablated PTFE vapor from the nozzle in the breaker is mainly responsible for the high pressure buildup inside the thermal expansion chamber. This high pressure buildup helps in the strong blowing of the arc in the arcing chamber during the second current zero period.

A perturbation model with a single-offset microstrip feed is used in the design of a corner-deleted square patch microstrip antenna. It is shown that the use of the offset-feed significantly increases the size of the deleted segments and thus relaxing the fabrication tolerance.

The behavior of a wall stabilized argon arc at atmospheric pressure subjected to a transverse magnetic field is investigated by solving the arc conservation equations based on local thermal equilibrium (LTEj and relevant Maxwell's equations. The Lorentz force consists of two components: one due to the interaction of the arcing current with the extemally imposed magnetic field and the other with its own magnetic field. Two methods, the net emission coefficient and the partial characteristic method, are used to calculate the radiation transport. The Lorentz force produces two vortices symmetrical with respect to the tube diameter, which is parallel to the Lorentz force. The highest temperature region is moved towards the wall in the direction of the Lorentz force. Computational results are given for currents from 40A to 120A and the imposed magnetic field up to 22.5mT. The computed temperature, electric field, and pressure are compared with the experimental results of Sauter [I]. At high currents, there is a good agreement between prediction and experimental results. The agreement becomes progressively poorer when the current is reduced. This is attributed to the assumption of LTE, which is no longer valid in certain regions of the arc at low currents. ReferencesA Two-temperature Model for a Microwave GeneratedThe plasma jet under investigation is generated by a microwave discharge in high-speed argon gas flow operating at 896MHz.Recent spectroscopic results show that the plasma state deviates from local thermodynamic equilibrium (LTE). This is because the energy acquired by the electrons from the microwave fields cannot he readily transferred to the heavy particles. It is anticipated that the electron temperature will be higher than the translational temperature of the heavy particles A two-temperature model is thus developed to simulate the plasma behaviour of the system under practical working conditions. The electron and the heavy particles are treated as two different perfect gases. Maxwell-Boltzmann distribution shall prevail among electrons as well as among heavy particles, but with different temperatures. The electromagnetic field disbihution inside the cavity and around the nozzle is computed using finite-difference time domain (FDTDj method. An iterative process is used to compute the self-consistent solutions of the electromagnetic fields and plasma properties.[I] K. Sauter, 2 Naturforsch, 24A (1969j, pp 1694-1706 The two-temperature plasma model predicts a much higher electron temperature than that of the heavy particles, which is consistent with our experimental results. It is also shown that gas flow from the nozzle plays an important role in stabilizing the microwave plasma jet because electron diffusion towards the ambient tends to expand the discharge, thus mahng the plasma jet unsustainable. The plasma jet interacts with the work piece and supplies energy for melting and cutting processes. By using this model, the performance of the plasma jet system will be optimized in terms of the energy and...