Numerical Investigation of Supersonic Hybrid Argon–Water-Stabilized Arc for Biomass Gasification
This paper presents a numerical simulation of temperature and flow fields in the discharge and near outlet regions of the hybrid argon-water-stabilized electric arc. The calculations for an argon mass flow rate of 0.450 g ldr s-1 reveal the transition from a transonic plasma flow for 400 A to a supersonic one for 600 A with the maximum Mach number of 1.57. The comparison with available experimental data for 400 A shows satisfactory agreement.
Water-vortex-stabilized electric arc: III. Radial energy transport, determination of water-vapour-boundary and arc performance
This paper is concerned with numerical modelling of an electric arc stabilized by a water vortex. The two-dimensional axisymmetric model presented includes the arc discharge area between the cathode and the outlet nozzle of the water plasma torch. The aims of the numerical simulations are: (1) to assess the influence of radial position of the water-vapour-boundary in the discharge chamber on arc performance and overall radial energy transport within the arc; (2) to determine the most probable mass flow rates and radii of the water-vapour-boundary in the discharge chamber for a prescribed current; (3) to demonstrate arc performance for two radiation models involved; and (4) to estimate validity of local thermodynamic equilibrium (LTE) conditions within the arc column. The rate of evaporation of water is calculated from the conduction and radiation heat fluxes at the water vapour surface for the specified mass flow rate. The behaviour of such an arc has been studied for a range of current 300–600 A. It is shown that changes of bulk magnitudes of different terms in the momentum and energy equations within the arc column as a function of arc radius enable us to reveal transitions of temperature and velocity fields from one steady state to a qualitatively different one. The best fit between experiment and numerical simulation for all currents exists for the mean arc radius ~3.3 mm. Deviations from LTE within the arc column are estimated with the criteria for kinetic equilibrium and spatial temperature gradients.
Reduction of patient exposure during dental radiography.
We investigated the effect of using additional accessories with a conventional X-ray machine to reduce patient exposure during full-mouth dental radiography. LiF extruded-rod thermoluminescent dosimeters were placed in 23 anatomical sities of a Randophantom and the phantom was exposed to a Turkish dental X-ray machine operated at 60 kV, 10 mA for 0.5 sec periods. Maximum reductions were observed at the eyes (80%), in the thyroid (70.6%). under the collar bone (59.9% average) and the gonads