Parametric study of the flow and temperature fields in an inductively coupled r.f. plasma torch

A theoretical investigation of the effect of different parameters on the flow and the temperature fields in a radiofrequency inductively coupled plasma is carried out. The parameters studied are: central injection gas flow rate, total gas flow rate, input power, and the type of plasma gas. The results obtained for argon and nitrogen plasmas at atmospheric pressure indicate that the flow and the temperature fields in the coil region, as well as the heat flux to the wall of the plasma confinement tube, are considerably altered by the changes in the torch operating conditions.     

Thermally Induced Measurement Error by a Water-Cooled Enthalpy Probe

Errors in stagnation-pressure measurement, due to a large temperature gradient at the face of a water-cooled enthalpy probe, were experimentally measured and numerically simulated. Two probes were used to measure the stagnation-pressure in a dc plasma jet; a standard water-cooled enthalpy probe and an uncooled ceramic (Thoria) probe. There was a maximum difference of 10% between the two measurements, with the water-cooled probe measuring lower pressures. Numerical simulations of plasma flow around the probe showed that the magnitude of the error depends on the thickness of the thermal boundary layer. The measurement error causes a maximum of 3% error in velocity measurements, using the Bernoulli equation. This error is no worse than other measurement errors associated with water-cooled enthalpy probe meaurements.     

Signature of non-Fickian solute transport in complex heterogeneous porous media

We simulate transport of a solute through three-dimensional images of different rock samples, with resolutions of a few microns, representing geological media of increasing pore-scale complexity: a sandpack, a Berea sandstone, and a Portland limestone. We predict the propagators (concentration as a function of distance) measured on similar cores in nuclear magnetic resonance experiments and the dispersion coefficient as a function of Péclet number and time. The behavior is explained using continuous time random walks with a truncated power-law distribution of travel times: transport is qualitatively different for the complex limestone compared to the sandstone or sandpack, with long tailing, an almost immobile peak concentration, and a very slow approach to asymptotic dispersion.     

Measurement of thermal conductivities of soils

Energy conservation in buildings, in particular in underground constructions, is strongly affected by the thermal properties of the soil surrounding such buildings. Experimental results of thermal conductivity studies of different soils are reported based on a quasisteady method [1]. The soil sample is placed in the annular space between two concentric tubes and is heated uniformly on the inside wall keeping the outside wall insulated. Four different types of soils (Moon Valley, River Sand, In-situ, and Ridgedale), are studied over a temperature range from ?5°C to 30°C for three different densities and moisture contents ranging from 0.5 to approximately 12% (by weight). The results indicate that the moisture content is by far the most important parameter. The thermal conductivity may increase by almost an order of magnitude as the moisture content increases. In addition, there may be a strong variation of the thermal conductivity in the phase transition region from unfrozen to frozen soils.     

ML-LBM: Predicting and Accelerating Steady State Flow Simulation in Porous Media with Convolutional Neural Networks

Transport in Porous Media - Fluid mechanics simulation of steady state flow in complex geometries has many applications, from the micro-scale (cell membranes, filters, rocks) to macro-scale...     

On the spreading and solidification of molten particles in a plasma spray process effect of thermal contact resistance

The spreading and simultaneous solidification of a liquid droplet upon its impingement onto a substrate permitting thermal contact resistance has been numerically simulated; the effect of contact resistance and the importance of solidification on droplet spreading are investigated. The numerical solution for the complete Navier-Stokes equations is based on the modified SOLA-VOF method using rectangular mesh in axisymmetric geometry. The solidification of the deforming droplet is considered by a one-dimensional heat conduction model. The predictions are in good agreement with the available experimental data and the model may be well suited for investigating droplet impact and simultaneous solidification permitting contact resistance at the substrate. We found that the final splat diameter could be extremely sensitive to the magnitude of the thermal contact resistance. The results also show that for the condition of higher Reynolds and/or higher Stefan numbers the effect of solidification on the final splat diameter is more important.     

A fast response thermocouple for internal combustion engine surface temperature measurements

A fast response thermocouple was developed for measuring surface temperatures of aluminum components in ICE combustion chambers. The key features of the design are the use of the aluminum substrate as one of the thermocouple metals and the use of a thick copper layer as the hot junction at the surface. The copper equalizes the hot junction temperature with the surrounding aluminum to correct for the differences in thermal properties between the two materials. FEA determined the optimum thickness of the copper layer to be between 100 and 125 μm. Under typical SI engine heat flux conditions, the thermocouple should be able to measure average surface temperatures within 0.19 °C and the magnitude of temperature swings within 6% of true values.Following the FEA, the optimized thermocouple was tested in a SI engine. Experimental results displayed the same trends as the FEA at measuring average temperatures and temperature swings, suggesting the thermocouple was performing as predicted.     

A new nozzle design for dc plasma spray guns

A new design is proposed for dc plasma spray gas shroud attachments. It has been found experimentally that the performance of a conventional conical gas shroud is not satisfactory due to the entrainment of the cold air inside the gas shroud. Numerical simulations confirmed this finding. Parameters such as the cone angle and the main gas flow rate can significantly influence the flow pattern inside the nozzle, resulting in air entrainnient and formation of a circulation zone at the exit region. A new design is proposed which can considerably improve the performance of shrouded nozzles. The superior performance of the proposed design has been demonstrated by numerical simulation. The new design is based on a modification of the conical shape by optimizing the profile of the nozzle from a conical shape with a constant angle to a streamlined configuration. The optimized shape was obtained from an analysis of the streamlines of a fixed angle nozzle.     

Modeling Injection of Dense Liquid Sprays in Radio Frequency Inductively Coupled Plasmas

A spray model and a droplet collision model are implemented into a radio frequency inductively coupled plasma model. The discrete parcel technique combined with the stochastic Monte Carlo method is used to solve the spray equation and determine the outcomes of droplet collisions in dense sprays. Plasma--spray interactions are considered by adding source terms to the conservation equations of mass, momentum and energy of the plasma phase. Two types of the outcomes of water droplets collisions, coalescence and grazing, are predicted and compared to the experimental and analytical results. The agreement is quite good. The effects of droplet collisions on droplet size distribution of the spray and the spray evaporation are investigated. It is found that the droplet collisions can increase the average droplets size of the spray. For the mono-disperse spray, the collisions can lead to a delay on the spray evaporation. However, for the poly-disperse spray, the effect of droplet collisions on the spray evaporation could not be predicted before the calculation due to the randomness of droplet collisions.