Combined Diffusion Coefficient Research Articles

Kinetics of voids evolution during diffusion bonding of dissimilar metals on consideration of the realistic surface morphology: Modeling and experiments

A comprehensive model for analyzing the kinetics of void evolution and shrinkage during dissimilar diffusion bonding is proposed based on the sinusoidal profile. The model incorporates atom accumulation at void tip to determine the curvature radius of void neck, and integrates the local effect of surface diffusion to quantify the contribution of surface diffusion, thus avoiding the unrealistic void evolution observed in previous models. Furthermore, the model utilizes a combined diffusion coefficient for multicomponent alloys under the effect of stress and concentration gradients, to determine the interfacial diffusion coefficient for dissimilar joints. In contrast to previous models, the current model demonstrates significant improvements in predicted accuracy, efficiently depicting the realistic void evolution and interpreting the formation of various interfacial voids, which can be applied in various bonding cases, including for the dissimilar base metals with different surface conditions. Simulation results from bonding between austenitic steel and ferritic steel with different surface roughness reveal that interfacial voids predominantly form on the side of the base metal with the rougher bonding surface. Additionally, as surface roughness decreases, the prevailing surface source diffusion and interface source diffusion mechanisms promote void evolution and shrinkage, resulting in a significant reduction of the final bonding time. To achieve a high-quality bonding joint, it's suggested to place the smoother bonding surface on the higher creep-resistant base metal, which can accelerate the void closure process.

Combining ADC values in DWI with rCBF values in arterial spin labeling (ASL) for the diagnosis of mild cognitive impairment (MCI).

We aimed to investigate the role of combined apparent diffusion coefficient (ADC) values and relative cerebral blood flow (rCBF) values in the diagnosis of mild cognitive impairment (MCI) patients. The present prospective research enrolled 156 MCI patients and 58 healthy elderly people who came to our hospital from January 2021 to February 2023. T1W, T2W, diffusion-weighted imaging, and arterial spin labeling sequences were performed on all subjects, and ADC values and rCBF values were measured at the workstation. Clinical and demographic data of all patients were collected while mini-mental state examination (MMSE) and Montreal cognitive assessment (MoCA) scores were used to assess patients' cognitive abilities. The MCI group had significantly lower rCBF values in the left frontal lobe, left occipital lobe, right frontal lobe, and right occipital lobe than the HC group. The ADC values in the left frontal lobe as well as the right frontal lobe were remarkably elevated in the MCI group than in the HC group. MoCA and MMSE scores were positively correlated with rCBF values in the left frontal, right frontal, left occipital, and right occipital lobes and negatively correlated with ADC values in the left and right frontal lobes. Combined ADC values and rCBF values from the left frontal lobe for the diagnosis of MCI had a higher sensitivity and specificity with the AUC was 0.877, sensitivity 81.0%, specificity 82.7%. Additionally, pressure fasting plasma glucose, ADC of the left frontal lobe, right frontal lobe, rCBF of left frontal lobe and rCBF of left frontal lobe were the risk factors of patients with MCI. In summary, our results indicated that the ADC values and rCBF values were changed in MCI group compared to HC group and correlated with MMSE and MoCA scores.

Modelling and measurements of gas tungsten arc welding in argon–helium mixtures with metal vapour

Argon–helium mixtures in gas tungsten arc welding of an iron workpiece are investigated using an axisymmetric computational model that includes the cathode, workpiece, and arc plasma in the computational domain. The three-gas combined diffusion coefficient method is used to treat diffusion of helium, argon, and iron vapour. Calculations for argon–helium mixtures without metal vapour are performed; good agreement with previous numerical results is found. A transition from a helium-like to an argon-like arc occurs when the argon mole fraction increases above about 0.3. Calculations for a wide range of argon–helium mixtures including iron vapour are then performed. Adding helium to argon alters the arc properties and affects the weld geometry. Iron vapour cools the arc for all argon–helium mixtures. Iron vapour is present above the workpiece, near the cathode and in the arc fringes for very low argon mole fractions. As the argon mole fraction increases, the iron vapour becomes increasingly confined to the region above the workpiece, with small amounts near the cathode tip. Emission spectroscopy measurements of arcs in argon–helium mixtures with water-cooled copper and uncooled iron workpieces were performed. The measured distributions of atomic helium and iron emission show good agreement with the predictions of the model.

Numerical investigation of transport phenomena of arc plasma in argon-oxygen gas mixture

Mixtures of gases are utilized widely in a variety of arc welding processes to improve the arc property and thus the welding quality. This research focuses on the properties of the arc plasma in argon-oxygen gas mixture and a two dimensional (2D) axial symmetrical model is developed to investigate the transport phenomena in such arc, with diffusion treated by using combined diffusion coefficient approach. The gas mixture is applied to conventional tungsten inert gas (TIG) arc torch and a double-gas-shielding arc torch, respectively. Two different mass fractions of oxygen, i.e. 5% and 20%, in input gas mixture, are considered for the TIG arc, whereas that of 20% is taken into account for the outer shielding gas in the double-gas-shielding arc. The influence of the arc current on the demixing in the two types of arc is highlighted. The effect of the oxygen addition to argon on the TIG arc temperature is exhibited. It is found that for the TIG arcs, the oxygen concentrates in the regions close to the arc axis and to the electrodes, and increased current reduces the oxygen concentration near the cathode tip, but facilitates the mass transfer of the oxygen near the arc axis towards the anode; while for the double-gas-shielding arcs, the oxygen concentrates markedly in the periphery region of the arc and diffuses slightly towards the arc axis, with much lower mass fraction of the oxygen near the anode, for all the cases considered. Adding oxygen to the argon constricts the arc columns near the anode as compared with those in the pure argon for TIG arc. The oxygen mass fraction distribution 0.1 mm above the anode is uneven for the both types of the arc, implying nonuniform distribution of the oxygen reacting with the surface of the molten anode.

Numerical study of the effects and transport mechanisms of iron vapour in tungsten inert-gas welding in argon

Tungsten inert-gas (TIG) welding uses an electric arc between a tungsten cathode and a metal anode to partially melt the anode workpiece, forming a weld pool. Metal vapour emanating from the weld pool has important effects on the arc welding process. An axisymmetric computational model of the arc and weld pool is used to examine the transport and influence of iron vapour on an argon arc plasma. In contrast to previous studies that use approximate and incomplete treatments of diffusion, the present model incorporates the combined diffusion coefficient method, which takes into account all important driving forces. The influence of metal vapour is first examined for an arc current of 400 A. Metal vapour is predicted to be present in high concentrations above the anode and near the cathode tip, and in a lower concentration in the arc column. The presence of metal vapour in the arc is found to lead to a substantial reduction in arc temperature (up to 1600 K) and current density, resulting in a significant decrease in the weld pool depth and volume. It is shown that ordinary diffusion leads to iron vapour transport upward from the anode region along the arc fringes and into the recirculating convective flow, which carries the iron vapour to the cathode region. Here the upward diffusion driven by the electric field and temperature gradient traps the iron vapour below the cathode tip, leading to a high concentration in this region. The influence of arc current is investigated in the range from 150 to 400 A. The results obtained for standard welding currents of 150, 200 and 250 A also predict significant concentrations of iron vapour in the arc, with the concentration increasing with current in the arc column and near the anode. The concentration near the cathode tip is lower at 400 A because the temperature and electric field diffusion coefficients are lower at the higher temperatures present near the cathode. Spectroscopic measurements of atomic chromium emission for argon TIG welding of a chromium anode are presented and compared to predictions of the code. The measurements show the presence of metal vapour in both the cathode and anode regions, in agreement with the model.

Numerical study of the metal vapour transport in tungsten inert-gas welding in argon for stainless steel

Metal vapour emanating from the weld pool during tungsten-inert-gas (TIG) welding affects the arc welding process. To understand the transport mechanisms of metal vapour in a TIG arc, an axisymmetric computational model is developed that includes the tungsten cathode, stainless-steel anode workpiece and the arc plasma region self-consistently. The combined diffusion coefficient method, which calculates diffusion coefficients due to mole fraction gradients (ordinary diffusion), temperature gradients, pressure gradients and the electric field is used to treat iron–chromium–argon and iron–chromium–helium plasmas. It was found that in both cases, metal vapours can reach the cathode region. The effect of different diffusion coefficients on metal vapour transport was investigated. It was found that ordinary diffusion is the main driving force for upward metal vapour diffusion away from the anode workpiece in an argon arc. The diffusive transport carries the metal vapour into the recirculating convective flow, which then transports the metal vapour to the cathode region. Here the upward diffusion driven by the temperature gradient and electric field leads to the build of high concentrations of the metal vapours adjacent to the cathode. In the helium arc, in contrast, metal vapour is transported upwards from the workpiece by electric field diffusion, which is much stronger in this case. Spectroscopic measurements of atomic chromium emission show that metal vapour can reach the cathode region in an argon TIG arc, providing support for the predictions of the model. Only by taking into account all diffusion driving forces is it possible to predict the distribution of metal vapour in a TIG welding arc.

Intravoxel Incoherent Motion MR Imaging of Pediatric Intracranial Tumors: Correlation with Histology and Diagnostic Utility.

Intravoxel incoherent motion imaging, which simultaneously measures diffusion and perfusion parameters, is promising for brain tumor grading. However, intravoxel incoherent motion imaging has not been tested in children. The purpose of this study was to evaluate the correlation between intravoxel incoherent motion parameters and histology to assess the accuracy of intravoxel incoherent motion imaging for pediatric intracranial tumor grading. Between April 2013 and September 2015, 17 children (11 boys, 6 girls; 2 months to 15 years of age) with intracranial tumors were included in this retrospective study. Intravoxel incoherent motion parameters were fitted using 13 b-values for a biexponential model. The perfusion-free diffusion coefficient, pseudodiffusion coefficient, and perfusion fraction were measured in high- and low-grade tumors. These intravoxel incoherent motion parameters and the ADC were compared using the unpaired t test. The correlations between the intravoxel incoherent motion parameters and microvessel density or the MIB-1 index were analyzed using the Spearman correlation test. Receiver operating characteristic analysis was used to evaluate diagnostic performance. The perfusion-free diffusion coefficient and ADC were lower in high-grade than in low-grade tumors (perfusion-free diffusion coefficient, 0.85 ± 0.40 versus 1.53 ± 0.21 × 10-3 mm2/s, P < .001; ADC, 1.04 ± 0.33 versus 1.60 ± 0.21 × 10-3 mm2/s, P < .001). The pseudodiffusion coefficient showed no difference between the groups. The perfusion fraction was higher in high-grade than in low-grade tumors (21.7 ± 8.2% versus 7.6 ± 4.3%, P < .001). Receiver operating characteristic analysis found that the combined perfusion-free diffusion coefficient and perfusion fraction had the best diagnostic performance for tumor differentiation (area under the curve = 0.986). Intravoxel incoherent motion imaging reflects tumor histology and may be a helpful, noninvasive method for pediatric intracranial tumor grading.

Numerical simulation of mixture gas arc of Ar-O&lt;sub&gt;2&lt;/sub&gt;

Mixture gas arcs are used extensively in welding manufacturing. A two-dimensional steady mathematical model for Ar-O&lt;sub&gt;2&lt;/sub&gt; mixture gas arc is developed to understand further the heat and mass transfer of the mixture gas arc. The model is based on the assumption of local thermodynamic equilibrium, and the thermodynamic parameters and transport coefficients are dependent on both the temperature and the oxygen content. In the present model, the diffusion between the argon species and oxygen species is depicted by the approach of the combined diffusion coefficient, i. e. the mixture gas arc is simplified into two different species, and the diffusion between them is formulated by combined ordinary diffusion coefficient and combined temperature diffusion coefficient; the oxygen distribution and its influence on the temperature and flow field of the arc are investigated for two different current conditions. It is shown that the oxygen species presents significant non-uniform distribution for argon gas mixed with 5% oxygen; the oxygen content is higher than that in mixed shielding gas in the regions close to the electrodes and arc axis, while its content is lower than that of the mixed shielding gas in other regions. For high current, oxygen concentrates more to the flat anode, while it concentrates more to tungsten cathode for low current. For both cases, oxygen content is inhomogeneous in the region 0.1 mm above the anode. The 5% oxygen mixed in argon constricts the arc plasma to some extent and thus raises the arc temperature as well as the plasma flow velocity.

A computational model of gas tungsten arc welding of stainless steel: the importance of considering the different metal vapours simultaneously

A 2D computational model of the mixing of multiple metal vapours into a helium arc in gas tungsten arc welding of stainless steel is presented. The combined diffusion coefficient method, extended to three-gas mixtures, is used to treat helium–chromium–iron and helium–manganese–iron plasmas. It is found that all metal vapours penetrate to the arc centre and reach the cathode, with iron vapour confined near the cathode tip, while chromium and manganese vapours accumulate about 1.5 mm above the tip. The predicted distributions of chromium, manganese and iron show reasonable agreement with published photographic images and radial distributions of atomic line emission intensities. The results are also consistent with published measurements of the deposition of the metals on the cathode surface. A detailed examination of the influence of the different diffusion coefficients, net emission coefficients and vapour pressures of the metals on the metal vapour transport in the arc plasma is presented. It is shown that cataphoresis (diffusion due to applied electric fields) leads to the penetration of the metal vapours into the arc. The different distribution of iron vapour from those of chromium and manganese vapours near the cathode is strongly influenced by the lower ordinary diffusion coefficients of iron at low temperatures. Radiative emission is found to be important since it leads to cooling of the arc, which decreases the influence of cataphoresis. The vapour pressure only influences the concentration of the metal vapour close to the workpiece. Results for the two-gas helium–chromium and helium–iron systems are compared to those for the three-gas helium–chromium–iron system. It is shown that it is important to consider the different metal vapours simultaneously to obtain an accurate calculation of the metal vapour and arc temperature distributions.

Combined Diffusion Coefficients in CO2 Thermal Plasmas Contaminated with Cu, Fe or Al

Our work aims at the computation of combined diffusion coefficients in CO2–metal (Cu, Fe, Al) mixtures at a temperature interval of 2000–30,000 K at 0.1 MPa and aims at the investigation of the impact of the concentration and nature of metal vapor (Cu, Fe, Al) on diffusion phenomena. The combined diffusion coefficients have four components, more specifically, combined ordinary diffusion coefficient, combined electric field diffusion coefficient, combined temperature diffusion coefficient and combined pressure diffusion coefficient due to the gradients of the species densities, applied electrical field temperature and pressure. The results indicate that, for Cu and Fe, the combined diffusion coefficients are quite identical under the condition of same metal concentrations (1 and 10% mass concentration). Compared with Cu and Fe under the same metal concentrations (1 and 10%), Al results in a larger enhancement of combined electric field and ordinary diffusion coefficients while smaller enhancement of combined temperature diffusion coefficients. All the combined diffusion coefficients exhibit an upward trend with metal concentrations except for combined electric field, temperature and pressure diffusion coefficients. These three mentioned coefficients are attenuated by the metal vapor above the certain concentration such as, in the case of combined temperature diffusion coefficients, 70% Cu, 70% Fe and 50% Al for CO2–Cu, CO2–Fe and CO2–Al mixtures respectively. Namely, compared with Cu and Fe, less quantity of Al is required to achieve the maximum of combined diffusion coefficients. Maximum peaks for the combined coefficients are shifted to the higher temperature with increasing metal concentrations.

Usefulness of apparent diffusion coefficient value and proton magnetic resonance spectroscopy as a noninvasive techniques in recurrent cerebral gliomas

ObjectiveConventional MRI does not provide sufficient information to differentiate post-radiotherapy necrosis from brain tumor recurrence, recent studies have investigated the use of more advanced imaging modalities that are able to differentiate between the two entities. Aim of the studyTo assess the usefulness of combined apparent diffusion coefficient (ADC) value and single voxel spectroscopy (SVS) in the differentiation between recurrent brain gliomas and post-radiotherapy necrosis. MethodsTwenty-two patients with suspected tumor recurrence after surgical resection and radiotherapy treatment were included in our study. MRI with contrast, diffusion weighted MRI with ADC value and MR spectroscopy were done to all patients. ResultsADC values were ≤1.150 × 10−3 mm2/sec for recurrent high grade gliomas, >1.150–≤1.370 × 10−3 mm2/sec for recurrent low grade gliomas and >1.370 × 10−3 mm2/sec for post radiation necrosis. NAA/Cr ratio could significantly differentiate between recurrent gliomas and post radiation necrosis (p value = .019), also Cho/Cr was significant p value = .006. Also NAA/Cr and Cho/Cr were statistically significant in differentiating recurrent high grade from low grade gliomas (p value < .001). ConclusionCombination of calculated ADC value and MR spectroscopy added more information and increase the accuracy of conventional MR imaging in the differentiation of patients with suspected recurrent brain glioma from post-radiotherapy necrosis.

Mixing of multiple metal vapours into an arc plasma in gas tungsten arc welding of stainless steel

A computational model of the mixing of multiple metal vapours, formed by vaporization of the surface of an alloy workpiece, into the thermal arc plasma in gas tungsten arc welding (GTAW) is presented. The model incorporates the combined diffusion coefficient method extended to allow treatment of three gases, and is applied to treat the transport of both chromium and iron vapour in the helium arc plasma. In contrast to previous models of GTAW, which predict that metal vapours are swept away to the edge of the arc by the plasma flow, it is found that the metal vapours penetrate strongly into the arc plasma, reaching the cathode region. The predicted results are consistent with published measurements of the intensity of atomic line radiation from the metal vapours. The concentration of chromium vapour is predicted to be higher than that of iron vapour due to its larger vaporization rate. An accumulation of chromium vapour is predicted to occur on the cathode at about 1.5 mm from the cathode tip, in agreement with published measurements. The arc temperature is predicted to be strongly reduced due to the strong radiative emission from the metal vapours. The driving forces causing the diffusion of metal vapours into the helium arc are examined, and it is found that diffusion due to the applied electric field (cataphoresis) is dominant. This is explained in terms of large ionization energies and the small mass of helium compared to those of the metal vapours.

Combined diffusion coefficients for a mixture of three ionized gases

The combined diffusion coefficient method has been demonstrated to greatly simplify the treatment of diffusion in the modelling of thermal plasmas in gas mixtures without loss of accuracy. In this paper, an extension of this method to allow treatment of diffusion of a three-gas mixture has been achieved, provided that the gases are homonuclear and do not react with each other, and satisfy local chemical equilibrium. Formulas for the combined diffusion coefficients are presented, and combined diffusion coefficients for different mixtures of helium, argon and carbon at temperatures up to 30 000 K and at atmosphere pressure are calculated as an example.

Calculation of combined diffusion coefficients in SF6-Cu mixtures

Diffusion coefficients play an important role in the description of the transport of metal vapours in gas mixtures. This paper is devoted to the calculation of four combined diffusion coefficients, namely, the combined ordinary diffusion coefficient, combined electric field diffusion coefficient, combined temperature diffusion coefficient, and combined pressure diffusion coefficient in SF6-Cu mixtures at temperatures up to 30 000 K. These four coefficients describe diffusion due to composition gradients, applied electric fields, temperature gradients, and pressure gradients, respectively. The influence of copper fluoride and sulfide species on the diffusion coefficients is shown to be negligible. The effect of copper proportion and gas pressures on these diffusion coefficients is investigated. It is shown that increasing the proportion of copper generally increases the magnitude of the four diffusion coefficients, except for copper mole fractions of 90% or more. It is further found that increasing the pressure reduces the magnitude of the coefficients, except for the combined temperature diffusion coefficient, and shifts the maximum of all four coefficients towards higher temperatures. The results presented in this paper can be applied to the simulation of high-voltage circuit breaker arcs.

Apparent diffusion coefficient and Magnetic resonance spectroscopy in grading of malignant brain neoplasms

AimThis work aims to study the role of combined apparent diffusion coefficient (ADC) and Magnetic resonance spectroscopy (MRS) in grading malignant brain neoplasms. MethodsA prospective study included 40 patients who were evaluated by standard contrast enhanced MRI, diffusion weighted imaging and multivoxel spectroscopy. ResultsStatistically significant difference was found between tumoral ADC values in low grade versus high grade tumors and metastasis and also between the peritumoral ADC values in metastasis versus low and high grade tumors. Statistically significant difference is noticed between tumoral Cho/Cr ratio values in low grade versus high grade tumors and metastasis, and also peritumoral Cho/Cr ratio values in low grade and metastasis versus high grade tumors. Statistically significant difference between tumoral Cho/NAA ratio in low grade versus high grade tumors and metastasis and lastly between peritumoral Cho/NAA ratio in low grade and metastasis versus high grade tumors was found. Lipid and lactate peaks were found frequently in high grade tumors and metastasis. ConclusionThe combination of calculated ADC values and MR spectroscopy is useful in grading of malignant brain tumors and were more useful together than each on its own.

Calculation and application of combined diffusion coefficients in thermal plasmas

The combined diffusion coefficient method is widely used to treat the mixing and demixing of different plasma gases and vapours in thermal plasmas, such as welding arcs and plasma jets. It greatly simplifies the treatment of diffusion for many gas mixtures without sacrificing accuracy. Here, three subjects that are important in the implementation of the combined diffusion coefficient method are considered. First, it is shown that different expressions for the combined diffusion coefficients, arising from different definitions for the stoichiometric coefficients that assign the electrons to the two gases, are equivalent. Second, an approach is presented for calculating certain partial differential terms in the combined temperature and pressure diffusion coefficients that can cause difficulties. Finally, a method for applying the combined diffusion coefficients in computational models, which typically require diffusion to be expressed in terms of mass fraction gradients, is given.

Multiparametric 3T Prostate Magnetic Resonance Imaging to Detect Cancer: Histopathological Correlation Using Prostatectomy Specimens Processed in Customized Magnetic Resonance Imaging Based Molds

We determined the prostate cancer detection rate of multiparametric magnetic resonance imaging at 3T. Precise one-to-one histopathological correlation with magnetic resonance imaging was possible using prostate magnetic resonance imaging based custom printed specimen molds after radical prostatectomy. This institutional review board approved prospective study included 45 patients (mean age 60.2 years, range 49 to 75) with a mean prostate specific antigen of 6.37 ng/ml (range 2.3 to 23.7) who had biopsy proven prostate cancer (mean Gleason score of 6.7, range 6 to 9). Before prostatectomy all patients underwent prostate magnetic resonance imaging using endorectal and surface coils on a 3T scanner, which included triplane T2-weighted magnetic resonance imaging, apparent diffusion coefficient maps of diffusion weighted magnetic resonance imaging, dynamic contrast enhanced magnetic resonance imaging and spectroscopy. The prostate specimen was whole mount sectioned in a customized mold, allowing geometric alignment to magnetic resonance imaging. Tumors were mapped on magnetic resonance imaging and histopathology. Sensitivity, specificity, positive predictive value and negative predictive value of magnetic resonance imaging for cancer detection were calculated. In addition, the effects of tumor size and Gleason score on the sensitivity of multiparametric magnetic resonance imaging were evaluated. The positive predictive value of multiparametric magnetic resonance imaging to detect prostate cancer was 98%, 98% and 100% in the overall prostate, peripheral zone and central gland, respectively. The sensitivity of magnetic resonance imaging sequences was higher for tumors larger than 5 mm in diameter as well as for those with higher Gleason scores (greater than 7, p <0.05). Prostate magnetic resonance imaging at 3T allows for the detection of prostate cancer. A multiparametric approach increases the predictive power of magnetic resonance imaging for diagnosis. In this study accurate correlation between multiparametric magnetic resonance imaging and histopathology was obtained by the patient specific, magnetic resonance imaging based mold technique.

Calculation of diffusion coefficients in air–metal thermal plasmas

This paper presents the combined diffusion coefficients of metal vapours (silver, copper and iron) in air thermal plasmas for temperatures ranging from 300 to 30 000 K. The theory used to calculate these coefficients is remembered and validated by comparison with the literature values in several cases such as Ar–He, Ar–Cu and N2–O2 mixtures. The results are discussed showing the influences of the metal concentration, of the vapour nature and of the pressure. The results show rather similar behaviour for the three metals. The maximum values of the combined ordinary diffusion coefficient in the evolution with temperature are obtained for temperature around 10 000 K but this peak is shifted to the highest temperatures when the metal proportion increases. Another result shows that the diffusion coefficient decreases when pressure increases.

Effects of natural convection on the characteristics of long laminar argon plasma jets issuing upwards or downwards into ambient air—a numerical study

A modelling study has been performed on the effect of natural convection on the characteristics of a long laminar argon plasma jet issuing into ambient air. In this study the plasma jet is taken to be flowing vertically upwards or downwards, and the combined diffusion coefficient method has been used to treat the diffusion of ambient air into the argon plasma jet. It has been shown that although a temperature difference as large as 104 K is involved in the long laminar plasma jet system, in total the effect of natural convection on the fluid flow and heat/mass transfer within the plasma jet is small for the typical plasma jet parameters under study. Only at low jet inlet velocities and near the jet edge in the jet downstream region can the natural convection effect be detected.

Three-dimensional modelling of the characteristics of long laminar plasma jets with lateral injection of carrier gas and particulate matter

A long laminar plasma jet has adjustable high-temperature region length, small temperature and velocity gradients in the axial direction, low noise emission and weak entrainment of ambient air into the jet, and thus it has potential applications in materials processing. A three-dimensional modelling approach is used in this paper to study the spatial distributions of plasma parameters in the long laminar plasma jet for the case with and without lateral injection of particulate matter and its carrier gas. The combined diffusion coefficient method is employed in the modelling to treat the diffusion of ambient air into the plasma jet. Typical computed distributions of temperature, velocity and species concentration in the jet are presented using the long laminar argon plasma jet issuing into ambient air as a calculation example. It is shown that similarly to the turbulent plasma jet case, the long laminar plasma jet has good enough stiffness to endure the impact of the laterally injected carrier gas, although the laminar jet assumes slight deflection from its original geometrical axis in the injection plane due to the action of laterally injected carrier gas. The three-dimensional effects caused by the lateral carrier-gas injection on the jet characteristics and thus on the particle moving trajectories and heating histories are shown to be appreciable. Particulate matter can be fed into the high-temperature region of the laminar plasma jet with the aid of the carrier gas.