Chamber Axis Research Articles

Self-excited transverse combustion instabilities in a high pressure lean premixed jet flame

An experimental investigation of self-excited combustion instabilities in a high pressure, lean premixed natural gas jet flame is presented. The combustor is designed with optical access and is instrumented with high frequency pressure transducers at multiple axial and circumferential locations. OH*-chemiluminescence measurements performed at a frequency of 50 kHz were temporally synchronized with the acoustic measurements recorded from the pressure transducer array during the test. Two representative test conditions are analyzed in detail: Flame 1 (F1) that presents longitudinal mode dynamics (p′/pc=3%) and Flame 2 (F2) that presents high amplitude transverse instabilities (p′/pc=15%). Singular Spectrum Analysis (SSA) and Dynamic Mode Decomposition (DMD) analysis indicate a strong correlation of both instabilities to flame-vortex interactions. Longitudinal mode instabilities are correlated with axisymmetric vortex shedding about the combustor axis that result in periodic axial variations in heat release at the 1L frequency. Transverse mode instabilities correspond to asymmetric vortex shedding pattern that drive transverse variations in heat release at the fundamental 1T frequency of the combustion chamber. The phase relationship of the flame emission intensity and the chamber head-end pressure measurement at the 1T frequency indicates presence of a non-stationary transverse mode that rotates about the chamber axis at 55 Hz.

Removal of Very Small Submicrometric Particles by Water Nucleation: Effects of Chemical–Physical Properties of Particles

The control of particle emissions from industrial plants is a crucial point in pollution control mainly because the commonly used abatement devices are inefficient in the dimensional range between 0.1 and 1 μm. An innovative technique to control particle emissions exploits the water vapor condensation onto submicrometric particles acting as condensation nuclei. In this way, particle sizes increase from nanometric up to micrometric scale. The aim of this work is to analyze the 150 nm particle growth process, activated via a heterogeneous water condensation mechanism, as a function of the vapor concentration. Particle chemical–physical features are also taken into account. The evolution of the particle growth process has been followed at a lab scale along the axis of a laminar flow chamber by means of a spatially resolved measurement of the polarization ratio of the condensation nuclei and growing droplets. The main result reported here is the scheme of interpretation of the temporal profile of the polarization ratio related to the composite particle (particle embedded in the water layer) growth. The controlling mechanism of the overall condensation process has been identified with respect to the saturation conditions, evaluated on the basis of different theories available in the literature. The covering process has been found to be active also under conditions far from saturation of the vapor bulk phase. Moreover, it has been clearly shown that, irrespective of the particle nature, the nucleation activation and droplet growth occur almost simultaneously on all particles present in the control volume, with a capture efficiency close to unity. The water nucleation activation time also depends upon the particle chemical–physical characteristics. This paper also demonstrates that the experimentally determined characteristic times of nucleation and growth of the liquid layer are compatible with residence times of an industrial unity and can be used to condition its design.

OA025] Response of ionization chambers in the presence of magnetic fields

Purpose The next generation of medical electron linear accelerators will integrate Magnetic Resonance Tomography (MRI). Therefore it will be possible to take direct images of the moving tumor during radiotherapy treatment. However serious consideration must be given to the strong magnetic field, which has an impact on the trajectories of the produced secondary electrons, because of the Lorentz force. This force affects both the dose distribution in water and the dose response of used detectors. For an accurate patient dosimetry these effects must be taken into account. Methods Monte Carlo methods correctly describe the radiation transport in different media, even in presence of magnetic fields and are therefore the gold standard for the evaluation of the impact of magnetic fields on clinical dosimetry. In this present study, the beam quality correction factors Kq and the relative response in magnetic fields of different ion chambers (PTW-31013, PTW-31021, EXRADIN-1ASL, NE2571) were investigated with Monte Carlo simulations, using the code EGSnrc. The chambers were modelled in detail according to the information given by the manufacturer and placed in a water phantom (30 × 30 × 30 cm3). The chambers were irradiated under reference conditions, following the recommendations of present dosimetry protocols, such as IAEA TRS-398: i.e. the field size at the phantom surface was 10 × 10cm2; the focus-surface-distance 100 cm and the depth of the chamber’s reference point was 10 cm. The source of the photons were several spectra of clinical medical accelerators applying nominal energies between 4 and 24 MV-X. The magnetic field was applied in different directions relative to the beam axis (z-direction) and the chamber’s symmetry axis and was varied between 0 and 3T. Results All chambers successfully passed the Fano test, the response of all chambers varied up to about 8% depending on the magnetic field strength and the field directions. Conclusions The response of the chambers with the magnetic fields, has a complex dependence on chamber radius, magnetic field strength, the orientation between radiation beams, chamber axis and magnetic field, and lastly the energy spectrum. Those variables consequently played a major role in the increase or decrease of correction factor, Kq.

Investigation of the Olive Mill Solid Wastes Pellets Combustion in a Counter-Current Fixed Bed Reactor

Combustion tests and gaseous emissions of olive mill solid wastes pellets (olive pomace (OP), and olive pits (OPi)) were carried out in an updraft counter-current fixed bed reactor. Along the combustion chamber axis and under a constant primary air flow rate, the bed temperatures and the mass loss rate were measured as functions of time. Moreover, the gas mixture components such as O2, organic carbon (Corg), CO, CO2, H2O, H2, SO2, and NOx (NO + NO2) were analyzed and measured. The reaction front positions were determined as well as the ignition rate and the reaction front velocity. We have found that the exhaust gases are emitted in acceptable concentrations compared to the combustion of standard wood pellets reported in the literature (EN 303-5). It is shown that the bed temperature increased from the ambient value to a maximum value ranging from 750 to 1000 °C as previously reported in the literature. The results demonstrate the promise of using olive mill solid waste pellets as an alternative biofuel for heat and/or electricity production.

Склеп “македонського типу” з некрополя Німфею

Склеп “македонського типу” з некрополя Німфею

A new reference-type ionization chamber with direction-independent response for use in small-field photon-beam dosimetry – An experimental and Monte Carlo study

The frequently applied narrow and non-standard transverse dose profiles of intensity modulated photon-beam radiotherapy, lacking lateral secondary electron equilibrium, require the use of high-resolution dosimetry detectors, and small air-filled detectors are recommended as the reference detectors for cross-calibration of the high-resolution detectors. The present study focuses on the dosimetric properties of a novel cylindrical ionization chamber, the PTW Semiflex 3D 31021. The chamber's effective point of measurement was found to lie at (0.41±0.04) r downstream the tip of the inner surface of the spherical front wall in the axial orientation and (0.46±0.04) r upstream the chamber axis in the radial orientation. Due to its symmetrical design, the sigma values of its lateral dose response functions for all chamber's orientations are the same (2.10±0.05mm). The polarity correction factors obtained in this work do not exceed 0.1% and the saturation correction factor was below 1% up to a dose-per-pulse value of 0.956mGy. The radiation quality correction factor kQ of the chamber as a function of the tissue-phantom-ratio, TPR20,10, has been calculated by Monte Carlo simulation and has been determined experimentally at the German Metrology Institute (Physikalisch-Technische Bundesanstalt, PTB). The values of the non-reference condition correction factor kNR have been Monte-Carlo-calculated for use of the chamber at various depths and field sizes.

Mixing of fluids with dissimilar viscosities in Confined Impinging Jets

An elastic analogue model that describes the equilibrium between opposed jets have been validated for Confined Impinging Jets (CIJs) mixers using fluids with the same physical properties for a wide range of flow rate ratios between the opposed jets. Using this model as a design tool CIJs can efficiently mix fluids at non-unitary flow rate ratios. This paper extends the experimental and numerical characterization of the flow in CIJs for fluids with a viscosity ratio of 1:2 for a range of flow rate ratio up to 1:2. Experimental characterization is made with Planar Laser Induced Fluorescence, and numerical study is based on 3D CFD simulations of the CIJs. Experimental and numerical results coincide and show that the balance of kinetic energy rate of the opposed jets plays the key role on the jets impingement point positioning, although viscosity also has an impact on this. The elastic analogue model makes a good prediction of the impingement point position of the opposed jets. This paper shows that the operation at a flow regime with high mixing efficiency, a chaotic flow regime, depends on impinging the opposed jets at the CIJs mixing chamber axis and operating at Reynolds number larger than 125 for the lower Reynolds number jet.

Test of simulator-based assessment of psychomotor skill in transthoracic echo.

We developed a transthoracic echo simulator that measures technical skill in image acquisition in terms of the deviation angle between an acquired image and the anatomically correct plane for that view. We studied whether this metric reflects the clinical experience of providers. Attendees at an echo course or at the annual meeting of the Swedish Heart Association were invited to test themselves on the simulator by scanning a mannequin and acquiring four views in 15min: parasternal long axis (pLAX) in patient 1, apical four chamber and apical long axis (aLAX) in patient 2 and pLAX in patient 3. Their experience with echo was assessed from duration in years and procedure volume in the past year. Image acquisition error was assessed from the deviation angle. Of 61 participants, there were 37 physicians and 24 non-physicians (22 sonographers and two nurses). Non-physicians had higher procedure volume than physicians (850±599 versus 312±393 testsyear-1 , P<0·001); both had similar duration of experience (9±8 versus 12±11years, P=NS). The deviation angle for aLAX (55±37 degrees) was higher than for any other view (P<0·00001). aLAX was the only view whose deviation angle correlated significantly with experience and only with procedure volume (r=-0·357, P=0·008). These results demonstrate that deviation angle, a novel metric of technical skill in image acquisition, reflects clinical experience. Simulator-based testing provides objective and quantitative assessment that may be of value in the certification of trainees and for maintenance of certification.

Analysis of Combustion Process in Industrial Gas Engine with Prechamber-Based Ignition System

Application of a pre-combustion chamber (PCC) ignition system is one of the methods to improve combustion stability and reduce toxic compounds emission, especially NOx. Using PCC allows the operation of the engine at lean combustion conditions or the utilization of low calorific gaseous fuels such as syngas or biogas. The paper presents the results of an experimental study of the combustion process in two stroke, large bore, stationary gas engine GMVH 12 equipped with two spark plugs (2-SP) and a PCC ignition system. The experimental research has been performed during the normal operation of the engine in an industrial compression station. It was observed that application of PCC provides less cycle-to-cycle combustion variation (more than 10%) and nitric oxide and carbon monoxide emissions decreased to 60% and 26% respectively. The total hydrocarbon (THC) emission rate is 25% higher for the engine equipped with PCC, which results in roughly two percent engine efficiency decrease. Another important criterion of engine retrofitting was the PCC location in the engine head. The experimental results show that improvement of engine operating parameters was recorded only for a configuration with one port offset by 45° from the axis of the main chamber. The study of the ignition delay angle and equivalence ratio in PCC did not demonstrate explicit influence on engine performance.

Development of the Technique for Calculating the Ejectors with Low Entrainment Ratios

This paper presents the results of an investigation of ejectors with the low entrainment ratio. A technique for calculating the ejectors with a curvilinear axis has been developed. Comparative studies of the performance characteristics of ejectors with the rectilinear axis of the mixing chamber and the curvilinear initial section of the mixing chamber are carried out.

GRAVITY MIXERS WITH VIBRATION ACTIVATOR IN CONSTRUCTION ENGINEERING

Vibration processes and corresponding machinery and equipment are widely used in construction, production of construction materials and other industries. Compaction, crushing, separation, piling, dosing and transportation of bulk materials are just several processes where it is expedient to use vibration. The article presents original designs of gravity (drum) mixers with vibration activators placed inside the mixing chamber. A vibration activator is installed in dead zones located along the geometrical axis of the mixing chamber where intensity of convective mixing is low. Methods of design of balanced eccentric vibration activators of precessing type are considered. Results of production tests with regard to the industrial design of the gravity vibration mixer are presented. Considerable attention is paid to measurement of the vibration level reflecting the quality of dynamic balancing of the vibration activator. Vibrational impact on the environment and maintenance personnel amounts to ~ 5 m/s2, corresponding to standard values for processing equipment as per GOST 22061-76.

Calibration and error analysis of metal-oxide-semiconductor field-effect transistor dosimeters for computed tomography radiation dosimetry.

Metal-oxide-semiconductor field-effect transistors (MOSFETs) serve as a helpful tool for organ radiation dosimetry and their use has grown in computed tomography (CT). While different approaches have been used for MOSFET calibration, those using the commonly available 100mm pencil ionization chamber have not incorporated measurements performed throughout its length, and moreover, no previous work has rigorously evaluated the multiple sources of error involved in MOSFET calibration. In this paper, we propose a new MOSFET calibration approach to translate MOSFET voltage measurements into absorbed dose from CT, based on serial measurements performed throughout the length of a 100-mm ionization chamber, and perform an analysis of the errors of MOSFET voltage measurements and four sources of error in calibration. MOSFET calibration was performed at two sites, to determine single calibration factors for tube potentials of 80, 100, and 120kVp, using a 100-mm-long pencil ion chamber and a cylindrical computed tomography dose index (CTDI) phantom of 32cm diameter. The dose profile along the 100-mm ion chamber axis was sampled in 5mm intervals by nine MOSFETs in the nine holes of the CTDI phantom. Variance of the absorbed dose was modeled as a sum of the MOSFET voltage measurement variance and the calibration factor variance, the latter being comprised of three main subcomponents: ionization chamber reading variance, MOSFET-to-MOSFET variation and a contribution related to the fact that the average calibration factor of a few MOSFETs was used as an estimate for the average value of all MOSFETs. MOSFET voltage measurement error was estimated based on sets of repeated measurements. The calibration factor overall voltage measurement error was calculated from the above analysis. Calibration factors determined were close to those reported in the literature and by the manufacturer (~3mV/mGy), ranging from 2.87 to 3.13mV/mGy. The error σV of a MOSFET voltage measurement was shown to be proportional to the square root of the voltage V: σV=cV where c=0.11mV. A main contributor to the error in the calibration factor was the ionization chamber reading error with 5% error. The usage of a single calibration factor for all MOSFETs introduced an additional error of about 5-7%, depending on the number of MOSFETs that were used to determine the single calibration factor. The expected overall error in a high-dose region (~30mGy) was estimated to be about 8%, compared to 6% when an individual MOSFET calibration was performed. For a low-dose region (~3mGy), these values were 13% and 12%. A MOSFET calibration method was developed using a 100-mm pencil ion chamber and a CTDI phantom, accompanied by an absorbed dose error analysis reflecting multiple sources of measurement error. When using a single calibration factor, per tube potential, for different MOSFETs, only a small error was introduced into absorbed dose determinations, thus supporting the use of a single calibration factor for experiments involving many MOSFETs, such as those required to accurately estimate radiation effective dose.

Abstract ID: 53 Impact of the true sensitive volume on ion chamber response in magnetic fields

Development of magnetic resonance guided radiation therapy (MRgRT) has sparked interest in evaluating the performance of ion chambers in the presence of magnetic fields. The effect of the field on electron trajectories alters ion chamber response [1] . In most Monte Carlo (MC) simulations, the geometric sensitive volume, often beginning at the edge of chamber’s stem, is used instead of the potentially unknown true collection volume [2] . This work evaluates the sensitivity of chamber response in the presence of magnetic fields to the collection volume used in the MC calculation. The egs_chamber application of the EGSnrc system is used with a recently validated magnetic field transport algorithm [3] to simulate the response of several ion chambers. The chambers are simulated in a PMMA phantom with an incident Co-60 photon beam and magnetic fields between 0 and 2 T, perpendicular to both the incoming photon field and the long axis of the ion chamber. The dose, normalized to 0 T, is calculated in the geometric sensitive volume with either the first 0, 0.5, or 1.0 mm of the volume away from the stem excluded. Increases in chamber response with a maximum of 1.77 ± 0.03% and 3.33 ± 0.03% are observed for a reduction in the length of the collection volume by 0.5 mm and 1.0 mm, respectively. For four chambers, the reduced volumes generally give better agreement with experimental results [4] . Various chamber orientations are under investigation to minimize the effect. This is an important effect that must be addressed to ensure proper calibration of MRgRT machines.

Optimal orientation for ionization chambers in MRgRT reference dosimetry

Abstract The interest in hybrid systems combining magnetic resonance imaging and medical linear accelerator (MR-Linac) is rapidly increasing due to the clinical availability of different systems. Reference dosimetry is a critical issue for integrating these devices into clinical practice. However, the response of ionization chambers changes according to the distinct orientation of the chamber with respect to the magnetic field. In this study, we have carried out Monte Carlo simulations to identify an optimal orientation for thimble type chambers in MRgRT reference dosimetry. Our findings suggest that an orientation where the chamber axis is parallel to the magnetic field axis should be preferred.

Ionization chamber radial response deconvolution in megavoltage photon beam

The aim of this paper is to study a radial response model as a method, to correct output factor results gathered with ionization chambers of different size and shape in cone collimated RT fields. An enhanced version of a non-parametric super-resolution deconvolution method able to model a radial response function of a small cylinder symmetric ionization chamber is described and demonstrated. The radial response of four ionization chambers with different geometry and radius are estimated using 6 MV photon beam in water at the isocentre plane. Finally the validity of the estimates is tested by applying the response functions to the output factor measurements of 4–20 mm conical collimators. The enhanced method is demonstrated by obtaining the response function characteristics with a spatial uncertainty smaller than 0.1 mm when the distance from chamber axis is larger than 0.5 mm. In all studied ionization chambers, a significant local response maximum is found close to the air cavity boundary. The agreement between the output factor results of different chambers is promising, the largest difference (max—min) in output factor is 4% obtained for the smallest 4 mm cone size.

Radiation dosimetry in magnetic fields with Farmer-type ionization chambers: determination of magnetic field correction factors for different magnetic field strengths and field orientations

The aim of this work was to determine magnetic field correction factors that are needed for dosimetry in hybrid devices for MR-guided radiotherapy for Farmer-type ionization chambers for different magnetic field strengths and field orientations. The response of six custom-built Farmer-type chambers irradiated at a 6 MV linac was measured in a water tank positioned in a magnet with magnetic field strengths between 0.0 T and 1.1 T. Chamber axis, beam and magnetic field were perpendicular to each other and both magnetic field directions were investigated. EGSnrc Monte Carlo simulations were compared to the measurements and simulations with different field orientations were performed. For all geometries, magnetic field correction factors, , and perturbation factors were calculated. A maximum increase of 8.8% in chamber response was measured for the magnetic field perpendicular to chamber and beam axis. The measured chamber response could be reproduced by adjusting the dead volume layer near the chamber stem in the Monte Carlo simulations. For the magnetic field parallel to the chamber axis or parallel to the beam, the simulated response increased by 1.1% at maximum for field strengths up to 1.1 T.A complex dependence of the response was found on chamber radius, magnetic field strength and orientation of beam, chamber axis and magnetic field direction. Especially for magnetic fields perpendicular to beam and chamber axis, the exact sensitive volume has to be considered in the simulations. To minimize magnetic field correction factors and the influence of dead volumes on the response of Farmer chambers, a measurement set-up with the magnetic field parallel to the chamber axis or parallel to the beam is recommended for dosimetry.

Application of the similarity theory for vortex chamber superchargers

On the basis of similarity in vortex chamber superchargers criteria of similarity are defined and their check by numerical researches is made. Vortex chamber superchargers have the big power efficiency of pumping, in comparison with classical jet pumps, at the expense of association of advantages of centrifugal and jet pumps on the basis of the vortex chamber. The concept of vortex chamber superchargers is based on a new principle of energy transfer in jet superchargers at the expense of hydrodynamic effects of rotating flows use. In consequence of pressure decrease near to an axis of the vortex chamber occurs intaking particles of a pumped over flow. Having got to the vortex chamber, particles get tangential velocity interact with a rotating flow at the expense of a momentum exchange. The received criteria take into account of three major factors of similarity: the geometrical sizes, pressure of an active stream on an input in the device, working medium density. Validity of the received criteria is confirmed by a finding of pressure-flow rate characteristics of similar operating modes of a supercharger and their further combination on one characteristic.

VESSEL MIXERS WITH VIBRATION ACTIVATOR IN CONSTRUCTION ENGINEERING

Construction mixes are classified as polydisperse heterogeneous systems, where surface phenomena occurring at the phase interface, exert a great influence on formation of such systems. As for mixing processes, adsorption and diffusion are the most important ones. Their speed depends on mobility of mineral constituents' particles, size of the active interfacial area, binder dispersion, technological peculiarities of the process and other factors. It is known that the vibration is one of the ways to increase mixing intensity. The article presents original designs of vessel mixers of forced action with vibration activators placed inside the mixing chamber. A vibration activator is installed in "dead" zones located along the geometrical axis of the mixing chamber where intensity of convective mixing is low. Methods of design of balanced eccentric vibration activators of precessing and plane-parallel type are considered. Results of production tests with regard to industrial designs of vibration mixers are presented. Considerable attention is paid to measurement of the vibration level reflecting the quality of dynamic balancing of the vibration activator. Vibrational impact on the environment and maintenance personnel amounts to ≈ 5 m/s2, corresponding to standard values for processing equipment as per GOST 22061-76.

Influence of a centered dielectric tube on inductively coupled plasma source: Chamber structures and plasma characteristics**Project supported by the National Natural Science Foundation of China (Grant Nos. 11305028, 11305032, and 11320101005).

A high-density RF ion source is an essential part of a neutral beam injector. In this study, the authors attempt to retrofit an original regular RF ion source reactor by inserting a thin dielectric tube through the symmetric axis of the discharge chamber. With the aid of this inner tube, the reactor is capable of generating a radial magnetic field instead of the original transverse magnetic field, which solves the E × B drift problem in the current RF ion source structure. To study the disturbance of the dielectric tube, a fluid model is introduced to study the plasma parameters with or without the internal dielectric tube, based on the inductively coupled plasma (ICP) reactor. The simulation results show that while introducing the internal dielectric tube into the ICP reactor, both the plasma density and plasma potential have minor influence during the discharge process, and there is good uniformity at the extraction region. The influence of the control parameters reveals that the plasma densities at the extraction region decrease first and subsequently slow down while enhancing the diffusion region.

Study on three-dimensional expansion characteristics of four wall combustion-gas jets in confined liquid space

To explore further the launch mechanism of the new underwater launching technology proposed in this paper, the expansion characteristics of four wall combustion-gas jets in confined liquid space must be studied firstly. The experimental device is designed, and the high-speed digital photographic system is adopted to obtain the expansion sequence processes of Taylor cavities formed by the four wall jets. Meanwhile, the influence of the injection pressure on the axial expansion property of the four wall jets is discussed. Based on the experiments, a three-dimensional unsteady mathematical model is established to simulate the turbulent flow process of the four wall jets expanding in liquid, and the temporal and spatial distribution laws of phase, pressure, temperature, and velocity and the evolution rules of vortices are illustrated in detail. Results show that, accompanied by the jets expanding downstream, the four wall combustion-gas jets get close to each other and achieve convergence eventually under induction of the interference effect between multiple jets. Meanwhile, the heads of the Taylor cavities separate from the observation chamber wall and offset to the central axis of the observation chamber with time going on. The numerical simulation results of the four wall combustion-gas jets coincide well with the experimental data.