Operation Of Chamber Research Articles

The HARP RPC time-of-flight system

The time-of-flight system based on thin-gap glass resistive plate chambers (RPCs) for the HARP detector at CERN is described and first experience with the chamber operation and performance is reported. The system consists of 46 chambers, covers an area of 10m2 and has 368 readout channels. The chambers are 2m long, 150mm wide, and 10mm thick and have four gas gaps of 0.3mm each, the glass plates are 0.7mm thick. The RPCs are operated in avalanche mode with a mixture of 90% C2F4H2, 5% SF6, and 5% C4H10.

The radiation measurement applied to beam lifetime study on the synchrotron radiation facilities

To collect beam loss information from an accelerator radiation field is helpful to machine study and operation. For a synchrotron radiation storage ring, shower electrons give a distinct clue to loss location and a BLM-XS model detector is suitable to detect them. Recently, we set up a new beam loss monitoring system by this method for National Synchrotron Radiation Laboratory (NSRL) storage ring. It does not interfere with the vacuum chamber and machine operation. Different from other systems, the detectors are used in pairs, fixed on opposite sides of the chamber separately. Some interesting phenomena about beam lifetime were observed. We located exactly where an excessive beam loss took place during ramping process and solved the problem. It was proved that gas accumulated at the front ends of photo-beam lines strongly impacted the electron beam and led to beam lifetime decreases. The cause of beam lifetime decrease because of superconducting wiggler is discussed.

Infrared thermographic image processing for the operation and control of heterogeneous combustion chambers : Manca, D. and Rovaglio, R. Combustion and Flame, 2002, 130, (4), 277–297

Infrared thermographic image processing for the operation and control of heterogeneous combustion chambers : Manca, D. and Rovaglio, R. Combustion and Flame, 2002, 130, (4), 277–297

Thermal diffusion cloud chamber: new criteria for proper operation

We report results of new nucleation experiments involving 1-pentanol with hydrogen as the background gas obtained from constant temperature critical supersaturation experiments utilizing the high-pressure diffusion cloud chamber. We have observed significant background gas effects on vapor nucleation that differ somewhat from that we have reported previously. In this paper, we discuss the important issue of stability (the absence of buoyancy-driven convective motion of the gas–vapor mixture) and cloud chamber operation; and we focus now on the lower total pressure limit required for stable chamber operation. We describe how violating this limit is manifested by the experimental data, and we show actual results for the nucleation of 1-pentanol with hydrogen as a background gas which illustrates the importance of considering these stability issues. For the first time, we identify three regions of operation for the diffusion cloud chamber. Region I corresponds to the range of total pressures below this lower total pressure limit; Region III corresponds to the range of total pressures above the upper total pressure limit (described earlier); and, Region II corresponds to the range of total pressures that permit “proper” operation of the diffusion cloud chamber. Here we define proper operation as operation under conditions that are believed to be well represented by a one-dimensional model of diffusion in a stagnant gas. We provide, for the first time, an empirical procedure for determining the lower total pressure limit. We also argue against the commonly used pressure ratio as a predictor for “proper” cloud chamber operation.

A Small Whole-Body Exposure Chamber for Laboratory Use

With the development of transgenic and specialized mouse strains, there is an increased need for inhalation exposure systems designed for smaller exposure groups. An inhalation exposure chamber, designed specifically for the exposure of up to 40 mice, was characterized. The chamber was fabricated from 0.32-cm-thick (1 / 8 -in) aluminum sheets with outside dimensions of 61 cm long by 32 cm high by 34 cm deep, resulting in an internal volume of 65 L. Two stainless-steel open-mesh cages, separated by an absorbent barrier, can be stacked within the central portion of the chamber. Access is provided through a gasketed door with a safety-glass face. Tests were performed to determine the chamber leakage rate, degree of mixing, and spatial variation of two aerosols within the chamber. Results indicated that the fractional leakage rate was 0.0003 min -1, well below a reported criterion for an operating chamber. Chamber operation gave similar mixing performance with, or without, use of an interior fan. For aerosols with a mass median aerodynamic diameter (MMAD) of 2.56 µm and 3.14 µm, the spatial variation of particulate matter concentration resulted in coefficients of variation (CVs) of 4.8% and 11.0%, respectively. These CV values are comparable to those obtained from similar studies involving other inhalation exposure chambers.

Infrared thermographic image processing for the operation and control of heterogeneous combustion chambers

The measurement of temperature in a combustion chamber, using conventional devices such as thermocouples, can be misleading. An infrared thermographic camera can achieve a non-intrusive measure. Having acquired a still image of, for example, a klin, it can be used to produce a map of the effective temperature of the waste bed, walls, and combustion gases. This paper describes a technique for processing an infrared image to identify what really happens within such a combustion chamber. The use of a thermographic camera, to produce a temperature map of a combustion chamber, can be helpful, particularly for control purposes. This paper addresses the criteria adopted in the selection of the thermographic system, in terms of both wavelength sensitivity and geometric location within the chamber. Moreover, a detailed description of the zonal method is reported, together with the identification procedure adopted to infer the temperature map from an infrared image. As a matter of fact, the presence of soot and fly-ash within the combustion chamber does complicate the radiative model, because a gray gas analogy must be accounted for. Soot and fly-ash give rise to a foggy and diffusive effect on the image with a consequent apparent homogeneous temperature profile. To simulate the effective radiative energy flux entering the camera lens and impinging on the CCD photoelectric cell, a raytracing technique has been developed. Each discrete area and volume, within the combustion chamber, emits a pencil of radiation, which after passing through the hot gases, reaches the CCD device. Such a light pencil is generated by the energy emitted and reflected from the discrete surfaces, plus all the energies emitted by the volumes of gas distributed along the path, minus any attenuation. The total energy balance equations, coming from the zonal method, must be coupled with the temperature-energy maps acquired by the infrared camera to identify the unknown effective temperatures. Once the temperatures of the walls and bed are known, it is possible to use them to improve the control strategy by means of a set of new measures and combustion efficiency indexes, which are usually unavailable when conventional thermocouples are adopted. Finally, a validation of the proposed procedure is presented with an online application to an incinerator for industrial solid waste. The combustion dynamics within the primary kiln is analyzed and quantified, in terms of both absolute temperatures and characteristic times.

Investigation of nitrogen removal in a cascaded membrane bioreactor

Two different plants in different scales were compared. The main characteristic of the plants is the division of the nitrification volume into separate chambers. To gain more information about the internal conversion processes, concentration profiles of COD, NO3-N and NH4-N along the pathway of the waste water were measured. Moreover, the effect of different plant configurations and different operation conditions involving the internal circulation streams on the biological conversion processes were studied. Except for some temporary operation problems, the treatment performance of the plants was very stable and on a high level. There was a high correspondence between the plants. Operation without internal recirculation leads to lower effluent concentrations of ammonium. Beside this, operation of several nitrification chambers instead of only one chamber results in lower ammonium effluent concentrations.

Test of freonless operation of resistive plate chambers with glass electrodes—[formula omitted] gas gap vs [formula omitted] gas gap

Non-freon gas mixtures (Ar/iso-C4H10) were tested as the chamber gas for 1 and 2mm gas gap Resistive Plate Chambers (RPCs) with float glass as the resistive electrodes, operated in the streamer mode. With the narrower (1mm) gas gap, streamer charge is reduced (∼1/3), which reduces the dead time (and dead area), associated with each streamer, improving the detection efficiency. The best performance was obtained for two cases: Ar/iso-C4H10=50/50 and 60/40. For the 50/50 mixture, a detection efficiency of better than 98% was obtained for the 1mm gap RPC, while the efficiency was 95% for the 2mm gap RPC, each operated as a double-gap RPC. The measured time resolution (rms) was 1.45±0.05(2.52±0.09)ns for the 1(2)mm gap RPC for the 50/50 mixture.

Acoustic instability while combusting aluminum particles in MHD facilities

In this paper, the theoretical study of acoustic-vibration excitation while combusting aluminum particles in a gas mixture is carried out. At long distances, aluminum particles are considered to be monodisperse and immobile with respect to the gas. In determining the excitation conditions for acoustic vibrations, the gas mixture used was considered as a perfect gas. Expressions for the frequency and excitation increment of acoustic vibrations are obtained, characteristics of a fuel and of an oxidizer explicitly entering into these expressions. In [1], powders prepared on the basis of carbon and metals were suggested as a fuel for pulsed MHD generators. Air or oxygen are oxidizers in this case. Characteristics of MHD generators while operating with these fuels, in fact, do not differ from those obtained using solid rocket propellants. In this case, the powder-like fuel presents the possibility for profound control of the device power when changing the mass flow-rate of components and provides for long-term operation of powerful MHD generators. It was shown in [2] that aluminum fuel is optimal for pulsed MHD generators, provided that the air oxidizer is employed. It is known [3] that in the process of burning a disperse fuel the acoustic vibrations can be excited, which results in violation of the normal operation of combustion chambers and even in their destruction. In the practice of rocket-engine development [4], engines having pressure-vibration amplitudes of not more than 5% from the nominal value are related to those exhibiting stable combustion. It was shown in [5] that the requirements for stability of the combustion process in the MHD-generator combustion chamber should be more rigorous than in rocket engines. This is caused by the fact that for such pressure vibrations electric-power pulsation phenomena hinder the normal operation of an MHD generator. Therefore, consideration of acousticvibration excitations in the case of combusting a powder-like fuel in the combustion camber of an MHD generator is an urgent problem. Usually, in studies of acoustic-vibration excitation, it is suggested that, in the case of combusting a disperse fuel, the burning zone is substantially smaller than the length of the combustion chamber [3, 4]. In actual conditions, the burning zone has a certain extension along the longitudinal axis of the combustion chamber, which is comparable with its length [6]. Therefore, in the case of acoustic vibrations of pressure, disturbances of the velocity and temperature of the gas mixture along the length of the combustion chamber are different, which affects the stability of the combustion process [3, 4]. In this paper, in studies of the excitation of acoustic vibrations, a distributed combustion model is used. In other words, we assume that the zone of burning aluminum particles is approximately equal to the length of the combustion chamber.

Liquid-xenon γ-camera with ionisation readout

The successful operation of a liquid-xenon ionisation chamber with imaging capability is reported. A bi-dimensional readout based on a mini-strip plate—a glass slab with metal strips deposited along two perpendicular directions—was developed and studied both experimentally and by computation. An image of a 122 keV γ-source of 5 mm diameter was obtained with a liquid-xenon ionisation chamber equipped with such readout. A position resolution better than 2 mm was achieved.

Modeling of the gas–particle flow in industrial classification chambers for design optimization

A computational approach has been developed for the prediction of gas–particle flow and the simulation of the classification-settling characteristics of a particulate material flow in a gravitational classification chamber (GCC). By taking into account the classification chamber geometry and operating parameters, as well as the particulate material physical properties, the developed computational code allows the simulation, improvement and control of the operational characteristics of industrial settling, classification and/or separation chambers commonly used in process industries. The work assesses the performance of the computational code and demonstrates the capability of dedicated computational tools to model with accuracy complex industrial multiphase flows in order to support design criteria.

Construction and operation of an ion chamber consisting of lead plates immersed in 2,2,4,4 tetramethylpentane

A small test ion chamber has been constructed using 2,2,4,4 Tetramethylpentane as the ionizing liquid in direct contact with an array of lead plates used as the high voltage and ground planes. The transient response resulting from the passage of cosmic ray muons through the ion chamber was monitored for a period of 54 weeks to measure possible degradation of the signal due to contamination of the ionizing liquid that may have come from the lead plates. Over the first 17 weeks of the experiment, the loss of pulse height was measured to be less than 11% per year at 95 confidence. During the following 37 weeks, a more sensitive measurement was consistent with zero loss, or a limit of less than 2.9% per year at 95% confidence.

The effect of carrier gas pressure and wall heating on the operation of the thermal diffusion cloud chamber

Experimental observations indicate that the nucleation behavior within the thermal diffusion cloud chamber (TDCC) changes with increasing carrier gas pressure and applied sidewall heating, even though such an effect is not predicted by typical nucleation theories and it is not seen in typical expansion-based nucleation studies. In this work we present a model of the chamber which shows that both of these effects are likely due to buoyancy-induced convection within the TDCC. As the chamber pressure is increased, the calculated critical supersaturation within the chamber decreases. Results from a simple model of the chamber wall heating are also presented. Previously, it was argued that unheated chamber walls result in a significant, radial concentration gradient which lowers the vapor concentration and condensation flux within the chamber center. In contrast, we show that this reduction is due primarily to a convective flow induced by the sidewall concentration gradient. The model has been applied to recent experimental data for n-pentanol. Results indicate that, with respect to buoyancy-induced convection, the typical 1D model should be regarded as an upper limit to the maximum attainable supersaturation within the chamber.

Dynamic flux chamber measurement of gaseous mercury emission fluxes over soils: Part 2—effect of flushing flow rate and verification of a two-resistance exchange interface simulation model

Both field and laboratory tests demonstrated that soil Hg emission fluxes measured by dynamic flux chamber (DFC) operations strongly depend on the flushing air flow rates used. The general trend is an increase in the fluxes with increasing flushing flow rates followed by an asymptotic approach to flux maximum at sufficiently high (optimum) flushing flow rates. This study indicates that the DFC measurements performed at low flushing flow rates can underestimate Hg emission fluxes over soils, especially Hg-enriched soils. High flushing flow rates therefore are recommended for accurate estimation of soil Hg emission fluxes by DFC operations. The dependence of DFC-measured soil Hg emission fluxes on flushing flow rate is a physical phenomenon inherent in DFC operations, regardless of DFC design and soil physical characteristics. Laboratory tests using DFCs over different soils confirmed the predictions of a two-resistance exchange interface model and demonstrated the capability of this model in quantitatively simulating Hg emissions from soils measured by DFC operations.

Use of a MicroStrip Gas Chamber conductive capillary plate for time-resolved X-ray area detection

The stable operation of MicroStrip Gas Chamber (MSGC) was successfully performed using glass capillary plate as an intermediate gas multiplier. Detection area of 95 mm 2 was available and fine position resolution of 90 μm using digital readout was attained. A charge-up problem of capillary plate under intense radiation source was perfectly removed by surface conductivity inside of capillaries. The quantitative measurements using MSGC is now available in X-ray imaging. This paper also presents novel applications of X-ray diffraction studies and their preliminary results using an MSGC. Rapid measurements for X-ray crystallography of the order of a few tens of seconds were attained successfully.

Dynamic flux chamber measurement of gaseous mercury emission fluxes over soils. Part 1: simulation of gaseous mercury emissions from soils using a two-resistance exchange interface model

A two-resistance exchange interface model (TREIM) was developed to simulate gaseous mercury (Hg) emissions from soils measured by dynamic flux chamber (DFC) operations. The model is based on mass balance principles and a Hg air/soil exchange theory that considers the influence of flushing flow rate on Hg air/soil exchange. We used this model to examine the effect of the flushing flow rate and understand the optimum conditions for DFC measurements of Hg emission fluxes over soils. Our model simulations indicate that the flushing flow rate is a most critical operation condition. We recommend adoption of high flushing flow rates (e.g., ∼15–40 l min −1 for DFCs of common design) based on our simulation findings that underestimation of actual emission fluxes can occur at low flushing flow rates. The biased low fluxes are caused by suppression of emission potential resulting from internal accumulation of emitted Hg and by higher exchange resistance both at low flushing flow rates. This model provides a useful means for estimating maximum steady-state fluxes and soil air Hg concentrations and for adjustment of the fluxes measured under different operating conditions. The model also finds its value in understanding mechanical processes of Hg emissions from soils.

The Impact of Convective Flow on Thermal Diffusion Cloud Chamber Operation

We report here new results that further elucidate the role of buoyancy-driven convective flows in determining the distribution of vapor mole fraction and temperature in the thermal diffusion cloud chamber. A two-dimensional model describing both diffusion and convection in the presence of chamber sidewalls is presented. The model equations are used to analyze 1-butanol and 1-pentanol nucleation data obtained earlier. The results of the investigation show that convective flow is nearly always present and, in the cases considered here, result in a reduction in the value of the calculated critical supersaturation (as compared to the one-dimensional case). The dependence of critical supersaturation with total pressure reported earlier is smaller but is not eliminated.

2-D Model for the Description of Thermal Diffusion Cloud Chambers: Description and First Results

In thermal diffusion cloud chambers (TDCCs), a decrease of nucleation rate with increasing total pressure was observed repeatedly, both near atmospheric pressures and at elevated pressures. Because this pressure effect was observed almost only using TDCCs, there have been some concerns inside the nucleation community whether it is not an experimental artifact. One questionable point in this context is that, to calculate the profiles of temperature and saturation ratio in TDCCs it is assumed that if the chamber is sufficiently “flat”, a 1-d model can be used for the description of the transport processes in the central part of the chamber. The major concern in this context is that the heated chamber wall may cause a buoyancy driven convection that can propagate toward the center of the chamber and cause a slow motion of the gas mixture. To investigate this effect, a 2-d model of coupled mass, heat, and momentum transport in TDCCs has been developed. In the paper this model is described, and its predictive force is shown in comparison with a state-of-the-art 1-d model and with experimental data from the system n-propanol−He. Furthermore, results concerning the effects of wall heating, total chamber pressure, carrier gas, and chamber geometry on nucleation rates are presented. The influence of wall heating on the nucleation rate was found to be significant when transport processes inside TDCC are dominated by buoyant convection. Using the 2-d model made it possible to partly (but not completely) explain the pressure effect observed in TDDCs. It was also shown that including the process of thermal diffusion in the model may have a significant influence on the resulting profiles of nucleation rate. It was confirmed that the choice of the carrier gas in the chamber can strongly influence stability of chamber operation. With respect to the optimal chamber geometry it was shown that TDCCs should have a diameter as small and a diameter-to-height ratio as large as possible to minimize the 2-d effects. All in all, it was proven that application of 1-d models to describe the heat and mass transfer in TDCC may lead to an erroneous determination of temperature, saturation ratio, and nucleation rate profiles.

Operation of sealed microstrip gas chambers at the ILL

Microstrip Gas Counters (MSGCs) were introduced at the ILL as a response to the problem of fabricating the large area neutron detector of the D20 neutron powder diffractometer. This banana-like detector consists of 48 MSGCs, each comprising 32 counting cells. It was in operation during 18 months before being stopped due to the progressive deterioration of the anode strips. In order to increase its lifetime, significant modifications were introduced in the recently assembled new version. Another instrument, D4C, was recently equipped with a modular detector made of nine MSGCs, each of them in an individual gas vessel. Besides the unidimensional individual readout MSGC of D20 and D4C, the ILL has developed bidimensional MSGCs with a charge division readout. All these detectors employ sealed vessels containing a gas mixture at a pressure which can be as high as 15 bar, necessitating very clean conditions. This paper describes the experience acquired at the ILL in the fabrication and operation of these detectors.

Operation of sealed microstrip gas chambers at the ILL

Microstrip gas chambers (MSGCs) were introduced at the Institut Laue Langevin [(ILL), Grenoble, France] as a response to the problem of fabricating the large-area neutron detector of the D2O neutron powder diffractometer. This banana-like detector consists of 48 MSGCs, each comprising 32 counting cells. It was in operation during 18 months before being stopped due to the progressive deterioration of the anode strips. To increase its lifetime, significant modifications were introduced in the recently assembled new version. Another instrument was equipped with a modular unidimensional detector made of nine MSGCs, each of them in an individual gas vessel. The ILL has also developed bidimensional MSGCs with a charge division readout. All these detectors employ sealed vessels containing a gas mixture at a pressure that can be as high as 15 bars, necessitating very clean conditions. This paper describes the experience acquired at the nL in the fabrication and operation of these detectors.