Tracers helium

The atmospheric rig is also used for fuel placement studies. Initially, these will be conducted using an inert tracer — Helium — to label a surrogate fuel flow, with mass spectrometry as the measurement method. The local fuel distribution can be applied to the numerical model to assess the effects of distortion in fuel-air... 

Hot atom reactions have also been used to label organic compounds with T. Irradiation of helium-3 with neutrons according to the nuclear reaction produces very energetic tritium atoms that can displace ordinary hydrogen in organic compounds. This procedure is not very selective, and the labeling pattern must be determined to enable the tritiated product to be used effectively as a tracer (34). 

Capture efficiency is the fraction of generated contaminant that is directly captured by the hood. Measurement of capture efficiency involves measuring concentration of process-generated contaminant or a tracer material. Using process-generated contaminant requires use of instruments suited to each specific contaminant and its conditions (temperature, pressure, concentration, form, etc.). In order to facilitate these measurements, a tracer is often substituted for the process-generated contaminant. The tracer is usually a gas (sulfur hexafluoride, nitrous oxide, helium, or similar), but an aerosol (particles) can also be used (potassium iodide, polystyrene particles, microbiological particles, etc.). The chosen tracer should be as similar to the real contaminant as possible, but at the same time should... 

Dunn et al. (D7) measured axial dispersion in the gas phase in the system referred to in Section V,A,4, using helium as tracer. The data were correlated reasonably well by the random-walk model, and reproducibility was good, characterized by a mean deviation of 10%. The degree of axial mixing increases with both gas flow rate (from 300 to 1100 lb/ft2-hr) and liquid flow rate (from 0 to 11,000 lb/ft2-hr), the following empirical correlations being proposed ... 

The general operation of the pilot scale reactor has be previously described by Pareek et. al. [3]. However, modifications were required to allow the injection of the gas and liquid tracers, and their subsequent detection at the outlets. The liquid tracer, 5mL Methyl blue solution (lOgL" ), was injected via a syringe inserted into the liquid feed line. Outlet samples were measured with a Shimadzu 1601 UV-Vis Spectrophotometer at a wavelength of 635nm. A pulse (20mL) of helium gas tracer was introduced using an automated control system, with the outlet concentration monitored in real-time with a thermal conductivity detector. Runs were carried out based on a two-level... 

Top Z, Brand LE, Corbett RD, Burnett W, Chanton J (2001) Helium and radon as tracers of groundwater input into Florida Bay. J Coast Res 17 859-868... 

Reductions in expiration flow rate are indicative of bronchial disease, such as asthma or bronchitis. Reductions in FVC are due to reduction in the lung or chest volume, possibly as a result of fibrosis (an increase in the interstitial fibrous tissue in the lung). The air remaining in the lung after exhalation is called the residual volume (RV). An increase in the RV is indicative of deterioration of the alveoli, possibly because of emphysema. The RV measurement requires a specialized tracer test with helium. 

A step increase in the concentration of helium (tracer A), from 1.0 to 2.0 mmol L-1, was used to determine the mixing pattern in a fluidized-bed reactor. The response data were as follows ... 

Shetty et al. (1992) studied gas-phase backmixing for the air-water system in bubble-column reactors by measuring RTDs of pulse-injected helium tracer. 

Test methods described in the literature inelude the bubble method, helium mass speetrometiy, liquid tracer (dye), head spaee analysis, vacuum and pressure decay, weight loss and gain, and high voltage leak deteetion [6]. 

The molar fraction ratio between helium and nitrogen in the flue gas was determined from gas chromatographic measurements. The molar flow of the tracer gas of helium was measured. Because Rogers applied batch methods to measure water vapour in flue gas and the helium-nitrogen ratio, the overall method become a semi-continuous method. The water vapour of the flue gas was measured batchwise by freezing it out in an U-tube placed in an acetone-dry ice mixture. 

According to the definition formulated above it is easy fo understand that the size of a gas leak, i.e. movement through undesired passages or pipe elements, w/ill also be given in mbar I s" A leak rate is often measured or indicated w/ith atmospheric pressure prevailing on the one side of the barrier and a vacuum at the other side (p < 1 mbar). If helium (wrfiich may be used as a tracer gas, for example) is passed through the teak under exactly these conditions, then one refers to standard helium conditions . 

The detection of a test gas using mass spectrometers is far and away the most sensitive leak detection method and the one most widely used in industry. The MS leak detectors developed for this purpose make possible quantitative measurement of leak rates in a range extending aaoss many powers of ten (see Section 5.2) whereby the lower limit = 10 mbar l/s, thus making it possible to demonstrate the inherent gas permeability of solids where helium is used as the test gas. It is actually possible in principle to detect all gases using mass spectrometry. Of all the available options, the use of helium as a tracer gas has proved to be especially practical. The detection of helium using the mass spectrometer is absolutely ( ) unequivocal. Helium is chemically inert, non-explosive, non-toxic, is present in normal air in a concentration of only 5 ppm and is quite economical. Two types of mass spectrometer are used in commercially available MSLD s ... 

Continuation of the study of the radioactive elements produced by cyclotron bombardment of lower elements led in 1950 to isolation by tracer techniques of numbers 97 and 98. Bombardment of Am241 with helium ions by S. G. Thompson, A. Ghiorso, and G. T. Seaborg produced 97243 which resembled its analogue, terbium, in its elution from ion-cxchange resins. Since terbium was named from the city of Ytterby, 97 was named from the city in which so many new elements had been discovered, Berkeley, and the name berkelium and symbol Bk have been accepted (89, 90). 

Helium-3 >7.7 x 10"14 cc STP/g Tracers of interactions with particles 1% 1/h Mass spectromi... 

A very convenient way of detecting and measuring leaks is to use a tracer gas (such as He) and a selective tracer gas detector, such as a helium leak detector. In addition to the mass spectrometer, MSLD include a high vacuum pumping system of definite pumping speed. 

Helium or nitrogen were used as carrier gas and methane was the tracer gas. A pulse of tracer gas was injected through a six-way valve into the carrier gas flow. The concentration of the tracer in the effluent was continuously measured by means of a thermal conductivity detector and recorded. 

The use of helium as a probe (or tracer) gas in leak detection is not new. Before the mass spectrometer, it was used with thermocouple and/or Pirani gauges because of the greater thermal conductivity of helium than air. If you list all the attributes of a perfect probe gas, helium obviously does the job ... 

Detector-probe technique It can find the location of a leak when the tracer gas is on the inside of the piece in question. This technique is time-consuming. Because the probe is collecting both air and helium, it is about 10% as sensitive as the tracer-probe technique. It cannot tell you the size of the leak. 

Aside from permeability and absorbency complications, other universal concerns of helium leak detection are factors such as source operating pressure, spraying patterns (for tracer-probe technique), response time, clean-up time, and cold trap usage. Pump use and general helium leak detector maintenance operations are also fairly universal. 

The source operating pressure is the vacuum necessary to operate the leak detection device. This pressure is not specific, rather it is a pressure range within the leak detector which works. Optimistically, we want the helium leak detector, and the system to which it is connected, to have the greatest possible vacuum. This gives the tracer-probe technique the maximum sensitivity with the quickest response time. As an added benefit, when one is operating at a very high vacuum,... 

Most helium leak detectors will not operate with pressures above lO"4 torr to 10 5 torr. At these greater pressures, the main element to the mass spectrometer will bum out. Fortunately most, if not all, helium leak detectors have various safety check mechanisms that automatically shut off the current to the main filament if the pressure goes above a set limit. So, you must depend on alternate leak detection methods, or use the detector-probe technique to discover large leaks. Once large leaks have been discovered and closed, you can concentrate on the smaller leaks that can be found with the tracer-probe technique. 

Fig. 7.65 A suggested pattern for spraying helium on a vacuum system when using the tracer-probe technique. The pattern is a compromise between proximity to the leak detector and spraying high before low areas.

Cleanup time is almost always longer than response time because of the difficulty in desorption of helium from a vacuum system, compounded by helium permeation into porous materials. So, when using the tracer-probe technique do not overspray helium onto your system. The more helium that enters your system, the more that can permeate into porous materials and the longer the cleanup time. 

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