Heating Strip Research Articles

Determination of CHFCl2(CFC21) in the troposphere

Abstract In the frame of the controversy about stratospheric ozone depletion by halocarbons, it has been hypothesized that CFC21, which has no industrial use, could be a decomposition product of CFCl1. However the quantitative analysis of this compound is quite difficult because of: 1. its low concentration 2. difficult GC separation fom other halocarbons and possible interferences and sample contamination. This problem has been solved by using analytical techniques based on the following points: 1. Sampling is carried out by trapping air on Carbopack B (graphitized carbon black) at low temperature and injecting via the heat stripping technique (1). This allows sampling of lagre air volume (up to 30 liters). 2. Analysis is performed by GC-ECD and GC-MS. An extremely selective GC column is used which allows the seperation of most halocarbons possibly present in the atmoshpere (1). The mass-spectrometer, used in the multiple ion monitoring mode (M.I.D.) (2), offers a very reliable method for the qualitative and quantitative determination of halocarbons (3). 3. Calibration is carried out by means of permeation tubes that allow to obtain the most reliable primary standard because of the accuracies of gravimetric measurements (4). Samples collected at different locations have been analyzed. Depending on metereological conditions, latitude and seasons, concentrations of CFC21 much larger than expected have been found. The regularities connected to the appearances and disapperances of CFC21 are such that the need for more extensive measurements are imperative to ascertain wether the hypotesis made about its origin can be feasible or not.

Catalyzed combustion of H 2/air mixtures in a flat-plate boundary layer: I. Experimental results

A study has been made of the combustion characteristics of lean hydrogen-air mixtures flowing over a heated catalytic platinum plate. The objectives of the investigation were to develop a better understanding of the interaction between fluid mechanics, gas-phase combustion, and surface reaction in high-temperature surface-catalyzed combustion. The experimental system consisted of a thin quartz plate with vacuum-deposited platinum heating strips mounted over an open atmospheric-pressure jet of premixed hydrogen and air. Boundary-layer density profiles were measured using differential interferometry for flow visualization studies and Rayleigh scattering for point-density measurements. Laser Doppler velocimetry was also used to measure the velocity distribution. The presence of heat release due to surface reaction was determined from changes in heating-strip power inputs with fuel addition. Results were obtained for a range of equivalence ratios from 0.05 to 0.3 and plate surface temperatures from 470 to 1300 K. Significant surface heat release was found for all mixtures at plate temperatures as low as 470 K. At increased equivalence ratios and plate temperatures heat release due to gas-phase reaction was present. This was characterized by local increases in temperature across the boundary layer and an increase in thermal boundary-layer thickness. Comparisons with numerical calculations based on a surface reaction model which included finite-rate surface oxidation of H 2 and radical recombination indicated qualitative agreement in general boundary-layer behavior, but the predicted gas-phase heat-release rate was considerably higher than found experimentally.

Electrically quiet temperature controller

YEANDLE, S. Electrically quiet temperature controller. BRAIN RES. BULL. 4(1) 139–140, 1979.—A circuit for an electrically quiet temperature controller is described that is suitable for controlling the temperature of a neurophysiological preparation above ambient temperature. By not generating spurious electrical signals it facilitates the recording of low level biological potential changes when temperature control is required. The device, constructed of standard electronic components, uses a thermistor as a sensing element and an ordinary heat lamp or heating strip as a heating element.

The effect of temperature changes on tachyphylaxis to angiotensin in vitro.

The effect of heat on the contractility and binding of 14C-angiotensin to guinea pig aortic strips was studied. It was found that heating strips to 47 °C for 20 min causes an increase in maximal response as well as a shift to the left of the dose–response curve for angiotensin while responses to noradrenaline (NA) remain unchanged. This procedure also increases the onset of tachyphylaxis to 10−5 M angiotensin. Heating (47 °C) for varying periods of time decreases the binding of 14C-angiotensin by about 60%. This effect does not seem to be related to the time of heating. It is postulated that this reduction in binding reflects denaturation of nonspecific binding sites on the cell membrane. Heating (47 °C, 20 min) enhanced the binding of 14C-angiotensin to aortic strips which had been rendered tachyphylactic to 10−5 M angiotensin. It is suggested that this is due to the induction of new binding sites.

The growth of calcite single crystals by travelling solvent zone melting

Travelling Solvent Zone Melting has been used to grow calcite CaCO3 single crystals. In order to obtain an interface as flat as possible a heating strip is embedded in the molten solvent zone. Some small holes in the strip ensure the liquid contact on both sides. The solvent is driven along the solid by the displacement of the solid phases with respect to the strip. Some characteristics of the transport process in this zone are considered in more detail. Experiments show that the formation of single crystals is determined by the transport process more than by kinetics.Some physical properties of the synthetically grown crystals are compared with those of the natural crystals.

Angular Dependence of Critical Currents in Plasma-Plated Nb3Sn Strip Superconductors

In many instances it appears that the limiting performance of a superconductive device is determined by low-field instabilities rather than by the high-field current density. If the device is made of flat-strip superconductors, a further complication may arise from the fact that in the low-field regions the magnetic field usually is oriented at some nonzero angle to the surface of the strip. To see how these conditions affect the performance of plasma-plated superconductors, we have measured critical currents in flat strips of Nb3Sn in transverse applied field, varying the angle θ between the surface of the strip and the magnetic field. When transport current is applied first and the field increased until the specimen undergoes a normal transition, the relationship Hc(IT) = H0(IT)+H1(IT) cos2θ is roughly obeyed, where IT is the transport current and H0 and H1 are found to be of comparable magnitude. When the magnetic field is applied first and the transport current increased to its critical value, virtually no angular dependence is observed. We tentatively explain this result by describing the plasma-plated material as a matrix of miniature hollow cylinders aligned with the magnetic field. Because of the anisotropy of the plating process the effective wall thickness of the ``cylinders'' varies with the specimen orientation. When the field is applied first, the transport current can find paths around these ``cylinders'' which will not result in locally exceeding the critical current density of the material until nearly all the specimen is critical. However, when the transport current is applied first, the additional shielding currents induced by the magnetic field are forced to travel in paths which are already carrying transport current, and locally the critical current density may be exceeded, precipitating a normal transition before the entire specimen is critical. Further tests are being carried out to determine the effect of heat treatment and strip dimensions on this angular dependence of the critical current. These results should discriminate between our proposed explanation and the possibility that the effect is simply a demagnetization phenomenon.

The use of radiothermoluminescent dosimeters in the field of diagnostic radiology.

Our investigation deals only with the applicability of synthetic CaF2:Mn, lithium fluoride, calcium sulfate, and preliminary work with lithium borate to medical and radiobiological dosimetry. In order to protect radiothermoluminescent phosphors from ambient atmospheric gases which may cause spurious thermoluminescence and to reduce the possibility of tribothermoluminescence, a protective carrier was developed. In an earlier report (1), radiothermoluminescent dosimeters were employed which were permanently encapsulated, following an out-gassing and flushing procedure with inert gas as specified by Schulman (2, 3). Accordingly, calcium fluoride, lithium fluoride, lithium borate, and calcium sulfate phosphors were encapsulated and outgassed. Some of these dosimeters were stimulated by conduction heating; that is, they were placed upon a platinum heating strip through which direct current was passed for thirty seconds. Due to the varying spectral response of each of the phosphors investigated, several separat...

Melting Curves of Copper, Silver, Gold, and Platinum to 70 kbar

The melting curves of Cu, Ag, Au, and Pt have been measured versus pressure to 60 or 70 kbar using the discontinuity in electrical resistance of a wire enclosed in parallel heating strips. The results, which compare favorably with other measurements at lower pressures, were fit to a Simon's equation. Only in the case of gold do the measured parameters in this equation closely agree with that predicted theoretically. Pressure corrections to the thermocouple measurement and temperature corrections on the pressure calibration are considered. The melting curves for Au and Ag and probably Pt are normal in the sense that they curve toward the pressure axis, but the melting curve for Cu is linear over the pressure range measured to within the accuracy of the experiment.

Corrosion Measurements in a Hydrogen Sulfide-Water Absorption Pilot Plant

Abstract In evaluating gas processing facilities to sweeten an extremely sour natural gas, technologists estimated high pressure water absorption followed by simple low pressure flashing would be attractive. Consideration of reduced heat exchange and stripping heat requirements indicated that appreciable savings in investment and operating costs could be effected by the process. Accordingly, a water absorption pilot plant was constructed and operated for a brief period to establish the absorption and desorption characteristics under the existing field conditions. Since corrosion problems were anticipated, a series of corrosion evaluation tests were conducted concurrently in the pilot plant. Carbon steel corrosion rates, although very high during the first few hours or days, were found to diminish to a tolerable level within the 19-day test. Killed carbon steel, stainless steel Type 304, In-conel and K-Monel, were found resistant to sulfide stress corrosion cracking. Inconel, Monel, and 304 also showed low...