Flame, conductivity

The first Damkohler number quantifies the ratio between the heat transferred from the flame (conduction time) and the energy required to heat the reactants to the ignition temperature (residence time). Extinction will occur when heat cannot be transferred fast enough. Equation 3.53 is written in terms of the ratio between conduction and convection (residence time), but in a more general form, could include all forms of heat transfer like gas-phase radiation. The second Damkohler number indicates if the reaction has sufficient time to proceed. In general, extinction is attained when either of the Damkohler groups is reduced below unity. 

Unlike the radiant loss from an optically thin flame, conductive or convective losses never can be consistent exactly with the plane-flame assumption that has been employed in our development. Loss analyses must consider non-one-dimensional heat transfer and should also take flame shapes into account if high accuracy is to be achieved. This is difficult to accomplish by methods other than numerical integration of partial differential equations. Therefore, extinction formulas that in principle can be used with an accuracy as great as that of equation (21) for radiant loss are unavailable for convective or conductive loss. The most convenient approach in accounting for convective or conductive losses appears to be to employ equation (24) with L(7 ) estimated from an approximate analysis. The accuracy of the extinction prediction then depends mainly on the accuracy of the heat-loss estimate. Rough heat-loss estimates are readily obtained from overall balances. 

The alkah flame detector had a short but turbulent history (20), Just how short is a matter of some controversy. The question, in a nutshell, is whether the so-called leak detector (21) and the so-called thermionic detector owe their function to the same mechanism. The choice of the word alkah-flame in this paper is simply one of convenience. Giuffrida termed her discovery a "thermionic detector (22), It has also been called "Karmen-Giuffrida detector, "phosphorus detector, and "alkali-sensitized flame detector. The term "thermionic, I think, carries mechanistic overtones, and there is little definite knowledge on the mechanism of this detector. "Phosphorus detector describes its most prominent feature but implies too narrow a range of apphcation. "Alkali flame, on the other hand, is a broad, innocuous, and unobtrusive term. There exists, incidentally, one other detector which uses an alkali flame. It monitors changes in alkah emission and flame conductivity (6). 

The FPD with dual photomultiplier arrangement and dual channel output can monitor P and S simultaneously if the appropriate circuitry is added, it can also record flame conductivity. Such an arrangement invites studies of P/S ratios it can also answer the question whether a particular peak in the chromatogram contains P, or S, or both. 

Ann. Phys.y 1806, xxii, 14-50 an alcohol flame conducts only from the positive wire, soap conducts only from the negative wire this was the first current rectifier. Ohm, J. Chem. Phys.y 1830, lix, 385 1830, lx, 32, explained it for solids by the deposition of a non-conducting layer (e.g. fatty acid) on one wire. Erman divided bodies into (i) non-conductors, (2) complete conductors, (3) incomplete conductors, (4) unipolar positive conductors, (5) unipolar negative conductors. 

The chromatogram can finally be used as the series of bands or zones of components or the components can be eluted successively and then detected by various means (e.g. thermal conductivity, flame ionization, electron capture detectors, or the bands can be examined chemically). If the detection is non-destructive, preparative scale chromatography can separate measurable and useful quantities of components. The final detection stage can be coupled to a mass spectrometer (GCMS) and to a computer for final identification. 

The flash point of a petroleum liquid is the temperature to which it must be brought so that the vapor evolved burns spontaneously in the presence of a flame. For diesel fuel, the test is conducted according to a closed cup technique (NF T 60-103). The French specifications stipulate that the flash point should be between 55°C and 120°C. That constitutes a safety criterion during storage and distribution operations. Moreover, from an official viewpoint, petroleum products are classified in several groups according to their flash points which should never be exceeded. 

A shallow metal vessel containing sand, the so-called sand bath, heated by means of a flame, was formerly employed for heating flasks and other glass apparatus. Owing to the low heat conductivity of sand, the temperature control is poor the use of sand baths is therefore not... 

Its conductivity increases slightly with exposure to light. It can be doped with silver, copper, gold, tin, or other elements. In air, tellurium burns with a greenish-blue flames, forming the dioxide. Molten tellurium corrodes iron, copper, and stainless steel. 

Schematic diagram of a flame ionization detector. Ions and electrons formed in the flame provide an electrically conducting path between the flame at earth potential and an insulated cylindrical metal electrode at high potential. surrounding the flame the flow of current is monitored, amplified, and passed to the recording system.

The special problems for vaUdation presented by chiral separations can be even more burdensome for gc because most methods of detection (eg, flame ionization detection or electron capture detection) in gc destroy the sample. Even when nondestmctive detection (eg, thermal conductivity) is used, individual peak collection is generally more difficult than in Ic or tic. Thus, off-line chiroptical analysis is not usually an option. Eortunately, gc can be readily coupled to a mass spectrometer and is routinely used to vaUdate a chiral separation. 

Electrically Conducting Fibers. FlectricaHy conducting fibers are useful in blends with fibers of other types to achieve antistatic properties in apparel fabrics and carpets. The process developed by Nippon Sanmo Dyeing Co., for example, is reportedly used by Asahi in Casbmilon 2.2 dtex (2 den) staple fibers. Courtaulds claims a flame-resistant electrically conductive fiber produced by reaction with guanadine and treatment with copper sulfide (97). 

Thermal Theory. The thermal approach to flame retardancy can function in two ways. Eirst, the heat input from a source may be dissipated by an endothermic change in the retardant such as by fusion or sublimation. Alternatively, the heat suppUed from the source maybe conducted away from the fibers so rapidly that the fabric never reaches combustion temperature. 

Oxygen and nitrogen also are deterrnined by conductivity or chromatographic techniques following a hot vacuum extraction or inert-gas fusion of hafnium with a noble metal (25,26). Nitrogen also may be deterrnined by the Kjeldahl technique (19). Phosphoms is determined by phosphine evolution and flame-emission detection. Chloride is determined indirecdy by atomic absorption or x-ray spectroscopy, or at higher levels by a selective-ion electrode. Fluoride can be determined similarly (27,28). Uranium and U-235 have been determined by inductively coupled plasma mass spectroscopy (29). 

The third characteristic of interest grows directly from the first, ie, the high thermal conductance of the heat pipe can make possible the physical separation of the heat source and the heat consumer (heat sink). Heat pipes >100 m in length have been constmcted and shown to behave predictably (3). Separation of source and sink is especially important in those appHcations in which chemical incompatibilities exist. For example, it may be necessary to inject heat into a reaction vessel. The lowest cost source of heat may be combustion of hydrocarbon fuels. However, contact with an open flame or with the combustion products might jeopardize the desired reaction process. In such a case it might be feasible to carry heat from the flame through the wall of the reaction vessel by use of a heat pipe. 

Fire-Resistant Hydraulic Fluids. Fire-resistant hydrauhc fluids are used where the fluid could spray or drip from a break or leak onto a source of ignition, eg, a pot of molten metal or a gas flame (17). Conditions such as these exist in die-casting machines or in presses located near furnaces. Specific tests for fire resistance are conducted by Factory Mutual in the United States. 

The reported characteristics of methane oxidation at high pressures are interesting. As expected,the reaction can be conducted at lower temperatures eg, 262°C at 334 MPa (3300 atm) (100). However, the cool flame phenomenon is observed even under these conditions. At high pressures. 

Flame spray metallising is widely used for the protection of metal against corrosion, especially for in situ protection of stmctural members. The principal metal used for spraying of plastics is sine. Aluminum and copper are also used. If the distance from the part is too great, the zinc solidifies before it touches the part and adhesion is extremely poor. If the molten zinc oxidizes, conductivity and adhesion are poor. If the distance is too short, the zinc is too hot and the plastic warps or degrades. These coatings are not as dense as electrically deposited coatings because of numerous pores, oxide inclusions, and discontinuities where particles have incompletely coalesced. 

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