Direct flow tubes

Many experimental methods may be distinguished by whether and how they achieve time resolution—directly or indirectly. Indirect methods avoid the requirement for fast detection methods, either by detemiining relative rates from product yields or by transfonuing from the time axis to another coordinate, for example the distance or flow rate in flow tubes. Direct methods include (laser-) flash photolysis [27], pulse radiolysis [28]... 

Coriolis-Type Flow Meters. In CorioHs-type flow meters the fluid passes through a flow tube being electromechanically vibrated at its natural frequency. The fluid is first accelerated as it moves toward the point of peak vibration ampHtude and is then decelerated as it moves from the point of peak ampHtude. This creates a force on the inlet side of the tube in resistance to the acceleration and an opposite force on the outlet side resisting the deceleration. The result of these forces is an angular deflection or twisting of the flow tube that is directly proportional to the mass flow rate through the tube. 

To identify the isomeric form of the product of the collisionally stabilized analog of reaction 44 experimentally, Scott et al.92 studied reactions of C3H30+ (C2Hj/CO) produced in that reaction and compared it with that produced directly from propynal in an electron impact ion source or by proton transfer from HCO+ to propynal in the flow tube (these latter two production methods yielded ions with... 

Note The reactions were studied by Wilson et al. in a SIFT at 300 K.93 HCNH+/C2H4 and CHj/CH,CN were produced in the flow tube by reactions 46 and 47a. CjHjNCH and C2HSCNH+ were produced directly from Cj NC and C2H5CN in a high pressure ion source and by proton transfer to these neutrals from HCO+ in the flow tube. Proton affinities (kcal mol-1) are given below each reactant neutral and the proton detachment energies of the ions are below the ion identification.2 30 his indicates not studied. 

For this purpose, the flow tube emptied directly into a high-pressure ion source. This source was essentially a sealed box with a gas inlet for the Cl reagent gas, a 0.58 mm hole to allow injection of a magnetically collimated electron beam, and a 0.99 mm hole to allow ions to exit into the mass spectrometer. The flow tube was coupled to the source using a 0.1 mm annular gap that thermally isolates the source from the flow tube, but allows little of the gas flow to escape. Even at a flow tube temperature of 1000 K, the source temperature increased no more than 50 K. To avoid any variations in source conditions with flow tube temperature, the source was thermostated to a constant temperature of 100 K. 

Figure 23.3 shows axial normalized static pressure P/Pt (where P is the static pressure and Pt is the pressure in the preheater) distributions on the combustor walls for the test runs No. 9 (elliptic nozzles) and No. 10 (round nozzles). In this test, kerosene was barbotated with air and fuel was injected at an angle of 45° relative to the main-stream air flow direction throughout tube-micropylons. The flow in the combustor remained supersonic in test runs No. 9 and No. 10 over the range of ER given in Table 23.2. 

CIO and BrO abundances are detected simultaneously and continuously as the airstream passes through the instrument. They are not detected directly but are chemically converted to Cl and Br atoms by reaction with reagent nitric oxide gas that is added to the airstream inside the instrument. The Cl and Br atoms are then detected directly with resonance fluorescence in the 2D5/2 -> 2P3/2 transitions in the vacuum ultraviolet region of the spectrum. In resonance fluorescence, the emissions from the light sources are resonantly scattered off of the Cl and Br atoms in the airstream and are detected by a photomultiplier tube set at right angles to both the light source and the flow tube. The chemical conversion reactions... 

Head-type flowmeters include orifice plates, venturi tubes, weirs, flumes, and many others. They change the velocity or direction of the flow, creating a measurable differential pressure, or "pressure head," in the fluid. Head metering is one of the most ancient of flow detection techniques. There is evidence that the Egyptians used weirs for measurement of irrigation water flows in the days of the Pharaohs and that the Romans used orifices to meter water to households in Caesar s time. In the 18th century, Bernoulli established the basic relationship between the pressure head and velocity head, and Venturi published on the flow tube bearing his name. 

Variable-area meters are well suited for the local indication of low flow rates, but are not limited to those applications. They are available in both glass and metal tube constructions (Figure 3.99). In the glass tube design, the position of the float can be visually observed as an indication of flow rate. Their advantages include their low cost, low pressure loss, direct flow indication, and the ability to detect very low flow rates of both gases and liquids, including viscous fluids. 

Selected ion flow tube mass spectrometry (SIFT-MS) is an analytical technique used for direct and quantitative determination of VOCs in mixtures of gases. SIFT-MS was introduced in 1976 by N. G. Adams and D. Smith. The technique can be applied for parallel real-time monitoring of a few substances [126]. A scheme of the SIFT-MS system is presented in Fig. 14.9 [127]. The principle of gas mixture analysis is based on the reaction of reagent ions with molecules of analyte within a specific time (a few milliseconds). In this method, chemical ionization is applied reagent ions are generated in the ion source by a suitable ionization gas (nitrogen, oxygen, or water vapor). Of aU the obtained ions, only cations of the desired m/z... 

In such a straight tube reactor, it is clear that the activation of monomer, or the creation of polymerizable species, occurs at the tip of glow where the incoming monomer molecules interact with the luminous gas phase. Thus, the opening of double bond and detachment of F occur at this point, and the further reaction of the free radicals, the species created by the detachment of F, and the detached F s with gas phase species occurs while all gaseous species are moving toward the downstream side of the reactor. Under such a one directional flow conditions, particularly with monomer that contain -CF3, the analysis based on the formation of -CF3 from monomers that do not contain -CF3 might become the focal point of discrepancy. 

Boiler Deposits. Deposition is a principal problem in the operation of steam generating equipment. The accumulation of material on boiler surfaces can cause overheating and/or corrosion. Both of these conditions frequently result in unscheduled downtime. Common feed-water contaminants that can form boiler deposits include calcium, magnesium, iron, copper, aluminum, silica, and (to a lesser extent) silt and oil. Most deposits can be dassifi ed as one of two types scale that crystaUized directly onto tube surfaces or sludge deposits that precipitated elsewhere and were transported to the metal surface by the flowing water. 

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