Internal liquid injection

Internal liquid injection into the diffuser passage is used in a few applications for direct contact cooling. The quantity and quality of the liquid must be carefully controlled. 

A possibility is to saturate at different temperatures the reactants before they enter into the stack [33]. This approach can be accomplished by several procedures based on external dewpoint, external evaporation, steam injection with downstream condensers, or flash evaporation. High temperature values allow to absorb significant water amount in gas streams and then transport it inside the stack compensating the water losses due to internal fast evaporation. However, the main problem with external humidification is that the gas cools after the humidifier device, the excess of water could condense and enter the fuel cell in droplet form, which floods the electrodes near the inlet, thereby preventing the flow of reactants. On the other hand, internal liquid injection method appears preferable for example with respect to the steam injection approach because of the need of large energy requirement to generate the steam. 

The values for polytropic conditions represent an uncooled compressor, that is, no internal diaphragm cooling, no liquid injection, and no external coolers for the pressure range being considered. 

Vecchioli, J., Ehrlich, G.G., Godsy, E.M., and Pascale, C.A., Alterations in the chemistry of an industrial waste liquid injected into limestone near Pensacola, Florida, in Hydrogeology ofKarstic Terrains, Case Histories, Vol. 1, Castany, G., Groba, E., and Romijn, E., Eds., International Association of Hydrogeologists, 1984, pp. 217-221. 

All of the above points about liquid injection should be considered even when using a standard technique that does not require an accurate volume to be known. Selective evaporation cannot be tolerated even with the internal standard method. The size measurement errors obvious from the above discussion certainly point to the substantial advantage of the internal standard technique for accurate analysis. 

The gas-side mass-transfer coefficients kefl and ko increase with liquid feed rate or with gas velocity at each given position in the venturi scrubber and decrease at constant liquid rate and gas velocity with increasing distance from the point of liquid injection (J7, VI1). The values ofkifl generally increase with increasing liquid flow rate or gas velocity (often referred to as the velocity at the throat). However, ki,a will sometimes exhibit a maximum when the gas velocity increases the explanation is that, at higher gas velocities, an increase in turbulence in the throat of the venturi results in the formation of droplets smaller than the thin filaments first formed at lower gas velocities. Internal circulation is reduced in these smaller droplets, and there is also a reduction in the size of the zone of intense turbulence. These two phenomena lead to a maximum for the values of/cL. as found experimentally by Kuznetsov and Oratovskii (K15) and Virkar and Sharma (VI1). The values of the effective interfacial area a increase with both gas and liquid flow rates. 

Figure 6 Apparatus For Internal Liquid Chromatography. A still collection reservoir or storage bottle, B 3-way valve-inert gas/solvent, C adjustable pump, D 3-way valve-sample injection/solvent, E chromatography column,...

The external circulating nozzle does the GL mixing outside the column and injects the mixture into the top of the vessel. This is a vertical column with no internals. Liquid is withdrawn at the bottom and pumped through a venturi that induces air. The air-liquid mixture enters at the top of the column. 

Figure 15.5 Separation of Voriconazole and an internal standard by using SEC-HPLC. Adapted from Journal of Chromatography, B 691, D.A. Stopher and R. Gage, Determination of a new antifungal agent, voriconazole, by multidimensional high-perfomiance liquid chromatography with direct plasma injection onto a size exclusion column , pp. 441 -448, copyright 1997, with permission from Elsevier Science.

This system requires direct steam injection into the still with the liquid, all the steam leaves overhead with the boiled-up vapors (no internal condensation) in a steady-state operation, and system at its dew point. Steam is assumed immiscible with the organics. Steam distillation is usually applied in systems of high boiling organics, or heat sensitive materials which require separation at vacuum conditions. 

It should be noted here that the difficulty of accurately injecting small quantities of liquids imposes a significant limitation on quantitative gas chromatography. For this reason, it is essential in quantitative GLC to use a procedure, such as the use of an internal standard, which allows for any variation in size of the sample and the effectiveness with which it is applied to the column (see Sections 9.4(5) and 9.7). 

Pirie. R. L., Davies, T., Khan, A. R. and Richardson, J. F. 2nd International Coni, on Flow Measurement — BHRA, London (1988) Paper F3, 187. Measurement of liquid velocity in multiphase flow by salt injection method. 

Successful use of modern liquid chromatography in the clinical laboratory requires an appreciation of the method s analytical characteristics. The quantitative reproducibility with respect to peak height or peak area is quite good. With a sample loop injector relative standard deviations better than 1% are to be expected. The variability of syringe injection (3-4% relative standard deviation) requires the use of an internal standard to reach the 1% level (2,27). 

Heat and reflux a 5-g portion of soil sample with 50 mL of methanol-phosphate buffer (pH 7)-water (15 7 28, v/v/v) solvent mixture in a round-bottom flask for 1 h. After cooling, transfer a 10-mL portion of the supernatant to a test-tube and mix with 11 mL of 0.02M H3PO4 solution. Load this solution on to a silica-based SPE cartridge (Analytichem International Clin-Elut 1020) at a flow rate of 1-2 drops per second. Discard this fraction. Elute the analytes with 30 mL of dichloromethane. Concentrate the eluate to dryness with air in a water-bath at a temperature of 40 °C (do not use vacuum). Dissolve the residues in 5mL of HPLC injection solution [900 mL of water - - 50 mL of phosphate buffer (pH 7) 4-50 mL of ACN 4-4 g of TBABr]. Pinal analysis is performed using liquid chromatography/ultraviolet detection (LC/UV) with a three-column switching system. 

Peek, H.M. and Heath, R.C., Feasibility study of liquid-waste injection into aquifers containing salt water, Wilmington, North Carolina, in Symposium on Underground Waste Management and Artificial Recharge, Braunstein, J., Ed., publication 110, International Association of Hydrological Sciences, 1973, pp. 851-875. 

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