Transport with steam

Transport Properties. Viscosity, themial conductivity, the speed of sound, and various combinations of these with other properties are called steam transport properties, which are important in engineering calculations. The speed of sound (Fig. 6) is important to choking phenomena, where the flow of steam is no longer simply related to the difference in pressure. Thermal conductivity (Fig. 7) is important to the design of heat-transfer apparatus (see HeaT-EXCHANGETECHNOLOGy). The viscosity, ie, the resistance to flow under pressure, is shown in Figure 8. The sharp declines evident in each of these properties occur at the transition from Hquid to gas phase, ie, from water to steam. The surface tension between water and steam is shown in Figure 9. 

Chemical Reactivity - Reactivity with Water Slow reaction with water to produce hydrochloric acid fumes. The reaction is more rapid with steam Reactivity with Common Materials Slow corrosion of metals but no immediate danger Stability During Transport Not pertinent Neutralizing Agents for Acids and Caustics Soda ash and water, lime Polymerization Does not occur Inhibitor of Polymerization Not pertinent. 

When relatively small amounts of hydrogen are required, perhaps in remote locations such as weather stations, then small transportable generators can be used which can produce I-I7m h. During production a 1 1 molar mixture of methanol and water is vaporized and passed over a base-metal chromite" type catalyst at 4(X)°C where it is cracked into hydrogen and carbon monoxide subsequently steam reacts with the carbon monoxide to produce the dioxide and more hydrogen ... 

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. 

Vapor phase inhibitors (VPIs), also called volatile corrosion inhibitors (VCIs), are compounds that are transported in a closed system to the site of corrosion by volatilization from a source. In boilers, volatile basic compounds such as morpholine or octadecylamine are transported with steam to prevent corrosion in condenser tubes by neutralizing acidic carbon dioxide (Boles et al. 2009). Compounds of this type inhibit corrosion by making the environment alkaline. In closed vapor spaces, such as shipping containers, volatile solids such as the nitrite, carbonate, and benzoate salts of dicyclohexylamine, cyclohexylamine, and hexamethyleneimine are used. 

A schematic presentation of chemical reactions and steam transport of nitrogen species in a BWR primary system is shown in Fig. 4.1., demonstrating that the yields of the different products depend on the ambient conditions, i. e. on the redox potential of the aqueous system. Earlier measurements in a BWR with forward-... 

Law, R. J., Indig, M. E., Lin, C. C., Cowan, R. L. Suppression of radiolytic oxygen produced in a BWR by feedwater hydrogen addition. Proc. 3. BNES Conf Water Chemistry in Nuclear Reactor Systems, Bournemouth, UK, 1983, Vol. 2, p. 23-30 Lin, C. C. Chemical behaviour and distribution of volatile radionuclides in a BWR system with forward-pumped heater drains. Proc. 3. BNES Conf. Water Chemistry in Nuclear Reactor Systems, Bournemouth, UK, 1983, Vol. 1, p. 103—110 Lin, C. C. Chemical behaviour and steam transport of nitrogen-13 in BWR primary systems. 

Fission product noble gases entering the water-steam circuit in the event of a tube leak are completely volatilized and transported with the steam to the main condenser where they are extracted and released via the off-gas stack. This release is monitored by a continuously operating detector device located in the condenser off-gas line. Non-volatile fission and activation products which are transported over the leak to the water-steam circuit remain completely in the water phase of the steam generator by the action of the blowdown purification system their activity concentration is kept at a level which is controlled by the injection rate on the one hand and by the purification rate on the other. Because of the very low vapor pressures of these elements and their chemical compounds (dissolved ions or insoluble oxides/hydroxides), their transport to the steam under the prevailing conditions (270 °C, 7 MPa) is only possible by droplet entrainment. This means that partitioning between liquid and steam phases is proportional to the steam moisture content, which is usually well below 0.1%. 

According to experiments performed under appropriate conditions, about 1% of the fission product iodine present in the flashed primary coolant volume is transported with the steam phase, about half of it in form of aerosols (Aim and Dreyer, 1980). This figure agrees well with that reported by Morell et al. (1985) and Hellmann et al. (1991), obtained in flashing experiments from small-diameter pipes (see Section 6.2.2.). In the experiments of Aim and Dreyer (1980), which were carried out in an uncoated steel vessel, only particulate iodide and elemental h were detected in the atmosphere of the vessel. The rate of plate-out of iodine from the atmosphere was found to depend on the specific geometric conditions of the experimental setup. In a comparatively small vessel, deposition halftimes of 8.5 hours for h and of 0.9 hours for aerosol iodide were measured within the first two hours after blowdown these values increased to 9.9 and 5.7 hours, respectively, during the following 22 hours. From other experiments markedly different values have been reported (e. g. CSE tests, see Section 7.3.S.3.8.). The reasons for these differences are not only due to the dimensions and true surface areas present in the respective experimental facility, but also to various other parameters, such as initial concentrations, turbulences in the atmosphere, rate of water droplet plate-out and of steam condensation. 

Cubicciotti, D., Sehgal, B. R. Fission product and material transport during molten coreconcrete interactions. Proc. 5. Intemat. Meeting on Thermal Nuclear Reactor Safety, Karlsruhe 1984, Report KfK 3880/3, p. 1535-1553 Elrick, R. M., Sallach, R. A., Ouelette, A. L., Douglas, S. C. Boron carbide-steam reactions with cesium hydroxide and with cesium iodide at 1270 K in an Inconel-600 system. Report NUREG/CR-4963 (1987)... 

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