Mixture Of Steam Research Articles

Chemical variations in hydrothermal minerals of the Los Humeros geothermal system, Mexico

The Los Humeros geothermal system is composed of more than 2200 m of Quaternary altered volcanic rocks and an underlying Cretaceous sedimentary sequence. The low salinity of the fluids discharged at present (Na + and Cl − concentrations <500 ppm), and the excess steam, indicate that the reservoir contains a mixture of steam and dilute groundwater. Water-rock equilibrium is not attained. Hydrothermal minerals are present in veinlets, vugs, and replacing primary minerals. Three mineral zones are recognized: 1) a shallow argillic zone (<400 m depth), 2) a propylitic zone (ranging between 500 and 1800 m) and 3) a skarn zone (>1800 m). Petrographic examination of cuttings from five wells and temperature data indicate at least two stages of hydrothermal activity. Temperature is the main factor that affects the chemical composition of chlorite, epidote and biotite. Fe 2+ and Al IV increase in chlorite with temperature [from 1.4 formula position unit (fpu) to 2.8, and from 0.7 to 2.4 fpu, respectively]. The pistacite content of epidote varies from 18 to 33 mol% in high-temperature regions (>270 °C) and from 13 to 26 mol% in low-temperature regions (<250 °C). Biotite displays a slight increase in Al IV contents (1.55–2.8) and octahedral occupancy (5.93–6.0 fpu) with temperature. Whole rock composition and variations in oxygen fugacity conditions are factors that also affect the concentrations of Fe, Al and Mg in the octahedral sites of chlorite, epidote, biotite and amphiboles. Chemical variations observed in alteration minerals at different depths in the Colapso Central-Xalapazco region could be used as indicators of relict physico-chemical conditions in the reservoir, before the present economic exploitation.

Thermodynamics of Geysers: Application to Titan

General constraints on geyser phenomena are developed and applied to speculative methane geysers on Titan. Variation of boiling point with depth of ethane–methane–nitrogen fluids is found to be of order 0.3 K m −1, in contrast with around 2 K m −1 for water on Earth. It is found that geysers are possible on Titan but require enhancements of ∼100 above global-average geothermal heat flux, a factor similar to that required on Earth. Eruption velocities of order 25 m s −1 appear to be typical for 10-m-deep geyser vents on both Earth and Titan. While eruption velocities on Earth are usually limited by the low sound speed in water–steam mixtures, sound speeds in Titan fluids are higher and the Titan limit is imposed by the available energy in the boiling fluid. Eruption intervals should be nearly the same for geysers with equivalent plumbing. There is an interesting symmetry between geysers on Titan and those on Earth: The volatility of the relevant fluid scales with the available heat flow.

D233 空気あるいは CO_2 を多量に含む水蒸気の水平円管上への体積力対流凝縮

D233 空気あるいは CO_2 を多量に含む水蒸気の水平円管上への体積力対流凝縮

D232 空気を多量に含む水蒸気の水平円管上への強制対流凝縮

D232 空気を多量に含む水蒸気の水平円管上への強制対流凝縮

Thermochemical treatment of biomass in a flow of steam or in a mixture of steam and carbon dioxide

Thermochemical treatment of biomass in a flow of steam or in a mixture of steam and carbon dioxide

TEPSS–Technology enhancement for passive safety systems

The objective of the technology enhancement for passive safety systems (TEPSS) project TEPSS Final Report, INNO-TEPSS(99)-D21 (1999)) was to make significant additions to the technology base of the European simplified boiling water reactor (ESBWR). The project focused on mixing and stratification phenomena in large water pools, passive decay heat removal from containments, and effects of aerosol deposition inside a passive heat exchanger. The Paul Scherrer Institut (PSI) experimental facility—large-scale investigation of natural circulation and mixing—has been used to investigate venting of steam and steam/non-condensable gas mixtures into water pools. The test revealed that no significant steam bypass could be detected when injecting a mixture of steam or air and that mixing was very efficient. In addition to the tests, 3-D numerical computations and initial model development have been performed to study the behaviour of bubble plumes in water pools. The major part of the TEPSS project studied selective aspects of the response technology of modern pressure-suppression-type containment designs and of passive-type decay heat removal systems. The work included an experimental phase using the large-scale experimental facility—Passive Nachwarmeabbführ und DrückAbbau (PANDA), operated by PSI, where eight experiments successfully have been executed to test the performance of the ESBWR containment configuration. The PANDA tests have been analysed successfully using thermal–hydraulic system analysis codes and 3-D CFD codes. The aerosol impaction and deposition analysis experimental facility of PSI has been used to investigate the degradation of passive decay heat removal due to fission product aerosols deposited on the inside surfaces of the passive containment cooler (PCC) heat exchanger tubes. One test performed revealed that the degradation of the heat transfer in the PCC tubes due to the deposition of aerosols reached about 20%. The test has been analysed using the MELCOR severe accident analysis code.

Removal of NAPLs from the unsaturated zone using steam: prevention of downward migration by injecting mixtures of steam and air

Steam injection for remediation of porous media contaminated by nonaqueous phase liquids has been shown to be a potentially efficient technology. There is, however, concern that the technique may lead to downward migration of separate phase contaminant. In this work, a modification of the steam injection technology is presented, where a mixture of steam and air was injected. In two-dimensional experiments with unsaturated porous medium contaminated with nonaqueous phase liquids, it was demonstrated how injection of pure steam lead to severe downward migration. Similar experiments, where steam and air were injected simultaneously, resulted in practically no downward migration and still rapid cleanup was achieved. The processes responsible for the prevention of downward migration when injecting steam–air mixtures were analyzed using a nonisothermal multiphase flow and transport model. Hereby, three mechanisms were identified and it was demonstrated how the effectiveness of these mechanisms depended on the air-to-steam mixing ratio.

Physicochemical and biological aspects of Nitinol as a biomaterial

The rapid increase in the development of medical devices using nearly equiatomic Ni–Ti alloys (Nitinol) provides evidence of their advantages as biomaterials. Two generic properties of Nitinol, thermally induced shape recovery and superelasticity, are successfully employed for medical uses. However, several aspects of the alloys' short and long term efficacy have yet to be comprehensively determined, especially parameters relating to surface and corrosion performance. The present review surveys studies carried out internationally over about the past 10 years aiming at an improved understanding of Nitinol's surface, corrosion, and biocompatibility features. A critical survey is given of the surface condition of alloys modified using various advanced techniques, oxidised in air–water–steam mixtures, and passivated using chemical–electrochemical procedures. Surface parameters and their importance to the improvement of Nitinol's corrosion resistance and biological performance are discussed on the basis of XPS, Auger, SEM, and BSEM studies. In vivo and in vitro corrosion studies using potentiodynamic, potentiostatic, and scratch tests on as cast alloys, wire, and actual devices are surveyed. The effects of stress, strain, heat treatment, microstructure, precipitates, and alloy composition on corrosion are evaluated and compared with data for stainless steels, cobalt base alloys, and titanium. Release of nickel, observed in vitro and in vivo, is also surveyed. Biocompatibility aspects are briefly discussed with emphasis on their possible correlation with surface condition.

Assessment of the ATHENA Code for Calculating the Void Fraction of a Lead-Bismuth/Steam Mixture in Vertical Upflow

Lead-bismuth is currently being considered as a coolant for fast reactors designed to produce low-cost electricity as well as burn actinides. Lead-bismuth fluid properties have been added to the ATHENA code so that it can be used in the thermal-hydraulic analysis of lead-bismuth-cooled reactors. The capability of ATHENA to calculate the void fraction of a two-component, two-phase mixture of liquid lead-bismuth and steam in cocurrent upflow was assessed using the El-Boher and Lesin void correlation. The assessment showed that the drift flux correlations currently available in the code predicted trends that were in reasonable agreement with the El-Boher and Lesin void correlation, but the predicted void fractions were significantly too high. For example, the Kataoka-Ishii correlation, which was the best of the available correlations, predicted void fractions that were up to 30% greater than the values from the El-Boher and Lesin correlation. Consequently, the El-Boher and Lesin correlation was implemented in a modified version of ATHENA. The implementation was complicated by the fact that the El-Boher and Lesin correlation was an explicit correlation for void fraction rather than a drift flux correlation. An approach was developed so that the code’s basic drift flux formulation could be used to easily implement an explicit void correlation. The predictions of the modified code were in excellent agreement with the El-Boher and Lesin void correlation.

Sintering of Nickel Steam-Reforming Catalysts on MgAl2O4 Spinel Supports

Sintering significantly contributes to the deactivation of Ni-based steam-reforming catalysts. We have investigated the effect of Ni loading and surface area of the support on sintering of Ni particles on MgAl2O4 spinel supports. The experiments were performed under simulated industrial pre-reforming conditions, i.e., in a 10:1 mixture of steam and hydrogen at 500°C and 30 bar total pressure. The Ni particle size of fresh and sintered catalysts was determined from sulfur chemisorption capacity, X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). It was found that most of the sintering occurs in the first 200 h; after that period the Ni particle size changes only slightly. A remarkable result is that the average Ni particle size after sintering reaches a limiting value that depends only weakly on the Ni loading and surface area of the support. Sintering of the catalysts with a lower Ni loading is slower and they exhibit a greater loss in Ni surface area compared to those with a higher Ni loading. Because the sintered particles are polycrystalline agglomerates, the XRD estimates of particle size are lower than those obtained by the other techniques such as TEM or chemisorption. The particle size distributions derived from TEM and STEM follow a log normal distribution, suggesting that sintering occurs through crystallite migration and coalescence. The limiting size of the Ni particles after sintering, and the low sintering rate after 200 h, can both be related to the lower mobility of the larger Ni particles on the support.

Numerical and Experimental Study of Large Steam-Air Bubbles Injected in a Water Pool

In certain passive, future boiling water reactor concepts, during emergency cooling conditions, mixtures of steam and nitrogen are blown into a pool of water via a downward-facing open pipe; at its end, large gas bubbles form, break up, and rise in the water. We have developed a computer simulation program for the hydrodynamics of the process using an isothermal piecewise linear interface construction-volume of fluid method and carried out an experiment with flow rates up to 50 l/s into a tank of 1 m3 volume. Bubble frequencies and volumes can be predicted fairly well for the case of air injection. The experiments show that most of the condensation takes place before the bubble detaches from the pipe exit. The phenomena depend mainly on the volumetric flow rate of the gas and on a parameter measuring the shrinkage due to condensation. The rates of condensation were estimated to be very high.

Experimental research on the gravity-driven boron injection system for a 200 MW nuclear heating reactor

The gravity-driven boron injection system (GDBIS), designed by the Institute of Nuclear Energy Technology (INET) of the Tsinghua University, PR China, is a new type of passive system to be applied in the 200 MW nuclear heating reactor (NHR-200), also designed by INET. The function of this system is to shut down the reactor in an emergency, in case control rods do not operate properly. A borate water tank is located 10 m above the top of the pressure vessel. When the pressure of the reactor and the boron tank balances, the borate water will be driven by gravity to flow into the reactor, and thus shut down the reactor. The thermal hydraulic performances of the system for cold (room temperature nitrogen) and hot (mixture of hot steam and nitrogen) operating conditions, especially the response time of pressure and water injection, have been researched under different initial conditions. Firstly, several factors, e.g. orifice on steam lines, and the volume ratio of the gas–steam spaces of the reactor and the boron tank, have effects on the pressure and water injection response time and other thermal hydraulic performance of the system. Secondly, the steam and liquid communication modes, namely the acting time and sequence of the action of valves connecting steam and liquid lines, have great influences on the performance of the system. Thirdly, the limited pressure balance time (about 1.0 s) can be achieved under the cold condition. This investigation shows that GDBIS can be properly used in the 200 MW nuclear heating reactor.

Adjoint Sensitivity Analysis of the RELAP5/MOD3.2 Two-Fluid Thermal-Hydraulic Code System—II: Applications

This work presents results that illustrate the validation of the Adjoint Sensitivity Model (ASM-REL/TF) corresponding to the two-fluid model with noncondensable(s) used in RELAP5/MOD3.2. This validation has been carried out by using sample problems involving (a) a liquid phase only, (b) a gas phase only, and (c) a two-phase mixture (of water and steam). Thus, the “Two-Loops with Pumps” sample problem supplied with RELAP5/MOD3.2 has been used to verify the accuracy and stability of the numerical solution of the ASM-REL/TF when only the liquid phase is present. Furthermore, the “Edwards Pipe” sample problem, also supplied with RELAP5/MOD3.2, has been used to verify the accuracy and stability of the numerical solution of the ASM-REL/TF when both (i.e., liquid and gas) phases are present. In addition, the accuracy and stability have been verified of the numerical solution of the ASM-REL/TF when only the gas phase is present by using modified “Two-Loops with Pumps” and the “Edwards Pipe” sample problems in which the liquid- and two-phase fluids, respectively, were replaced with pure steam. The results obtained for these sample problems depict typical sensitivities of junction velocities and volume-averaged pressures to perturbations in initial conditions and indicate that the numerical solution of the ASM-REL/TF is as robust, stable, and accurate as the original RELAP5/MOD3.2 calculations.This work also illustrates the role that sensitivities of the thermodynamic properties of water play for sensitivity analysis of thermal-hydraulic codes for light water reactors. The well-known 1993 ASME Steam Tables are used to present typical analytical and numerical results for sensitivities of the thermodynamic properties of water to the numerical parameters that appear in the mathematical formulation of these properties. Particularly highlighted are the very large sensitivities displayed by the specific isobaric fluid and gas heat capacities Cpf and Cpg, respectively; the specific fluid enthalpy hf; the specific gas volume Vg; the volumetric expansion coefficient for gas βg; and the isothermal coefficient for gas kg. The dependence of βg and kg on the most sensitive parameters turns out to be nonlinear, while the dependence of Cpf, Cpg, hf, and Vg on the most sensitive parameters turns out to be linear, so the respective sensitivities predict exactly the effects of variations in the respective parameters. On the other hand, the sensitivities of the specific fluid volume Vf, the volumetric expansion coefficient for fluid βf, the specific gas enthalpy hg, and the isothermal coefficient of compressibility for fluid kf to the parameters that appear in their respective mathematical formulas are quite small. Finally, it is noted that such deterministically calculated sensitivities can be used to rank the respective parameters according to their importance, to assess the effects of nonlinearities and, more generally, to perform comprehensive sensitivity/uncertainty analyses of thermal-hydraulic codes that use a water substance as the working fluid.

Testing of the CuO/Al2O3 Catalyst−Sorbent in Extended Operation for the Simultaneous Removal of NOx and SO2 from Flue Gases

A series of CuO/Al2O3 catalyst−sorbents have been subjected to a large number of reaction−regeneration cycles and their physical and chemical properties compared before and after operation. The reaction phase of the cycle involved exposing the catalyst−sorbents to a mixture of SO2, NO, NH3, O2, and steam at 350 °C, during which time NO conversion was always greater than 90% and the SO2 was converted into CuSO4. The regeneration phase involved reduction of CuSO4 to copper metal by CH4 at 500 °C, followed by oxidation in air at 450 °C. In some tests the reaction or regeneration conditions were made more severe in an attempt to accelerate deactivation. The SO2 sorption capacity of one sample, which had been subjected to 1525 cycles, was reduced by about 25%, but generally there was no significant change in reactivity. Small changes in physicochemical properties are interpreted in terms of redispersion of the supported copper phase.

Modeling condensation heat transfer on a horizontal finned tube in the presence of noncondensable gases

European designs for the next generation of nuclear reactors incorporate innovative passive systems in their containments to enhance heat removal by condensation under postulated accident conditions. These systems consist of several units of cross-flow finned tube bundles internally cooled with water. So far most of the studies that have been addressed to the issue of heat transfer onto finned surfaces under condensing conditions have involved refrigerants and pure vapor conditions. This study presents a model (HTCFIN) capable of predicting condensation of a cross-flow air–steam mixture onto a single horizontal finned tube. The comparison of HTCFIN predictions to the available databases shows its acceptable accuracy in a wide range of conditions and allows an interpretation of the influence of major variables acting on the scenario. As a consequence, HTCFIN model represents a step forward in the present theoretical capability to estimate heat transfer within containments of next generation of European reactors in the case of a hypothetical accident.

Fluidized-bed co-gasification of residual biomass/poor coal blends for fuel gas production

Experiments involving the co-gasification of residual biomass/poor coal blends and gasification of individual feedstocks used in the blends were performed in a bench scale, continuous fluidized-bed working at atmospheric pressure. Two types of blends were prepared, mixing pine chips (from Valcabadillo, Spain) with black coal, a low-grade coal from Escatrón, Spain, and Sabero coal, a refuse coal from Sabero, Spain, in the ratio range of 0/100–100/0. Experimental tests were carried out using as a gasification agent mixtures of air and steam with dew points of 74–85°C at gasification temperatures of 840–910°C and superficial fluidized gas velocities of 0.7–1.4 m/s. Feasibility studies were very positive, showing that blending effectively improved the performance of fluidized-bed co-gasification of the low-grade coal, and the possibility of converting the refuse coal to a low-Btu fuel gas. This study indicates that a blend ratio with no less than 20% pine chips for the low-grade coal and 40% pine chips for the refuse coal are the most appropriate. The dry product gas low heating value augments with increasing blend ratio from 3700 to 4560 kJ/N m 3 for pine chips/low-grade coal, and from 4000 to 4750 kJ/N m 3 for pine chips/refuse coal. Dry product gas yield rises with the increase of the blend ratio from 1.80 to 3.20 N m 3/kg (pine chips/low-grade coal), and from 0.75 to 1.75 N m 3/kg (pine chips/refuse coal), respectively. About 50% co-gasification process overall thermal efficiency can be achieved for the two types of blend.

00/01437 Thermochemical treatment of biomass in a flow of steam or in a mixture of steam and carbon dioxide

00/01437 Thermochemical treatment of biomass in a flow of steam or in a mixture of steam and carbon dioxide

Steam reforming of chlorocarbons: chlorinated aromatics

Effective dechlorination of chloroaromatics, such as C6H5Cl, 1,2-C6H4Cl2, 1,3-C6H4Cl2 and 1,2,4-C6H3Cl3, using catalytic steam reforming has been confirmed with laboratory experiments on nickel and platinum catalysts. Using a feed comprising a mixture of steam and chlorocarbon with a H2O/C ratio of 10, complete conversions (>0.99999) were obtained with GHSVs of less than 4–5×105h−1 for a 23wt.% Ni/CaAl2O4 catalyst and 1–2×105h−1 for a 0.5wt.% Pt/γ-Al2O3 catalyst in the temperature range 500–700°C. The reactions followed pseudo-first-order kinetics for these catalysts and chloroaromatics, and kinetic parameters obeyed a compensation effect that was statistically sound, with isokinetic temperatures of 596 and 650°C for Ni and Pt, respectively.Product distributions indicated two parallel catalytic reactions: steam reforming, leading to complete destruction of the aromatic ring and production of H2, CO, CO2, and HCl; and hydrogenolysis, giving less chlorinated aromatic intermediates, C6H6 and HCl. The aromatic intermediates further react by steam reforming. Platinum was found more selective towards C6H6 formation than Ni, with selectivity increasing at lower temperatures.Comparisons between C6H11Cl and C6H5Cl revealed that saturation of the ring increases the rate of overall dechlorination. Above 596°C for Ni and 650°C for Pt, reactivities increase for higher chlorine levels of the aromatic ring.

Experimental investigation on the pressure response characteristic of the gravity driven boron injection system / Experimentelle Untersuchung zur Druckantwortcharakteristik eines gravitationsgetriebenen Boreinspeisesystems

The gravity driven boron injection system (GDBIS), designed by the Institute of Nuclear Energy Technology (INET) of the Tsinghua University, PR China, is a new type of passive system to be applied in the 200 MW nuclear heating reactor also designed by INET, The purpose of this system is to shutdown the reactor in an emergency, in case the control rods do not operate properly, The pressure response time and the thermal hydraulic performance of the system have been investigated under different initial conditions. The research results for cold (room temperature nitrogen) and hot (mixture of hot steam and nitrogen) operating conditions are presented. Firstly several factors, e. g. the flow resistance character of the steam and liquid lines, and the volume ratio of the upper spaces of reactor and boron injection tank, affect the pressure response time and the thermal hydraulic performance of the system. Secondly, the steam and liquid communication modes, namely, the time and sequence of the action of valves connecting steam and liquid lines, have great influence on the performance of the system. Thirdly, the limited pressure balance time (about 1.5∼2.0 s) can be achieved under cold operating conditions. This investigation shows that GDBIS can be properly used in the 200 MW nuclear heating reactor.

Dropwise Condensation of Steam on a Small Tube Bundle at Turbine Condenser Conditions

Application of dropwise condensation to utility turbine condensers is investigated by comparing the thermal performance of dropwise and filmwise bundles at industrially relevant conditions. Steam and steam-air mixtures were condensed on bundles of in-line, titanium tubes. The row-by-row heat transfer coefficients are presented against bundle position. They show the expected behavior for filmwise condensation but demonstrate a different one for dropwise. In air-free steam, the dropwise heat transfer coefficients are much larger and do not vary significantly with bundle position. In air-steam mixtures the dropwise values decrease similarly to their filmwise equivalents. The findings are in accord with those found for other geometries. The findings indicate that significant reductions in condenser size can be obtained if permanent dropwise condensation can be produced at industrially relevant conditions.