Wall Condensation Research Articles

ASTEC, COCOSYS, and LIRIC Interpretation of the Iodine Behavior in the Large-Scale THAI Test Iod-9

The large-scale iodine test Iod-9 of the German Thermal hydraulics, Hydrogen, Aerosols, Iodine (THAI) program was jointly interpreted by means of post-test analyses within the THAI Circle of the Severe Accident Research NETwork (SARNET)/Work Package 16. In this test, molecular iodine (I2) was injected into the vessel dome of the 60 m3 THAI vessel to observe the evolution of its distribution between water, gas, and surfaces. The main processes addressed in Iod-9 are (a) the mass transfer of I2 between the gas and the two sumps, (b) the iodine transport in the main sump when it is stratified and then mixed, and (c) the I2 adsorption onto, and desorption from, the vessel walls in the presence and absence of wall condensation. The codes applied by the THAI Circle partners were the Accident Source Term Evaluation Code (ASTEC)-IODE (IRSN, Saint Paul Lez Durance, France), Containment Code System (COCOSYS)-Advanced Iodine Model (AIM) (GRS, Garching, Germany), and Library of Iodine Reactions in Containment (LIRIC; AECL, Chalk River, ON, Canada). ASTEC-IODE and the Advanced Iodine Model (AIM) are semi-empirical iodine models integrated in the lumped-parameter codes ASTEC and COCOSYS, respectively. With both codes multicompartment iodine calculations can be performed. LIRIC is a mechanistic iodine model for single stand-alone calculations. The simulation results are compared with each other and with the experimental measurements. Special issues that were encountered during this work were studied in more details: I2 diffusion in the sump water, I2 reaction with the steel of the vessel wall in gaseous and aqueous phases, and I2 mass transfer from the gas to the sump. Iodine transport and behavior in THAI test Iod-9 are fairly well simulated by ASTEC-IODE, COCOSYS-AIM, and LIRIC in post-test calculations. The measured iodine behavior is well understood and all measured data are found to be consistent. The very slow iodine transport within the stratified main sump was simulated with COCOSYS only, in a qualitative way. Consequently, this work highlighted the need to improve modeling of (a) the wet iodine adsorption and the washdown from the walls, (b) the I2 mass transfer between gas and sump, and (c) the I2/steel reaction in the gaseous and aqueous phases. In any case, the analysis of the large-scale iodine test Iod-9 has been an important validation step for the codes applied.

The Influence of Wall Heat Transfer, Friction, and Condensation on Detonation Tube Performance

The authors investigated the influence of heat transfer, friction, and condensation on the performance of a single-pulse detonation tube using a combination of numerical analysis and experiments. Several different 1-D modeling strategies were considered for quantitatively predicting wall heat loss and shear stress. The merits of each approach were evaluated using benchmark results from an axisymmetric, reacting Navier-Stokes model in which the wall losses are directly resolved for a low-pressure (P 1 = 6.67 kPa) model problem. These benchmark results represent the first known attempt at directly modeling wall heat transfer and shear stress behind a multidimensional detonation wave. Comparison of the 1-D models to the benchmark results reveals a Reynolds analogy approach with a constant friction coefficient can be used to simultaneously predict convective heat loss and shear stress at the walls. The 1-D models are extended for use at higher pressure (P 1 = 1 atm) via calibration with experimental heat flux data. Although the magnitude of the wall losses increases at higher initial pressure, the relative influence of these losses on performance diminishes. To rigorously test the developed 1-D models, thrust-wall pressure measurements are recorded for stoichiometric C2H4-O2 detonations in 1.6 m long tubes with 8, 16, and 32 mm diameters. Unheated (293 K) tube wall experiments result in pressure traces showing large deviations from ideal theory. Comparison of measurements with the 1-D wall loss models reveals heat transfer and friction alone are not sufficient to reconcile theory with experiment. Additional experiments are conducted with heated (376 K) tube walls to test whether condensation of water vapor on the facility walls might account for the additional disparity between theory and measurement. Pressure traces from the heated wall experiments start closer to theory at early times and produce 66%, 31%, and 12% more specific impulse (I sp ) than the corresponding cold wall experiments for the 8, 16, and 32 mm diameter tubes, respectively. An approximate condensation model is developed and incorporated into the existing 1-D heat loss and shear stress model. It is shown for the first time that condensation can be the dominant wall loss mechanism leading to substantial performance decrement in large L/D detonation tubes.

OECD International Standard Problem ISP-47 on containment thermal-hydraulics—Conclusions of the TOSQAN part

The main objective of the ISP-47 is to assess the capabilities of Lumped-Parameter and Computational Fluid Dynamics codes in the area of nuclear containment thermal-hydraulics. Three experimental facilities TOSQAN, MISTRA and ThAI were involved in this project. The present paper summarizes the specifications, the results and the conclusions obtained for the TOSQAN open benchmark exercise. Wall condensation, steam injection in air or air/helium atmospheres, and buoyancy were addressed under well-controlled initial conditions in the simple TOSQAN geometry. Detailed gas velocity and gas concentration (air, steam and helium) fields were obtained for the first time in such an exercise. It is found that the model predictions fit with a generally good accuracy the experimental results obtained during condensation steady-state conditions, but the flow conditions in the transition regime are not well reproduced by the calculations: some of the major transient phenomena are not always correctly modelled and if so, the transient evolutions or the levels of the concerned variables are not the same in the calculations and in the experiment. Furthermore, two kinds of measurements were specific for TOSQAN: boundary layer measurements and turbulence variables, which were addressed for the first time in such an exercise. It is concluded that more sophisticated modelling in CFD codes for the boundary layers should be developed and that turbulence variables should be addressed more intensively in further exercises.

Simulation of containment jet flows including condensation

The validation of a CFD code for light-water reactor containment applications requires among others the presence of steam in the different flow types like jets or buoyant plumes and leads to the need to simulate condensation phenomena. In this context the paper addresses the simulation of two “HYJET” experiments from the former Battelle Model Containment by the CFD code CFX. These experiments involve jet releases into the multi-compartment geometry of the test facility accompanied by condensation of steam at walls and in the bulk gas. In both experiments mixtures of helium and steam are injected. Helium is used to simulate hydrogen. One experiment represents a fast jet whereas in the second test a slow release of helium and steam is investigated. CFX was earlier extended by bulk and wall condensation models and is able to model all relevant phenomena observed during the experiments. The paper focuses on the simulation of the two experiments employing an identical model set-up. This provides together with other validation exercises the information on how well a wider range of flowing conditions in a full containment simulation can be covered with a single set of models (e.g. turbulence and condensation model). Some aspects related to numerical and modelling uncertainties of CFD calculations are included in the paper by investigating different turbulence models together with the modelling errors of the differencing schemes applied.

Analytical and Experimental Analysis of a High Temperature Mercury Thermosyphon

High temperature thermosyphons are devices designed to operate at temperatures above 400°C. They can be applied in many industrial applications, including heat recovery from high temperature air fluxes. After a short literature review, which shows a deficiency of models for liquid metal thermosyphons, an analytical model, developed to predict the temperature distribution and the overall thermal resistance, is shown. In this model, the thermosyphon is divided into seven regions: three regions for the condensed liquid, including the condenser, adiabatic region, and evaporator; one region for vapor; one for the liquid pool; one for the noncondensable gases; and another for the tube wall. The condensation phenomenon is modeled according to the Nusselt theory for condensation in vertical walls. Numerical methods are used to solve the resulting equations and to determine the temperature distribution in the tube wall. Ideal gas law is applied for the noncondensable gases inside the thermosyphon, while the evaporator and condenser heat transfer coefficients are obtained from literature correlations. Experimental tests are conducted for thermosyphon with mercury as working fluid, designed and constructed in the laboratory. The results for two thermosyphons with different geometry configurations are tested: one made of a finned tube in the condenser region and another of a smooth tube. The finned tube presents lower wall temperature levels when compared with the smooth tube. The experimental data are compared with the proposed model for two different liquid pool heat transfer coefficients. It is observed that the comparison between the experimental data and theoretical temperature profiles is good for the condenser region. For the evaporator, where two distinct regions are observed (liquid film and pool), the comparison is not so good, independent of the heat transfer coefficient used. In a general sense, the model has proved to be a useful tool for the design of liquid metal thermosyphons.

The IRIS pressurizer: Simulation of out-surge transients and optimization procedure to design scaled experiments

Numeric models of the IRIS reactor pressurizer having either two or three volumes were employed to simulate a typical out-surge transient. The vapor volume may contain liquid drops. Vapor bubbles can be generated in the liquid volume. The mass, the energy, the constitutive, and the state equations, represent all relevant phenomena. A pressure equation is derived by the substitution of the mass and energy equations onto the pressurizer volume constraint, assuming that the instantaneous pressure is the same in all volumes. The pressurizer experimental data of a loss of load transient in the Shippingport reactor are used to validate these pressurizer models. These models are also employed to verify the capacity of the thermal power controller to restore the pressure in the IRIS out-surge transient. The preliminary validation, using the Shippingport experimental data, and the close agreement reached by all the developed software, for the IRIS out-surge transient, recommends further validation of these models for the test evaluation and the design of scaled experiments for the IRIS pressurizer. The proper choice of the pressure number was employed to obtain the best form of the non-dimensional conservation equations for a two-volume pressurizer. This form and the non-dimensional constitutive models, define the similarity numbers of scaled systems similar to the IRIS reactor pressurizer. The similarity numbers represent the scaled transport of mass and energy, and of the local rainout, flashing, and wall condensation mass and energy transport. The genetic algorithm (GA) search variables of scaled models are the geometric sizes, the surge mass flow rate, and the heater power needed to control the pressure. The similarity numbers are used to define a “fitness function” to evaluate the quality of the defined variables. The operation of the systems is verified using a two-volume transient model to simulate a typical out-surge transient. The agreement of the non-dimensional pressure as the model pressure increases, and the good agreement of the non-dimensional volumes of different scaled systems recommends this non-dimensional formalism, the GA optimization, and the numeric simulation of a surge transient, to design scaled experiments for modeling the IRIS pressurizer.

Particulate Emission Reduction in Small-Scale Biomass Combustion Plants by a Condensing Heat Exchanger

Use of biomass fuels for energy purposes has gained increasing importance as a method to reduce greenhouse gas emissions. In comparison to gaseous and liquid fossil fuels, the emissions of particulate matter are higher, leading to concerns about the availability of cost-effective techniques to reduce aerosol emissions in small-scale biomass combustion plants. In this work, the applicability of reducing aerosol emissions by stimulating condensation of aerosol-forming vapors on the heat-exchanger furnaces is investigated. A first-order estimation indicates that the heat-exchanger passage has to be in the order of millimeters to obtain a higher wall condensation rate compared to heterogeneous condensation, a result verified with purpose-built heat exchangers connected to a grate furnace. The measurements show that heat exchangers with an equivalent tube diameter of approximately 2 mm can reduce the aerosol emissions by approximately 70% compared to conventional boiler designs.

Effect of hydrothermal treatment on the structure, stability and acidity of Al containing MCM-41 and MCM-48 synthesised at room temperature

The effect of hydrothermal treatment of the synthesis gel on the structure, hydrothermal and mechanical stabilities and acidity of MCM-41 and MCM-48 aluminosilicates synthesised at room temperature has been investigated by X-ray diffraction, nitrogen adsorption at 77 K and DRIFTS with pyridine as probe molecule. The influence of the Al content and pore size on the structure of the resulting treated Al-MCM-41 materials has also been studied. For all samples improvement of the structural ordering and increase of the pore size, was observed, with pore wall thickness remaining practically unchanged. For Al-MCM-48 an improvement of the pore size uniformity occurs during the treatment. Only a small loss of pore size uniformity occurred for Al-MCM-41 prepared with hexadecyltrimethylammonium bromide, but with samples prepared with tetra and octadecyltrimethylammonium bromide the treatment generated a bimodal pore size distribution. The pore volume increased (17%) in the case of Al-MCM-48 but decreased (5.5–14%) for Al-MCM-41, suggesting a decrease in surface roughness resulting from increase of the degree of condensation of the pore walls. Both treated and untreated samples presented relatively strong Brønsted sites and increase of the Lewis acidity was found to occur upon treatment. Treated samples were found to be more resistant to refluxing in boiling water and mechanical compaction, which was attributed to more polymerised pore walls, with Al-MCM-41 samples tested demonstrating higher stability than Al-MCM-48. However, the differences in stability of samples prepared with or without hydrothermal treatment were not significant. Both treated and untreated samples presented high hydrothermal stability. Although refluxing in boiling water lead to some loss of structural ordering, only a small decrease of pore volume (3–5.5% for Al-MCM-41 and 8-14% for Al-MCM-48) occurred, with practically no alterations in pore size and wall thickness. Ordered mesopore structure, with narrower pores and thicker walls, was still observed after compression at 590 MPa for most of the samples tested.

International standard problem on containment thermal–hydraulics ISP47: Step 1—Results from the MISTRA exercise

The understanding of hydrogen distribution during severe accidents in a nuclear reactor containment is still an open issue. Several containment thermal–hydraulics international standard problems (ISP) have been conducted to address this topic. However, the predictions made by the available lumped parameter or CFD computer codes were generally not satisfactory. Therefore, a new exercise was launched in 1999 using new state-of-the-art experimental facilities TOSQAN, MISTRA and ThAI that included sophisticated 3D instrumentation and well-controlled boundary conditions. Predictive capabilities of important and still uncertain phenomena such as wall condensation, natural circulation and gas stratification are assessed. In addition, comparison between lumped parameter (LP) and CFD codes and assessment of the capability of CFD codes to deal with scaling effects are performed. This article reports on the part of the exercise which concerns the MISTRA facility including experimental results and blind benchmark exercises.

Development of nonequilibrium pressurizer model with noncondensable gas

To investigate thermal–hydraulic characteristics of a steam–gas pressurizer in the integral type reactor, the steam–gas pressurizer model based on the two-region nonequilibrium concept was developed and introduced into RETRAN-3D/INT code. The model includes an explicit solution method for the one-dimensional governing equations and the equation of the state solution method to determine the thermal–hydraulic state of the steam–gas pressurizer volume. In addition, the wall condensation model based on the diffusion layer modeling was included to consider the effect of the noncondensable gas. The developed model was verified with the results from the pressurizer insurge experiment conducted at Massachusetts Institute of Technology. From the verification results, it was concluded that the developed steam–gas pressurizer model can sufficiently predict the pressurizer transient and it can be used as a component model of the one-dimensional system code based on the homogeneous equilibrium model.

Gas centrifugation with wall condensation

Current large throughput gas cleaning processes are not able to deal with highly contaminated gas fields. Amine treatment is typically used for removing these contaminants — CO2 and H2S — from gas, but is not economic or practicable for highly contaminated gas, that is, where the concentrations of CO2 or H2S are above ca. 10 and 5%, respectively.1,2 Another major disadvantage is the low pressure at which waste gas is produced — compression is then required for waste disposal processes, such as reinjection. An alternative candidate process which has recently been evaluated is centrifugal gas separation.3 A gas centrifuge is basically a cylinder, filled with a gas mixture, and rotating at high speed. Due to the large centrifugal forces, the gas is pushed to the wall, resulting in a pressure gradient. Gases with different molecular weights have different partial pressure profiles and their mole fraction profiles vary with radius. In a methane/carbon dioxide mixture, the concentration of the CO2 increases near the wall by diffusion along the concentration gradient. We have shown experimentally that a purely gaseous process is too slow for practical application. Increasing the pressure is not that helpful for component separation in the gas phase, because to a first approximation the product of diffusion constant and pressure pD is constant that is, at high pressures the diffusion constant decreases.4 However, at the higher pressures generated in a centrifuge, there is a second much more dominant mechanism which will also cause separation — namely condensation due to the radial compression.5 This effect has some similar physical properties to what happens in the so-called evaporative centrifuge which has been previously analyzed for isotope separation, and which we have recently shown to be quite different from natural gas separation behavior in a centrifuge.6 In this study we examine whether condensation speeds up the separation process for a contaminated natural gas scenario. We identify two mechanisms for this condensation. A model is constructed which simulates the effect of condensation by centrifugal enrichment. The results of this model are compared to results of simulations of a gas/gas centrifuge. It is investigated in how far the concept of wall condensation leads to a significant increase of the separator performance in comparison with that of pure gas/gas separation by centrifugation.

A BUBBLE MECHANISTIC MODEL FOR SUBCOOLED BOILING FLOW PREDICTIONS

Population balance equations combined with a three-dimensional two-fluid model are employed to predict subcooled boiling flow at low pressure in a vertical annular channel. The MUSIG (Multiple-Size-Group) model implemented in CFX4.4 is extended to account for the wall nucleation and condensation in the subcooled boiling regime. Comparison of model predictions against local measurements is made for the void fraction, bubble Sauter diameter, interfacial area concentration, bubble population density, and gas and liquid velocities covering a range of different mass and heat fluxes and inlet subcooling temperatures. Good agreement is achieved with the local radial void fraction, bubble Sauter diameter, interfacial area concentration, bubble population density, and liquid velocity profiles against measurements. However, further improvement is needed for the accurate prediction of the vapor velocity using the present bubble mechanistic model. A proposal to include an algebraic slip model to account for bubble separation in the MUSIG boiling model is presented.

Aerosol nucleation and growth during laminar tube flow. II: quenching effects and wall condensation

Homogeneous nucleation during the flow of a vapour–gas mixture along a tube with cooled wall is considered in cases where nucleation is “self-quenching”, that is, vapour depletion by the condensational growth of previously nucleated particles is sufficient to reduce the vapour saturation to a level where nucleation is negligible. Approximate results are derived by matching the rate of rise of the nucleation rate, ignoring vapour depletion, to its rate of fall due to condensational growth alone. The nucleation rate when these two rates are equal is identified as its peak value J p, and 2 J p divided by the rate gives the number of particles nucleated. Agreement between this approximation and accurate numerical results for dibutyl phthalate vapour in Nitrogen is very good for the cases considered. For moderate inlet–wall temperature differences, particle production is roughly constant over much of the tube cross-section but falls near the wall. However, for large temperature differences, a peak in particle production occurs near the wall, due to the very rapid rate of change in conditions there. As the nucleation increases, the fraction of inflowing vapour condensing on the wall decreases and an approximate analytic formula for this fraction is presented. This formula is very accurate provided more than about 20% of the vapour condenses on the wall. For lower wall condensation fractions, the formula under predicts the aerosol mass, however these results ignore the effect of particle deposition. The influence of seed aerosol on quenching nucleation is considered and found to depend on whether significant particle production occurs near the wall. An estimate of deposition by thermophoresis suggests that it is negligible for moderate wall–inlet temperature differences, but important for high temperature differences where there is significant particle production and growth near the wall.

Enhancement of Physical Gas Absorption by utilizing Wall Condensation and Mist Formation

Enhancement of Physical Gas Absorption by utilizing Wall Condensation and Mist Formation

冷房時における夏型壁体内結露に関する研究 : その1 人工気候室における非定常結露実験

The aim of this paper focuses on explicating phenomena of concealed condensation in wood frame construction walls caused by the undesirable temperature rise due to sun burn. Two types of laboratory experiments were carried out to explicate these phenomena. One was a humidity response test for small specimens of porous material, the other was a wood frame wall model test in which specimens of wall were sandwiched between two test chambers, one representing a room and the other representing the outdoor environment simulated to standardized meteorological data for Tokyo. We conclude that concealed condensation was caused by desorption of moisture which porous materials contain and a vented wall can reduce these condensation. But this paper suggest that more study should be done on the prevention of concealed condensation too.

Heat transfer, condensation and fog formation in crossflow plastic heat exchangers

In this paper heat transfer of air-water-vapour mixtures in plastic crossflow heat exchangers is studied theoretically and experimentally. First, a model for heat transfer without condensation is derived, resulting in a set of classical differential equations. Subsequently, heat transfer with wall condensation and fog formation are considered in some detail. Separate attention is paid to the heat transfer and condensation of pure steam in the heat exchanger. Finally, the experiments performed are reported and the results compared with the models presented. From this comparison it can be learnt that the models are well able to predict the rate of heat transfer and phenomena such as condensation and fog formation.

Studies on ordered mesoporous materials III. Comparison of MCM-41 to mesoporous materials derived from kanemite

MCM-41 and mesoporous materials derived from kanemite are synthesized and characterized by X-ray powder diffraction (XRD), N 2 adsorption-desorption, cyclohexane and water physical adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analyses (TGA), Fourier transform infrared (FTIR) and 13C and 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Both preparations yield mesoporous materials with narrow-pore-size distributions and somewhat similar physicochemical properties. However, due to a higher degree of condensation in the silicate walls of the materials derived from kanemite, these samples have higher thermal and hydrothermal stability than MCM-41. Additionally, the mechanisms by which these two types of materials are formed are dramatically different.

Monitoring of gas-phase species in metalorganic vapor phase epitaxy by fiber-optics based Fourier transform infrared spectroscopy

Fiber-optics based Fourier transform infrared (FTIR) spectroscopy is demonstrated as a technique for remote in-situ monitoring of concentration levels of organometallic species in gas delivery lines to metalorganic vapor phase epitaxy (MOVPE) systems. The concentration measurements are based on infrared absorption at 2800–3000 cm -1 corresponding to C-H stretching vibrations in alkyl ligands. Trimethylgallium (TMG), trimethylindium (TMI), tertiary butyl phosphine (TBP), and tris-dimethylaminophosphine (DMAP) are used in sample monitoring studies. The detection limit varies with the number of C-H bonds from 0.05 Torr at room temperature for TMG and TMI, to 0.006 Torr for DMAP. The ability of the technique to detect chemical species, as well as to monitor concentration levels, is illustrated by the appearance of methane in turn-on transients of TMG and TMI bubblers that have been stored for a length of time. A mathematical analysis of turning on and off low from a bubbler containing an organometallic precursor is presented and used to identify wall condensation and chemical interactions for TMI and DMAP in gas delivery lines.

Thin Crystals of Urea Grown by Hot Wall Condensation Technique

Crystallization of thin crystals of urea by hot wall condensation technique is described. Powder X-ray diffraction (XRD) reveals that some decomposition of urea takes place during evaporation

An improved tangency condition for fog formation in cooler-condensers

In 1950 Johnstone et al. ( Ind. Engng Chem. 42, 2298–2302 (1950)) introduced the tangency condition to determine fog (or mist) formation in binary mixtures in cooled channels. In the present analysis it is demonstrated that their condition is erroneous and an improved equation is derived. The condition is based on the heat and diffusional mass transfer rates to a condenser wall, and the slope of the saturation line of the vapour component at the wall temperature. The transfer rates follow from a thorough analysis of the energy and diffusion equation in a stagnant film next to the wall (the classical ‘film model’ or ‘film theory’). The validity of the improved tangency condition is assessed against wall condensation experiments by Johnstone et al., concerning mixtures of nitrogen with vapours of water and n-butyl alcohol, yielding satisfactory agreement.