Qualitative motion of a liquid in an accelerating gas stream

Experimental data are examined on the interaction of liquid drops with the gas stream in a Venturi scrubber, the most promising available equipment.     

Janus electrode with simultaneous management on gas and liquid transport for boosting oxygen reduction reaction

Nano Research - Oxygen reduction efficiency holds the key for renewable energy technologies including fuel cells and metal-air batteries, which involves coupling diffusion-reaction-conduction...     

Mass transfer in porous injection of an inert gas into a liquid

Measurements are reported on mass-transfer coefficients for a liquid containing a porous body through which an inert gas is injected. The data are compared with measurements on heat transfer on porous injection and on boiling.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 3, pp. 410–414, September, 1986.     

Long-term moisture transport in high performance concrete

Moisture is decisive for a large number of binding and transport processes in high performance concrete affecting the durability, shrinkage and performance in various environments. An experimental study on the moisture transport properties of 20 concrete mixes was made during seven years, with type of binder, additives and waterbinder ratio as parameters. An upside-down glass cup method was used to obtain the steady-state flow through concrete discs. The moisture diffusion coefficient decreases with a lower water-binder ratio, increasing amount of silica fume, especially when combined with fly ash and it continues to decrease also after four years for w/B lower than 0.40. The moisture diffusion coefficient is much less moisture dependent for HPC than for normal concrete, which means that steady-state moisture profiles through HPC structures will be almost linear. Long-term moisture profiles in submerged HPC will be affected by self-desiccation for a very long time because of the extremely small moisture flow.

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Résumé L'humidité a une influence prépondérante sur un grand nombre de processus d'interaction et de transport qui affectent de manière directe la durabilité, le retrait et le comportement des bétons à haute performance (BHP) soumis à différents types de conditions d'exposition. Une étude expérimentale sur les propriétés de transport d'humidité de 20 mélanges de béton a été effectuée durant une période de sept ans. Les variables étudiées concernaient le type de ciment et d'ajouts ainsi que le rapport eau/liant. Une procédure spéciale a été utilisée de manière à être en mesure de réaliser les essais de transfert d'humidité en régime permanent. Les résultats des essais indiquent que le coefficient de diffusion d'humidité diminue avec une réduction du rapport eau/liant, une augmentation de la teneur en fumée de silice, tout particulièrement lorsque celle-ci est utilisée avec des cendres volantes. Pour des bétons de rapports eau/liant inférieurs à 0,40, la réduction du coefficient d'humidité se poursuit toujours même après 4 ans d'hydration. Le coefficient de diffusion d'humidité des BHP semble être beaucoup moins sensible à la teneur en eau que celui des bétons ordinaires ce qui signifie que les profils d'humidité en régime permanent sont presque linéaires. Les profils d'humidité à long terme dans BHP submergés seront fortement affectés par l'autodessiccation.

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Editorial Note Prof. Lars-Olof Nilsson is a RILEM Senior Member. He participates in RILEM TC 178-TMC ‘Testing and modelling chloride penetration in concrete’.     

Transport of organic fluids through concrete

The absorption of fluids in concrete is influenced by various parameters such as the surface tension and dynamic viscosity of the fluid, and also the porosity, pore size distribution and the interconnection of the pores in concrete. In addition, chemical reactions between the penetrating fluid and concrete may occur, which affect the absorption behaviour. Chemical reactions can cause deviations from the square-root-of-time relation and a reduction of sorptivity. Both are observed if using water or ethylene glycol as testing fluids. The deviation from the square-root-of-time relation is caused by the dissolving of Ca(OH)₂ from the cement matrix by the absorbed fluid. In the case of water, the reduction of the sorptivity is due to rehydration and wetting expansion. If a fluid is being absorbed in concrete, the effective porosity is smaller than the available porosity. The greater the surface tension of the fluid, the greater the measured effective porosity. This can be explained by trapped air inside the pores, which cannot get out and is being compressed by the capillary pressure, either in dead-end pores or due to fingering of the penetrating fluid. Experimental results on sequential absorption of two different fluids in concrete can only be explained if a trapped pore volume is assumed.     

Statistical analysis of concrete transport properties

Results of a statistical analysis of transport properties measurements carried out on a number of concrete mixtures are presented. Migration and drying experiments were performed to evaluate the ionic diffusion coefficients and permeability of concrete mixtures. Seven concrete mixtures were tested. The mixtures were either batched under laboratory conditions or sampled from construction sites. For each mixture, approximately eighty concrete samples from a single batch were tested. Ionic diffusion coefficients were calculated by analyzing the evolution of the electrical current passing through concrete samples during the migration tests. Calculations took into account the volume of permeable pores of the materials and the pore solution chemistry. Permeability was calculated from mass loss measured during drying tests. The study indicates that the coefficient of variation of ionic diffusion coefficients is 11.1 % on average, with a maximum of 23.5 %, and that the coefficient of variation of permeability is 20.6 % on average, with a maximum of 37.3 %.     

Features of heat transport in organic and cuprate superconductors

Thermal conductivity measurements in the cuprates have established two unusual and distinct features of quasi-particle transport in the superconducting state. Both these features (i.e. the abrupt increase in the relaxation time at the onset of superconductivity and a finite zero-energy transport due to presence of nodes in the superconducting gap) may also be present in – (ET) ₂ Cu(NCS) ₂ according to the first study of heat transport in this two-dimensional organic superconductor. In the case of optimally-doped Bi-2212, the modification of low-temperature thermal conductivity by the introduction of point defects was investigated. Results provide new information on the structure of low-energy electronic excitations of the superconducting state.     

Thermal imaging of hazardous organic fluids in concrete

Thermal imaging is a simple method by which it is possible to visualize volatile fluids in concrete specimens. For this purpose test specimens are split after being exposed to a volatile fluid, so that the fluid distribution at the split surface can be determined. This is possible because the region of the split surface which is saturated with the volatile fluid has a lower temperature than the dry region. The decrease in temperature in the fluid saturated region is caused by the evaporation of the fluid. A theoretical explanation of this phenomenon is given, and it may be used to calculate the fluid distribution provided that the temperature distribution at the split surface is known. It is also possible to predict the decrease in temperature, provided that the physical parameters of the concrete and fluid are known. The temperature distribution at the split surface is nearly constant with time. Therefore the fluid distribution can be observed over a certain period of time with high accuracy. The experimental investigations were carried out using water and different organic fluids in concrete with different moisture content.     

Electron transport in xenon-hydrogen gas mixtures

We present the results of numerical solution of the Boltzmann equation in a two-term approximation taking into account both elastic and inelastic electron collisions in Xe-H₂ gas mixtures. Using the obtained electron energy distribution functions, the electron transport properties (drift velocities, mobilities, mean and characteristic energies, diffusion coefficients) are calculated for the E/N parameter (the electric field strength to gas density ratio) ranging within several townsends. A similarity rule is derived for the properties of Xe-H₂ mixtures of various densities, which allows the electron transport coefficients to be determined for the mixtures with small (below 4%) hydrogen content.     

Nonlinear mass transfer between a gas and a falling liquid film. 3. Multicomponent mass transport

A solution is obtained for the problem of multicomponent mass transfer between a gas and a falling liquid film. The case is considered in which the mass transfer of one of the components is limited by the nonlinear mass transport in the gas phase. The rates of multicomponent mass transport in the gas and liquid phases are determined.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 59, No. 4, pp. 593–602, October, 1990.     

Test for gas permeablity of concrete

RILEM Technical CommitteesRILEM TC 116-PCD: Permeability of Concrete as a Criterion of its Durability Recommendations

Test for gas permeablity of concrete A. Preconditioning of concrete test specimens for the measurement of gas permeability and capillary absorption of water     

Simultaneous heat and moisture transport in porous building materials: evaluation of nonisothermal moisture transport properties

The paper presents a mathematical model for calculating the nonisothermal moisture transfer in porous building materials. The simultaneous heat and moisture transfer problem was modeled. Vapor content and temperature were chosen as principal driving potentials. The coupled equations were solved by a numerical method. An experimental methodology for determining the temperature gradient coefficient for building materials was also proposed. Both the moisture diffusion coefficient and the temperature gradient coefficient for building material were experimentally evaluated. Using the measured moisture transport coefficients, the temperature and vapor content distribution inside building materials were predicted by the new model. The results were compared with experimental data. A good agreement was obtained.     

Motion of gas bubbles in an infinite volume of stationary liquid in a gravitational field

The resisting forces, velocities, and shape parameters of gas bubbles rising in an infinite volume of liquid are found analytically.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 1, pp. 107–111, January, 1960.     

液体中包膜气泡的非线性振动特性

1引言 液体中气泡振动学是一个具有理论及实用意义的课题,以往已有很多研究,并取得了相当的进展[1-4].一般自由气泡在液体中容易溶解,而如在气泡外附加一粘弹材料表面层则可使气泡在液体中的稳定性大大提高.因此包膜气泡更具有实用价值,已作为超声造影剂获得重要应用.包膜气泡的应用研究已涉及气泡的线性散射,非线性二次谐波成像.近年来更出现次谐波成像的研究,Church推导了包膜气泡模型并给出了弱非线性情况下的逐级近似解[5].但是至今尚无用动力学方法分析包膜气泡非线性特性的相关工作.     

Moisture conditioning and transport properties of concrete test specimens

An experimental investigation is reported of drying and conditioning concrete at 50°C to obtain a uniform moisture distribution, prior to testing for air permeability and water absorption rate. The use of 100 mm cubes of concrete with a cast-in cylindrical cavity facilitated assessment of moisture distribution and measurement of air permeation through the surface layers of concrete: the moisture distribution was assessed by comparing the relative humidities measured within the cavity and at the surface of the test specimen. Partial drying followed by sealed storage at 50°C for a few days provided a rapid and convenient method of obtaining a uniform moisture distribution. The test results for a range of concretes indicated that air permeability and water absorption rate were very sensitive to the moisture content of the concrete, particularly at relative humidities above 60% and which were common for field exposure. The transport properties of the empty capillary pore system could be assessed using test specimens preconditioned at 60% relative humidity, but preconditioning at 85% relative humidity might be more appropriate for assessing field performance if there is a risk of carbonation induced corrosion.