Showing papers on "Air entrainment published in 1990"
TL;DR: The air entrainment of aerators on spillways is governed by a number of independent parameters, that include the sl... as discussed by the authors, which is used for aerodynamic protection against cavitational erosion.
Abstract: Aerators on spillways may be regarded as an effective protection against cavitational erosion. The air entrainment of aerators is governed by a number of independent parameters, that include the sl...
67 citations
TL;DR: In this paper, the effects of air entrainment and cavitation on the synchronous response of squeeze film supported rigid rotors were analyzed and the fluid film force coefficients were obtained from experimental measurements corresponding to a wide spectrum of operating conditions.
Abstract: This paper analyzes the effects of air entrainment and cavitation on the synchronous response of squeeze film supported rigid rotors. The fluid film force coefficients are obtained from experimental measurements corresponding to a wide spectrum of operating conditions. These conditions include regimes in which air entrainment effects are dominant. Other conditions where vapor cavitation and fluid inertial effects are dominant are included for comparison. The effects of air entrainment are shown to produce a nonlinear response representative of a softening spring effect not previously known to exist in squeeze film dampers.
39 citations
Patent•
09 Mar 1990
TL;DR: In this paper, a hydraulic air compressor is used as a compressed air source for a turbine, and several different structures for negating a loss of water velocity are also disclosed, and different turbine systems are disclosed.
Abstract: Hydraulic air compressor and turbine apparatus includes a hydraulic air compressor having an air intake disposed above the water intake for entraining air in falling water, and the output of the hydraulic air compressor is used as a compressed air source for a turbine. The turbine apparatus includes a regenerator for heating the incoming compressed air output from the hydraulic air compressor. The hydraulic air compressor may include a pump for providing a flow of water for entraining and compressing air to provide a closed cycle system, and it may include an air pump or fan to increase the amount of air entrained in a given flow of water. Several different structures for negating a loss of water velocity are also disclosed, and several different turbine systems are disclosed.
37 citations
TL;DR: In this paper, two formulas for the characteristic time of filling a void with the vapor of the surrounding liquid, and one of filling the void by diffusion of the dissolved gas in the liquid, are derived.
Abstract: Two formulas, one for the characteristic time of filling a void with the vapor of the surrounding liquid, and one of filling the void by diffusion of the dissolved gas in the liquid, are derived. By comparing these time scales with that of the dynamic operation of oil film bearings, it is concluded that the evaporation process is usually fast enough to fill the cavitation bubble with oil vapor; whereas the diffusion process is much too slow for the dissolved air to liberate itself and enter the cavitation bubble. These results imply that the formation of a two phase fluid in dynamically loaded bearings, as often reported in the literature, is caused by air entrainment. They further indicate a way to simplify the treatment of the dynamic problem of bubble evolution.
36 citations
27 citations
TL;DR: In this article, the authors show that cavitation damage can start at clear water velocities of between 12 to 15 m/s and can be prevented by streamlining the boundaries, improving the surface finishes or using resistant materials.
Abstract: Irregularities on spillway surfaces will, in a high speed flow, cause small areas of flow separation. In these regions the pressure will be lowered and, if the velocities are high enough, the pressure may fall to below the local vapor pressure of the water. Vapor bubbles will form and, when they are carried away downstream into high pressure region, the bubbles collapse and possible cavitation damage may occur. Experimental investigations (Volkart and Rutschmann (1984) show that the damage can start at clear water velocities of between 12 to 15 m/s. Up to velocities of 20 m/s the surfaces may be protected by streamlining the boundaries, improving the surface finishes or using resistant materials. When air is present in the water the resulting mixture is compressible and this damps the high pressure caused by the bubble collapses (Peterka (1953). Peterka, Russell and Sheehan (1974) performed experiments on concrete specimens and showed that air concentrations of 1-2 percent reduce substanA‚¬tially the cavitation erosion and above 5-7 per cent no erosion was observed. When there is not enough surface aeration (i.e., downstream of a gate) or if the tolerances of surface finish required to avoid cavitation are too severe (i.e., V > 30 m/s), air can be artificially introduced by aeration devices (called aerators) located on the spillway floor and sometimes on the side walls.
26 citations
Journal Article•
TL;DR: In this article, three different mechanisms for the air-pore instability of fresh concrete are described quantitatively, together with their effects on the concrete properties, especially the freeze/that resistance.
Abstract: Three different mechanisms for the air-pore instability of the fresh concrete are described quantitatively, together with their effects on the concrete properties-especially the freeze/that resistance: Loss of coarse air-bubbles due to handling and compaction. Dissolution of small bubbles in the water. Transfer of air from small bubbles to coarser bubbles
21 citations
TL;DR: In this paper, the effect of homogenous and heterogenous roughness on entrainment and dispersion rates was assessed by collecting experimental data in a boundary-layer wind tunnel point and area sources were simulated at a 1:100 model scale with homogenous surface roughness configurations ranging from flat grass land to an urban area.
17 citations
01 Jan 1990
TL;DR: An air entraining admixture is simply one that is added to either portland cement paste, mortar, or concrete for the purpose of entraining air in the respective masses as discussed by the authors.
Abstract: While the early history of the use of air entraining admixtures is ambiguous, the author has heard, but not read, that the early Romans and Greeks added them to their pozzolanic mixes to increase their workability. Probably blood or animal fat was used for this purpose. Before proceeding further with the evolution of this class of admixtures, it should be defined in acceptable and modern terms. An air entraining admixture is simply one that is added to either portland cement paste, mortar, or concrete for the purpose of entraining air in the respective masses . As you will read later in this chapter, the entrainment of air in concrete has a number of beneficial effects, when used properly, on certain of its properties. The most important of these is an increase in resistance to frost attack and to deterioration, due to exposure to repeated freezing and thawing.
15 citations
TL;DR: In this article, consistent and significant variations in the critical speeds of air entrainment with the angle were observed in a roll-coating system, in agreement with predictions made by Blake and Rushack.
Abstract: Consistent and significant variations in the critical speeds of air entrainment with the angle were observed in a roll-coating system. This is in agreement with predictions made by Blake and Rushack.
TL;DR: In the recent edition of the SFPE Handbook of Fire Protection Engineering, correlations for calculating air entrainment into pool and jet fires below the flame height have been developed as discussed by the authors.
Abstract: In the recent edition of the SFPE Handbook of Fire Protection Engineering1, correlations for calculating air entrainment into pool and jet fires below the flame height have been developed. An example for using these correlations is presented in this work, together with expressions for air entrainment above the flame tip which allow the determination of a virtual source origin for a pool fire.
Journal Article•
TL;DR: In this paper, the basic demands on the concrete for the platforms can be divided into three categories: Strength, Durability, Constructibility, and Constructibility for offshore exploitation of petroleum resources in the North Sea.
Abstract: High-strength concrete has been utilized for offshore exploitation of petroleum resources in the North Sea since 1973. The Norwegian concrete industry is preparing for the use of even higher concrete strengths in both onshore and off-shore work in the near future. The critical demands due to high strength, durability, and constructibility requirements, the magnitude of the structures, and the rate of construction have enforced the development of special cements and the use of pozzolans, hydraulically processed sand, and refined super-plasticizers and other chemical admixtures to achieve satisfactory concrete mix designs. The basic demands on the concrete for the platforms can be divided into three categories: Strength, Durability, Constructibility.
TL;DR: In this paper, a fiber optic probe is used to measure the distribution of air bubbles in fresh concrete during mixing, pouring, and placement of fresh concrete blocks, and the system has the ability to rapidly sample air content at different locations or depths in plastic concrete.
01 Nov 1990
TL;DR: In this paper, the authors developed and validated computer-based models to calculate the release properties in addition to simulating jet and plume behavior downwind of an accidental release of hydrogen fluoride.
Abstract: The thermodynamic behavior of hydrogen fluoride when diluted with air, particularly moist air, is very different from that of a simple ideal gas. The gas-air mixture can, depending on conditions, be denser than ambient air or substantially less dense than air. This behavior of an HF cloud would have a major influence on the dispersion behavior of HF in the atmosphere if it were released accidentally. For gases such as LNG thermodynamic effects must be included in dispersion models in order to accurately simulate such releases. Because of the unique thermodynamic properties of HF, it was felt that those properties would be important in accurately simulating an HF release. This program identified three major areas in which substantial uncertainties existed in previous models: (1) the modeling of the complex thermodynamics of HF/H{sub 2}O/Air mixtures (including aerosol effects on cloud density); (2) the treatment of a wide range of surface roughness conditions (including possible multiple surface roughness conditions) and (3) jet flow and air entrainment for pressurized releases of HF, followed by transition to ground-based dense gas dispersion. Major objectives of this study were to develop and validate computer-based models to calculate the release properties in addition to simulating jet and plume behavior downwind of an accidental release of HF. This report is the HGSYSTEM Program User's Manual.
01 Jan 1990
TL;DR: The concentration and temperature of air entrained into argon and helium plasma jets have been measured using coherent anti-Stokes Raman spectroscopy (CARS) in this article, where the entrainment process in this case is controlled by molecular diffusion rather than turbulent mixing.
Abstract: The concentration and temperature of air entrained into argon and helium plasma jets has been measured using coherent anti-Stokes Raman spectroscopy (CARS). The argon plasma flow field is characterized by a short region of well behaved laminar flow near the nozzle exit followed by an abrupt transition to turbulence. Once the transition of turbulence occurs, air is rapidly mixed into the jet core. The location of the transition region is determined by the rapid cooling of the jet and the resulting increase in Reynolds number. In contrast, the helium plasma flow field never exceeds a Reynolds number of 200 and remains laminar. The entrainment process in this case is controlled by molecular diffusion rather than turbulent mixing. 9 refs., 5 figs., 1 tab.
01 Sep 1990
TL;DR: In this paper, the authors evaluated the performance of RCC pavement mixtures using various dosage rates and aggregate gradings to evaluate frost resistance and investigate material, construction, and site conditions which might influence the frost resistance.
Abstract: : Roller-compacted concrete (RCC) pavement use a paving technique in which a zero-slump portland cement concrete mixture is placed using asphalt concrete pavers and compacted with vibratory and rubber-tired rollers. A reason for using RCC pavements is its durability in freezing and thawing conditions. Conventional concrete pavements are air-entrained for protection in freezing and thawing conditions. However, attempts to air-entrain RCC mixtures have met with little success. Nonair-entrained RCC has performed well in freezing and thawing field conditions in the past, but laboratory samples have demonstrated poor frost resistance. Objectives of this study are: (a) to determine if a proper air-void system can be entrained in RCC pavement mixtures using various dosage rates and aggregate gradings, and (b) to evaluate frost resistance and investigate material, construction, and site conditions which might influence the frost resistance. Results of the study demonstrated that various RCC mixtures may be entrained with air voids sufficient to protect the concrete from frost damage. RCC may also be effectively air-entrained in field applications. Studies of selected sites have shown that nonair-entrained RCC pavements have performed well in freezing and thawing climates. Keywords: Air entrainment/voids; Pavements/frost heave; Frost/resistance; Aircraft/parking facilities; Concrete/mixtures; Construction materials. (MM)
01 Nov 1990
TL;DR: In this paper, the authors developed and validated computer-based models to calculate the release properties in addition to simulating jet and more generally plume behavior downwind of an accidental release of hydrogen fluoride.
Abstract: The thermodynamic behavior of hydrogen fluoride when diluted with air, particularly moist air, is very different from that of a simple ideal gas. The gas-air mixture can, depending on conditions, be denser than ambient air or substantially less dense than air. This behavior of an HF cloud would have a major influence on the dispersion behavior of HF in the atmosphere if it were released accidentally. For gases such as LNG thermodynamic effects must be included in dispersion models in order to accurately simulate such releases. Because of the unique thermodynamic properties of HF, it was felt that those properties would be important in accurately simulating an HF release. This program identified three major areas in which substantial uncertainties existed in previous models: (1) the modeling of the complex thermodynamics of HF/H{sub 2}O/Air mixtures (including aerosol effects on cloud density); (2) the treatment of a wide range of surface roughness conditions (including possible multiple surface roughness conditions) and (3) jet flow and air entrainment for pressurized releases of HF, followed by transition to ground-based dense gas dispersion. Major objectives of this study were to develop and validate computer-based models to calculate the release properties in addition to simulating jet andmore » plume behavior downwind of an accidental release of HF. This report is the HGSYSTEM Program User`s Manual.« less
01 Nov 1990
TL;DR: In this article, the authors developed and validated computer-based models to calculate the release properties in addition to simulating jet and more generally plume behavior downwind of an accidental release of hydrogen fluoride.
Abstract: The thermodynamic behavior of hydrogen fluoride when diluted with air, particularly moist air, is very different from that of a simple ideal gas. The gas-air mixture can, depending on conditions, be denser than ambient air or substantially less dense than air. This behavior of an HF cloud would have a major influence on the dispersion behavior of HF in the atmosphere if it were released accidentally. For gases such as LNG thermodynamic effects must be included in dispersion models in order to accurately simulate such releases. Because of the unique thermodynamic properties of HF, it was felt that those properties would be important in accurately simulating an HF release. This program identified three major areas in which substantial uncertainties existed in previous models: (1) the modeling of the complex thermodynamics of HF/H{sub 2}O/Air mixtures (including aerosol effects on cloud density); (2) the treatment of a wide range of surface roughness conditions (including possible multiple surface roughness conditions) and (3) jet flow and air entrainment for pressurized releases of HF, followed by transition to ground-based dense gas dispersion. Major objectives of this study were to develop and validate computer-based models to calculate the release properties in addition to simulating jet andmore » plume behavior downwind of an accidental release of HF.« less
TL;DR: In this paper, the concentration and temperature of air entrained into an argon plasma jet have been measured using coherent anti-Stokes Raman spectroscopy (CARS) and the flow field is characterized by a short region of well behaved laminar flow near the nozzle exit followed by an abrupt transition to turbulence.
Abstract: The concentration and temperature of air entrained into an argon plasma jet has been measured using coherent anti-Stokes Raman spectroscopy (CARS). The flow field is characterized by a short region of well behaved laminar flow near the nozzle exit followed by an abrupt transition to turbulence. Once the transition to turbulence occurs, air is rapidly entrained into the jet core. The location of the transition region is thought to be driven by the rapid cooling of the jet and the resulting increase in Reynolds number. 8 refs., 6 figs.
TL;DR: In this paper, an experimental program in which entrainment and movement of air bubbles within the voids of rubble-mound breakwater models were investigated is described, and the relative extent of aeration was a function of the type of breaking wave observed.
Abstract: An experimental program in which entrainment and movement of air bubbles within the voids of rubble‐mound breakwater models were investigated is described. Aeration was evaluated as a function of type of armor unit (stones, spheres, and cubes), breakwater slope, relative geometry of the structure, and type of core material. Aeration resulting from both external wave breaking and flow separation was observed. The relative extent of aeration was a function of the type of breaking wave observed. Aeration was more severe in structures constructed with highly permeable cores. Variations in void geometry and orientation had a significant influence on the motion of air bubbles into the structure.
TL;DR: In this article, the influence of CaCl2 or a chloride-based accelerating admixture on the freeze-thaw resistance of concrete was evaluated using ASTM C666-84, Stan...
Abstract: The influence of CaCl2 or a chloride-based accelerating admixture on the freeze–thaw resistance of concrete was evaluated. Three air entrained mix designs were investigated using ASTM C666-84, Stan...
01 Jan 1990
TL;DR: In this paper, the effectiveness of calcium nitrite in concrete has been evaluated and shown that it can be further improved with the use of the proper concrete mix designs and concrete cover.
Abstract: Extensive testing shows that calcium nitrite is an effective corrosion inhibitor for steel in concrete. Furthermore, in most cases, calcium nitrite improves the compressive strength of the concrete mix, and with proper air entrainment is freeze-thaw durable. In this paper data is presented documenting the effectiveness of calcium nitrite, and it shows how corrosion performance can be further improved with the use of the proper concrete mix designs and concrete cover. (Author/TRRL)
01 Jan 1990
TL;DR: In this article, the authors investigated the air entraining admixtures for concrete and found that air contents significantly exceeded target air contents; traditional methods of measuring air content could not be relied upon; low compressive strength; and large variations between the measured air content of fresh concrete and that of the hardened concrete.
Abstract: In the past decade, several new air entraining admixtures for concrete have been introduced. With increasing use of these products, some field problems have been reported. Specifically, it has been reported that: air contents significantly exceeded target air contents; traditional methods of measuring air content could not be relied upon; low compressive strength; and large variations between the measured air content of fresh concrete and that of the hardened concrete. To investigate the reported problems, a testing program was initiated. Parameters investigated include the variation of air content with mixing time, the variation of strength versus mixing time and the degree of agreement between plastic air content and the air content of hardened concrete. (Author/TRRL)
Journal Article•
TL;DR: In this article, a system is described which, when installed in a large commercial ready-mix plant and fed with normal concrete and aggregate test data, integrates this with actual batch proportion data to show the interaction of such factors as strength, slump/workability, sandiness/cohesion, entrained air content, setting time, and aggregate characteristics, cement quality, concrete temperature, batch proportions, and admixture dosage.
Abstract: A system is described which, when installed in a large commercial ready-mix plant and fed with normal concrete and aggregate test data, integrates this with actual batch proportion data to show the interaction of such factors as strength, slump/workability, sandiness/cohesion, entrained air content, setting time, and aggregate characteristics, cement quality, concrete temperature, batch proportions, and admixture dosage. The system has the ability to automatically compensate for all variations advised or detected.
01 Jan 1990
TL;DR: In this paper, the authors investigated the nature of these problems and concluded that the problems derive from two related variables Variation of the level and nature of the carbon from source to source has been identified as a significant problem, which may be insurmountable where large variations of carbon content occur or where uncontrolled changes in source of ash are made.
Abstract: It is a well established fact that entraining air into concretes containing certain pulverised fuel ashes can present technical problems Published work has demonstrated that the most likely cause of these problems relates to the presence of small quantities of residual carbon resulting from the combustion of the pulverised fuel This paper has further investigated the nature of these problems and concluded that the problems derive from two related variables Variation of the level and nature of the carbon from source to source has been identified as a significant problem This problem may be insurmountable where large variations of carbon content occur or where uncontrolled changes in source of ash are made A second problem has been identified as being related to the destablilisation of the air after it has been entrained This variable has been investigated and probably relates to the adsorption of either surfactant or the air voids themselves onto the highly active surface of the carbon particles Novel air entraining agents have been developed which overcome this second, de-stabilising problem These air entraining agents contain deliberate additions of polar species which are preferentially adsorbed onto the carbon surface, satisfying this activity, leaving the surfactant free to fulfil its prime role Data is presented relating to the performance of such air entraining agents with various commonly available United Kingdom pulverised fuel ashes (Author/TRRL)