Entrainment increase

In a recent publication, Gill et al. (G12) present results of new studies of film thickness and entrainment for upward annular flow of air and water at constant rates in a long, l -in. pipe. A porous inlet section for liquid was used, so that all entrainment arose from the annular film itself. These authors conclude that entrainment increases steadily along a tube, and arises from the continuous presence of film surface waves, so that a very long tube might be required to reach equilibrium (which might never occur if surface waves never disappeared). 

The commonly used ratios of admixture to cement for the purpose of shrinkage compensation are 9-11 (admixture) to 91-89 (cement). At these ratios the properties of CSA concrete are similar to Portland cement concretes of similar mix proportions. At admixture dosages exceeding 11% however, concrete workability and strength decrease, while expansion and air entrainment increase. When expansion is umestrained and exceeds 0.3%, strength is reduced [74]. 

Surfactants enable the polymer particles to disperse effectively without coagulation in the mortar and concrete. Thus, mechanical and chemical stabilities of latexes are improved with an increase in the content of the surfactants selected as stabilizers. An excess of surfactant, however, may have an adverse effect on the strength because of the reduced latex film strength, the delayed cement hydration and excess air entrainment. Consequently, the latexes used as cement modifiers should have an optimum surfactant content (from 5 to 30% of the weight of total solids) to provide adequate strength. Suitable antifoamers are usually added to the latexes to prevent excess air entrainment increased dosages causes a drastic reduction in the air content and a concurrent increase in compressive strength [87, 92-94]. 

K = 0.18 to 0.25 tray operation close to its best efficiency point K = 0.35 to 0.40 tray suffering from entrainment—increase in reflux rate, noticeably reduces tray efficiency K = >0.5 tray is in fully developed flood—opening a vent on the overhead vapor line will blow out liquid, with the vapor K = 0.10 to 0.12 tray deck is suffering from low tray efficiency, due to tray deck leaking... 

Effect of Gas Velocity Entrainment increases with gas velocity to a high power. Generally, smaller powers, indicative of a relatively gradual change, are typical of low-pressure systems. Higher powers, which indicate a steep change, are typical of high-pressure systems. 

Downcomer vapor underflow ("vapor entrainment" or "gas recycle1 ) is analogous to liquid entrainment. It reduces both tray capacity and efficiency (17,44,45). In low- and medium-pressure distillation systems, where gas density is significantly lower than liquid density, it takes only a small quantity of gas to generate volumes comparable to the liquid volumetric flow rate. The quantity of gas recycle is therefore small, and it has little effect on tray performance. At high pressures, the quantity of gas recycled is significant. An analysis of some FRI data (44) for iC4-nC4 distillation showed vapor entrainment increases from about 7 percent at 165 psia to about 50 to 60 percent at 400 psia on a molar basis. 

Effect of liquid rate. At low liquid rates, entrainment diminishes with higher liquid loads, while at high liquid rates entrainment increases with liquid loads (22,24,26,33,40,53-55 Fig. 6,15), When most of the dispersion is in the form of a spray, entrainment diminishes with higher liquid loads (22,24,27). The point at which the trend reverses, and entrainment begins to increase with liquid rate, has been interpreted either as the point where the dispersion changes from partially developed spray to froth (40,53), or where the dispersion changes from the spray to froth regime (22-24,45,55). 

Table I shows that, as the boiling point of the hydrocarbon used as the entrainer increases so does that of the azeotrope with water and the percent of water therein. A high percentage of water in the azeotrope is desired for the heat required for the distillation, which is mainly that of the latent heat of the water plus that of the entrainer. Sufficient entrainer should be available in the azeotrope for reflux to the column although this requirement is not large. Also, the solubility or dilution effect is better with lower-boiling hydrocarbons. Thus there are several factors to be balanced in choosing the azeotrope. The effect of relative boiling points, vapor pressures, and amounts of different entrainers in their azeotropes with water has been discussed as affecting the choice of entrainers for separating water from acetic acid (5). However, that represents a much more difficult selection because there the quantity of reflux is important and also the solvent characteristics of the entrainer for the acetic acid also control the choice.

With increasing vapor rate, the oscillations become more violent, and liquid entrainment increases up to 70%, decreasing the tray efficiency. On sieve trays, extra weep ing occurs up to 150% compared to a stable tray. Full-wave oscillation is represented by a peak wave forming along the center of the tray with a trough at each wall. This position then reverses itself, and is called full-wave oscillation. The full-wave occurs at lower vapor rates than halfwave oscillation. Increases in entrainment and weeping also occur, and are most likely to be characteristic of medium- to smaU-sized columns, particularly those operating at reduced pressure. 

Two soil systems were considered contaminated dry and wetted soil. Pure supercritical carbon dioxide was able to remove phenol from both systems equally effectively. For the contaminated dry soil, both entrainers increased the distribution coefficient of phenol. However, methanol was by far the most effective. The presence of 2 mol % methanol (based on carbon dioxide) provided almost complete removal of the phenol from the soil. This is probably due to an increase in the polarity of the supercritical phase with the addition of methanol (li). The benzene/carbon dioxide mixture doubled the distribution coefficient, which can be attributed to structural similarities between the benzene and the phenol. 

In ERD in situ separation is used to improve the yield of reaction whereas an entrainer feed is added to make the separation feasible by selectively increasing the relative volatility of one of the products, ERD promises to be advantageous for the synthesis of fatty acid esters. The entrainer increases the relative volatility of water (by-product) compared to the alcohol (reactant), such that during the reaction the water can be continuously removed by distillation. In this way the chemical equilibrium is shifted such that higher conversions can be obtained. In Figure 1 the flowsheet of the desired process is given, in which RS stands for Reactive Section and DS for Distillation Section. 

Here, g is fhe gravitational acceleration, p the density of the gas, ps the density of a particle, Ap = ps — p, and p is the gas viscosity. The is calculated as an inverse weighted average from a sieve analysis. Entrainment increases with gas velocity and viscosity, vessel diameter, and particle attrition. It decreases with increasing freeboard height and particle density. Pressure drop is nearly constant across the fluidization region. Clusters of particles can be a... 

Frost resistance. Air entrainment increases resistance to frost damage. 

Air entrainment increases workability. Typically 5% air entrainment will increase slump by 10—50 mm. 

The use of an air entrainer increases the yield of concrete by the volume of the entrained air. This has a significant effect on the apparent cost of using an air-entraining admixture. 

The water-containing binary or ternary azeotropes will always have lower boiling points than the solvents they are being used to dry. Since the chance of an azeotrope existing decreases as the boiling point between solvent and potential entrainer increases it... 

Specific Gravity WRA and HRWRA increase the specific gravity of concrete provided that they do not result in air-entrainment. Increases of 0.6-1.2% were recorded [27]. 

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