Entrainment Performance Research Articles

The Performance of Low Air-Entraining Polycarboxylate Superplasticizer

A new low air-entraining polycarboxylate superplasticizer (denoted as L-PCE) was synthesized by using oxirane/epoxypropane (denoted as EO/PO) block-polyether as one of monomers. The molecular structure of EO/PO block-polyether monomer was characterized by proton nuclear magnetic resonance spectroscopy (denoted as 1H NMR). The pore parameters, workability, and compressive strength of the concrete added with L-PCE were compared to that added with conventional polycarboxylate superplasticizer (denoted as G-PCE) or the G-PCE compounding with defoaming agent. The results demonstrate that the air entraining performance of the L-PCE has been greatly improved than the G-PCE and the G-PCE compounding with defoaming agent. Then the problems, which the workability and slumps of fresh concrete decrease when G-PCE compounding with defoaming agent are added, can be solved. What is more, the interior pore structure of concrete has been optimized. The spacing factor of hardened concrete added with the L-PCE is 27% lower than that added with the G-PCE compounding with defoaming agent. And the 28d strength of the concrete added with the L-PCE is 10% higher than that added with the G-PCE compounding with defoaming agent.

Experimental and analytical studies on the shock wave length in convergent and convergent–divergent nozzle ejectors

The shock cell structure and the entrainment were investigated for convergent and convergent–divergent nozzle ejectors. The shock wave structures after the nozzle with over-expanded supersonic flow were captured by optical Schlieren measurements at different inlet pressures and temperatures. The first shock wave length was analyzed by using an image processing method. An analytical model was then proposed to predict the wavelength of the first shock wave in both convergent and convergent–divergent nozzle ejectors. The model results agree well with the measurements for the first shock wave length with a maximum difference of 11%. The influence of the first shock wave length on the ejector entrainment performance was analyzed to show that the ejector entrainment performance decreases as the shock wave wavelength is increased at a given primary flow inlet pressure.

The Goodwin model revisited: Hopf bifurcation, limit-cycle, and periodic entrainment

The three-variable Goodwin oscillator is a minimal model demonstrating the emergence of oscillations in simple biochemical feedback systems. As a prototypical oscillator, this model was extensively studied from a theoretical point of view and applied to various biological systems, including circadian clocks. Here, we reexamine this model, derive analytically the amplitude equation near the Hopf bifurcation and investigate the effect of a periodic modulation of the oscillator. In particular, we compare the entrainment performance when the free oscillator displays either self-sustained or damped oscillations. We discuss the results in the context of circadian oscillators.

Experimental study on a new method for improving the performance of thermal vapor compressors for multi-effect distillation desalination systems

A new method is proposed in this study to improve the entrainment performance of thermal vapor compressors (TVCs) that are widely used in multi-effect distillation (MED) desalination systems by preheating entrained vapor. In order to confirm its effectiveness and study the influences of the entrained vapor superheat on the TVC entrainment ratio, a four-effect-parallel-flow MED-TVC experimental system was set up. Hot water from a solar heating system and steam from an electric boiler were used as heat source of the entrained vapor preheating, respectively. The preliminary experimental results show that the entrained vapor preheating could greatly increase the TVC entrainment ratio and the TVC entrainment ratio increases with the entrained vapor superheat. Due to the poor performance of the TVC used in this study, further verification experiments of the proposed method need to be conducted in future work.

Bypass ejector with an annular cavity in the nozzle wall to increase the entrainment: Experimental and numerical validation

A bypass ejector geometry with an annular cavity in the nozzle wall was tested for various operating conditions to evaluate the entrainment performance. The results were compared with those of a conventional ejector. The data shows that the primary mass flow rate in the bypass ejector is always about 20% less than that in the conventional ejector. The results show that the bypass ejector is better than the conventional ejector at relatively high primary and secondary flow pressures with a maximum improvement in the entrainment performance of 31.5%. The bypass ejector has better entrainment performance in the critical mode. Since most ejectors operate in the critical mode, this ejector will have many applications requiring more entrainment.

Isobaric Vapor–Liquid Equilibria for Water + Acetic Acid + 1-Ethyl-3-methylimidazolium Diethylphosphate at 101.32 kPa

The removal and recycling of acetic acid from aqueous solutions is important for environmental protection and resource utilization. In this work, ionic liquid (IL) 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]) as an entrainer for the extractive distillation of the system water + acetic acid was investigated. Isobaric vapor–liquid equilibrium (VLE) data of the systems acetic acid + water, water + [EMIM][DEP], acetic acid + [EMIM][DEP], and water + acetic acid + [EMIM][DEP] have been measured at 101.32 kPa by using an improved Rose–Williams equilibrium still. The addition of [EMIM][DEP] showed a remarkable entrainer performance for the separation of acetic acid from its aqueous solution. The boiling point difference of the water + acetic acid system increased from 17.88 K (0 wt % IL) to 42.41 K (about 50 wt % IL), and the relative volatility (x1′ = 0.9) increased from 1.60 (0 wt % IL) to 5.28 (about 50 wt % IL). On the basis of the chemical theory and the Hayden–O’Connell (HOC) method, the parameters of the NRTL model for the binary systems were obtained, and the predicted values of the ternary systems of water + acetic acid + [EMIM][DEP] fitted the experimental VLE data well.

Isobaric vapor–liquid equilibrium for water + acetic acid + 1-butyl-3- methylimidazolium dibutylphosphate at 101.32 kPa

The removal and recycling of acetic acid from acetic acid+water mixture has a great significance for environmental protection and resource utilization. After the addition of ionic liquid (IL) 1-butyl-3-methylimidazolium dibutylphosphate [BMIM][DBP], the boiling point difference of the water+acetic acid system increased from 17.88K (0 mass % IL) to 41.13K (about 59 mass % IL), and the relative volatility (x1′=0.9) increased from 1.60 (0 mass % IL) to 9.81 (about 57 mass % IL). [BMIM][DBP] showed a remarkable entrainer performance for the separation of acetic acid from aqueous solution. In this work, Isobaric vapor-liquid equilibrium (VLE) data of the systems water+acetic acid, water+[BMIM][DBP], acetic acid+[BMIM][DBP], and water+acetic acid+ [BMIM][DBP] were determined at 101.32kPa by using an improved Rose–Williams equilibrium still. Based on the chemical theory and Hayden–O’Connell (HOC) method, the parameters of NRTL model for the binary systems were obtained, and the predicted values of the ternary systems of water+acetic acid+[BMIM][DBP] fitted the experimental VLE data well.

Experimental and numerical investigation of the effect of shock wave characteristics on the ejector performance

The entrainment performance and the shock wave structures in a three-dimensional ejector were investigated by Computational Fluid Dynamics (CFD) and Schlieren flow visualization. The ejector performance was evaluated based on the mass flow rates of the primary and secondary flows. The shock wave structures in the ejector mixing chamber were captured by the optical Schlieren measurements. The results show that the expansion waves in the shock train do not reach the mixing chamber wall when the ejector is working at the sub-critical mode. Decreasing of the shock wave wavelength increases the secondary mass flow rate. A three-dimensional CFD model with four turbulence models was then compared with the experimental data. The results show that the RNG k-ε model agrees best with measurements for predictions of both the mass flow rate and shock wave structures.

Configuration dependence and optimization of the entrainment performance for gas–gas and gas–liquid ejectors

This paper describes a numerical study of entrainment behavior and its configuration dependence for gas–gas and gas–liquid ejectors. A computational fluid dynamics (CFD) model is developed and experimental validation is undertaken over a wide range of operation conditions for ejector with different configurations. The predicted values by CFD simulation prove to be in good agreement with the experimental data. The investigation results indicate that pseudo-shock length has a dominant effect on entrainment performance and geometry optimization. Significant difference is noted in pseudo-shock length for gas–gas and gas–liquid ejectors, and this is mainly because the viscosity similarity markedly differs within the range of 0.01–1.0, depending on the primary and secondary fluids of usage. Therefore the optimum mixing tube length to diameter ratio is about 1–2 for general gas–liquid ejectors while 5–7 for gas–gas ejectors. As an exception to the general gas–liquid ejectors, the optimum L/D ratio in He–LH2 ejector is about 4, lying between that of the gas–gas ejector and gas–liquid ejector but still consistent with the pseudo-shock length. If the maximum allowable length of ejector mixing tube is less than the optimum value, placing the primary nozzle exit upstream of the mixing tube can greatly improve the entrainment performance.

Investigation of entrainment behavior and characteristics of gas–liquid ejectors based on CFD simulation

The aim of this paper is to investigate the entrainment behavior and performance of gas–liquid ejectors. computational fluid dynamics (CFD) model and the corresponding algorithm are developed and validation experiment has been carried out over a wide range of operation conditions for ejector with different configurations. Good agreement has been achieved between the predicted values from CFD simulation and the actual data by experimental measurement. The flow patterns that occur within the primary nozzle region are analyzed on the basis of one-dimensional isentropic compressible flow theory. The fluid pairs, consisting of the motive and the entrained fluids, are considered during the investigation with N2–H2O and He–LO2 selected as the representative fluids. The investigation results indicate that for fixed primary flow and secondary flow pressures (PP and PS, respectively), the entrained mass flow rate mS decreases linearly with the increasing pressure difference ΔP, while for fixed ΔP and secondary flow pressure PS, the entrainment rate mS monotonically increases with an increase in primary flow pressure PP until a constant value is reached. Moreover, the mixing tube length has proven to be an important design parameter and can exert a remarkable influence on ejector performance. The optimum mixing tube length of gas–liquid ejector is about 1–2 times the mixing tube diameter, and deviation from the optimum value can dramatically degrade its entrainment performance. In other words, an obvious peak value of entrainment ratio appears at the optimum L/D. However, the optimum value of L/D for single-phase ejector happens in the range of 5–7, which differs significantly from that of gas–liquid ejector. Moreover, an inapparent effect has been observed when the mixing tube of single-phase ejector is longer than the optimum value. A detailed description of this phenomenon is presented in this paper. The conclusions of the research can be served as a guideline for ejector design.

Numerical investigation of entraining performance and operational robustness of thermal vapor compressor having swirled motive steam inflow

The importance of improving TVC's entraining ability in enhancing the efficiency of a multi-effect desalination (MED) system has been stressed for a long time. Moreover, the side effect detrimental to the system's operational stability when TVC is adopted for the MED plant has been frequently reported. In this study, an iterative CFD analysis was conducted to discover the TVC's shape that maximize its entraining performance, but we included a new design parameter of the motive flow's swirl intensity, which has never been previously considered as a TVC design parameter. Under the given reference operating pressures, the performance map was created in wide ranges of design parameters including the motive flow's swirl intensity. We tested whether the TVC will work in a stable double-choking range through an analysis of performance changing patterns for various operating conditions. Adopting the motive flow's swirl effect, a high entraining performance at reference condition as well as a good operational stability in wide operating ranges was achieved. This was impossible in the past when only the exteriorly geometrical parameters (like the mixing tube diameter and the primary nozzle exit diameter) were simply adjusted.

ON ENTRAINING AIR OF POLYCARBOXYLATE TYPE WATER REDUCER

From the results obtained in this study, it is concluded that the quantity of bubbles that PC-n, which is polycarboxylate having poly (n) ethylene glycol groups as side chains, introduces in concrete can be reduced when the side chains' length ‘ n’ is designed to be longer than 25 mol. But basically it is suggested that PC-n would have the air entraining performance in itself; By using the specific AE agent and anti-foaming agent, the stable bubbles can replace the unstable ones PC-10 introduced in concrete. As a result the excellently durable concrete can be manufactured that maintains the relative dynamic Young's modulus beyond 90% till about 1,200 cycles.

Enhancement of Entraining Performance on Thermal Vapor Compressor for Multi-Effect Desalination Plants by Swirl Effects of Motive Steam

Efficiency of a multi-effect desalination (MED) system with a thermal vapor compressor (TVC) is highly affected by the entraining performance of TVC. TVC's high entraining ability makes it possible to reduce the heat transfer area in evaporators or keep the top brine temperature (first effect cell-side temperature) lower. Therefore, to achieve a higher entrainment ratio of TVC, we investigate the cases in which the motive steam flows into the primary nozzle with a swirl component. The compressible, axisymmetric, and swirled flow is numerically solved for various swirl-to-axial component ratios. The Mach number, isobars, radial velocities, and shock patterns are compared to evaluate the effect of the swirled motive steam inflow on the entrainment ratio. This numerical study revealed that there exists an optimum swirl angle that maximizes the entrainment ratio.

Robust numerical analysis based design of the thermal vapor compressor shape parameters for multi-effect desalination plants

A thermal vapor compressor (TVC) that is to be adopted for use in a multi-effect desalination (MED) plant isdesigned with a high entraining performance and is appraised with respect to its stability robustness of operating inthe double choking region under abrupt changes in the operating conditions such as the motive and suction steampressures which can be easily caused due to external disturbances. Firstly the shape of the TVC having a highentraining performance is determined by performing an iterative CFD analysis for the various shape conditionsunder the given design pressure conditions. Then the entrainment ratio of the TVC is determined numerically in acertain fluctuating range of the operational pressure. Alteration patterns of the entrainment ratio are then consideredto assess whether the working of the TVC transfers to the unstable operating region or not.

ON AIR ENTRAINING PERFORMANCE OF POLYCARBOXYLATE TYPE WATER REDUCER

This paper describes the air entraining performance of polycarboxylate type water reducer. From the results obtained in this study, it is concluded that Methoxypoly (n=10) ethyleneglycol methacrylate - methacrylic acid copolymer (PC-10) can be purified by utilizing its cloud point; The purified polymer obtained from PC-10 through using its cloud point shows the lower air entraining performance than that of PC-10, and the ingredient that displays the strongest air entraining effect for PC-10 is methoxypoly (n=10) ethylene glycol, which remains in PC-10 as a raw material or an elimination product generated by an alkaline hydrolysis of PC-10 in the cement-water system; In order to decrease the air entraining performance of PC, the side chains of it should be sufficiently hydrophilic: we reached the preliminary conclusion that as the end group of side chains, -H or -CH3 group should be required and the side chains' length should be more than 30 moles in the additional number of ethylene oxide when the end group is -CH3 group.

Separation of azeotropic mixtures using hyperbranched polymers or ionic liquids

AbstractIn this work the suitability of selected commercially available hyperbranched polymers and ionic liquids as entrainers for the extractive distillation and as extraction solvents for the liquid–liquid extraction is investigated. Based on thermodynamic studies on the influence of hyperbranched polymers and ionic liquids on the vapor–liquid and liquid–liquid equilibrium of the azeotropic ethanol–water and THF–water systems, process simulations are carried out, which allow evaluating the potential of hyperbranched polymers and ionic liquids as selective components for the mentioned applications in terms of feasibility and energetic efficiency. Both hyperbranched polymers and ionic liquids break a variety of azeotropic systems. Since their selectivity, capacity, viscosity, and thermal stability can be customized, they appear superior to many conventional entrainers and extraction solvents. For the ethanol–water separation, the nonvolatile substances hyperbranched polyglycerol and [EMIM]+[BF4]− show a remarkable entrainer performance and therefore enable extractive distillation processes, which require less energy than the conventional process using 1,2‐ethanediol as an entrainer. Evaluation of a new THF–water separation process indicates the competitiveness of the suggested process and a considerable potential of using hyperbranched polymers as extraction solvents. © 2004 American Institute of Chemical Engineers AIChE J 50: 2439–2454, 2004

Investigation of fly ash carbon by thermal analysis and optical microscopy

A previous study investigated various fly ashes that had comparable loss on ignition values, but significant differences with respect to air entrainment performance. Thermal analysis data suggested that a poorly performing fly ash, with respect to air entrainment, contained a higher proportion of carbon that gasifies (oxidizes) at comparatively low temperatures. A relatively high abundance of isotropic carbon was identified in the poor-performing ash using optical microscopy. The present investigation examined a larger collection of fly ash samples to determine if thermal analysis could be used as a prognostic tool for fly ash performance. An attempt was made to correlate mortar air and foam index values for each sample with differential thermal analysis (DTA) data. Optical microscopy and BET surface area analysis were used as supportive techniques. No clear relationship could be established with the thermal or optical methods, although fly ash performance did correlate well with BET surface area. A low temperature component of the DTA exotherms was considered to be a function of inorganic catalytic species that reside on the carbon surface and lower the ignition temperature.

Ejector performance at high temperatures and pressures

Attention has recently been given to the use of thrust augmenting ejectors in the wings of V/STOL aircraft. Laboratory experiments using low temperature and pressure primary air have measured high-performance levels with well-designed ejectors. The present experiments were motivated by aircraft designers' questions regarding the effects of realistic temperatures and pressures on ejector performance. The simplest geometry was used: a convergent nozzle issuing into an axisymmetric duct that entrained from and exhausted to ambient conditions. The length of the ejector was varied from 12 to 0.75 diam. Primary temperatures and pressures spanned the intervals 60 to 1000°F and 10 to 80 psig. In support of existing theory, the mass entrainment performance usually decreased with increasing primary pressure although an aeroacoustic interaction reversed the trend over small intervals. Increasing the primary temperature decreased the performance of long ejectors but had little effect on the performance of short ejectors. The results are interpreted in terms of measurements of the pressure along the wall of the mixing duct and total pressure and temperature profiles acquired at the exhaust plane of the ejector.

On the Characteristics of Steam Ejectors and a Method of Calculating Their Performances

Steam ejectors can have various kinds of performance characteristics, but when high vacuum for mixing chamber or high compression ratio for entrained fluid is required for their performances, as is usual with such a case, the mixture of driving steam and entrained fluid should be kept in supersonic and fulfilled flow state at the diffuser throat inlet. The characteristics of steam ejectors in this flow state are called high vacuum characteristics.In this flow state, the entrainment performance of an ejector, as expressed by the relation between the pressure of mixing chamber and the entrained flow rate, is dctermined independently of the back pressure of the diffuser. Therefore, a method of calculating the entrainment performance has been proposed, taking into consideration the drag force of steam jet from the nozzle and the entrained fluid passage area as measured cross-sectionally at the convergent part of the diffuser.This desirable flow state depends largely on the outside conditions of the ejector. When the back pressure of the diffuser is raised above the limit value-the critical back pressure-, the high vacuum characteristics cannot be observed and the vacuum of mixing chamber will suddenly decrease. For the compression performance of the diffuser, another calculation method has been proposed for the purpose of obtaining the critical back pressure, taking into consideration the mixing of driving steam and entrained fluid with the mean velocities of the mixture relative to flow rate, momentum and energy, though, in the previous calculation methods the mixing process was neglected.From the calculation method presented in this paper, Eq. (24) has been obtained for the entrainment ratio which is the ratio of the flow rate of entrained fluid to that of fluid taken as a basis or at a base state. Comparison of Eq. (24) with the experimental results by Holton and Schulz3, 4) has proved that the drag coefficient of steam jet χ' is independent of the molecular weight of entrained fluid, but has a tendency to increase with the temperature rise of entrained fluid. If the drag coefficient χ' and χ are kept constant, the following formula may hold which represents the fact that the flow rate of entrained fluid will be proportional to the square of dimension ratio, when ejectors are geometrically similar.