Drag reduction effectiveness,shear stability and biodegradation resistance of guargum-based graft copolymers

Guargum is a seed galactomannan and is known to be a shear stable drag reducing agent. However, the aqueous solutions of guargum are very susceptible to microbial degradation. In the present investigation, seven graft copolymers of guargum and polyacrylamide have been synthesized and their drag reduction effectiveness, shear stability, and biodegradation resistance have been determined. It has been shown that the drag reduction effectiveness and shear stability of the graft copolymer depend upon the length of the graft and number of grafts in the molecule. None of the graft copolymer solutions show any microbial degradation up to 10 days.     

Turbulent drag reduction by polymer-fiber mixtures

The turbulent drag reduction studies by asbestos fiber mixtures with purified guargum, purified xanthangum, and their graft copolymers have been conducted at low concentration and Re 14000 using turbulent flow rheometer designed by Hoyt. A method for making stock suspension of asbestos fibers is also suggested which gives better drag reduction. It has been found from the present studies that purified guargum–asbestos fiber mixtures give positive synergistic effect even at low concentration and synergism in drag reduction may be caused by a mixture when its constituents are rigid. A simple mixture rule equation having interaction parameter may be used for the prediction of drag reduction by the mixture.     

Drag reduction by polymer–polymer mixtures

An extensive study on the turbulent drag reduction caused by the various mixtures of polyacrylamide, purified guargum, xanthangum, and their graft copolymers has been conducted at low concentrations and Re = 14,000 using a turbulent flow rheometer. It has been found in most of the cases that the drag reduction caused by mixtures shows a positive deviation from the linearly additive straight line. This effect is more prominent when the drag reduction caused by both the constituents differ appreciably. In most of the cases, the drag reduction caused by the mixtures is higher than the DR caused by either of the constituent polymers; however, the drag reduction caused by the mixture is less than the sum of the drag reduction caused by both the constituents at their respective concentration in the mixture. It has also been noticed that there is no evidence of synergism in these mixtures at low concentrations.     

Water-superabsorbent polymers through gamma radiation-induced graft-copolymerization of acrylonitrile on guargum

Superabsorbent polymers based on guargum have been prepared through a graft-copolymerization reaction using acrylonitrile as the monomer by a gamma ray-induced irradiation technique. Various grafting parameters have been studied. The grafted products have been characterized using infrared spectroscopy, thermogravimetric, and differential thermal analysis. The thermograms reveal the superior thermal stability of the grafted product over the control at all stages of its degradative cycle. The maximum absorbency obtained of the superabsorbent product was around 300 g/g.     

天然瓜尔胶改性研究

研究了阳离子瓜尔胶的制备方法、影响因素。通过对反应时间,反应温度,反应中氢氧化钠用量及溶剂等各因素的研究,得出最佳工艺条件:当瓜尔胶的用量为10.0 g时,CTA用量为1.50 g,氢氧化钠与CTA摩尔比为2.3左右,反应温度控制在80℃,反应时间为9.0 h,所得产物的取代度为0.062,反应效率为41.5%。     

天然气减阻剂减阻机理探讨

对现有天然气减阻剂减阻机理进行了较深入的分析,重点介绍了光滑减阻、粘弹减阻和光滑一粘弹减阻机理。从微观结构分析了输气管道近壁区阻力的成因,进一步证实了输气管道近壁区是实现湍流控制和减阻增输的关键区域;从实验研究和理论研究两方面对各个减阻机理进行了评述,并列举了各减阻机理的理论依据或事实依据。此外,简要介绍了天然气减阻剂的应用条件,并提出了减阻机理的研究重点。     

工业水处理表面活性剂的减阻性能研究

为了探讨将工业水处理表面活性剂作为循环水管道减阻剂使用的可行性,用旋转黏度计对十二烷基二甲基苄基氯化铵杀菌灭藻剂和椰油酸二乙醇酰胺缓蚀阻垢剂组成的多功能减阻剂配方进行了初步筛选,然后在室内模拟环道评价装置上进一步评价。当循环水中减阻剂质量浓度为1.2g/L和循环水流速为2.55m/s时减阻率为52.3%。     

CFD simulation of two-phase flow in pulsed sieve-plate column – Identification of a suitable drag model to predict dispersed phase hold up

Computational Fluid Dynamics (CFD) simulations of two-phase flow to predict dispersed phase hold up in a pulsed sieve-plate column have been performed and validated with reported experimental data. Suitability of different drag models for predicting dispersed phase hold up has been evaluated. Drag models applicable for concentrated dispersions are found to be better than the drag models applicable for lean dispersions. Kumar–Hartland drag model is found to be the best among the reported drag models with average error between predicted and experimental hold up being about 15%. Parameters of the Kumar–Hartland drag model are modified to further reduce the error to about 10%.     

继续重视减阻剂的研究开发

简述了国内外减阻剂的发展应用概况。国内数次现场试用减阻剂已取得成效,也发现了不足。讨论了减阻剂的合成及后处理等问题。提出建议和发展方向。     

Review on the applications and developments of drag reducing polymer in turbulent pipe flow

Drag reduction phenomenon in pipelines has received lots of attention during the past decades due to its potential engineering applications, especially in fluid transporting industries. Various methods to enhance drag reduction have been developed throughout the years and divided into two categories;non-additives method and additives method. Both categories have different types of methods, with different formulations and applications which will generally be discussed in this review. Among all the methods discussed, drag reduction using polymer additive is as one of the most enticing and desirable methods. It has been the subject of research in this field and has been studied extensively for quite some time. It is due to its ability to reduce drag up to 80% when added in minute concentrations. Reducing drag in the pipe will require less pumping power thus offering economic relieves to the industries. So, this paper will be focusing more on the use of polymer additives as drag reducing agent, the general formulations of the additives, major issues involving the use of drag reducing polymers, and the potential applications of it. However, despite the extensive works of drag reduction polymer, there are still no models that accurately explain the mechanism of drag reduction. More studies needed to be done to have a better understanding of the phenomenon. Therefore, future research areas and potential approaches are proposed for future work.     

Turbulent flow behaviour of dilute polymer solutions in an annulus

An experimental study has been carried out to investigate the turbulent flow behaviour of dilute polymer solutions in an annulus. The polymers used are two grades of Separan, AP30 and MG500, both are known to exhibit drag reduction characteristics in turbulent pipe flow. Similar drag reduction phenomena have been observed in annulus flow. At a given Reynolds number, the friction factor decreases with increase in polymer concentration and appears to reach a minimum (or maximum drag reduction) at certain optimum concentration. An estimate of the critical wall shear stress, which marks the onset of drag reduction, is consistent with pipe flow results, suggesting that the critical value is independent of flow geometry and size. A lower drag reduction, achieved in an annulus in comparison with circular pipes, is attributed mainly to a diameter effect.     

An overview of electro-osmosis in fuel cell polymer electrolytes

Electro-osmosis, the transport of water with protons, in polymer electrolyte fuel cell membranes is important because it effects water management within an operating cell on both a global and local level. The electro-osmotic drag coefficient is the number of water molecules transported per proton and is a quantitative measure of the extent to which electro-osmosis occurs in a given polymer electrolyte. The methods for which electro-osmotic drag coefficients have been determined are reported. An effort is made to report proton electro-osmotic drag coefficients extensively, while a few non-proton cation electro-osmotic drag coefficients have been chosen for illustrative purposes. The results reported have implications for fuel cell performance and in the development and characterization of new polymer electrolyte membranes.     

Turbulent drag effectiveness and shear stability of xanthan-gum-based graft copolymers

A number of graft copolymers of xanthan gum and polyacrylamide have been synthesized by grafting acrylamide onto xanthan gum using the ceric-ion-initiated solution polymerization technique. The effects of various synthesis parameters such as amount of catalyst, reaction time, and ratio of xanthan and acrylamide on drag reduction effectiveness of the graft copolymers have been studied. The scaling up of grafting reaction has been accomplished in 40-L reactor. The drag reduction effectiveness of the graft copolymers is investigated over a wide range of concentrations and Reynolds numbers. It is shown that the maximum drag reduction obtainable in xanthan gum solutions above 300 ppm can be obtained in solutions of graft copolymers at concentrations of 100–150 ppm. The grafting also improves the shear stability at higher Reynolds numbers. The shear stability of the graft copolymers at constant wall stress has been found to be superior to polyacrylamide and the mixtures of polyacrylamide and xanthan gum. In general, the shear stability of graft copolymers and polyacrylamide is shown to increase with concentration. The drag reduction characteristics and shear stability have been discussed in terms of structural features of the graft copolymers. The drag reduction characteristics of the graft copolymers are found to be similar to those of flexible polymers.     

Heterogeneity analysis of gas-solid flow hydrodynamics in a pilot-scale fluidized bed reactor

Mesoscale drag model is of crucial significance for the reliability and accuracy in coarse-grid Eulerian-Eulerian two-fluid model (TFM) simulations of gas-solid flow hydrodynamics in fluidized bed reactors. Although numerous mesoscale drag models have been reported in the literature, a systematic comparison of their prediction capability from the perspective of heterogeneity analysis is still lacking. In this study, in order to investigate the effect of several typical drag models on the hydrodynamic behaviors, the nonuniformity analysis and the sensitivity to material properties, extensive coarse-grid TFM simulations of a bubbling pilot-scale fluidized bed reactor are carried out. The results demonstrate that the mesoscale drag models outperform the empirical drag model in terms of nonuniformity due to the consideration of the influence of the mesoscale structures on the drag force in the bubbling region. Furthermore, the results reveal that our previously developed three-marker gradient-based drag model considering the solid concentration gradient exhibits satisfactory performance in predicting the bubbling flow hydrodynamics. Besides, the material-property-dependent drag model considering the explicit effect of material properties on drag corrections is most sensitive to the particle diameter. This work provides guideline for possible future improvements of mesoscale models to simulate gas-solid flow more accurately and universally.     

Drag reduction characteristics of graft copolymers of xanthangum and polyacrylamide

Graft copolymers of xanthangum and polyacrylamide have been prepared by grafting acrylamide onto xanthangum using ceric-ion-initiated solution polymerization technique. These graft copolymers have been tested for their drag reduction effectiveness, shear stability, and biodegradability. It has been shown that the grafting enhances the drag reduction effectiveness and biodegradation resistance of xanthangum considerably.     

Numerical investigation for the suitable choice of bubble diameter correlation for EMMS/bubbling drag model

Mesoscale bubbles exist inherently in bubbling fluidized beds and hence should be considered in the constitutive modeling of the drag force. The energy minimization multiscale bubbling (EMMS/bubbling) drag model takes the effects of mesoscale structures (i.e., bubbles) into the modeling of drag coefficient and thus improves the coarse-grid simulation of bubbling and turbulent fluidized beds. However, its dependence on the bubble diameter correlation has not been thoroughly investigated. The hydrodynamic disparity between homogeneous and heterogeneous fluidization is accounted for by the heterogeneity index,H_d, which can be affected by choice of bubble diameter correlation. How this choice of bubble diameter correlation influences the model prediction calls for further fundamental research. This article incorporated seven different bubble diameter correlations into EMMS/bubbling drag model and studied their effects onH_d. The performance of these correlations has been compared with the correlation used previously by EMMS/bubbling drag model. We found that some of the correlations predicted lower H_d by order of a magnitude than the correlation used by the original EMMS/bubbling drag. Based on such analysis, we proposed a modification in the EMMS drag model for bubbling and turbulent fluidized beds. A computational fluid dynamics (CFD) simulation using two-fluid model with the modified EMMS/bubbling drag model was performed for two bubbling and one turbulent fluidized beds. Voidage distribution, time averaged solid concentration and axial solid concentration profiles were studied and compared with the previous version of the EMMS/bubbling drag model and experimental data. We found that the right choice of bubble diameter correlations can significantly improve the results for CFD simulations.     

运动发酵单胞原生质球的形成和再生

运动发酵单胞(Zymomonas mobilis)ATCC29191菌株在含1～3g/L甘氨酸的液体培育12小时的菌体,用含20g/L的溶菌酶溶液处理12小时,可以稳定得到80％～90％的原生质球。原生质球稀释后在底层再生培养基上涂布,上面复盖一层半固体培养基,30℃培养5～7小时,再生率可达10~(-2)水平。     

The drag reduction of dilute polymer solutions as a function of solvent power,viscosity, and temperature

The frictional drag reduction of high molecular weight poly(ethylene oxide) and polystyrene solutions under turbulent flow conditions has been studied as a function of temperature, solvent power, and solvent viscosity. A rotating-disc apparatus was used to make the drag reduction measurements. For aqueous poly(ethylene oxide) solutions, at concentrations well above that needed to produce maximum drag reduction, all drag reduction data reduced to a common curve when per cent drag reduction was plotted against the Reynolds number for the flow. However, for poly(ethylene oxide) solutions below this optimum concentration, the drag reduction-versus-Reynolds number curves showed decreasing drag reduction with increasing temperature. The data are explained primarily in terms of the inverse temperature solubility characteristics of poly(ethylene oxide) in water. The per cent drag reduction of polystyrene in nonaqueous liquids was found to be greater in good solvents than in poor ones. It was also found that increases in solvent viscosity and decreases in temperature increased the per cent drag reduction. The results are discussed in relation to the current drag reduction theories and are shown to be in opposition to Virk's theory. It is concluded from the data that drag reduction is very likely a function of a relaxation time phenomenon involving the polymer molecules and the flow system. The results also emphasize the importance of considering solvent power, viscosity, and temperature in the design of an efficient drag reduction system.     

Modification of Ergun equation for application in trickle bed reactors randomly packed with trilobe particles using computational fluid dynamics technique

Based on a slit model, a pellet scale model has been developed for calculation of drag force imposed on trilobe catalyst particles in a packed bed reactor. The drag coefficient for single gas phase flow in a porous media has been calculated by CFD simulation and the results compared to the Ergun equation. The results show that the drag coefficient predicted by Ergun equation should be modified for various bed porosities, particle aspect ratio and gas densities. Therefore, a correction factor has been proposed to correct the Ergun equation constants in various conditions for trilobe particles. Comparison between the proposed corrected Ergun equation results and experimental data indicates considerable agreement.     

快速流化床中颗粒团聚现象的数值模拟--曳力关联式的选择

Drag force is a key parameter in the numerical modeling of gas-particle flow in circulating fluidized beds.The reliability of current drag force correlations over the regime of fast fluidization has,however,not been thoroughly investigated.In this article,a drag force correlation accounting for the clustering effects for Geldart A particles is used to simulate the behaviors typical of fast fluidization,including dynamic evolution of clusters as well as time- averaged axial and lateral voidage profiles.Diverse images of clusters are captured and the time-averaged profiles of voidage are shown to be in quantitative agreement with the present empirical correlation.The results based on different constitutive correlations of drag force show the importance of the choice of drag force in modeling fast-fluidized beds.This drag force correlation,based on a simple averaging assumption,could give some basic insights about the magnitude of the drag reduction.