CO2水合物浆在水平圆管中的传热特性

在CO₂水合物浆流动传热特性测试实验系统上,采用套管式电加热的方法对CO₂水合物浆进行了分解实验,并对CO₂水合物浆的流动传热特性进行了分析。对CO₂水合物浆的相变特性进行了研究,得到CO₂水合物浆的相变温度在8～12℃。研究了在固相体积分数为13.2%以及流速为0.45m/s的条件下CO₂水合物浆在内径为8mm的水平不锈钢管中的传热特性,计算得到CO₂水合物浆在不锈钢水平圆管中的对流传热系数为1500～1800 W/(m²·K),并且其在流动传热过程中呈现先增大随后趋向平稳的趋势,在水合物的相变区相应的对流传热系数表现最大。研究了分解加热功率对管壁温和对流传热系数的影响,发现加热功率对管壁温度的影响较强。在实际应用中可利用CO₂水合物浆的相变作用来增强传热,提高传热效率。     

CO2水合物在管道中的生成及堵塞特性

为明确CO₂水合物在管道中的流动及堵塞特性,通过高压可视水合物环路研究了不同持液量下的水合物生成及堵塞特性,研究结果表明：水合物生成诱导时间随着持液量的增大出现非线性变化,呈V形,先减小后增大;管道持液量越大,水合物生成量越少,水合物发生堵塞时的临界体积分数降低,如在持液率86.6%下,堵塞时水合物体积分数为4.32%,持液率为66.7%时,堵塞时水合物体积分数为7.45%。通过可视管路发现当CO₂水合物大量生成后,管道中压降将突然增大,颗粒之间快速聚集生长,流速迅速降低,CO₂水合物快速充满管道使管道发生堵塞,水合物颗粒不断生长及在聚集层处的聚集导致流动阻力的增加是其产生堵塞的根本原因。研究结果可为CO₂水合物浆液流动保障提供技术支撑。     

液化条件对多孔介质中CO2水合物生成过程的影响

为了研究液化条件对多孔介质中CO₂水合物生成过程的影响机制及其规律,在初始压力为3.9、4.2、4.5、4.8和5.1 MPa,温度为273.5、274.5和275.5 K条件下研究粒径为700μm的石英砂介质中CO₂水合物的生成过程。结果表明：在相同条件下,随着初始压力的增加,多孔介质中CO₂水合物的生成速率逐渐增大;当压力低于液化压力时,随着初始压力的增加,CO₂水合物的生成速率逐渐增大,且温度越高,水合物生成速率增加的趋势越明显;当CO₂气体压力达到液化压力时,随着初始压力的不断升高,CO₂水合物的生成速率明显增大;多孔介质中CO₂水合物的最大生成速率达到了9.297×10^-3 mol·s^-1。研究结果进一步表明：液化可有效强化多孔介质中CO₂水合物的生成过程,提高CO₂水合物的生成速率。     

金红石型TiO2分散浆的制备及其流变特性

研究了金红石型TiO₂颗粒在水相体系的分散性及其流变特性,通过zeta电位、黏度等参数表征浆体的分散状况,确定了合适的分散剂为聚丙烯酸钠、其用量为4%（与TiO₂质量比）,分散浆中TiO₂合适的固含量为20%。通过稳态剪切测量法,发现分散浆中的固含量、pH和盐强烈影响其流变特性。分散浆存在剪切稀化现象,符合幂律模型,并呈现假塑性流体行为且无触变性。NaCl导致分散浆黏度降低, Na⁺离子浓度越大,浆体黏度越小;而CaCl₂的存在会使分散浆出现絮凝现象。分散浆合适的pH为12,增大或减小体系pH,浆体黏度均降低。当温度从25℃提升到50℃时,分散浆黏度略微降低,通过阿伦尼乌斯方程可以很好地描述温度对黏度的影响。频率扫描结果显示,分散浆在低频下呈凝胶状态,在高频下表现得更像是溶液。随着固含量的下降,分散浆交叉频率值降低。     

水合物法平衡级分离CO2/N2流程模拟分析

化石燃料燃烧排放烟气中CO₂的量占CO₂总排放量的75%,为了缓解CO₂导致的全球温室效应,需将CO₂/N₂中的CO₂分离出来。水合物法分离是一种高效、低能耗的CO₂/N₂分离技术。本文研究了水合物法平衡级分离CO₂/N₂过程中,进料CO₂体积分数、反应条件与反应特性三者间的关系,利用CPA-SRK方程+Chen-Guo模型对其进行平衡级分离流程模拟分析。经计算发现,进料干基CO₂体积分数对水合物法分离CO₂/N₂工艺的反应压力、平衡级级数均有较大影响。随着体积分数的增加,反应压力呈减小趋势,减小幅度随体积分数增加而减小,当进料CO₂体积分数小于20%时,压力下降较快,当体积分数大于50%时,压力降低幅度变小。温度为277K时,CO₂体积分数小于10%时,需四个水合物平衡级分离才能得到满足要求的气样;当体积分数为10%~20%时,需三个水合物平衡级分离;体积分数大于30%时为两个水合物平衡级分离。温度对水合分离的反应压力有较大影响,但对所需平衡级分离级数的影响并不大。随着温度的升高,水合反应压力呈增加趋势,增加幅度随进料干基CO₂体积分数的增加而降低。针对所研究气样,在不同温度下,均需三个水合物平衡级分离才能达到工艺要求。     

纳米粒子对CO2水合物导热性能的影响

试验研究了不同种类（Al₂O₃、Cu、SiO₂）、不同质量分数（0.05%、0.1%、0.15%）及不同粒径（10、30、50 nm）的纳米粒子对CO₂水合物热导率的影响。结果表明温度为-5~5℃时,纯CO₂水合物热导率为0.553~0.5861 W·m^-1·K^-1,具有玻璃体的变化特性。分散剂SDBS的加入,可改善CO₂水合物-纳米粒子体系的导热性能。在相同的质量分数和粒径下,纳米Cu粒子对CO₂水合物热导率的增强作用最好,但综合考虑水合物生成特性和溶液悬浮稳定性,选用纳米Al₂O₃粒子较合适。Al₂O₃粒子粒径越小,水合物热导率越大,15 nm比50 nm纳米粒子体系中CO₂水合物热导率的增长率平均提高了12.7%。此外,CO₂水合物热导率随Al₂O₃粒子质量分数的增大而增大,质量分数由0.05%增加到0.15%时,水合物热导率的增长率由4.2%提高到8.2%。     

低渗油藏用CO2泡沫压裂液的黏度影响因素分析

在高温高压(HTHP)、泡沫稳定剂存在的条件下制备了较稳定的CO₂泡沫,并考察了表面活性剂质量分数、盐度和剪切速率对CO₂泡沫黏度的影响,试验结果表明,表面活性剂质量分数和盐度对幂定律指数(K,n)的影响较大。流动稠度指数(K)与表面活性剂质量分数呈二次函数关系,流动行为指数(n)与表面活性剂质量分数呈线性关系。K和n均为盐度的二次函数。修正后的幂函数模型在表面活性剂质量分数为0.25%～1%、盐度为0.5%～8%、剪切速率为10～500 s^-1的条件下均可适用,且试验值和预测值匹配度较高。     

四氢呋喃水合物浆流动特性

利用实验环道进行了水合物颗粒体积分数为0～65.2%的四氢呋喃(THF)水合物浆的流动实验。管道生成四氢呋喃水合物后,水合物浆的压降梯度随着流速的增加而增加;随水合物体积分数的变化存在一个临界体积分数,当管道中的水合物体积分数小于临界值时,压降随体积分数的增加而出现很小的增加,管道中水合物呈稀浆状,浆体为牛顿流体;当管道中体积分数大于临界值时,压降梯度随体积分数的增加急剧增加,管道中水合物呈泥状,浆体为Bingham流体。临界体积分数随着浆体流速的增加而增大,在0.5～3.5m/s的范围内,临界体积分数为39.4%～50.4%,文中回归了泥状水合物的屈服应力及表观黏度。并根据水合物浆的流动特性分段回归了水合物浆在管道中流动的压降计算公式,实验验证表明回归的计算公式可以比较准确地计算管道中水合物浆流动的压降,可以为THF水合物的流动及其它水合物浆的流动提供指导。     

固相缩聚半芳香透明聚酰胺的流变性能

采用毛细管流变仪对固相缩聚半芳香透明聚酰胺(Semi-AromaticTransparent Polyamide,简称SATPA)的流变性能进行了研究。研究结果表明:固相缩聚SATPA熔体属假塑性流体,非牛顿指数随剪切速率的增大而减小;表观黏度随温度、剪切速率和剪切应力的升高而降低。随着剪切速率的增大,黏流活化能减小,表观黏度对于温度的敏感性减弱。     

纳米二氧化硅/热塑性聚酯弹性体复合材料的流变行为

利用毛细管流变仪研究了纳米二氧化硅/热塑性聚酯弹性体(n-SiO₂/TPEE)复合材料在圆形流道流动过程中的剪切流变行为。n-SiO₂/TPEE复合材料在剪切流变中并不表现为典型的抛物线曲面“柱塞流”,而是表现为平面“柱塞流”流动行为，且随着n-SiO₂含量增大，其假塑性非牛顿流体特性越明显，幂律指数越小于1;同时，剪切应力/黏度与熔体强度越大，平面“柱塞流”的壁面滑移速率与熔体流动速率越大。此外，引入n-SiO₂可降低TPEE复合材料体系的挤出胀大比，且随着n-SiO₂含量增大，TPEE复合材料体系的挤出胀大比逐渐减小。     

Effects of pore fractal structures of ultrafine coal water slurries on rheological behaviors and combustion dynamics

The ultrafine coal water slurry (CWS) with the particle size of 1-10 μm, ash content of 1-2%, solid concentration of 50% is a promising substitute fuel for diesel oil. The effects of pore fractal structures of three ultrafine CWSs on their rheological behaviors and combustion dynamics were studied in this paper. When the pore fractal dimensions of Yanzhou, Huainan and Shenhua ultrafine CWSs increase, their apparent viscosities all increase and the increase extents gradually enlarge with decreasing shear rates, while their ignition temperatures and apparent activation energies all decrease. For example, when the pore fractal dimension of Yanzhou coal increases from 2.31 to 2.43, the CWS apparent viscosity at a low shear rate of 12 s⁻¹ increases from 75 mPa s to 2400 mPa s, and that at a high shear rate of 100 s⁻¹ increases from 80 mPa s to 820 mPa s. Meanwhile, the ignition temperature of Yanzhou CWS decreases from 445 °C to 417 °C at a heating rate of 12.5 °C/min, and the apparent activation energy decreases from 104 kJ/mol to 32 kJ/mol.     

Thermodynamic stability, spectroscopic identification and cage occupation of binary CO2 clathrate hydrates

The hydrate phase behavior of CO₂/3-methyl-1-butanol (3M1B)/water, CO₂/tetrahydrofuran (THF)/water and CO₂/1,4-dioxane (DXN)/water was investigated using both a high-pressure equilibrium viewing cell and a kinetic pressure-temperature measurement system with a constant volume. The dissociation pressures of CO₂/3M1B/water were identical to those of pure CO₂ hydrate, indicating that CO₂ is not acting as a help gas for structure H hydrate formation with 3M1B, thus the formed hydrate is pure CO₂ structure I hydrate. The CO₂ molecules could be encaged in small cages of the structure II hydrate framework formed with both of THF and DXN. For a stoichiometric ratio of 5.56 mol% THF, we found a large shift of dissociation boundary to lower pressures and higher temperatures from the dissociation conditions of pure CO₂ hydrate. From the measurements using the kinetic pressure-temperature system, it was found that the solid binary hydrate samples formed from off-stoichiometric THF and DXN aqueous solutions are composed of pure CO₂ hydrate with a hydrate number n=7.0 and THF/CO₂ and DXN/CO₂ binary hydrates with a molar ratio of xCO₂·THF·17H₂O and xCO₂·DXN·17H₂O, respectively. The X-ray diffraction was used to identify the binary hydrate structure and Raman spectroscopy was measured to support the phase equilibrium results and to investigate the occupation of CO₂ molecules in the cages of the hydrate framework.     

Rheological behavior and curing deformation of paste containing 85 wt% Al2O3 ceramic during SLA-3D printing

The preparation of high solids loading Al₂O₃ paste is of great significance for improving the properties of ceramics formed by UV-curing. However, the solid contents of alumina slurry used by digital light processing (DLP) and traditional alumina paste for stereolithography (SLA) are both less than 80 wt%. With increase in solid content, the viscosity of paste increases sharply, and rheological property deteriorates. In this study, ceramic paste containing 85 wt% (62 vol%) Al₂O₃ was prepared for SLA-3D printing of ceramics, and more than 85 wt% solid content was achieved by dispersant and other additives. Effects of different dispersants on rheological and curing properties of Al₂O₃ ceramic paste were studied. At room temperature, the viscosity of 85 wt% Al₂O₃ ceramic paste was 51733 mPa s at shear rate of 30 s^?1. A novel method was proposed to control curing deformation of parts during printing. As-manufactured ceramic did not show any cracks by naked eye and exhibited excellent mechanical properties, with three-point bending strength of 540 MPa, fracture toughness of 4.19 MPa m^1/2, Vickers hardness of 16 GPa, surface roughness of 0.463 μm, and density of 3.86 g/cm³.     

Preparation of high solid loading,low viscosity ZrB2–SiC aqueous suspensions using PEI as dispersant

PEI was used as dispersant for ZrB₂ and SiC powders in water. The dispersion behavior of ZrB₂ and SiC in water was studied by zeta potential measurements, particle size distribution measurements and interparticle interaction calculations. Well-dispersed ZrB₂ and SiC aqueous suspensions were obtained using 0.6 wt% PEI at pH 6. The rheological behavior of ZrB₂–SiC aqueous suspensions was also investigated. Finally, a high solid loading (52 vol%), low viscosity (980 mPa s at 100 s⁻¹) ZrB₂–SiC aqueous suspension was successfully prepared.     

High solid loading,low viscosity photosensitive Al2O3 slurry for stereolithography based additive manufacturing

Photosensitive Al₂O₃-resin slurries with high solid loading, low viscosity used for stereolithography based additive manufacturing were prepared in this paper. The dispersion behavior and rheological behavior of the Al₂O₃-resin slurries were studied by rheology observation and sedimentation tests. The dispersant type, concentration and solid loading had significant effects on the rheological behavior and stability of the photosensitive Al₂O₃-resin slurries. A long term stability and homogeneity slurry was obtained when the dispersant and concentration were KOS110 and 5?wt%, respectively. The Al₂O₃ slurry prepared with a high solid loading up to 60?vol%, low viscosity of 15.4?Pa?s at 200?s^?1 was chosen for stereolithography based additive manufacturing.     

An investigation on gas hydrate formation and slurry viscosity in the presence of wax crystals

Clarifying the interaction effect between hydrate and wax is of great significance to guarantee operation safety in deep water petroleum fields. Experiments in a high‐pressure hydrate slurry rheological measurement system were carried out to investigate hydrate formation and slurry viscosity in the presence of wax crystals. Results indicate that the presence of wax crystals can prolong hydrate nucleation induction time, and its influence on hydrate growth depends on multiple factors. Higher stirring rate can obviously promote hydrate growth rate, while its influence on hydrate nucleation induction time is complicated. Higher initial pressure will promote hydrate formation. Gas hydrate slurry shows a shear‐thinning behavior, and slurry viscosity increases with the increase of wax content and initial pressure. A semiempirical viscosity model showing a well‐fitting is established for hydrate slurry with wax crystals by considering the aggregation and breakage of hydrate particles, wax crystals, and water droplets. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3502–3518, 2018     

Constant rotational rheological behaviors of the PAN/DMSO/nonsolvent systems

The constant rotational rheological behaviors of PAN/DMSO solutions with two kinds of nonsolvent (water and ethanol) have been investigated, respectively, using a cone‐plate rheometer. From viscosity measurements, the flow behavior was described within the shear rate range 0.1–1000 s^?1. The PAN solutions show shear thinning at high shear rates. The viscosities of the solutions decreased with the rising of the temperature at low shear rate. H₂O content has great influence on the viscosity of the solutions, depending on the hydration of H₂O and PAN or desolvent effect, according to different H₂O content. The role of ethanol compared with H₂O was also researched and higher viscosity was found. Non‐Newtonian index, structural viscosity index Δη, and flow activation energy of the PAN/DMSO/H₂O systems were also studied. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological properties of poly(trimethylene terephthalate) in capillary flow

The shear viscosity, extensional viscosity, and die swell of the PTT melt were investigated using a capillary rheometer. The results showed that the PTT melt was a typical pseudoplastic fluid exhibiting shear thinning and extensional thinning phenomena in capillary flow. There existed no melt fracture phenomenon in the PTT melt through a capillary die even though the shear rate was 20,000 s^?1. Increasing the shear rate would decrease the flow activation energy and decline the sensitivity of the shear viscosity to the melt temperature. The molecular weight had a significant influence on the flow curve. The flow behavior of the PTT melt approached that of Newtonian fluid even though the weight‐molecular weight was below 43,000 s^?1 at 260°C. The extensional viscosity decreased with the increase of the extensional stress, which became more obvious with increasing the molecular weight. The sensitiveness of the extensional viscosity to the melt temperature decreased promptly along with increasing the extensional strain rate. The die swell ratio and end effect would increase along with increasing the shear rate and with decreasing the temperature, which represented that the increase of the shear rate and the decrease of temperature would increase the extruding elasticity of the PTT melt in the capillary die. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 705–709, 2005     

Phase and kinetic behavior of the mixed methane and carbon dioxide hydrates

Large amounts of CH₄ are stored as hydrates on continental margins and permafrost regions. If the CH₄ hydrates could be converted into CO₂ hydrate, they would serve double duty as CH₄ sources and CO₂ storage sites in the deep ocean sediments. As preliminary investigations, both the phase behavior of CH₄ hydrates and kinetic behavior of CO₂ hydrate were measured at versatile conditions that can simulate actual marine sediments. When measuring three-phase equilibria (H-LW-V) containing CH₄ hydrate, we also closely examined pore and electrolyte effects of clay and NaCl on hydrate formation. These two effects inhibited hydrate nucleation and thus made the hydrate equilibrium line shift to a higher pressure region. In addition, the kinetic data of CO₂ hydrate in the mixtures containing clay and NaCl were determined at 2.0 MPa and 274.15 K. Clay mineral accelerated an initial formation rate of CO₂ hydrate by inducing nucleation as initiator, but total amount of formed CO₂, of course, decreased due to the capillary effect of clay pores. Also, the addition of NaCl in sample mixtures made both initial formation rate and total amount of CO₂ consumption decrease.     

Effect of supercritical carbon dioxide on morphology development during polymer blending

Supercritical carbon dioxide (scCO₂) was added during compounding of polystyrene and poly(methyl methacrylate) (PMMA) and the resulting morphology development was observed. The compounding took place in a twin screw extruder and a high‐pressure batch mixer. Viscosity reduction of PMMA and polystyrene were measured using a slit die rheometer attached to the twin screw extruder. Carbon dioxide was added at 0.5, 1.0, 2.0 and 3.0 wt% based on polymer melt flow rates. A viscosity reduction of up to 80% was seen with PMMA and up to 70% with polystyrene. A sharp decrease in the size of the minor (dispersed) phase was observed near the injection point of CO₂ in the twin screw extruder for blends with a viscosity ratio, ηPMMA/ηpolystyrene, of 7.3, at a shear rate of 100 s^?1. However, further compounding led to coalescence of the dispersed phase. Adding scCO₂ did not change the path of morphology development; however, the final domain size was smaller. In both batch and continuous blending, de‐mixing occurred upon CO₂ venting. The reduction in size of the PMMA phase was lost after CO₂ venting. The resulting morphology was similar to that without the addition of CO₂. Adding small amounts of fillers (e.g. carbon black, calcium carbonate, or nano‐clay particles) tended to prevent the de‐mixing of the polymer blend system when the CO₂ was released. For blends with a viscosity ratio of 1.3, at a shear rate of 100 s^?1, the addition of scCO₂ only slightly reduced the domain size of the minor phase.