Rheological Characterization of Metalized and Non‐Metalized Ethanol Gel Propellants

The gellation of metalized and non‐metalized ethanol with a methylcellulose gelling agent and its effect on the rheological properties (flow and dynamic study) of these gels is reported herein. The rheological study shows that increasing the shear rate reduces the apparent viscosity for a given yield stress (for a shear rate range of 1 to 12 s⁻¹) for both shear rate ranges (1 to 12 and 1 to 1000 s⁻¹) covered in present experiment. The gellant and metal particle concentrations significantly influence the gel apparent viscosity. Distinct changes in thixotropic behavior were observed, while decreasing the concentration of MC gellant and Al metal particles in the ethanol gels. The dynamic study showed that all of the linear viscoelastic regions (LVE) of the gel samples were independent of strain percentage (1 to 10). The G′ values depended on the frequency and exceeded the G′′ values, which indicated a gel‐like highly structured material. The tanδ values showed that all of the ethanol gels were elastic and weak physical gels with a high degree of cross‐linking.     

High-energy-density gelled fuels with high stability and shear thinning performance

Gelled fuels are the very promising propellants for new-generation rocket and ramjet propulsion. Here we report a new type of low-molecular mass organic gellant (Z), and prepared four kinds of stable gelled fuels based on HD-01, HD-03, RP-3 and QC liquid fuels, with the critical gellant concentration less than 1% (mass). The characterizations show that the gellant can form 3D network structure, via hydrogen bonding, π-π stacking and van der Waals forces, to fix fuel molecules during the formation of gelled fuels. So, the gelled fuels show high stability, with the remaining gel mass of 0.25% (mass) Z/HD-01 more than 90% even at high centrifugal speed of 7500 r·min^-1, but the rheological property test shows that all gelled fuels have obvious shear thinning property, which benefits its storage in gelled state while supply in liquid state. The gelation of liquid fuels by gellant Z can increase the volumetric net heat of combustion (for HD-01, it increases from 39.58 MJ·L^-1 to 40.76 MJ·L^-1 with 1% (mass) Z), and liquefied gelled fuels show the comparable ignition delay time with the pristine liquid fuels. So, the gelled fuels made by gellant Z have better stability, shear thinning and combustion performances, which have great potential for the practical application.     

Gelled Fuel Simulant Droplet Impact onto a Solid Surface

The dynamics of the impact process of a non‐Newtonian gelled fuel simulant droplet was studied experimentally. A comparison between the impact process of the gel simulant and that of a neat Newtonian fluid reveals a similar behaviour during the kinematic phase of the droplet impact. However, significant differences, both quantitatively and qualitatively, between the investigated fluids were found during the later spreading, relaxation and equilibrium phases of the impact process. Numerical simulations for the neat Newtonian fluid were found to accurately predict the centreline height during the kinematic phase for both of the fluids. A novel dynamic model for drop shape based on elastic spring and dashpot elements using the Bessel function to describe the periodic term is presented. Very good agreement of the dynamic model with the experimental data was obtained.     

Yield behavior of gelled waxy oil in water-in-oil emulsion at temperatures below ice formation

Paraffinic waxes precipitate from bulk oil when oil temperatures are lower than the oil wax appearance temperature. The oil can form a gel if the temperature goes below the pour point, especially under quiescent conditions. The strength of the gelled waxy oil increases as temperature decreases further. Application of a mechanical shear deforms and fractures the gel. It is shown that this strength reduction in the gel is irreversible under isothermal conditions. In subsequent cooling, the prior fractured gel even showed much less yield stress than the gel from the shear-free condition at measured temperature. This study explored the gel strength behavior in water-in-oil (w/o) emulsion state. Three different model oils, water-free oil, 10 wt.% w/o and 30 wt.% w/o, were used to determine the yield stress using vane method. Both emulsified oils showed less yield stress values at temperatures between the pour points and ice temperature. Compared to water-free oil at temperatures below ice formation, the higher yield stresses were observed in 10 wt.% w/o oil; however, the lower yield stresses in 30 wt.% w/o oil. Subsequent cooling option after prior gel breakage was also examined.     

The propagation of pressure in a gelled waxy oil pipeline as studied by particle imaging velocimetry

Paraffinic crude oils in pipelines may form waxy gels during flow shutdowns. These gels can be dislodged by applying pressure if the wall shear stress, proportional to the local pressure gradient, exceeds the gel yield stress. The simplest models assume that the axial pressure profile becomes linear immediately after a jump in upstream pressure, but this fails to account for gel time‐dependent rheology or the effect of gel voids on pressure wave propagation. To investigate the former factor, pressure profile and particle imaging velocimetry (PIV) measurements were performed on a model oil gelled under pressure to reduce void formation. After a jump in upstream pressure to a value insufficient to restart flow, the axial pressure profile becomes linear in a two‐step process, with an immediate small rise in downstream pressure followed by a time‐delayed jump. The local downstream gel deformation measured by PIV exhibits similar two‐step time dependence. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

大庆胶凝原油的循环剪切实验研究

胶凝含蜡原油由于其蜡晶的三维网状空间结构,具有复杂的流变性。胶凝原油的流变性质一直是研究的重点和热点。很多学者对胶凝原油的性质做了详细而又深入的研究,但这些研究一般集中在恒定剪切速率上,对胶凝原油的变剪切的研究较少。通过实验,研究了胶凝含蜡原油在剪切速率先线性增大后线性减小这一循环加载条件下其触变特性。通过控制不同降温速率和剪切速率增加的速率,来研究胶凝原油的触变性规律。试验结果表明,对于不同的降温速率,低降温速率时期剪切应力开始比较大,但随着剪切速率的增大,其应力逐渐靠拢,到最后无明显区别;而改变剪切速率增加的速率时,当剪切速率变化率越大时,在同一剪切速率下,其应力就愈大。     

Some Aspects on Safety and Environmental Impact of the German Green Gel Propulsion Technology

This article gives a short introduction into the technology of gelled propellant rocket motors and gas generators. A brief introduction outlines the specific features of the German green gelled propellant rocket motor technology and the family of monopropellants that cover a variety of requirements with respect to smoke, combustion temperature, and combustion pressure ranges. The discussion of the hazard potential comprises military insensitive munitions (IM) and civil classifications as well as a comparative assessment of the environmental and health impacts from manufacturing over use and finally to disposal. Summarizing the properties over all categories shows that gelled propellants provide a unique combination of good insensitivity and low environmental and health hazard potential compared to other liquid propellants, fuels, and oxidizers or solid rocket propellants.     

VISCOMETRIC MEASUREMENT OF CHROMIUM(III)-POLYACRYLAMIDE GELS†

Gelled polymers are being used increasingly to modify the movement of injected fluids in secondary and enhaced oil recovery processes. A common gelation process involves the reduction of Cr(VI) to Cr(III) in the presence of polyacrylamide. The Cr(III) reacts or interacts with the polymer to form a gel network. Although correlations of gelation time with principal process variables have been obtained, viscometric data have not been reported during or after gelation. These data are needed for fluid flow calculations in surface equipment and estimation of flow behaviour in reservoir rocks.

A Weissenberg Rheogoniometer, with cone and plate geometry, was used to obtain viscometric data for the gelation of polyacrylamide and chromium (III). Solutions consisting of polyacrylamide polymer, sodium dichromate-dihydrate and sodium bisulfite were gelled under a steady shear field at constant temperature. The shear stress versus time profile for the galation process was interpreted to define a gelation time and to determine the apparent viscosity of the gelled fluid. The gelation time decreased as the applied shear rate increased up to about 14.25 sec^?1 and was affected by shear rate history. Viscometric properties of the gelled solutions were determined. Apparent viscosity of the gelled solutions decreased as the shear rate under which they were formed increased.

Post gelation studies indicated that gels exhibited a residual stress at zero shear rate and behaved as Bingham plastics under steady shear. Gels formed at low shear rates were more viscous than gels formed at high shear rates. However, the structure of these gels was susceptible to shear degradation.     

VISCOMETRIC MEASUREMENT OF CHROMIUM(III)-POLYACRYLAMIDE GELS†

Gelled polymers are being used increasingly to modify the movement of injected fluids in secondary and enhaced oil recovery processes. A common gelation process involves the reduction of Cr(VI) to Cr(III) in the presence of polyacrylamide. The Cr(III) reacts or interacts with the polymer to form a gel network. Although correlations of gelation time with principal process variables have been obtained, viscometric data have not been reported during or after gelation. These data are needed for fluid flow calculations in surface equipment and estimation of flow behaviour in reservoir rocks.

A Weissenberg Rheogoniometer, with cone and plate geometry, was used to obtain viscometric data for the gelation of polyacrylamide and chromium (III). Solutions consisting of polyacrylamide polymer, sodium dichromate-dihydrate and sodium bisulfite were gelled under a steady shear field at constant temperature. The shear stress versus time profile for the galation process was interpreted to define a gelation time and to determine the apparent viscosity of the gelled fluid. The gelation time decreased as the applied shear rate increased up to about 14.25 sec^-1 and was affected by shear rate history. Viscometric properties of the gelled solutions were determined. Apparent viscosity of the gelled solutions decreased as the shear rate under which they were formed increased.

Post gelation studies indicated that gels exhibited a residual stress at zero shear rate and behaved as Bingham plastics under steady shear. Gels formed at low shear rates were more viscous than gels formed at high shear rates. However, the structure of these gels was susceptible to shear degradation.     

Preparation and Characterization of Metalized JP‐10 Gel Propellants with Excellent Thixotropic Performance

The preparation and characterization of a series of D‐gluconic acetal supramolecular organic gelators (Gn) which can form gel with high‐energy density hydrocarbon fuel JP‐10 are reported. Rheological measurements show G8 gel exhibits strong mechanical strength at a concentration of 2 wt %, while G18 gel has a remarkable yield stress. What's more, JP‐10 gels show thixotropy with high viscosity, especially for the G8‐based gel, which has an instantaneous recovery ratio. The CGC (critical gelator concentration) of G8 is less than 0.1 wt %, known as a super gelator. More interestingly, G18 can gel JP‐10 at room temperature, which is the first example of room temperature gel propellant formed by a supramolecular gelator. Nano accelerants (Al, B) are dispersed into the gel propellant system, which can be stable for months. The presence of 50 nm Al powder in G8‐based gel can significantly increase its mechanical strength, yield stress and viscosity, as well as thixotropy.     

Effects of quasi‐nanogel particles on the rheological and mechanical properties of natural rubber: A new insight

The influence of sulfur‐crosslinked, quasi‐nanosized gels on the rheological and mechanical properties of raw natural rubber (NR) was investigated. Latex gels with different crosslink densities were prepared through the variation of the sulfur‐to‐accelerator ratio. These gels were characterized by dynamic light scattering, solvent swelling, and mechanical properties. The gels were mixed with raw NR latex at concentrations of 2, 4, 8, and 16 phr, and their effect on the rheological properties of NR was studied by Monsanto processability tester. The presence of gel in raw NR reduced the apparent shear viscosity and die swell considerably. Initially, the viscosity decreased up to a 8 phr gel loading and then increased with an increase in the gel loading. However, the change in the viscosity was related to the crosslink density of the gels. A new empirical equation relating the viscosity, volume fraction of the gels, and crosslink density was proposed. The die swell of gel‐filled raw NR was at least 10% lower than that of unfilled raw NR and decreased with an increase in the gel loading. The effect of the gels on the die swell properties was explained through the calculation of the principal normal stress difference of gel‐filled NR systems. Scanning electron photomicrographs of the extrudates revealed much better surface smoothness for the gel‐filled virgin rubber systems than for the unfilled rubber. The addition of the gels to raw NR increased the modulus and tensile strength, whereas the elongation at break decreased. The effect of the gels on the dynamic mechanical properties of NR was also investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

胶凝含蜡原油的连续剪切实验研究

胶凝含蜡原油由于其蜡晶的三维网状空间结构,具有复杂的流变性。胶凝原油的流变性质一直是研究的重点和热点。很多学者对胶凝原油的性质做了详细而又深入的研究,但这些研究一般集中在恒定剪切速率上,对胶凝原油的连续剪切的研究较少。通过控制不同的降温速率和胶凝温度,来研究胶凝原油连续剪切的变化规律。实验结果表明,当降温速率越大时,初始的粘度越小,但剪切一段时间后,不同降温速率下的粘度无多大差别;当胶凝温度越低是,其初始的结构强度越大,并且在结构破坏以后,在同一剪切速率下,其粘度也越大,但不同温度下的差距在减小;当从高到低的剪切情况下,其粘度随着剪切速率的减小,呈增大的趋势,并且这趋势越来越明显,相对于从低到高的剪切情况下,在同一剪切速率下,从低到高情况下的粘度比从高到低的粘度要大。     

Development and characterization of hydrocarbon polyol polyurethane and silicone magnetorheological polymeric gels

Magnetorheological polymeric gels (MRPG) have been developed for use in semi‐active magnetorheological fluid (MRF) dampers and other magnetorheological (MR) devices. The novel MRPGs are prepared by suspending iron particles in polymeric gels. Off‐state (i.e, no applied magnetic field) viscosity and settling behavior can be controlled through the selection of polymeric gels. In this study, tunable rheological properties were investigated with a piston‐driven flow type rheometer with a shear rate varying from 20 s^?1 to 6,000 s^?1. Silicone MRPG (with 84.5 wt % iron particles) has controllable viscosity and a high shear yield stress over a wide range of shear rates. Silicone MRPG (79.5 wt % iron particles) has the lowest viscosity of those studied. Polyurethane MRPG has the lowest settling rate. The order of addition of magnetic particles and polymer during the polymerization process affects the MRPG final off‐state apparent viscosity (80% increase in apparent viscosity for silicone MRPG polymerized after adding iron particles). This indicates that polymer gels modify the surface properties of the magnetic particles, causing interaction among particles. The dynamic shear yield stress is higher for fluids with better dispersion stability. Polyurethane MRPG, which has the lowest settling rate, has a high dynamic yield stress (23 kPa at 350 mT). Both dynamic and static shear stress values of the MRPGs were found to be similar in magnitude (5–8 kPa at 120 mT for silicone MRPG with 84.5 wt % iron particles and polyurethane MRPG), indicating that MRPGs can provide consistent performance in devices. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1176–1182, 2004     

不同剪切历史和热历史对原油滞回环的影响

胶凝含蜡原油由于其蜡晶的三维网状空间结构,具有复杂的流变性。胶凝原油的流变性质一直是研究的重点和热点。通过实验,研究了在不同剪切历史和热历史作用下胶凝原油滞回环的不同变化规律。实验结果表明,对于不同的降温速率,在同一剪切条件下,当降温速率较低时,其原油屈服应力较大,滞回环曲线凸起较高,但随着剪切速率的增加,其应力逐渐接近,滞回环曲线逐渐接近;对于不同的胶凝温度,在同一剪切条件下,胶凝温度越低的,其屈服应力较大,并且随着剪切速率的增加,应力之间的差别虽变小,但胶凝温度低的比胶凝温度高的大,在滞回环曲线上可以看到低温度的曲线比高温度的曲线所对应的应力大;对于不同的剪切速率,剪切速率变化率大的,其屈服应力大,但随着剪切速率的增大,滞回环曲线相接近,即其应力也逐渐相接近。     

凝胶单推–3流变性研究

制备了凝胶单推–3推进剂,并进行了流变性研究。结果表明,凝胶单推–3为假塑性非牛顿流体,稠度系数和假塑性系数与凝胶剂质量分数和胶体温度有关,胶体无触变性,屈服应力较小。     

Mullite—Alumina Composites by Extrusion

The rheological properties of a paste containing chopped alumina fiber and particulate silica suspended in a gelled boehmite liquid phase have been evaluated using a physically based extrusion model. When sintered, the paste formed a mullite-alumina fiber composite. Extrudates with fiber volumes up to 30% in the sintered product were prepared. During extrusion, the pressure drop was largely independent of extrudate velocity, fiber length, and the fiber concentration. All pastes showed significant yield behavior leading to good postextrusion shape retention. For any given fiber length, it was shown that there exists a critical volume fraction above which fiber-fiber interactions are so great that both yield and wall shear stresses increase. At these high concentrations of fiber, inhomogeneities also increase. Up to the critical volume fraction, dispersed wet fibers produced lower extrusion parameters than when dry fibers were used as the starting material. The observed behavior is explained in terms of low viscosity liquid formation above the yield point of the boehmite gel.     

Supramolecular magnetorheological polymer gels

Novel magnetorheological fluids—supramolecular magnetorheological polymer gels (SMRPGs)— were investigated. Supramolecular polymer deposited on the surface of iron particles was suspended in the carrier fluids. The supramolecular network was obtained by metal coordination between terpyridine monomers and zinc ion. These SMRPGs had such advantages as controllable off‐state viscosity, a reduced iron particle settling rate, and stability. The viscoelastic behavior of SMRPGs with small‐ and large‐amplitude oscillatory shear was investigated using the amplitude and frequency sweep mode. The effects of strain amplitude, frequency, and magnetic field strength on the viscoelastic moduli were measured. The linear viscoelastic (LVE) strain range was obtained by the oscillation and static stress strain methods. The maximum LVE value was equal to the preyield strain point, 0.3%. Microstructural variation of SMRPG is proposed as an explanation of the rheological changes in the oscillation tests. The results of this research indicate that off–state viscosity and particle settling can be controlled by adjusting the concentration of supramolecular polymer gel. Dynamic yield stress significantly increased with an external magnetic field up to ～23,500 Pa under a magnetic flux density of 500 mT. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2464–2479, 2006     

Rheological characteristics of wheat starch pastes measured under steady shear conditions

Wheat starch pastes consist basically of swollen gel particles of various sizes which are dispersed in a continuous phase containing dissolved polysaccharides. The rheological properties of such pastes have been measured in the steady shear mode. At high shear rates the pastes behave as shear thinning liquids, while at low shear rates they exhibit a yield stress. The rheological properties vary with wheat starch variety and paste preparation conditions; this variation is of considerable economic importance to the starch industry. The present investigation shows that the flow behavior of pastes depends largely on two factors, namely, the volume which the starch gel particles would occupy when close packed if excess solvent were present, and the size distribution of the particles. Starch variety and paste preparation conditions influence these two factors and hence steady shear properties.     

Preparation and Characterization of JP‐10 Gel Propellants with Tris‐Urea Low‐Molecular Mass Gelators

The preparation and characterization of high‐energy density hydrocarbon fuel JP‐10 supramolecular gel propellants are reported. The low‐molecular mass gelator 1,1′,1′′‐((2,4,6‐trioxo‐1,3,5‐triazinane‐1,3,5‐triyl)tris(hexane‐6,1‐diyl))tris(3‐octadecylurea) (HDIT‐18) shows powerful gelation ability for JP‐10, the critical gelator concentration for JP‐10 is as low as 0.0638 wt‐%. The JP‐10 supramolecular gel propellants exhibit high thermal stability. Scanning electron microscopy (SEM) studies reveal that the gelator molecules self‐assemble into 1–3 μm fibers in JP‐10. Rheological studies show the JP‐10 supramolecular gels are thixotropic and shear‐thinning (for a shear rate range from 0.3 to 30 s⁻¹), the dynamic strain sweep test shows that the critical strain percentage of the gel materials is 1 %. The studies reported herein provide a potential fuel material for gel propellants.     

Study on the properties of magnetorheological gel based on polyurethane

Magnetorheological gels (MRGs) known as a new kind of magnetorheological material are composite gels containing magnetic particles suspended in polymer gels. In this study, a category of MR polymer gels based on polyurethane (PU) were prepared. The microstructures of these MRGs were observed with a digital microscope. Their rheological properties under both steady shear and oscillation testing were characterized by using a MR rheometer. The viscosity of the PU MRG decreased with the increment of NCO/OH ratio and increased with the increment of the weight concentration of carbonyl iron particles, molecular mass of poly propylene glycol, and applied magnetic field. The storage modulus increased gradually with the increment of applied magnetic field and weight concentration of carbonyl iron particles. The PU MRG exhibits high static shear yield stress (60.8 kPa, at 573 mT) and dynamic shear yield stress (83.9 kPa, at 573 mT) and wide variation range (static shear yield stress: 6–62 kPa, dynamic shear yield stress: 15–85 kPa). These advantages indicate that PU MRG is able to satisfy wide applications. In addition, both static and dynamic shear yield stresses of the MRG samples increase with the increment of molar mass of polypropylene glycol. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010