Pressure Exponent Research Articles

Experimental and Simulation Analysis of Hydrogen Permeation Performance of Pd/Ag Permeator Used for Tritium Processing

Since the Pd/Ag membrane has a permselectivity for hydrogen isotopes, a permeator with a Pd/Ag membrane is developed to separate tritium from inert gases. First, a permeation experiment of pure H2 was carried out to determine the pressure exponent and the rate-determining step of permeation. It was found that the diffusion of H2 through the Pd membrane was the rate-determining step. Then, the separation of H2 from H2-Ar gas mixtures was carried out on the permeator to simulate the separation of tritium. Moreover, numerical simulation was utilized to study the concentration distribution of H2 in the permeator. The permeability of the Pd/Ag membrane was determined comparing the simulation results with the experimental data. The permeation flux of H2 through the Pd/Ag membrane is affected by permeability, the volume fraction of Ar in the feed gas, and the flow rate of the feed gas. In the condition of high permeability and Ar volume fraction, a phenomenon known as concentration polarization occurred. It can strongly affect the permeation of H2. Based on these results, an optimized design of the Pd/Ag permeator can be made to effectively separate tritium from other gases.

Pressure dependence of elastic deformation at multiple contacts and estimation of contact state of thin cracks

The pressure dependence of elastic deformation at multiple contacts in thin cracks has been investigated through the variation of elastic wave velocity. By extending previously introduced single-contact load-displacement relationships to those of multiple contacts and obtaining the first derivative of pressure with respect to the displacement at contacts, relationships for the pressure dependence of elastic deformation are obtained. The obtained relationships indicated that the pressure dependence is given by a pressure exponent [Formula: see text], which is the multiple contact state of thin cracks. This was correlated with a similar pressure exponent in an empirically derived elastic wave velocity relationship, and we found that the contact state can be obtained by the empirical relationship. The estimated multiple contact state has two ideal values of 0.67 and 0.5 for conical and flat contacts, respectively, and [Formula: see text] values between the ideal states give the pressure dependence of elastic deformation of contacts, formed by a mixture of two ideal states and their population. The contact state values smaller than 0.5 and values greater than 0.67 indicate closed and open state of cracks, respectively. From previously published data on elastic wave velocities of various rocks, it is verified that the pressure dependence of elastic deformation of multiple contacts can be quantitatively obtained by the estimated contact states from the pressure dependence of elastic wave velocity.

Innovative N2-selective metallic membranes for the potential use of CO2 capture

The permeability of nitrogen in Group V metal membranes having an approximate thickness of 40 μm was determined for the first time at conditions of relatively low temperature (400–600 °C) and pressure (300–600 kPa). Vanadium, niobium and tantalum membranes were investigated to evaluate the permeation characteristics towards nitrogen permeation. Analogous to the hydrogen transport mechanism through palladium-based membranes, the nitrogen permeating flux through the metallic membranes was determined to take place through a solution-diffusion mechanism. In particular, at 400 °C, the nitrogen permeability was found to be 1.15 × 10-12, 1.05 × 10-12, and 6.54 × 10-13 mol/(m s Pa0.5) for vanadium, niobium and tantalum, respectively.The optimal nitrogen partial pressure exponent value was found to be 0.5 for all the membranes investigated. The nitrogen permeability for the vanadium membrane was described by an Arrhenius-type relation where the pre-exponential factor and apparent activation energy for this correlation were 3.55 × 10-15 mol/(m s Pa0.5) and 31.8 kJ/mol, respectively. For niobium and tantalum membranes, it was not possible to perform any permeation tests due to cracks, which formed at temperatures higher than 500 °C.SEM and EDS analyses revealed the formation of metal oxides on the surface of V, Nb, Ta membranes, which may benefit the transport of nitrogen through the membrane as it may aid in preserving the structured nature of the bulk phase thereby preventing the formation of defects and/or grain migration at high temperature. Although the nitrogen permeability through metallic membranes is low and metal oxides form on the surface, this work describes the performance of metallic membranes toward nitrogen permeation, and it can be considered as the benchmark for future work related to this field.

HTPB‐Clay Nanocomposites (HCN): An Efficient Burning Rate Catalyst for Composite Propellant

AbstractIn present study, two types of montmorillonite clay, organically modified with polar and apolar moieties, are used, for preparation of HTPB‐clay nanocomposites (HCN) by dispersion of nanoclay in polymer matrix with high shear mixing. These nanocomposites are evaluated in composite propellants for their catalytic effect on decomposition of ammonium perchlorate a work horse oxidizer. Several composite propellant formulations containing 1–3 weight % of nanoclays over binder, were prepared. Along with this, formulations with conventional burning rate catalyst like iron oxide in 1–3 weight % over binder, and formulation without any burning rate catalyst as base composition were also processed. All these formulations were evaluated by means of theoretical prediction, end of mix viscosity, ballistic properties, mechanical properties, sensitivity parameters and thermophysical properties. Experimental results showed that HCN based compositions have lower or comparable end of mix viscosity than base compositions. Further characterization revealed that formulations with 3 weight % of nanoclays over binder have 70 % higher burning rate than base composition as well as 20–25 % higher burning rate than compositions having 3 weight % of iron oxide over binder. Pressure exponent values are determined for 3 to 11 MPa of pressure range and were found to be significantly higher for HCN based compositions (0.33 to 0.7) in comparison to the base composition. Mechanical properties and sensitivity data of HCN based compositions are comparable with base composition. Thermal studies revealed decrease in onset temperature of decomposition of AP with presence of nanoclay which may be the probable cause for enhancement in burning rate.

Isothermal compressibility in Fermi gases in an optical lattice

Isothermal compressibility ${\ensuremath{\kappa}}_{T}$, which measures the fluidity of the liquid or the stiffness of the solids, is one of the most important physical quantities in thermodynamic physics. In ultracold atoms, this quantity has been widely explored in the measurement of the transition from normal gas to Bose-Einstein condensate, as well as the transition from superfluids to solid phases, such as supersolids and Mott insulators. This physical quantity was also examined in the spin-orbit-coupled degenerate gases in free space, showing that the combined contribution of spin-orbit coupling (SOC) and the Zeeman field may pronouncedly enhance the isothermal compressibility in the gapless Weyl phases. Motivated by the differences between the free space and the optical lattice, in this work we examine this compressibility in the spin-orbit-coupled degenerate Fermi gases in a square lattice model, in which the filling factor and particle-hole symmetry about half filling become an important influencing factor. In this case, the particle density in compressibility should be replaced by the density of a particle or hole according to their filling to ensure symmetry about half filling. With increasing particle density $n$, the compressibility decreases to a small magnitude, while ${n}^{2}{\ensuremath{\kappa}}_{T}$ may increase monotonically with increasing $n$ from zero to half filling. In the strong-coupling regime, when the chemical potential and pairing strength are much larger than the tunneling strength and Zeeman field, this compressibility will approach ${n}^{2}{\ensuremath{\kappa}}_{T}=2/U$, where $U$ is the on-site interacting strength. This limit can be explained by a one-site Hubbard model. We show that SOC and the Zeeman field can play opposite roles in the behavior of compressibilities. The combination of these two terms can give rise to pronouncedly enhanced isothermal compressibility in some proper parameter regime. The anomalous compressibilities also give rise to a anomaly in the exponent of pressure. In the lattice model, the enhanced peak can be found in both the fully gapped phase and gapless Weyl phases, which is different from that in free space, which can be realized only in the gapless phases. We derive the formalisms from the Gibbs-Duhem formalism. These observations unveil important differences between the continuous model and discrete models. Our theory may also be useful to study the physics in other superfluids, including topological superfluids with finite-momentum pairings, in which the finite-momentum pairing may also have an implicit contribution to this compressibility. In this way, we may realize superfluids with some extraordinary physical properties.

Study on Burning and Thermal Decomposition Properties of HTPB Propellant Containing Synthesized Micro‐nano Ferric Perfluorooctanoate

AbstractA novel micro‐nano ferric perfluorooctanoate [Fe(PFO)3] was prepared and added in AP/Al/HTPB composite solid propellant as a catalyst to study its effects on burning and thermal decomposition properties of the propellant. To further discuss the possible thermal mechanism of the propellant containing Fe(PFO)3, the major effects of Fe(PFO)3 catalyst on Al were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and X‐ray diffraction (XRD). Results show that By adding 3 w.t.% Fe(PFO)3, the burning rate could increase by 27.8 % at 3 MPa, meanwhile, the pressure exponent decreased. The aggregation/agglomeration process of the propellant containing Fe(PFO)3 efficiently suppressed, and the particle size of condensed combustion products decreased clearly. In addition, Fe(PFO)3 could reduce the thermal decomposition temperature of the propellant and enhance the heat release. Thermite reaction between decomposition products of Fe(PFO)3 and Al was triggered at 635 °C, resulting in heat release and formation of α‐Al2O3.

High Pressure Fuel Regression Characteristics of Axial-Injection End-Burning Hybrid Rockets

This study is an investigation of axial-injection end-burning hybrid rockets aimed at revealing fuel regression characteristics under relatively high-pressure conditions. Firing tests are conducted using gaseous oxygen as the oxidizer at chamber pressures and oxidizer port velocities ranging from 0.22 to 1.05 MPa and 31 to , respectively. The results of 15 static firing tests show that the fuel regression rate increases as the chamber pressure increases, and regression rates range from approximately at 0.25 MPa to at 0.90 MPa. Furthermore, it is observed that the pressure exponent of the fuel regression rate is 1.05 and the fuel regression rate is not influenced by the oxidizer port velocity in this study. The model explains that the backfiring problem tends to occur in relatively high-pressure conditions, and it leads to the conclusion that increasing the nozzle throat diameter is an effective means of preventing backfiring from occurring.

Hydroxyl‐terminated Polybutadiene Curing by 1,3‐dipolar Cycloaddition of Energetic Nitrile N‐Oxides: Room Temperature Curing Property, Kinetics, Thermodynamics, and Propellant Combustion Characteristics

Abstract5‐nitro‐1,3‐benzenedichloroaldehyde oxime was designed and synthesized to achieve room temperature curing of HTPB binders, and its structures were characterized. A new kind of 1,3‐dipolar cycloaddition reaction system was formed by HTPB as main resin, 5‐nitro‐1,3‐benzenedichloroaldehyde oxime and triethylamine as curing agent. The results revealed that the formation of isoxazoline ring in cured HTPB elastomers mainly derived form the reaction of Nitrile N‐Oxide with cis alkene of HTPB, and the cured HTPB elastomers underwent three stages decomposition. The kinetic parameters and thermodynamic parameters for the 14 % curing agent's sample were obtained from the DSC data. The activation energy was computed to be 204.75 kJ mol−1 and pre‐exponential factor was 1.38×1023 s−1.The burning rate of the propellant showed that the propellant with HTPB cured by containing −NO2 Nitrile N‐Oxides (100 % HTPB, 14 % Nitrile N‐Oxides, 2 % Aluminum and 77 % Ammonium perchlorate, Curing at 25 °C for 5 days ) had a higher burning rate and pressure exponent compared to conventional HTPB propellant (100 % HTPB, 14 % toluene diisocyanate, Nitrile N‐Oxides, 2 % Aluminum and 77 % Ammonium perchlorate, Curing at 60 °C for 5 days). Therefore, the containing −NO2 Nitrile N‐Oxides curing system could be used as a novel promising curing system for HTPB‐based solid composite propellants.

Reconstruction of radial parametric pressure field near ground surface of landing typhoons in Northwest Pacific Ocean

The radial distribution of environmental pressure near the ground surface during typhoons is an initial input condition for height-resolving typhoon modeling widely used as a practical and relatively accurate method for rapid assessment of typhoon-induced natural hazards and wind-resistant design of structures. The radius to maximum wind speed Rmax and radial pressure distribution parameter βs, (usually named the Holland power exponent of atmospheric pressure) are two key pressure field parameters that fundamentally determine the parametric typhoon pressure field and collocated wind velocity field. Observations from the Joint Typhoon Warning Center (JTWC) show that Rmax follows a lognormal distribution and has strong correlation with central pressure difference Δps and typhoon center latitude ψ. However, it is still hard to satisfactorily reproduce the landing typhoon environmental pressure. By employing near-ground environmental pressure data involving several hundreds of meteorological stations distributed in coastline regions of the Northwest Pacific Ocean, evolution of typical environmental pressures during four strong typhoons, Khanun (0515), Wipha (0713), Krosa (0716) and Morakot (0908), have been recorded in Southeast China. Finally, a novel technique for modeling the radial surface pressure model is proposed utilizing an appropriate model for radius to maximum winds Rmax. The variation characteristics for directions, landfall states and probability distributions of βs are compared and discussed, and then probability correlations among βs and Rmax, Δps, ψ are fitted and validated, showing that the statistical correlation function model is obviously different from former formulations and is more suitable for rebuilding a wind velocity field, especially near the ground surface after typhoon landfalls along the southeast coastlines of China, which are typhoon-prone hazard regions during moving typhoons.

Preliminary Numerical Study of Fire-Induced Pressure Rise in a Passive House Compartment

Passive houses are becoming more and more popular due to energy efficiency requirements. An important aspect is their airtightness, i.e., they have a very low leakage. The present paper describes a preliminary numerical study on fire-induced pressure variations in a structure that resembles a passive house compartment. The configuration without ventilation system is considered in this paper. The fire source used in the experiment consists of wood cribs that have been simulated in the Fire Dynamics Simulator (FDS), version 6.5.2, as a cube with a prescribed heat release rate (HRR) curve (based on experimental measurements). The grid sensitivity study is conducted by using different mesh cell size and comparing the results of pressure variation. A cell size of 0.1 m is considered sufficient in this preliminary study. The maximum over-pressure obtained without ventilation reached up to 870 Pa in the experiment. Such high over-pressure will definitely hinder the escape of occupants. The structural integrity may also be affected by the over-pressure. Using a constant leakage area, which is the default option, the pressure difference without ventilation rises up to 2027 Pa in the simulation. A good agreement with the experimental data can only be achieved if the simulated leakage area is not kept constant when the room pressure rises. Tuning the leakage pressure exponent in FDS significantly reduces the deviation between the simulation and experimental results. The default setting of reference pressure difference in FDS is used to examine the influence of this parameter on the pressure prediction. When applying the default reference pressure difference, a smaller leakage pressure exponent is needed to reproduce experimental results. Therefore, the reference pressure difference has a certain influence on leakage area and should be set according to the pressure used in determining the reference leakage area during experiments. The overall pressure evolutions are qualitatively well captured in the FDS simulations, as these strongly depend on the fire heat release rate evolution, which was prescribed to match the experimental profile. However, in order to improve the current level of accuracy and address the general validity of the observations made in the present study, more experimental and numerical work need to be carried out.

Burning Rates of Nanoaluminum–Water Solid Propellants at Various Pressures

The burning rates of solid propellants comprising different nanoaluminum powders and distilled water were examined at pressurized conditions up to . Several aluminum powders were tested using a strand burner technique: uncoated nanopowder (ALEX), stearic-acid coated nanopowder (L-ALEX), Viton-coated nanopowder (V-ALEX) with two different particle sizes, and bimodal mixture of V-ALEX and micrometer-size powders. Propellants containing ALEX, L-ALEX, and bimodal compositions followed the power law relation throughout the pressure range, with pressure exponents of , 0.5, and 0.28, respectively. Propellants containing V-ALEX powder demonstrated two different regimes: at pressures lower than 1.8 MPa, the burning rates were constant with respect to pressure; whereas for higher pressures, the burning rates followed the power law relation with and for powder diameters of 60 and 100 nm, respectively. The combustion efficiency, defined as the fraction of aluminum that oxidized during combustion, showed high values (90–95%) for all tested compositions.

Iterative filter based estimation of fully 3D heterogeneous fields of permeability and Mualem-van Genuchten parameters

The accurate modeling of flow and transport in the vadose zone for agricultural and environmental applications requires knowledge about soil parameters. Soil parameters vary in space depending on soil texture and structure. In the present synthetic study we considered spatial variation of permeability (k), inverse of capillary entry pressure head (αVG) and exponent (n) of the Mualem-van Genuchten model. The iterative Ensemble Kalman filter (IEnKF) can estimate the spatially variable soil parameters if measurements of water saturation at different locations and times are available. We used as input daily precipitation data from the Berambadi catchment (southern India). We first considered that the parameters vary horizontally but are constant in the vertical direction. In this case log (k) and log (αVG) can be estimated satisfactorily with 30%–40% reduction of RMSE (compared to open loop runs), if the initial guess of the spatial correlation lengths of the heterogeneous fields is equal to or larger than the unknown, true values. The estimation of exponent n is poorer as the reduction of RMSE is just 20%. If vertical heterogeneity of the parameters is considered the estimation of log (k) and log (αVG) is only improved for the upper 1.5 m and estimation of n is not improved. We also demonstrate that the estimation problem can be simplified when flow in the unsaturated zone is predominantly vertical. If in this case soil hydraulic parameters are estimated with IEnKF at measurement locations and afterwards interpolated with kriging, results are produced with a similar quality as with 3D-IEnKF.

Burning rate and other characteristics of strontium titanate (SrTiO3) supplemented AP/HTPB/Al composite propellants

Abstract In a quest of search for a new burning rate modifier for composite propellant, strontium titanate (SrTiO3), a perovskite oxide has been chosen for evaluation in a composite propellant formulation based on its other catalytic applications. Initially, SrTiO3 was characterized for particle size, morphology and material/phase identification (using XRD). By varying SrTiO3 content in a standard composite propellant, different compositions were prepared and their performance and processing parameters like the end of mix (EOM) viscosity, mechanical properties, density, burning rate, pressure exponent (n-value), etc. were measured. The results reveal that 2% SrTiO3 causes more than 12% enhancement in propellant burning rate (at 70 ksc pressure) in comparison to the standard propellant composition. The pressure exponent also increases to 0.46, whereas the standard composition was having its value as 0.35.

Preparation and Evaluation of Effective Combustion Catalysts Based on Cu(I)/Pb(II) or Cu(II)/Bi(II) Nanocomposites Carried by Graphene Oxide (GO)

AbstractIn this work, the preparation and combustion catalysis effects of Cu2O−PbO/GO and CuO−Bi2O3/GO nanocomposites were systematically investigated. It was shown that the burning rate of the DB propellants can be significantly enhanced by both the nanocomposite catalysts, with reduced pressure exponent. In particular, the Cu2O−PbO/GO induced a burn rate enhancement for DB propellant in pressure range of 2–14 MPa, with the maximum catalytic efficiency of 3.87 at 2 MPa. More interestingly, it resulted in “mesa” burning of DB propellant in the pressure range of 12–20 MPa (n=‐0.05). The CuO−Bi2O3/GO have the same effect with a burning rate increasing from 2.15 to 8.57 mm s−1 at 2 MPa. Similarly, for the RDX‐CMDB propellant, the GO‐based composites of Cu2O−PbO/GO and CuO−Bi2O3/GO showed evident catalytic activities. Plateau combustion was achieved in their presence, which is of great importance for practical applications. The catalysis effects of the two composites are closely related to the high dispersion of metal oxide particles and GO with excellent thermal conductivity.

Effects of Dihydroxylammonium 5,5′‐Bistetrazole‐1,1′‐Diolate on the Properties of HTPB Based Composite Solid Propellant

AbstractSeveral industrial‐ and research‐type hydroxyl‐terminated polybutadiene (HTPB) composite solid rocket propellants, containing dihydroxylammonium 5,5′‐bistetrazole‐1,1′‐diolate (TKX‐50) particles and, featuring the same nominal composition, were prepared. The energetic properties of composite propellants containing different mass fractions of TKX‐50 particles were theoretically computed and experimentally evaluated. The effects of different mass fractions of TKX‐50 on the rheological properties of both TKX‐50/HTPB binder slurries and AP/HTPB/Al propellant slurries were investigated. The strand burning rates, the associated combustion flame structures, and the hazardous properties of the resulting propellants were experimentally analyzed. All of the properties mentioned above were also compared to those of the reference propellant without TKX‐50. The results show that the prepared TKX‐50 particles can sufficiently be dispersed in the HTPB binder plasticized by di‐2‐etylhexyl sebacate (DOS). The propellant compositions containing different mass fractions of TKX‐50 are insensitive to impact and friction, differentlyfrom the reference propellant without TKX‐50. Moreover, over the explored pressure range, TKX‐50 can affect the combustion behavior and decrease the burning rate as well as pressure exponent of composite solid propellants compared with the reference composition.

Insight into cooling agent addition on combustion activity and mechanism of catalyzed 5AT-Sr(NO3)2 based propellant

Thermal decomposition characteristics and combustion behaviors of 5-amino-1H-tetrazole-strontium nitrate (5AT-Sr(NO3)2) propellant are of great essence in determining fire-fighting efficiency of the novel Halon alternative technology-solid propellant gas generators (SPGGs). This study will seek to find the impacts on combustion mechanism of adding two kinds of coolants, aluminum hydroxide (Al(OH)3) and calcium carbonate (CaCO3) into 5AT-Sr(NO3)2 based propellant with the employments of experimental measurement and theoretical analysis. Results show that apart from three similar reactions occurring around the close temperature ranges for three different propellants, an endothermic reaction stemming from the breakdown of Al(OH)3 forms when adding Al(OH)3, and two extra exothermic reactions representing the reaction between CaCO3 and HCN, and the generation of isocyanato exist with CaCO3 addition. Especially, according to traditional Kissinger method calculation, great variations can be seen in the activation energy except for the 5AT decomposition reaction. With the presence of Al(OH)3 or CaCO3, the propellant's theoretical outlet temperature has been reduced by ∼300 °C, while experimental combustion temperature at different sampling points are lowered approximately by 342–417 °C. With the employment of closed-bomb test, it is discovered that the burning rate in the relatively-low pressure zone is mastered by condensed-phase thermal decomposition reaction of 5AT, whereas that in the relatively-high pressure area is dominant by the redox reaction. Unlike Al(OH)3, addition of CaCO3 could reduce the pressure exponent effectively. The specific shapes of burning surface are found to determine the flame shapes for three 5AT-Sr(NO3)2 based propellants, which turn out be parallel, divergent, and converging profile, respectively. Besides, a gas flow model for 5AT-Sr(NO3)2 based propellant is proposed in this study, which can well illustrate the burning rate differences from the perspective of porous structure for propellant particles. Results of this study have implications concerning designs for 5AT-Sr(NO3)2-based propellants widely used in SPGGs apparatus, which can provide a potential approach for making a novel 5AT-Sr(NO3)2-based propellant with low combustion temperature as well as low burning rate pressure exponent.

Combustion of hydro-reactive compositions on the base of a metal–polymer matrix

ABSTRACTThere are different methods of fast hydrogen generation by reaction of metal powder with water. Fundamental study of combustion of aluminum–water compositions with frozen water (aluminum–ice [ALICE]) is of great interest for the rocket technique applications. New solid hydro-reactive compositions of ALICE type on the base of permeable micro-porous metal–polymer matrices filled with water is reported. Magnesium (Mg) powder of 80 μm was chosen as a combustible. Combustion characteristics for these compositions in a nitrogen or argon atmosphere at different pressures were studied. It was found that the burning rate was 12–18 mm/s in the wide pressure range up to 80 atm, as the pressure exponent was close to zero. It was shown that the presence of a thin agglutinant polymer film on the Mg particle of the metal–polymer matrix did not significantly affect the burning rate of samples in comparison with mixtures of Mg powder with water but resulted in some combustion peculiarities. Preliminary experiments studying the combustion wave propagation along the metal–polymer matrix surface in water steam were carried out.

Highly energetic nitramines: A novel platonizing agent for double-base propellants with superior combustion characteristics

The burning rate-pressure relation of solid propellant is an exponential relation; this is means catastrophic combustion process in case of sudden increase in operating pressure. This study reports on novel approach to minimize the dependence of burning rate on combustion pressure using highly energetic nitramines (RDX). Nitramine-based double base propellants with RDX content up to 20 wt% were manufactured by solventless extrusion technology. The impact of RDX content on burning rate, specific impulse, exhaust velocity, and thrust were evaluated using small-scale ballistic evaluation rocket motor. Specific impulse (Is) was enhanced by 20%. The action burning time (tb) was increased by 14%. The total thrust impulse (IFT) was significantly improved by 22%. One of the main outcomes of this study is that burning rate pressure exponent (n) was decreased significantly from 0.35 to 0.05. This novel ballistic performance finding means minimal change in burning rate with pressure variation. These findings confirmed that RDX has a dual function as energetic filler and platonizing agent. RDX blowing effect could alter the combustion mechanism by pushing the luminous flame from the burning surface. Furthermore, RDX decomposition can strengthen the platonization action. This is the first time ever to report on burning rate platonization using RDX. It can be concluded that many advantages have been achieved with one shot.

Combustion characteristics of extruded nitramine double-base propellants

AbstractThe burning rate-pressure relation of solid propellant is an exponential relation; this is means catastrophic combustion process in case of sudden increase in operating pressure. This study reports on novel approach to minimize the dependence of burning rate on the operating pressure using highly energetic nitramines (RDX). Nitramine-based double base propellants with RDX content up to 20 wt % were manufactured by solventless extrusion technology. The impact of RDX content on burning rate, specific impulse, exhaust velocity, and thrust were evaluated using small-scale ballistic evaluation rocket motor. Specific impulse (Is) was enhanced by 20 %. The action burning time (tb) was increased by 14 %. The total thrust impulse (IFT) was significantly improved by 22%. One of the main outcomes of this study is that burning rate pressure exponent (n) which was decreased significantly from 0.35 to 0.05. This novel ballistic performance means minimal change in burning rate with pressure variation. These novel findings confirmed that RDX has a dual function as energetic filler and as a platonizing agent. This is the first time ever RDX has been reported to act as a platonizing agent. It can be concluded that many advantages have been achieved with one shot.

Metal-Water mixtures for Propulsion and Energy-Conversion Applications: Recent Progress and Future Directions

The metal-water system is attractive for propulsion and energy-conversion applications. Of all metals, aluminum is attractive due to its high energy density, relative safety, and low cost. Experimental studies provide new insight on the combustion and propulsive behaviors. The burning rate is found to be a strong function of both pressure and particle size. Furthermore, there is a wide scatter in the measured pressure exponents due to differences in particle size, pressure, pH, and equivalence ratio. A major problem with Al/H2O mixtures is incomplete combustion and poor impulses, thereby rendering Al/H2O mixtures unsuitable for practical applications. Efforts to improve the performance of Al/H2O mixtures have only met with moderate success. Although experiments have revealed these new trends, not much is offered in terms of the underlying physics and mechanisms. To explore the combustion mechanisms, theoretical models based on energy balance analysis have been developed. These models involve numerous assumptions and many complexities were either ignored or treated simplistically. The model also relies on empirical inputs, which makes it more a useful guide than a predictive tool. Future works must endeavor to conduct a more rigorous analysis of metal-water combustion. Empirical inputs should be avoided and complexities must be properly treated to capture the essential physics of the problem. The model should help us properly understand the experimental trends, offer realistic predictions for unexplored conditions, and suggest guidelines and solutions in order to realize the full potential of metal-water mixtures.