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Azodicarbonamide (ADC) based airbag gas generants with various potential oxidizers, including (1) C2H4O2N4/KNO3 (2) C2H4O2N4/NaNO3 (3) C2H4O2N4/Sr(NO3)2 (4) C2H4O2N4/Ba(NO3)2 (5) C2H4O2N4/KIO4 and (6) C2H4O2N4/NaIO4 were thoroughly tested to identify the best mixture for a real-time ballistic application. The evaluation of the gas generant mixtures is carried out based on the performance properties such as quantity of oxidizer decomposed (in g) to give 1 g of O2, residual mass % of the mixture, density of the oxidizer, oxygen balance percentage for the oxidizer, adiabatic flame temperature, onset temperature, activation energy, pre-exponential factor, critical ignition temperature, change in enthalpy, change in entropy, impact sensitivity and friction sensitivity of the gas generant mixtures. Using the TOPSIS methodology, a systematic approach was developed for the first time to determine the best suitable airbag gas generant for real-time ballistic application by taking into account all of these properties. TOPSIS findings revealed that the preferred order of the airbag gas generant mixture is C2H4O2N4/KIO4 > C2H4O2N4/NaIO4 > C2H4O2N4/KNO3 > C2H4O2N4/NaNO3 > C2H4O2N4/Sr(NO3)2 > C2H4O2N4/Ba(NO3)2. A similar methodology can also be used to discover the best fuel/oxidizer mixture for any other composition. [ABSTRACT FROM AUTHOR]

Large hydrocarbon fuels are used for ground and air transportation and will be for the foreseeable future. A key parameter when burning these fuels is the turbulent consumption speed, which is the velocity at which fuel and air are consumed through a turbulent flame front. Such information can be useful as a model input parameter and for validation of modeled results. In this study, turbulent consumption speeds were measured for three jet-like fuels using a premixed turbulent Bunsen burner. The burner was used to independently control turbulence intensity, unburned temperature, and equivalence ratio. Each fuel had similar heat releases (within 2%), laminar flame speeds (within 5–15%), and adiabatic flame temperatures. Despite this similarity, for constant ReD and turbulence intensity, A2 fuel (i.e. jet-A) has the highest turbulent flame speeds and remains stable (i.e. without tip quenching) at lower ϕ than the other fuels. In contrast the C1 fuel, which consists of heavily-branched alkanes, contains no aromatics and has a relatively high average molecular weight, has the slowest turbulent flame speeds and is the most prone to tip quenching. The C1 fuel has the highest stretch sensitivity, in general, as indicated by calculated Markstein numbers. This work shows that turbulent flame speeds and tip stability of multi-component large hydrocarbon fuels can be sensitive to the chemical class of its components. [ABSTRACT FROM AUTHOR]

High energy composite films made from high explosives has important applications in pyrotechnics. In this study, electrostatic spraying was used to prepare energy-containing films based on 1,2,3,4-butanetetrol tetranitrate (ETN). The results show that all energy containing films are made of nanofibres. They have excellent hydrophobicity and combustion properties. In particular, monolayer films in which ETN is the main energy containing substance. Once ignited, the trace monolayer film generates a maximum pressure of 0.85 MPa and an adiabatic flame temperature of 2,855 °C. For single and double layer films, the heat of combustion can reach 9899 J/g and 11975 J/g respectively. The level of combustion heat can also be controlled by adjustment of the ETN content. The results of the thermo-properties performance evaluation show that by optimizing the nanostructure, the ETN-based energy-containing fiber membranes can meet the requirements of advanced pyrotechnic products. In particular, there is great potential in the metastable intermixed composites (MICs) field. [ABSTRACT FROM AUTHOR]

Thermoelastic stress analysis (TSA) can be used to determine the stress field of structures or materials under cyclic loadings through temperature under adiabatic conditions. So high-frequency cyclic loadings are considered as a fundamental condition. However, loading frequencies in many practical applications do not meet the adiabatic conditions. In order to improve the accuracy of TSA under low-frequency fatigue loadings, the non-adiabatic response in TSA was derived by combining the classical thermoelastic equation and heat conduction equation. This response was used to create a modified model that accounted for heat transfer and temperature distribution under low-frequency loading conditions. Otherwise, fatigue test and finite element method were used to evaluate the correctness of the modified model using epoxy resin material. The results showed that the temperature change obtained from the modified model were in good agreement with the experiment results. The modified model can effectively evaluate the structural stress under low-frequency fatigue loadings. [ABSTRACT FROM AUTHOR]

In this study, three hydration heat controlling materials (HHCMs), respectively, containing pure hydroxyl (polyvinyl alcohol, PVA), carboxylic (polyacrylic acid, PAA) and ester groups (maleic acid-ethylene glycol ester, P(MA-EG)) were synthesized and mixed with cement-based materials, and the hydration heat and setting time of cement pastes and the SEMI adiabatic temperature rise and strength of mortars were tested. The results showed that PAA and P(MA-EG) reduced the peak value of hydration exothermic rate by 77.45% and 62.28%, respectively, and prolonged 54.14 h and 15.56 h, respectively. Mechanism studies showed that HHCMs containing carboxylic or hydroxyl groups adsorbed on cement particles by Ca2+ complexation, while HHCMs containing ester groups hydrolyzed to carboxylic groups in alkaline cement pastes, which hydrolysis rate changed with the hydration temperature of cement-based materials to regulate the hydration process. This study aims to provide technical feasibility and theoretical basis for exploring new avenues of synthesizing HHCMs with different functional groups. [ABSTRACT FROM AUTHOR]

Biodiesel is one of the most important alternative fuels due to limited conventional resources. Methyl octanoate with long alkyl chain and mono-alkyl ester is one of the surrogate fuels of actual biodiesel. In order to clarify distinctive combustion characteristics of methyl octanoate, comparison with alkane in traditional diesel is necessary. Therefore, this work chose n-nonane with same carbon number as methyl octanoate. The laminar flame speeds of two fuels were measured at different conditions (T = 423 K, P = 1 and 3 atm, and φ = 0.7–1.5) in a constant volume combustion bomb. Results show that laminar flame speed of n-nonane is higher than that of methyl octanoate in most conditions, but lower in fuel-rich conditions. The combined chemical kinetic model of methyl octanoate and n-nonane was developed through eliminating unnecessary reactions, which can well predict the experimental results of laminar flame speed and ignition delay time. The adiabatic flame temperature results from the updated kinetic model show that the temperatures of n-nonane are higher than methyl octanoate in whole conditions, which is unexpectedly opposite to their laminar flame speeds order in fuel-rich conditions. In overall conditions, the intermediates of methyl octanoate tend to produce CH3, which consumes H radicals, thereby reducing the laminar flame speed, which can explain the higher laminar flame speed of n-nonane in most conditions. Meanwhile, the oxidation reactions with oxygen molecules of intermediates of n-nonane are suppressed due to low combustion temperature at φ = 1.5 unlike at φ = 0.7 and 1.0. On the contrary, those of methyl octanoate have similar reactions between φ = 0.7, 1.0, and φ = 1.5. It means that the laminar flame speed of n-nonane decreases more significantly than methyl octanoate as the equivalence ratio increases from φ = 1.0 to φ = 1.5. [ABSTRACT FROM AUTHOR]

One method for reducing flue gas emissions is oxygen enrichment combustion. In this study, propane has been used as a fuel. The oxygen-enriched combustion study was carried out by increasing the oxygen ratio in the air used for combustion. Experiments have been performed at a constant equivalence ratio (1.2) and the number of swirl (s = 1) at 7 kW thermal power. Combustion has been performed under different oxygen ratios of 21%, 24%, 27%, and 28%, respectively. During combustion, acoustic enforcement has been carried out on the propane flame by utilizing loudspeakers, and so flame instability has been observed by changing enforcement levels and investigating dynamic pressure, luminous intensity, and flame images. The acoustic resonance of the combustion chamber was determined by basing abrupt changing dynamic pressure on 110, 175, and 330 Hz. The flue gas emission value and temperature effect of oxygen-enriched combustion were investigated under different acoustic excitations. Dynamic pressure and luminous intensity went up with oxygen enrichment. CO emission decreased about 97%, and adiabatic flame temperature increased, and NOx emissions increased about 2.5 times as the oxygen ratio increased. The flame length reduced under acoustic enforcement. The flue gas emissions decreased at all acoustic enforcement levels, especially at 110 Hz. As a result of acoustic enforcement, flame instability was reduced and the flame burned strongly. [ABSTRACT FROM AUTHOR]

Electrocaloric (EC) cooling has the potential to be an alternative to traditional cooling methods. The polyvinylidene fluoride-trifluoro ethylene-chlorofluoroethylene terpolymer (P(VDF-TrFE-CFE) is used as electrocaloric material. A 3D equation-based modeling and finite element simulations are performed for EC cooling, where the battery's heat generation is considered a heat source for analysis. The electric field waveform has been varied to obtain the maximum possible ECE. Electric field cycles with 0.3 sec holding provide the maximum EC temperature change. The magnitude of the electric field is also varied and a maximum adiabatic temperature change of 5.41 K is achieved under 100 MV/m. The EC effect shows that the heat transfer from the source (battery surface) to the sink (environment) is faster than without EC. [ABSTRACT FROM AUTHOR]

Motivated by the pioneering activation-energy asymptotic analysis of strained laminar premixed flames in counterflow by Libby and his coworkers, a rate-ratio asymptotic analysis is carried out to elucidate the structure and predict the critical conditions of extinction of strained premixed methane flames. Steady, axisymmetric, laminar flow of two counterflowing streams: a reactive mixture stream and a product stream toward a stagnation plane is considered. The temperature of the reactive mixture stream is T 1 and it is made up of methane (CH4), oxygen (O2) and nitrogen (N2), while the temperature of the product stream is T 2 , and it is made up of O2, carbon dioxide, water vapor and N2. The asymptotic flame structure is presumed to be made up of a thin reaction zone where all chemical reactions take place. On one side of the reaction-zone is an inert, preheat zone containing the reactants and on the other side a post-flame zone made up of products. Analysis of the preheat zone gives matching conditions that is required to analyze the structure of the reaction zone. A four-step, reduced mechanism is used to describe the chemical reactions. The reaction zone is presumed to be made up of an inner layer, where CH4 is consumed. The hydrogen (H2) and carbon monoxide that are formed in this layer are consumed in an oxidation layer that is made up of two layers: an H2-oxidation layer and a CO-oxidation layer. The results of the analysis are used to predict the flame location, y r , flame temperature, T r , and the speed of the convective flow, v b , in the reaction zone as a function of the strain-rate, a u . Classical C-shaped curves were obtained when y r , T r and v b are plotted as a function of a u and they were used to predict extinction. A key finding of this work is that v b is proportional to T r − T 0 , where T 0 is the crossover temperature predicted by the rate-ratio asymptotic analysis. Whether abrupt extinction will take place or not was found to depend on the value of T 2 relative to T 0 , which is different from the predictions of activation-energy asymptotic analysis where T 2 must be compared with the value of the adiabatic temperature. Similar to the analysis of Libby and his coworkers, the rate-ratio asymptotic analysis predicts the existence of "negative flame speeds," where the convective flow and the diffusive flow of reactants in the reaction zone, are in opposite directions. The predictions of the rate-ratio asymptotic analysis were found to agree with the results of computations with detailed chemistry and previous experimental data. [ABSTRACT FROM AUTHOR]

We present an asymptotic analysis of a strained premixed flame in the mixing layer between two counterflowing streams: one with fresh reactants at a temperature T u and other with the burned gases at temperature T b , which may be different from the adiabatic combustion temperature T e = q Y F u / c p + T u of the fresh gases. A one-step irreversible Arrhenius reaction model, of high activation energy, is used for the asymptotic analysis, together with the thermal-diffusive approximation of constant density and transport properties – easily generalized to variable density and transport properties with the use of a heat-conduction-weighted coordinate. The analysis for near unity Lewis numbers of the fuel by Libby, Liñán and Williams (1983) is extended here to arbitrary nonunity Lewis numbers, of relevance to a wide variety of applications, ranging from hydrogen-fueled combustors to heavy fuel systems. In analogy with Liñán's analysis of counterflow diffusion flames, three asymptotic distinguished regimes are identified for premixed flames for large activation energies and the appropriate Damköhler numbers – the ratio of the characteristic diffusion and reaction times. These regimes are the premixed flame regime, the partial burning regime and the nearly frozen ignition regime. The analytical expressions obtained for these regimes, of the dimensionless reaction rate as a function of the Damköhler number, are seen to describe with good accuracy the results obtained from the numerical integration of the full problem. [ABSTRACT FROM AUTHOR]

In this article, the thermal stability of tert-butyl perbenzoate (TBPB) mixed with different concentrations of toluene and p-tert-butylcatechol (TBC) was investigated. The exothermic onset temperature (T0), the heat of decomposition (ΔH), and the adiabatic temperature rise (ΔTad) of the samples were obtained by differential scanning calorimetry (DSC) and Phi-TEC II adiabatic calorimetry. The apparent activation energy (Ea) and the maximum reaction rate arrival time under adiabatic conditions were obtained by adiabatic kinetic calculations for 8 h (TD8) and 24 h (TD24). Based on Semenov's theory, the self-accelerated decomposition temperature was calculated as a support for safe storage and transport. The results of DSC and Phi-TEC II showed that toluene was effective in reducing the thermal hazard during the decomposition of TBPB. The addition of TBC caused side reactions. The moderate addition of toluene and TBC improves the thermal stability of TBPB and can improve the safety of TBPB in industrial applications. [ABSTRACT FROM AUTHOR]

This study investigated experimentally the effects of H2-enrichment on premixed oxy-methane flames stabilized on a micromixer-like burner for clean energy production in gas turbines. The stable combustion zone was established over ranges of fuel hydrogen fraction (HF: 25–70% by vol.) and equivalence ratio (ϕ: 0.1–1) at fixed oxidizer oxygen fraction (OF = 30% by vol.) and fixed jet velocity (5.2 m/s). The blowout limit was plotted within the HF-ϕ space, superimposed on the contours of some operating parameters, namely adiabatic flame temperature (AFT), combustor power density (PD), jet Reynolds number (Re), and unburnt-mixture density (ρmix). Furthermore, images of visible flame shape were acquired at distinct points within the stable zone to study the effects of ϕ, HF, AFT, PD, Re, and ρmix on flame macrostructure. Results show that H2-enrichment extends the blowout limit from ϕ = 0.35 down to ϕ = 0.1, thereby widening the stable combustion zone. The blowout limit has little correlation with AFT and PD but correlates strongly with ρmix, i.e., occurs consistently at the same ρmix. The analyses of blowout limit and flame images were used to infer that the flames blow out possibly at constant ignition delay. [ABSTRACT FROM AUTHOR]

Theoretical predictions of dust-explosion characteristics, such as the minimum explosive concentration (MEC), can help improve the accuracy of quantitative risk assessment. This paper presents a continuum model to simulate one-dimensional dust-cloud combustion. It is found that the dilution of dust by thermal expansion reduces the propagation speed of a combustion wave through a dust cloud. At the same time, the delay in the increase of particle velocity due to relaxation time counteracts the dilution effect. Therefore, neglecting the relaxation time results in the underestimation of propagation speed. In the absence of heat loss, extinction occurs when the adiabatic combustion temperature decreases to the ignition temperature; MEC is independent of particle size in such cases. With the presence of heat loss, on the other hand, extinction occurs at a higher dust concentration; MEC increases with particle size. Accurate evaluation of ignition temperature is key to the quantitative prediction of MEC. A particular focus is given to gravity effects, reflecting recent experimental efforts to obtain fundamental insights into propagation mechanisms without being affected by gravity. In upward propagation, particles fall toward the reaction front, enhancing combustion and increasing the propagation speed. The situation in downward propagation is the opposite, and extinction occurs when the gravity level is beyond a critical value. In upward propagation, MEC can decrease with an increase in particle size, owing to the influence of gravity. [ABSTRACT FROM AUTHOR]

Mixtures of CH4 and CO2, known as biogas, are considered as renewable gas with low heat energy, which makes it extremely difficult to use as fuel in conventional natural gas equipment. To better understand the behavior of biogas mixtures and their properties, numerical results of the impact of carbon dioxide on laminar burning velocity and flame temperature of methane (CH4)–carbon dioxide (CO2)–air combustion were done. One of the most promising methods to enhance combustion is the use of a plasma source to assist unstable flames. For this purpose, experimental results to investigate the effect of microsecond pulsed plasma on non-premixed biogas flames were conducted. In the first section, laminar burning velocities and adiabatic flame temperature have been numerically calculated by one-dimensional steady code using several chemical kinetic mechanisms. Numerical results were compared with several experimental results from the literature. The laminar burning velocity and the adiabatic temperature of biogas/air combustion were calculated with CO2 concentration ranging from 0% to 50% in the mixture. The equivalence ratio was varied from 0.4 to 1.4, the initial pressure was set at 1 bar, and the temperature was set to 300 K. The impact of CO2 addition on the CO and NOx emissions at equivalence ratios from lean to rich (0.4–1.4) was investigated. It was found that increasing CO2 in the biogas lowers NOx and increases CO. In the second section, the effects of microsecond pulsed plasma on non-premixed swirling biogas/air flames were experimentally investigated. The plasma-assisted combustion was carried out in a coaxial burner. It consists of two concentric tubes; the central tube delivers the biogas flow to the injector and the annular tube contains a swirler and supplies the airflow. To create plasma in the stabilization zone of the flame, a rod-ring microsecond plasma configuration was used. OH* chemiluminescence measurements are used to describe the structure and stability of the flame. Results showed that plasma generated by microsecond high-voltage (HV) pulses can improve flame stability. An analysis of the optical emission spectra (OES) showed that plasma generates chemically active species such as excited N2*, CH*, OH* molecules, and H* atoms, leading to improved flame stability. The dependence of their intensities on both the pulse repetition frequency (PRF) and the input electrical voltage was investigated. The gas analysis of the exhaust gas was carried out with and without plasma. The exhaust gas concentration measurements revealed that the rod-ring pulsed plasma reduces CO with a low impact on the NOx level. [ABSTRACT FROM AUTHOR]

This article focuses on the effect of radiative heat on natural convection heat transfer in a square domain inclined with an angle. The left vertical wall of the enclosure is heated while maintaining the vertical right wall at room temperature with both adiabatic upper and lower horizontal walls. The governing equations are Navier–Stokes equations subjected to Boussinesq approximation to account the change in density. The natural convection–radiation equations are solved continuously to obtain the temperature, velocity and pressure. Taylor–Hood finite element approach has been adopted to solve the equations using triangular mesh. Effects of Rayleigh number, Planck constant and optical depth on the results are considered, presented and analyzed. Results show that the adiabatic walls, Planck constant as well as the inclined angle play an important role in the distribution of heat transfer inside the cavity. [ABSTRACT FROM AUTHOR]

Methane explosions are among the main hazards in coal mines. Shock waves from methane explosions can cause damage near the explosion site, and combustion products can spread along the tunnel to locations far from the explosion source and endanger the lives and health of personnel. Therefore, the study of the propagation patterns of methane explosion shock waves and the distribution of high-temperature combustion products in tunnels. has significance for emergency decision-making in the event of methane explosions in a mine. This study uses the 3D Computational Fluid Dynamics (CFD) program GASFLOW-MPI, which models the one-step methane combustion mechanism with the addition of a heat transfer model. The methane explosion process is simulated and reproduced at the Lake Lynn Experimental Mine (LLEM) to analyze the process of gas deflagration. The results reveal that the overpressure in the tunnel after the methane explosion oscillates and decays with time. Gaseous products of the explosion "expand and compress" and flow back and forth in accordance with the oscillation of overpressure. The maximum expansion ratio of the CO2 concentration isosurfaces of 0.5% in the heat transfer simulation is 6.21, whereas the volume expansion ratio is 3.78 once the flow field stabilizes. The distribution of combustion products along the alleyway exhibits a Gaussian decay trend. The range of gaseous product distribution and temperature fields in the adiabatic tunnel is significantly higher than that in the heat transfer simulations, thus indicating that heat loss significantly influences the temperature characteristics and distribution pattern of combustion products in the full-scale tunnel. [ABSTRACT FROM AUTHOR]

Natural convection in a closed cavity with block-free, adiabatic and heat-conducting blocks was assessed for different inclination angles. The enclosure has vertical walls at different temperatures and adiabatic horizontal walls. The simulations were performed for the laminar regime and two-dimensional approximation. A cell-centered finite volume scheme was used to discretize the governing equations. This work addresses the influence of the Rayleigh number and cavity inclination in the flow pattern, temperature distribution, and local/global Nusselt numbers. It was observed that the largest heat transfer rates take place for heat-conducting blocks and inclination angles 15 ° ≤ ϕ ≤ 45 ° owing to higher velocity gradients. [ABSTRACT FROM AUTHOR]

Dependence of flame suppression concentration on the equivalence ratio was analyzed using modeling premixed propane/air flame inhibited by 2-BTP, Novec 1230, CF3Br, H2O, CO2, and N2. It was obtained that the suppression concentration of additives with fuel component is increased in the fuel-lean mixtures as a result of the increase of adiabatic flame temperature with their addition. Calculations of adiabatic explosion pressure (combustion temperature) under constant volume conditions demonstrate that the addition of inhibitors with fuel component to the lean mixtures increases the combustion pressure even for CF3Br additive. Suppression concentrations of inert additives (N2, CO2, H2O) were at the maximum for slightly rich mixtures where the maximum adiabatic flame temperature is observed. Calculations for the blend (inert and effective chemical inhibitor; CO2/2-BTP) demonstrate that their use might be effective in the lean mixtures close to the flammability limits. The suppression concentration of 2-BTP in the blend (2-BTP/CO2 = 50/50) was less than for pure inhibitor (2-BTP), thus leading to some decrease of the combustion pressure for inhibited flames near the flammability limits in comparison with pure 2-BTP. [ABSTRACT FROM AUTHOR]

Measurements of how the flame speed in suspensions of metal fuels depends on the initial temperature of the unburned mixture are important for understanding the role of mixture preheat by radiation heat transfer. This preheat can be an important stabilization mechanism for metal dust flames in energetic devices. A newly constructed counter-flow flat-flame metal dust burner allows for the measurement of burning velocities in aluminum-air suspensions preheated to temperatures up to 524 K using Particle Image Velocimetry (PIV). The experimental method was verified by measuring and comparing burning velocities in preheated methane-air mixtures at different fuel-oxygen equivalence ratios with previous experimental data and theoretical predictions. Whereas the flame speed in methane-air mixtures increases by 2.75 times with an increase in temperature to about 524 K, the flame speed in aluminum-air mixtures increases by less than 2 times over the same temperature interval. The independence of the adiabatic flame temperature of aluminum-air flames on the initial temperature of the mixture suggests practically constant reaction rates either for kinetically- or diffusion-controlled aluminum combustion. Thus, the observed moderate dependence of the aluminum-air flame speed on mixture initial temperature can be explained by a cumulative effect of the increased heat diffusivity, decrease in the amount of heat required to reach the particle ignition temperature, and increased flame sensitivity to preheat due to discrete source effects discussed in recent flame models. [ABSTRACT FROM AUTHOR]

The thermodynamic and physical characteristics of the starting components and the synthesized high-energy solid combustible materials are determined. It was established that the reaction of the formation of aluminum nitride in the endothermic mode is possible at a temperature of about 3000 K. The adiabatic combustion temperatures of the synthesized fuel systems in the combustion chamber are calculated. The dependence of the values of the adiabatic temperature and specific impulse on the excess of the oxidizing agent, the nature of the binder and energy additives is established. [ABSTRACT FROM AUTHOR]

Considering that the electric refrigeration temperature range of 0.94BNT-0.06BT ceramic materials is 100 ∼ 140 °C, the electric refrigeration performance of the 0.94BNT-0.06BT ceramic material system was modified by LiNbO3 doping to reduce the cooling temperature. As a result, the refrigeration temperature range of the 0.94BNT-0.06BT ceramic material system was lowered to 25 ∼ 80 °C, achieving its cooling effect near room temperature, and in this temperature range, the adiabatic temperature changes ΔT > 0.6K. [ABSTRACT FROM AUTHOR]

In this paper, we study the adiabatic kinetics of martensitic phase transition induced by shock loading. Our main goals are to reveal the effect of thermal–mechanical coupling on phase interface propagation by demonstrating the wave profiles to the impact loading. First, a kinetics and constitutive model for shape memory TiNi alloy with thermo-mechanical coupling effect was preliminarily established based on the laws of thermodynamics. Then the numerical results show that phase transformation shock waves during shock loading and unloading would be aroused due to the nonlinear hardening since adiabatic temperature rise. The shock front and the temperature interface were coupled to each other. Moreover, the adiabatic temperature rise across the transformation shock front effectively reduces the driving force of phase transition and increases the propagation velocity of phase transition wave. Finally, the theoretical results are compared with the experimental results. The comparison results reflect the intrinsic thermo-mechanical coupling characteristic of shape memory TiNi alloy with strong nonlinear constitutive behaviour and kinetics, which will be helpful for temperature controlling for TiNi alloy material and structures subjected to blast or impact loading. [ABSTRACT FROM AUTHOR]

Tert-butylperoxy-2-ethylhexanoate (TBEC)—an easily decomposable organic peroxide—is widely used as a polymerization initiator in industrial production. Sodium hydroxide solution and water are common impurities in the polymerization process. In this study, exothermic onset temperature (T0) and heat of decomposition (ΔH) of TBEC with impurities were obtained through differential scanning calorimetry. In addition, maximum pressure (Pmax), maximum temperature (Tmax), and adiabatic temperature rise (ΔTad) were obtained through accelerated rate calorimetry (ARC). Apparent activation energy (Ea) scores for pure TBEC and TBEC mixed with water (TBEC/H2O) and sodium hydroxide (TBEC/NaOH) were calculated. Subsequently, based on experimental data obtained through ARC, the self-accelerating decomposition temperature and temperature at the time to maximum rate under adiabatic conditions were calculated for 24 h (TD24) and 8 h (TD8). The experimental results indicated that H2O negligibly affected T0 but decreased ΔH, Pmax, Tmax, and ΔTad. Moreover, addition of H2O increased the TD24 and TD8 of TBEC. Thus, the thermal hazard of TBEC was reduced by addition of H2O. Addition of NaOH solution increased the complexity of the reaction because the initial decomposition temperature and activation energy were negatively correlated to the content of NaOH in the solution. [ABSTRACT FROM AUTHOR]

Recently, a massive magnetocaloric effect near the liquefaction temperature of hydrogen has been reported in the ferromagnetic material HoB2. Here we investigate the effects of Dy substitution in the magnetocaloric properties of Ho1-xDyxB2 alloys (x = 0, 0.3, 0.5, 0.7, 1.0). We find that the Curie temperature (TC) gradually increases upon Dy substitution, while the magnitude of the magnetic entropy change |ΔSM| and adiabatic temperature change ΔTad showed a gradual decrease. On the other hand, due to the presence of successive transitions in these alloys, the peak height of the above magnetocaloric properties tends to be kept in a wide temperature range, leading to a relatively robust figure of merit in a wide temperature span. These alloys could be interesting candidates for magnetic refrigeration in the temperature range of 10–60 K. [ABSTRACT FROM AUTHOR]

Recently, a massive magnetocaloric effect near the liquefaction temperature of hydrogen has been reported in the ferromagnetic material HoB2. Here we investigate the effects of Dy substitution in the magnetocaloric properties of Ho1-xDyxB2 alloys (x = 0, 0.3, 0.5, 0.7, 1.0). We find that the Curie temperature (TC) gradually increases upon Dy substitution, while the magnitude of the magnetic entropy change |ΔSM| and adiabatic temperature change ΔTad showed a gradual decrease. On the other hand, due to the presence of successive transitions in these alloys, the peak height of the above magnetocaloric properties tends to be kept in a wide temperature range, leading to a relatively robust figure of merit in a wide temperature span. These alloys could be interesting candidates for magnetic refrigeration in the temperature range of 10–60 K. [ABSTRACT FROM AUTHOR]

The application of hyperbolic sine equation and Artificial Neural Network(ANN) model to predict high temperature flow behaviour of Ti-6Al-4V preform is assessed for development of a constitutive equation to model ring rolling process. Uniaxial compression specimens were obtained from a specific location and direction, where the radial deformation is the major deformation location, to study the ring rolling process. The adiabatic temperature corrected data was used to find constants for hyperbolic sine equation and train the ANN model. The ANN model used normalised strain, strain rate and temperature as input variables and the output parameter was the flow stress. Comparison of the predicting capability of both models showed that the predictions of ANN were better. The hyperbolic sine equation was integrated in a user subroutine and finite element-based simulations of isothermal uniaxial compression were carried out for validation. [ABSTRACT FROM AUTHOR]

Zirconium-boron composite powders with the stoichiometric bulk composition corresponding to ZrB2 were prepared using high-energy milling in a shaker mill starting with elemental boron and zirconium. Milling times up to 3 hours were explored. The characterization of the prepared powders included measuring their particle size distribution, crystal structure, and assessment of particle structure and morphology. Reactions in the prepared powders were characterized using thermal analysis as well as custom ignition and combustion experiments. Composite powders consist of a Zr matrix with B inclusions mostly 100 nm or less in size. The homogeneity of mixing between boron and zirconium improves when the milling time increases from 1 to 2 hours; it is not affected by longer milling times. Boron and zirconium start reacting during milling; the degree of this reaction becomes appreciable when the milling time reaches 2 hours. In air, ignition of both pure zirconium and the prepared powders occurs in the same temperature range of ca. 400–700°C for the heating rates varied from 2000 to 20,000 °C/s. In fuel-rich conditions, ignition of the prepared powders is affected by the reaction between B and Zr, which occurs less readily for powders milled for 2 hours or longer. In air, particles of the prepared composite powders burn faster than either pure boron or zirconium. Flame temperatures for individual composite particles burning in air are reasonably close to those predicted as adiabatic flame temperatures for this composite-air system at stoichiometric and fuel-rich conditions. In combustion products of an air-acetylene flame, the burn rates of the prepared composites are lower than that of zirconium and are comparable to that of boron. Powders prepared by 1-hour milling burn faster than powders prepared using longer milling times. [ABSTRACT FROM AUTHOR]

This numerical study uses a Lagrangian–Eulerian formulation employing the point-source approximation to investigate nonpremixed axisymmetric spray diffusion flames stabilized between a stream of hot air and a stream of nitrogen carrying a monodisperse spray of fuel droplets injected at a distance zl from the stagnation plane. The computations consider moderately large values of the relevant thermal Peclet number, such that the thickness of the mixing layer separating both streams is much smaller than zl. A one-step irreversible reaction is assumed between the fuel vapor and the oxygen of the air. Most of the computations consider the thermochemical, vaporization, and transport properties of dodecane, with additional results for the properties of methanol used to assess effects of higher fuel volatility. The analysis considers moderately small values of the liquid mass loading ratio at the injection plane, consistent with the stoichiometric value of the fuel-to-air mass ratio of the global oxidation reaction of typical hydrocarbon and alcohol fuels. Attention is mainly focused on inertial droplets with associated Stokes numbers St of order unity or larger, for which the droplets penetrate far into the oxidizer stream, vaporizing over distances of order zl and leading to combustion occurring outside the mixing layer. In this inertial regime, besides solutions involving a diffusion flame separating the fuel and oxygen with a well-defined peak temperature of the order of the adiabatic flame temperature, the analysis reveals, for the first time, the existence of flameless solutions with distributed combustion and small temperature increments from the air-side value. The two solutions are found to exist for the same sets of boundary conditions. Integrations for increasing values of St identify a value of the Stokes number St2 above which the vaporization rate is too small to support a diffusion-flame solution, while integrations for decreasing St lead to the identification of another value of the Stokes number St1 < St2 below which a distributed reaction cannot occur. In the intermediate hysteretic range St1 ≤ St ≤ St2 where two different steady solutions may exist, the type of solution encountered depends on the initial conditions imposed. The preliminary results suggest that future efforts targeting quantification of the flameless regime, which is found to be relevant in applications with larger droplets, would benefit from consideration of different possible gas-phase chemical kinetics, including cool-flame chemistry. [ABSTRACT FROM AUTHOR]

The high entropy alloy concept offers unique opportunities for the design of advanced materials with unprecedented properties. However, hitherto most of the research efforts are focused on structural materials. Here, by employing the core effect of severe lattice distortion in high entropy alloys, a novel functional NiCuTiHf0.6Zr0.4 high entropy alloy exhibiting intriguing wide-temperature-range perfect superelasticity in a broad temperature range from 263 to 463 K and giant elastocaloric effect with the maximum adiabatic temperature change of 9.3 K is developed. This work opens the door for designing high-performance superelastic and elastocaloric functional materials with the high entropy alloy concept. A novel functional high entropy alloy with intriguing wide-temperature-range perfect superelasticity and giant elastocaloric effect is sucessfully developed by employing the severe lattice distortion which leads to high yield strength. [ABSTRACT FROM AUTHOR]

Electrocaloric effect (ECE) in two ferroelectric liquid crystalline (FLC) materials has been evaluated by mean of two indirect characterization methods: the photopyroelectric (PPE) technique and the polarization current reversal one. The obtained results show a good correspondence of the adiabatic temperature change associated with the ECE evaluated from both methods. This validates the possibility to use the PPE technique to investigate the ECE in FLCs. This study also demonstrates that FLCs can be used as electrocaloric material. More particularly, it shows that as for their solid homologous, liquid crystals displays more pronounced ECE in the vicinity of a first order transition than that measured near to second-order one. [ABSTRACT FROM AUTHOR]

Experimental and computational investigation is carried out to elucidate the influence of stoichiometric mixture fraction, , on the structure and critical conditions of extinction of nonpremixed dimethyl ether (DME) flames. The stoichiometric mixture fraction represents the location of a thin reaction zone in terms of a conserved scalar quantity. The counterflow configuration is employed, wherein two reactant streams flow towards a stagnation plane. One stream is made up of DME and nitrogen (N) and the other stream is oxygen and N. Previous studies have shown that critical conditions of extinction depend on and the adiabatic temperature. Therefore, the present investigation is carried out with the composition of the reactants in the counterflowing streams so chosen that the adiabatic temperature is the same for different values of. The strain rate at extinction, , is measured for values of up to 0.8. Computations are performed using detailed kinetic mechanisms and critical conditions of extinction and flame structures are predicted. The measurements and predictions show that, with increasing , the strain rate at extinction first decreases and then increases. The predictions agree with measurements for , but significant deviations between measurements and predictions are observed at higher values of. The scalar dissipation rate at extinction, is calculated using measured and predicted values of. With increasing , the measured and predicted values of first increase and then decrease. It is noteworthy that changes in values of with for dimethyl ether flames are similar to those for methane flames, while the changes in values of with are remarkably different. Flame structures are predicted and they are found to be qualitatively similar to those for hydrocarbon fuels. [ABSTRACT FROM AUTHOR]

In this work, we introduce a global kinetic model that includes fuel, oxygen, products and two radical species involved in the reversible chain-branching, chain-propagation and chain-termination reactions. The model naturally extends the Zeldovich–Liñán and Zeldovich–Barenblatt–Dold models and can be used to describe both premixed and diffusion flames. Here it is applied to the problem of the deflagration wave propagation in the hydrocarbon fuel/air mixture with arbitrary equivalence ratio under the simplifying thermal-diffusive approximation. The conservation equations are solved numerically in order to obtain the velocity and structure of the combustion wave. It is demonstrated that the peak values of the adiabatic flame temperature and deflagration velocity are shifted towards the rich mixture composition if the reverse reactions of product decomposition are taken into account. The dependence of the flame speed and temperature on parameters of the system is analysed. The prospects of further investigation are discussed. [ABSTRACT FROM AUTHOR]

Heat losses have the potential to substantially modify turbulent combustion processes, especially the formation of pollutants such as nitrogen oxides. The chemistry governing these species is strongly temperature sensitive, making heat losses critical for an accurate prediction. To account for the effects of heat loss in large eddy simulation (LES) using a precomputed reduced-order manifold approach, thermochemical states must be precomputed not only for adiabatic conditions but also over a range of reduced enthalpy states. However, there are a number of methods for producing reduced enthalpy states, which invoke different implicit assumptions. In this work, a set of a priori and a posteriori LES studies have been performed for turbulent premixed flames considering heat losses within a precomputed reduced-order manifold approach to determine the sensitivity to the method by which reduced enthalpy states are generated. Two general approaches are explored for generating these reduced enthalpy states and are compared in detail to assess any effects on turbulent flame structure and emissions. In the first approach, the enthalpy is reduced at the boundary of the one-dimensional (1D) premixed flame solution, resulting in a single enthalpy deficit for a single premixed flame solution. In the second approach, a variable heat loss source term is introduced into the 1D flame solutions by mimicking a real heat loss to reduce the post-flame enthalpy. The two approaches are compared in methane-air piloted turbulent premixed planar jet flames with different diluents that maintain a constant adiabatic flame temperature but experience different radiation heat losses. Both a priori and a posteriori results, as well as a chemical pathway analysis, indicate that the manner by which the heat loss is accounted for in the manifold is of secondary importance compared to other model uncertainties such as the chemical mechanism, except in situations where heat loss is unphysically fast compared to the flame time scale. A new theoretical framework to explain this insensitivity is also proposed, and its validity is briefly assessed. [ABSTRACT FROM AUTHOR]

Knocking combustion has been extensively studied in internal combustion engines in order to achieve higher thermal efficiency. However, the inherent mechanism for knocking combustion under homogenous charge compression ignition (CI) conditions has not been fully understood. In this study, the strong knocking characteristics under CI conditions were parametrically investigated through theoretical analysis and rapid compression machine (RCM) experiments, with addressing knocking intensity (KI) limits and autoignition (AI) modes. The characteristic time and energy release concerned with AI were firstly numerically obtained through constant-volume adiabatic conditions. It is found that despite longer ignition delay time within milliseconds and excitation time within microseconds, iso-octane shows almost the same level of maximum explosive pressure and obvious higher energy density compared with n-heptane with low octane rating, indicating the potential of strong knocking occurrence. Then, knocking characteristics were investigated through RCM experiments operated under different thermodynamic conditions for the different octane rating fuels. It shows that strong knocking combustion characterizing super-knock events is observed for both n-heptane and iso-octane. Meanwhile, initial pressure showed greater impact on knocking combustion, manifesting significant increases in KI at high pressures. The influence from initial temperature becomes more obvious for iso-octane fuel at low pressures with long ignition delay time. Finally, the AI modes for different knocking scenarios were qualitatively assessed through Bradley’s diagram, allowing for the uncertainties of hot-spot sizes and temperature gradients. It shows that most AI modes of strong knocking combustion were located in the developing detonation regime, illustrating the possibility of super-knock under CI conditions with high thermodynamic conditions. [ABSTRACT FROM AUTHOR]

This paper presents a method to find the adiabatic temperature rise of concrete by retro-analysing temperatures measured in the field. The construction phase is simulated with a 3D finite-element model that considers the coupling between thermal and chemical phenomena due to cement hydration. A genetic algorithm is used to find the main parameters that characterise the adiabatic temperature curve and that better fit the temperatures measured in the field for a given structure. This method was applied to the construction of the spillway gate pier of a hydroelectric power plant. The good agreement between numerical results and temperature measurements points to the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

The effects of three key parameters of feed temperature, pressure, and flow rate were investigated on the catalytic reaction of methanol dehydration to dimethyl ether in a large-scale fixed bed. A one-dimensional mathematical model was employed for development of the optimum design and evaluation of temperature and concentration profiles. The study of the temperature profiles considering the catalyst behavior revealed that a maximum conversion is obtained under the feed temperature range of 523 to 533 K and operating pressures range of 1 to 1.5 Mpa. The inlet temperature was found to be the most major factor controlling the yield and rate of reaction. Also, the Rate–Conversion–Temperature chart was plotted to appraise and determine the optimal reactor volume at operating conditions. [ABSTRACT FROM PUBLISHER]

The electrocaloric effect (ECE) of 0.85PbMg1/3Nb2/3O3–0.15PbTiO3(0.85PMN-0.15PT) thin films deposited on (111) Pt/TiO2/SiO2/Si substrate by pulsed laser deposition (PLD) has been calculated. The reversible adiabatic temperature was calculated indirectly using the Maxwell's relation. Permittivity and P-E measurements show an anomaly at 11°C on heating only. This anomaly previously reported are claimed to arise due to the PNR depolarization upon heating. The absence of this anomaly during cooling suggests that no structural phase transition takes place. A negative electrocaloric effect is observed which is explained by the increase in the entropy term. [ABSTRACT FROM PUBLISHER]

Steady simulations were performed to investigate tip leakage flow and heat transfer characteristics on the rotor blade tip and casing in a single-stage gas turbine engine. A typical high-pressure gas turbine stage was modeled with a pressure ratio of 3.2. The predicted isentropic Mach number and adiabatic wall temperature on the casing showed good agreement with available experimental data under similar operating condition. The present numerical study focuses extensively on the effects of tip clearance heights and rotor rotational speeds on the blade tip and casing heat transfer characteristics. It was observed that the tip leakage flow structure is highly dependent on the height of the tip gap and the speed of the rotor. In all cases, the tip leakage flow was seen to separate and recirculate just around the corner of the pressure side of the blade tip. This region of re-circulating flow enlarges with increasing clearance heights. The separated leakage flow reattaches afterwards on the tip surface. Leakage flow reattachment was shown to enhance surface heat transfer at the tip. The interaction between tip leakage flow and secondary flows that is induced by the relative casing motion is found to significantly influence the blade tip and casing heat transfer distribution. A region of critical heat transfer exists on the casing near the blade tip leading edge and along the pressure-side edge for all the clearance heights that were investigated. At high rotation speed, the region of critical heat transfer tends to move towards the trailing edge due to the change in inflow angle. [ABSTRACT FROM PUBLISHER]

The adiabatic temperature change (ΔTad) during the magnetization process of polycrystalline gadolinium and Ni51Mn33.4In15.6Heusler alloy is directly measured near the Curie temperature. The cooling factor (CF) is introduced as the area under the curve of adiabatic temperature change versus ambient temperature. The CF provides more representative measure of cooling performance in the operational temperature range. Selecting different temperature abscissas qualitatively changes the interpretation of the cooling performance of a magnetocaloric material. In particular, plotting ΔTadversus initial temperature gives a measurably different CF compared to that given by plotting ΔTadversus average temperature. [ABSTRACT FROM AUTHOR]