The dual-mode scramjet combustor is a promising candidate for the combined cycle engine of the hypersonic airplane, and the flame propagation and stabilization process in the dual-mode scramjet ...combustor has a great impact on its performance improvement. In this survey, the research progress on the flame propagation and stabilization in the dual-mode scramjet combustor is reviewed and summarized, and its main focus is on the flame stabilization mode, especially for the mode transition. The flame stabilization process in the dual-mode scramjet combustor is summarized from three aspects, namely the combustion mode classification, the mode transition and the vitiation effect. The obtained results show that the operational conditions and the geometric parameters both have a great impact on the flame propagation and stabilization process in the dual-mode scramjet combustor, and there exist strong interactions between the geometric parameters, as well as the operational conditions. This is a multiobjective design optimization problem, and the optimal operational conditions, as well as the optimal geometric parameters, should be obtained by the optimization algorithm based on the surrogate model with high fidelity.
•Calcium oxide is an appropriate catalyst for biodiesel production.•The waste mussel shell is a source of calcium oxide when calcined at T>950°C.•Using RSM effects of calcination T, catalyst wt.% and ...MeOH/oil ratio were studied.•Calcination T of 1050°C, catalyst 12wt.% and MeOH/oil ratio of 24:1 were optimum.
Calcium oxide is an appropriate catalyst for biodiesel production. In this study, an inexpensive and environment-friendly catalyst was used. The waste mussel shell collected in of Persian Gulf coast is a source of calcium carbonate which changes to calcium oxide in calcinations temperatures higher than 950°C. Transesterification reaction was done in the presence of soybean oil, methanol and mussel shell catalyst in a temperature of 60°C. Using response surface methodology (RSM) the effects of different parameters (calcination temperature, catalyst concentration and molar ratio of methanol to oil) were studied. Each parameter was set at three levels labeled as low, medium and high, respectively (calcination temperature of 950, 1000, and 1050°C; catalyst concentration of 6, 9 and 12wt.%; methanol to oil ratios of 12:1, 18:1 and 24:1). The results of the optimization implies that the calcination temperature of 1050°C, catalyst concentration of 12wt.%, and methanol to oil ratio of 24:1 provide the maximum values of purity and yield in biodiesel production. The reusability of mussel shell catalyst was studied for five times and the result showed that the catalyst re-calcination in reusability step has negative effects on the yield of biodiesel production.
Development of an innovative sensor for detection of hydrogen gas is essential for new applications and devices. In current article, inclusive parametric analysis has been performed to disclose the ...chief operative term on the performance of the micro sensor of MIKRA for the detection of the hydrogen in the mixture. The main mechanism of this micro actuator highly relies on the value of the exerted Knudsen force which occurs owing to the temperature gradient in the low-pressure region. The response surface methodology (RSM) is applied to obtain an optimized formula for the evaluation of sensor performance. Besides, analysis of variance (ANOVA) is employed to analyze the influence of individual factors on sensor formulation. This work tries to estimate the effect of major parameters such as a gap of the arm, the pressure of domain, mass fraction and temperature difference on the value of Knudsen force. Moreover, reliable correlations for the estimation of the Knudsen force are presented to determine the efficiency of the micro gas actuator in the various operating conditions. Our findings confirm that the precision of the sensor enhances as the temperature difference of the cold and hot arms as well as the hydrogen mass fractions augment in our actuator.
•Optimization of micro gas sensor is done by design of experiment.•The impact of significant factors for detection hydrogen by Knudsen force is revealed.•Comprehensive formula for mass analysis of hydrogen in the mixture by MEMS actuator is presented.•Optimum condition for high precision detection of hydrogen gas in the micro sensor is determined.
A multi-decade theoretical effort has been devoted to finding an efficient mechanism to use the rotational and electrodynamical extractable energy of a Kerr-Newman black hole (BH), to power the most ...energetic astrophysical sources such as gamma-ray bursts (GRBs) and active galactic nuclei. We show an efficient general relativistic electrodynamical process which occurs in the “inner engine” of a binary driven hypernova. The inner engine is composed of a rotating Kerr BH of mass
M
and dimensionless spin parameter
α
, a magnetic field of strength
B
0
aligned and parallel to the rotation axis, and a very low-density ionized plasma. Here, we show that the gravitomagnetic interaction between the BH and the magnetic field induces an electric field that accelerates electrons and protons from the environment to ultrarelativistic energies emitting synchrotron radiation. We show that in GRB 190114C the BH of mass
M
= 4.4
M
⊙
,
α
= 0.4, and
B
0
≈ 4 × 10
10
G can lead to a high-energy (≳GeV) luminosity of 10
51
erg s
−1
. The inner engine parameters are determined by requiring (1) that the BH extractable energy explains the GeV and ultrahigh-energy emission energetics, (2) that the emitted photons are not subjected to magnetic-pair production, and (3) that the synchrotron radiation timescale agrees with the observed high-energy timescale. We find for GRB 190114C a clear jetted emission of GeV energies with a semi-aperture angle of approximately 60° with respect to the BH rotation axis.
The efficiency of the scramjet is highly associated with the rate of the mixing through the combustion tank. In current article, simulation approach was used to inspect the effect of the sinusoidal ...wall on hydrogen mixing cross-flow jet. The key focus of current paper is to exhibit the role of various sinusoidal profiles on the flow structure and streamline pattern of the mainstream and fuel jet. To simulate the flow feature, a 3D model was chosen and Navier-stocks equations were solved with energy and species mass transport equations to evaluate the mixing rate of hydrogen jet. Hydrogen gas is injected through the nozzle in the downstream of the sinusoidal wave. The impact of total jet pressure on the flow feature is exclusively studied. Also, the mixing zones of the various models are compared. Attained results display that the appearance of the wavy wall augments the mixing rate when the frequency of the sinusoidal wave is high enough. Our findings also reveal that using extended surface has less effect in high pressure condition. The comparison of the mixing rate shows that the presence of sinusoidal wavy wall with frequency of 1200 increases the mixing rate more than 25% than simple flat surface.
In this research, nanofluid heat transfer enhancement in a pipe by means of twisted tape with alternate axis is presented. Finite volume method is selected as simulation tool. Influences of ...revolution angle and Reynolds number on nanofluid hydrothermal treatment have been demonstrated. Suitable formulas for Nusselt number and Darcy factor are provided. Results prove that temperature gradient augments with enhance of revolution angle because of increase in secondary flow but pressure loss augments with rise of revolution angle.
•Different ZnO nanostructures were prepared by carbothermal evaporation method on quartz substrates at different deposition temperatures.•We investigated the role of temperature, by keeping other ...parameters constant, on growth and morphological surface which is an important parameter for gas sensing.•Our results show that the sensitivity of sensor synthesized at 500°C temperature and operated at 350°C for 20ppm H2S gas is 80%, with 35s and 390s for recovery and response time respectively.
In this work, different ZnO nanostructures are prepared by carbothermal evaporation method on quartz substrates at various deposition temperatures. The mixture powders ZnO/C with 1:1 ratio as a source of materials inserted in the center of furnace tube. The effect of temperature, by keeping constant other parameters, on growth and morphological surface are investigated which is an important parameter for gas sensing. The crystalline structure of Zn is verified by X-ray diffraction and the surface morphology is analyzed by scanning electron microscopy. The results showed that the sensitivity of sensor synthesized at temperature of 500°C and operated at 300°C for 20ppm H2S gas, is 80% with 35s and 390s for recovery and response time, respectively.
•Drag and heat flux reduction induced by pulsed counterflowing jet was studied.•Influence of pulsation frequency on drag and heat flux reduction was investigated.•Larger period is beneficial for drag ...and heat flux reduction.•Heat flux reduction effect of pulsed counterflowing jet is evident.
In the current study, three different kinds of pulsed jets with the period being 0.5 ms, 1.0 ms and 2.0 ms are established, and sinusoidal waveforms are used in all three pulsed jets. The pulsed counterflowing jets with the same amplitude but different periods on the nose of a blunt body in supersonic flows are investigated numerically, and an axisymmetric numerical simulation model of the counterflowing jet on the supersonic vehicle nose-tip is established. The obtained results show that the wall Stanton number and surface pressure change periodically with the pulsed jet, and the variations of the parameters show a strong hysteresis phenomenon. The hysteresis phenomenon becomes less significant as the period increases. At the same time, a better drag and heat flux reduction is obtained under larger period pulsed jet conditions. With the increase of the period of the pulsed jet, there is a significant decline in the maximum peak values of the wall Stanton number and surface pressure. Compared with the steady jet, the pulsed jet is more effective in heat flux reduction, but the drag reduction of the pulsed jet is less effective than the steady jet.
The injection of the fuel is a highly important process for the enhancement of the scramjets. In this article, the presence of the backward-facing step on the mixing of the multi-fuel jets is ...expansively studied. The primary attention of this article is to scrutinize the flow feature of the fuel jet under the backward-facing step. The mixing mechanism of the fuel is also studied to compare this injection system with conventional methods. To do this, a 3-dimensional model is chosen to consider the real physic of the problem. Reynolds Average Navier-Stocks equations are solved with a computational fluid dynamic method to visualize the flow pattern of the fuel jet at the free stream Mach number of 4. SST turbulence model is also used for the calculation of the viscosity. Our results indicate that increasing the jet space from 4 to 10 times of jet diameter in the presence of the backward-facing step increases the mixing efficiency up to 20% in the downstream. Our findings depict that augmenting the number of fuel injectors from 4 to 8 augments the mixing rate up to 15% inside the combustor.
•The influence of backward step on the mixing characteristics is studied.•CFD is applied for the simulation of multi jet at supersonic flow.•The impact of jet space on mixing zone is studied.•Increasing the fuel jet space improves the fuel mixing in the far downstream.
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