Influence Of Initial Temperature Research Articles

Detailed kinetic analysis of synthetic fuels containing ammonia

The imperative to adopt environmentally sustainable energy sources has propelled the exploration of zero-carbon alternatives, such as hydrogen and ammonia for energy supply. Integrating these species with methane is recognized as a viable short-term solution. However, a complete understanding of their chemical behaviour in a wide range of conditions remains elusive, especially in terms of safety parameters, limiting the applicability of this solution. To this aim, this work presents a detailed analysis of the overall reactivity, expressed either in terms of laminar burning velocity or flammability limits, of hydrogen-ammonia-containing fuels. Additional considerations were obtained by the analysis of the maximum pressure rise and maximum pressure obtained in adiabatic conditions. A spectrum of nitrogen/oxygen mixtures was scrutinized, and the influence of initial temperature within the range of 300–500 K was systematically investigated. The estimation quality of the adopted mechanism was evaluated by comparing numerical predictions with experimental measurements obtained by different systems, when available. A tendency in slightly more conservative results on the safe side was detected for the assessment of flammability limits and minimum oxygen concentration. This trend was attributed to the assumption of perfectly adiabatic conditions posed for the numerical analysis, which does not perfectly match the experimental conditions. Conversely, an excellent agreement between numerical and experimental laminar burning velocity was observed. Therefore, the collected data were used for the quantification of input parameters required by well-established correlations suitable for synthetic fuels.

Analysis of processing map and parameters optimization during hot extrusion of 17 vol.% SiCp/2009Al composite

Hot extrusion process can improve the mechanical properties of materials. However, due to the presence of SiC particles, SiCp/Al composites are prone to fracture damage in the extrusion process. To determine the optimal processing parameters, the processing maps of 17 vol.% SiCp/2009Al composite were established using power dissipation rate and Murty instability criterion. Furthermore, taking aluminum canning into consideration, a three-dimensional macroscopic hot extrusion finite element model of SiCp/Al composite was constructed. The influences of initial temperature, canning morphology and canning thickness on extrusion properties were predicted, and verified by comparison of processing maps and experiments. The optimal extrusion parameters for SiCp/2009Al composite are located within the window of temperature, 450–475 °C and strain rate, 0.001–0.004 s−1 or 0.6–1 s−1. Additionally, the properties of the SiCp/Al composite can be greatly improved by hot extrusion with a suitable canning. Of these, the half canning finish the extrusion task faster, but the extrusion properties under the bottom canning are the best. When the ratio of the canning thickness to the diameter of the workpiece is about 0.17, the effective stress, strain and damage are minimum. The work performed in this research, for the first time, provides quantitative evaluations of process parameters on the hot deformation of SiCp/Al composite, which enables to provide useful guides for hot extrusion parameters selection of SiCp/Al composite.

Relation between characteristic temperature and elution temperature in temperature programmed gas chromatography - part I: Influence of initial temperature and heating rate

The development of new analytical methods can save resources, time and costs if there are prediction tools like computer simulation which support the optimization process. In GC the distribution-centric 3-parameter model (K-centric model) is well established for prediction of retention factors k and retention times but laborious isothermal measurements for determination of the characteristic parameters are needed. For the most important parameter, the characteristic temperature Tchar, the search for simpler determination methods or even estimates is an interesting research topic.In this work the elution temperatures for 37 fatty acid methyl esters, 6 BTEXs and 40 other volatile substances are determined by measurements under variable heating rates, initial temperatures, constant pressure mode and constant flow mode. The relationship between the measured elution temperature and the characteristic temperature was investigated. The novel multivariate curve fit model presented in this study describes accurately the relation between the characteristic temperature Tchar and elution temperatures Telu under variable heating rates RT, respectively, and initial temperature Tinit conditions. The novel model shows good accordance to earlier estimation models and expands the prediction range, especially for high volatile compounds. The model is suitable for determination of Tchar by estimated Telu and vice versa. Predictions of retention times of simple temperature programs were also possible by using the model with relative deviations < 5% compared to measurements.

Influence of initial temperature on laminar burning velocity in hydrogen-air mixtures as potential for green energy carrier

One of the most important parameters describing a combustible mixture is the laminar burning velocity. The determination of this value forms the basis for the calculation of backflow parameters, the flame cone angle in burners and the turbulent burning velocity. It is also an indispensable parameter in flame stabilization and quenching studies.In this regard, the present study compares the predictive performance of three relatively simple numerical models used to determine the laminar burning velocity of hydrogen-air mixtures: 1) Monton, Lewis et al., 2) Bradley and Mitcheson, and 3) Dahoe. Their performance was determined for three initial burning temperatures (298.15 K, 323.15 K, and 348.15 K), comparing the respective laminar burning rates of hydrogen with measurements made using the Cantera toolbox and the GRI-Mech 3.0 chemical reaction kinetics mechanism.The experimental results show that the models of Bradley and Mitcheson et al. and Dahoe, although relatively simple, have relatively satisfactory predictive power compared to the measurements of the Cantera toolkit. The difference between the two numerical models and Cantera was less than 0.05 m/s. On the other hand, due to the relative simplicity, Monton, Lewis et al. model showed the lowest accuracy compared to the Cantera toolkit, with an average error of the hydrogen burning rate of 0.3 m/s. The results presented in this study enrich the basic hydrogen combustion rate data, which is critical for further research related to the use of hydrogen as a renewable energy source.

Numerical simulation of heat-storage performance of filling body with uniformly mixed phase change paraffin

A PCM was added to filling materials in an appropriate proportion to realize the effective collection and storage of geothermal energy. Based on the theory of heat transfer and similarity, the heat-storage performance of filling body was numerically simulated in different states, then, the influences of paraffin proportion, initial temperature of filling body, surrounding rock temperature, stope air-flow temperature, and velocity on the heat-storage behavior of filling body were analyzed. The results revealed that reducing the initial heat-storage temperature of filling body, increasing surrounding rock temperature, and increasing the air-flow temperature in the stope all effectively increased the heatstorage capacity of filling body. In which the influence of initial temperature and surrounding rock temperature were more significant. At the end of 16 hours heatstorage period, when the initial temperature of filling body was reduced from 24?C to 18?C, the heat transfer capacity of filling body without paraffin and that with 5% paraffin decreased by 2.85 ? 103 kJ and 2.40 ? 103 kJ, respectively. When surrounding rock temperature increased from 35?C to 45?C, the amount of heat stored by two bodies increased by 3.89 ? 103 kJ and 4.51 ? 103 kJ, respectively.

Numerical evaluation of the influence of initial pressure/temperature on the explosion properties and soot formation of methane/coal volatiles mixtures

In this study, a model for describing both chain reactions and product growth for the explosions of methane/coal volatiles mixtures based on chemical reaction kinetics was established to calculate the impact of initial temperature and initial pressure on the deflagration features of the mixtures. The variation for the macroscopic explosion parameters and the microscopic reactions of methane/coal volatiles explosions under different conditions are investigated using reaction kinetics simulation. Results suggest that the Pmax increased by 64.496 %, 64.499 %, 64.502 %, and 64.504 % when the initial pressure changed from 0.8 to 1.3 atm. Whereas, under increasing initial temperature, the Pmax decreased by −18.167 %, −18.179 %, −18.190 %, and −18.200 % while the Tmax increased by 90.49 K, 90.07 K, 89.67 K, and 89.30 K, respectively. Meanwhile, the influence of initial temperature on the sensitivity of primary elementary reactions was more prominent than that of the initial pressure. The ROP of the key radicals H/O/OH unnecessarily presented an increasing tendency under the increasing initial temperature while the maximal molar fraction of each key radical increased. The increase in both initial pressure and initial temperature would greatly promote the growth of C(B), which in turn largely accelerated the formation of soot particles. This preliminary work would be beneficial for the preemptive precaution and effective control of the explosions in coal-derived industries.

Morphological characteristics and flashing mechanism of superheated liquid jets released from rectangular breaches

The leakage of liquefied gases such as liquefied hydrocarbons and liquid chlorine is usually accompanied by an intense phase transition that results in two-phase release. This two-phase release will lead to fire, explosion, toxic diffusion and other major dangerous accidents, seriously endangering the safety of personnel and ecological environment, resulting in inestimable losses. To deepen the understanding of such accidents, a 20L tank was used to simulate the accidental release of superheated liquid and study its accident behavior. This work simulated different breaches by using different shapes of nozzles with equal cross-sectional area and more focused on rectangular nozzles. Besides, the influence of initial temperature (110–130 °C) and pressure (6–16 bar) was also taken into account. A high-speed camera was used to record the external morphological characteristics of the superheated liquid jets released from the nozzles. The jet angle and half-width were extracted as the quantitative characterization of the external morphology by threshold processing algorithm. The results revealed that the rectangular nozzle jet (RNJ) has a different external morphology from the circular nozzle jet (CNJ) due to the presence of vortex and axis-switching phenomena. Aspect ratio plays an important role in the determination of external morphology of the RNJ and there is a critical aspect ratio AR = 3. In addition, this study also demonstrates that the rectangular nozzle has a different flashing mechanism from the circular nozzle, which is the underlying reason for the different external morphologies. In summary, compared to the traditional circular breach, rectangular breach has a significant promotion effect on the jet flashing, and the industrial medium released from the slit breach will have a greater impact range, resulting in more serious consequences of accidents.

The synergistic effect of equivalence ratio and initial temperature on laminar flame speed of syngas

The laminar flame speed of syngas (CO:H2 = 1:1)/air premixed gas in a wide equivalence ratio range (0.6–5) and initial temperature (298–423 K) was studied by Bunsen burner. The results show that the laminar flame speed first increases and then decreases as the equivalence ratio increasing, which is a maximum laminar flame speed at n = 2. The laminar flame speed increases exponentially with the increase of initial temperature. For different equivalent ratios, the initial temperature effects on the laminar flame speed is different. The initial temperature effects for n = 2 (the most violent point of the reaction) is lower than others. It is found that H, O and OH are affected more and more when the equivalence ratio increase. When the equivalence ratio is far from 2, the reaction path changes, and the influence of initial temperature on syngas combustion also changes. The laminar flame speed of syngas is more severely affected by H + O2 = O + OH and CO + OH = CO2 + H than others, which sensitivity coefficient is larger and change more greatly than others when the initial temperature and equivalence ratio change. Therefore, the laminar flame speed of syngas/air premixed gas is affected by the initial temperature and equivalence ratio. A new correlation is proposed to predict the laminar flame speed of syngas (CO:H2 = 1:1)/air premixed gas under the synergistic effect of equivalence ratio and initial temperature (for equivalence ratios of 0.6–5, the initial temperature is 298–423 K).

Influence of Initial Temperature and Convective Heat Loss on the Self-Propagating Reaction in Al/Ni Multilayer Foils.

A two-dimensional numerical model for self-propagating reactions in Al/Ni multilayer foils was developed. It was used to study thermal properties, convective heat loss, and the effect of initial temperature on the self-propagating reaction in Al/Ni multilayer foils. For model adjustments by experimental results, these Al/Ni multilayer foils were fabricated by the magnetron sputtering technique with a 1:1 atomic ratio. Heat of reaction of the fabricated foils was determined employing Differential Scanning Calorimetry (DSC). Self-propagating reaction was initiated by an electrical spark on the surface of the foils. The movement of the reaction front was recorded with a high-speed camera. Activation energy is fitted with these velocity data from the high-speed camera to adjust the numerical model. Calculated reaction front temperature of the self-propagating reaction was compared with the temperature obtained by time-resolved pyrometer measurements. X-ray diffraction results confirmed that all reactants reacted and formed a B2 NiAl phase. Finally, it is predicted that (1) increasing thermal conductivity of the final product increases the reaction front velocity; (2) effect of heat convection losses on reaction characteristics is insignificant, e.g., the foils can maintain their characteristics in water; and (3) with increasing initial temperature of the foils, the reaction front velocity and the reaction temperature increased.

Transport characteristics of pulsating high-temperature particles based on vortex structure analysis by large-eddy simulation

The pulsating high-temperature particles generated in the industrial production process are common pollutants in industrial buildings. Accurately grasping the transport characteristics of pulsating high-temperature particles is an important task to achieve high-efficiency industrial ventilation system design. In this study, large eddy simulation was used to study the transport characteristics of pulsating high-temperature particles with 5 μm ≤ dp ≤ 70 μm. The aspects discussed mainly include the temperature variations of pulsating high-temperature particles, the interaction between airflow vortex structure and particles, the influence of initial temperature (303 K ≤ T0 ≤ 1273 K) on particle transport range, and the proportion variations of different particle diameters in the work area. The results show that particles with different diameters present similar heating effects on airflow. The vorticity of vortex structure is attenuated by being transferred to both sides during transport. The vorticity attenuation causes the particle transport to occur horizontally from the inside of the vortex structure to the outside. The variations in the particle concentration caused by horizontal transport will affect the shape of the small-scale vortex structure at the edge. When 0.297 ≤ St0 ≤ 0.783, the increase of the initial temperature promotes the vortex structure to carry more particles from airflow to surroundings. When T0 = 1273 K, particles with 0.003 ≤ St0 ≤ 0.107 are transported to the upper space from work area, while particles with 0.107 <St0 ≤ 0.582 are suspended in work area. The results help guide the refined design of local exhaust ventilation.

Microwave heating and deicing efficiency for asphalt concrete with SiC–Fe3O4 microwave enhanced functional layer

Traditional deicing methods such as manual deicing, infrared heating deicing, chemical deicing might bring serious environmental pollution and energy consumption. Microwave heating deicing technology with high microwave energy utilization efficiency and environmental protection has been widely studied. But the microwave heating deicing efficiency still cannot meet the practical application requirement at present. In order to improve the microwave deicing efficiency, the asphalt concrete with microwave enhanced functional layer (MEFL) and control specimens (asphalt concrete without MEFL) were designed. In the meanwhile, the effect of SiC–Fe3O4 content and thickness of MEFL on microwave heating efficiency (MHE) and ice-thawing time were studied. Moreover, the influence of initial temperature and ice layer thickness on ice-thawing time were also evaluated. Finally, the energy utilization efficiency of MEFL was calculated. Results show that the SiC–Fe3O4 content in MEFL had a positive effect on MHE and ice-thawing time. The MHE and ice-thawing time of 28.6% SiC–Fe3O4 were 2.42 times and 6.2 times shorter than that of control specimens, respectively. But the MEFL thickness had a negative effect on MHE and ice-thawing time. The ice-thawing time of MEFL with −15 °C initial temperature was 46s. it was increased about 1.7 times in contrast to −5 °C. In addition, the thicker ice layer thickness might increase the ice-thawing time. The ice-thawing time of 30 mm ice layer was 13s longer than that of the 10 mm ice layer. The microwave energy utilization efficiency of 10 mm MEFL could reach 79.21%. Overall, the MEFL can significantly improve the MHE and deicing efficiency of asphalt concrete.

Predicting the formation characteristics of titanium alloy self-locking nuts

Titanium alloy is important for the aerospace industry because of its high specific strength as well as excellent anti-corrosion and anti-oxidative properties. In this paper, a three-dimensional thermo-mechanical coupled simulation was carried out to predict the formation characteristics of a TC4 titanium alloy self-locking nut during the upset forging process. The stability of the upset-forged material was analyzed, and the influences of initial temperature and deformation velocity on the quality of the formed material were investigated. The results show that if the length:diameter ratio of the sample is less than 3.27, the upset-forged material tends to be stable, so we selected a length:diameter ratio of 2.89. Additionally, the properties of the TC4 self-locking nut improved when the initial temperature was increase, and decreased when the velocity of the upper die was increased. Our results provide a theoretical guidance for the formation of TC4 titanium alloy nuts using upset forging.

Pengaruh Suhu Awal dan Lama Penyeduhan terhadap Karakteristik Sensoris dan Warna Teh Putih Silver Needle (Camellia assamica) Produksi PT. Bali Cahaya Amerta

White tea is obtained from the shoots of Camellia assamica tea which are very young and still curled, have very fine silvery-white hairs or silver, and are kept out of the sun during the plucking process. Silver needle white tea produced by PT. Bali Cahaya Amerta is an excellent product promoted as functional drink. This research aimed to know the influence of initial temperature, and brewing time on the sensory characteristics and the color of silver needle tea; to decide the best initial temperature and brewing time in producing silver needle white tea. The design of experiment in this research used completely randomized design of organoleptic test and randomized complet block factorial in color intensity test with two treatment factors. The first factor was the initial brewing temperature which consisted of three levels namely, 75o ±10C, 850±10C, 950±10C. The second factor was the brewing time which consisted of three levels namely, three minutes, six minutes, and nine minutes. The analyzed variable was organoleptic characteristics, such as hedonic (the whole receiver), color score, taste, as well as aroma and color intensity system L*, a*, b*. The result of the research showed that the initial temperature and brewing time as well as the interaction of the two has a very significant effect to the whole tested variables. The treatment using 950C initial temperature and nine minutes of brewing time produced the best characteristic, in which the color 2.40 ± 0.64 (limpidly yellowish to yellowish), taste 4.24±0.43 (slightly sweet to sweet), aroma 4.48±0.51 (has a tea scent to extremely tea scent), the whole receiver 6.20±0.43 (like to extremely like), brightness level (L*) 55.32±0.17, redness level (a*) 16.32±0.17, yellowish level (b*) 36.37±0.10. &#x0D; Keywords: white tea, initial temperature, brewing time, organoleptic, color intensity.

Investigation of Chemical Kinetic Model for Hypergolic Propellant of Monomethylhydrazine and Nitrogen Tetroxide

Abstract Hypergolic bipropellant of monomethylhydrazine (MMH) and nitrogen tetroxide (NTO) is extensively used in spacecraft propulsion applications and rocket engines. But studies on the chemical kinetic mechanism of MMH/NTO are limited. So, in this study by integrating the submechanisms of MMH decomposition, NTO thermal decomposition, MMH/NTO and intermediates, and small hydrocarbons, the comprehensive chemical mechanism of MMH/NTO bipropellant is proposed. The present chemical mechanism consists of 72 species and 406 elementary reactions. In two respects of ignition delay times and combustion flame temperatures, the present model has been validated against the theoretical calculation results and also compared with other kinetic models in the literature. The validations show that the predicted ignition delay times by the present kinetic model are highly consistent with the theoretical data and well describe the pressure-dependent characteristic. For combustion flame temperature, the present model also exhibits better predictions to the theoretical calculation results, which are also the same as the predictions by the MMH-RFNA model. Furthermore, the influences of initial temperature, chamber pressure, and NTO/HHM mass ratio (O/F) on the ignition delay time and combustion flame temperature are investigated. The auto-ignition behavior of MMH/NTO propellant is sensitive to initial temperature and chamber pressure, and the combustion flame temperature is more sensitive to the O/F. This study provides a detail chemical kinetics model for further mechanism simplification and combustion numerical simulation.

Numerical simulation of self heating during stretch blow moulding of PET: viscohyperelastic modelling versus experimental results

During the stretch blow moulding (SBM) process of polyethylene terephthalate (PET) bottle, high viscous dissipation generates self heating phenomena. Since the influence of temperature on polymer’s behavior is important, it is necessary to evaluate the self heating values in order to manage accurately the simulation of the process. An anisotropic visco-hyperelastic model has been developed to manage numerical simulations of free blowing. The model takes into account the anisotropy and the effect of the temperature. It has been computed in a user-interface VUMAT implemented in the software ABAQUS/Explicit. The identification of the model is based on experimental data of biaxial tension tests. We identified the characteristics taking into account the self-heating effect by a semi analytical process followed by an adjustment using finite element. For sake of validation, PET preforms have been blown from different initial temperature and followed using a thermal camera. The increase of temperature is measured by comparing initial temperature and final temperature. Comparison between the experimental and numerical simulations is discussed and influence of initial temperature or blowing pressure is highlighted in a large numerical investigation.

Experimental investigation of end-gas autoignition-to-detonation transition for an n-decane/O2/Ar mixture

The transition between different combustion regimes is investigated experimentally for a stoichiometric argon-diluted n-decane/O2 mixture. The focus is put on the influence of initial temperature (T = 420–470 K) and pressure (P = 1.5–3 bar) on the regime transitions. Fast schlieren visualization (≥ 120 kHz) and high-speed pressure and temperature measurements are used to monitor the evolution of the reactive processes inside a combustion chamber of square cross-section (40 mm × 40 mm × 172 mm). Results for P ≥ 2.5 bar and the entire temperature range and for P = 2 bar and T ≥ 440 K show three distinct stages following the adiabatic compression of fresh gases induced by the propagation of a flame into the chamber/test section, namely a cool flame, a main heat release stage, and detonation onset. For P = 1.5 bar, however, only the first two stages of the process are observed in the temperature range studied. A two-stage autoignition phenomenon, typical of large hydrocarbons, occurs systematically in the end gas and generates consecutive reactive fronts. The transition to detonation appears to result from the acceleration of the aforementioned fronts toward the speed of sound in fresh gases. Notably, the compression history plays a key role in setting conditions for detonation onset. Our results are in agreement with classical transition maps available in the literature.

Influence of initial temperature and pressure on the explosion behavior of n-dodecane/air mixtures

There is an increasing industrial interest towards long-chain hydrocarbons, also due to the fact that they can be obtained from renewable organic materials. These substances are flammable and, under certain conditions, can explode. Nevertheless, very few experimental data are available on their thermal and kinetic characteristics and, more specifically, on their flammability and explosion behavior under various process conditions.In the work presented in this paper, the explosion behavior of n-dodecane has been investigated through experiments performed in a closed 5-l cylindrical vessel by varying the concentration of (vaporized) fuel in air at different initial temperatures - 130 °C and 160 °C - and pressures - 1, 2 and 3 bar. From the recorded pressure-time histories, the most important parameters for the assessment of process hazards and the safe design of process equipment - maximum pressure, maximum rate of pressure rise, and deflagration index - have been quantified. It has been found that, prior to feeding air and igniting the fuel/air mixture, the n-dodecane injected into the explosion vessel undergoes pyrolysis phenomena that interfere with combustion, thus affecting the performed measurements. On the basis of these results, it can be expected that pyrolysis also affects the flammability and explosion behavior of long-chain hydrocarbons others than n-dodecane involved in industrial processes at high temperature and, thus, it should be taken into consideration when addressing safety-related issues.

On Induced Properties and Self Heating during Free Blowing of PET Preform

Abstract The great influence of temperature on polymer's behavior is well known and a 10°C increase can lead to a 10-time reduction of the viscosity near the glass transition temperature. To manage accurate simulation of thermoforming processes, and particularly the stretch blow molding process that is managed in the vicinity of Tg, it is necessary to take into account the self heating phenomena that may have impact on induced properties. In the particular case of polyethylene terephthalate (PET), injected preforms have been blown with different initial temperature and followed using a thermal camera. For an identical final volume of the blown preform, the influence of initial temperature on self-heating is discussed. Back to room temperature, induced mechanical properties are measured using digital image correlation: bottles are blown under different pressures and the strain fields are measured. Using the virtual field method on a region of interest of the bottle, these results allow the identification of the induced mechanical properties. Comparison between the self-heating and the induced modulus is managed and the effect of the self heating on the free blown shapes and induced properties is discussed.

Molecular-dynamic investigation of the influence of initial temperature on the character of shock-wave processes in silicon carbide nanocluster

In the present study, using the molecular dynamics method, we investigated the impact interaction of a spherical cluster of 3C-SiC silicon carbide with a rigid wall at a wide range of velocities. The influence of cluster initial temperature on the fracture process was analyzed.

Theoretical and experimental research on the influence of initial temperature on the flammability of hydrocarbon-CO2 mixture using in organic Rankine cycle

As an effective waste heat recovery technique, the hydrocarbon-CO2 mixture based Rankine cycle is always operating on a specific temperature, which has a noticeable influence on flammability limits. Thus it is critical to research flammability limit of hydrocarbon-CO2 at various initial temperatures. Focusing on the hydrocarbon-CO2 mixture, this paper first measured its flammability limits at different initial temperatures using an experimental setup based on the ASTM E681-09. Results have shown that lower flammability limit decreases with the elevating initial temperatures while upper flammability limit increases, therefore the flammable zone expands leading to higher potential dangers. Moreover the expansion values of flammable zone from 30 °C to 70 °C have decreased by nearly 0.3 vol% with the dilute concentration changing from 0 to 0.9. A linear relationship between temperature and flammability limits of hydrocarbon-CO2 mixture has been proposed based on thermal theory and verified with experimental values. At the same time, a comprehensive method based on calculated adiabatic flame temperature theory was presented to predict the flammability limit at different temperatures with higher accuracy. The mean relative deviation between the predicted results and observed ones is 2.76% at upper flammability limit and 1.71% at lower flammability limit in the temperature range examined.