Increase In Initial Temperature Research Articles

Effects of initial conditions on MILD combustion for diesel in a constant pressure combustion bomb

The experimental and computational studies for MILD combustion of diesel were conducted in this paper. The experiment was carried out in a constant pressure bomb and the computation was completed with the SAGE combustion model. The initial condition in the experiment covers two temperatures (723 K and 773 K), two pressures (18 bar and 25 bar), with a constant fuel flow of 2 kg/h, an oxygen flow of 1 kg/h, and a wide range of carbon dioxide flow containing 35–160 kg/h. Normal combustion has bright yellow flame and MILD combustion has blue flame according to observation in the experiment. The effects of ejection ratio, initial temperature and pressure are investigated to illustrate the mechanism of MILD combustion. The results show an increase in ejection ratio and an increase in initial temperature are propitious to achieve MILD combustion, while increased pressure needs more strict requirements to realize MILD combustion. Generally, experiment results and computations have similar trends for the effects of initial conditions on MILD combustion.

Laminar burning velocity of microalgae oil/RP-3 premixed flame at elevated initial temperature and pressure

In the present work, algae-derived biocrude was collected from the hydrothermal liquefaction of algae slurry, and the mixtures of algae-derived biocrude and RP-3 aviation kerosene was used as aviation substitute fuel named as microalgae oil/RP-3 blend. In order to understand the laminar burning velocity (LBV) of microalgae oil/RP-3, experiments have been carried out in a constant volume chamber (CVC) to investigate the effects of initial temperature, initial pressure and microalgae oil addition on the LBV of microalgae oil/RP-3 blend over a wide equivalence ratio range from 0.8 to 1.4. Experimental result shows that with the increase of initial temperature and microalgae oil addition, the LBV of microalgae oil/RP-3 mixture increases, while with the increase of initial pressure the LBV of microalgae oil/RP-3 mixture decreases. According to the method of Metghachi, the relationship between the LBV and its influence factors was obtained, the exponents of αT(ϕ), βP(ϕ) and γR(ϕ) indicate that the change of initial temperature and pressure have less effect on LBV around equivalence ratio of 1.1 compared with other equivalence ratio conditions, while the change of microalgae oil addition has more significant effect to improve LBV at equivalence ratio of 1.1.

Shock-induced spallation in single-crystalline tantalum at elevated temperatures through molecular dynamics modeling

The effects of initial temperature on shock-induced spalling behavior and damage evolution of single-crystal Tantalum were investigated using molecular dynamics simulation. The wave profiles show that shock pressure and temperature increment rise as initial temperature increases, which can be explained utilizing the Rankine-Hugoniot relationship. It is found that strain rate and the initial temperature has a substantial effect on the spall strength. The spall strength will decrease with initial temperature increases, and the competition between the strain rate hardening and temperature softening effect on spall strength is discussed. The radial distribution function analysis reveal that the classical spallation occurs under shock velocity 1.5 km/s and micro-spalling state with material partially melted or melted happened in higher shock velocity. The simulations show that shock-induced spalling of Tantalum is characterized by void nucleation, growth, and coalescence. The void evolution characteristics in classical spallation and micro-spalling are discussed. Furthermore, it is found that the initial temperature has a dramatic effect on the void evolution. The total voids number increases as the initial temperature rises. The characteristics of the free surface velocity profile are also disscussed.

Numerical study on instantaneous heat transfer characteristics of AC arc-fault

Studying the heat transfer characteristics of alternating current (AC) arc-fault to electrodes is a key issue in electrical fires. In this paper, an instantaneous heat transfer numerical model of AC arc-fault is developed based on the magneto-hydrodynamic principle. The temperature distribution of the AC arc at the microseconds level and the influence of heat transfer on electrodes at the seconds level when the arc heats are studied. The numerical simulation of the axial temperature of the electrodes is verified by experiments, and the temperature variation in the electrodes at different currents and times is discussed. The results show that the arc temperature varies periodically similar to the current at the microseconds level but it does not go out when the current passes zero. The high-temperature region of electrodes diffuses with the increase in current or time. However, the axial temperature gradient of the electrode decreases with time and increases with current. Furthermore, the range of temperature increase in the electrode position decreases with the increase in current and time, but the electrode position near the arc has a higher initial temperature increase.

Numerical simulation of CH4 recovery from gas hydrate using gaseous CO2 injected into porous media

As for the replacement of CH4 by CO2 from CH4 hydrate-bearing sediment, the replacement rate strongly depends on the diffusion of gas through the hydrate layer, so it is necessary to investigate the diffusion-limited transportation as well as the mass and heat transfer in the porous media. In this paper, a two-dimensional numerical model combining thermodynamic equilibrium and kinetic model through effective fugacity was proposed to address the above issues when the total pressure and temperature are in the hydrate stable zone in poor water (<5%) sediment. Water existence location (sealed under the hydrate layer or distributes freely on the surface of the hydrate layer), the formations of mixed hydrate, and the storage of CO2 in hydrate through the reaction with water were taken into account. Then, this model was used to study the replacement process in a lab-scale core sample. The results showed that a high diffusion coefficient of mixed gases and low permeability can lead to both a relatively large replacement percentage and CO2 storage efficiency. An increase of initial pressure is only beneficial to the formation of CO2 hydrate but it has little influence on the replacement percentage, while an increase of initial temperature leads to a high replacement percentage and low CO2 storage efficiency. Water is adverse to the replacement while benefiting the formation of CO2 hydrate when it is freely distributed in pores. But when the water is sealed under the CH4 hydrate layer, it barely has an impact on the replacement. Besides, a little amount of water can be produced under low initial pressure. CO2 storage efficiencies are always larger than replacement percentages. The largest value of CO2 storage efficiency can exceed 50%, while that of the replacement percentage is less than 40% under present conditions.

Adsorption Characteristics and Mechanism of Cd and Pb in Tiered Soil Profiles from a Zinc Smelting Site

Vertically tiered soil profiles, comprising miscellaneous fill (S1), plain fill (S2), silty clay (S3), and completely weathered slate (S4), were collected from a zinc smelter site in Zhuzhou City, Hunan Province, and their Cd and Pb adsorption characteristics were examined. Static batch experiments were conducted with different initial Cd and Pb solution concentrations, at temperatures of 288-308 K and pH values of 2-6. The results showed that a pseudo first-order model could be fitted to the kinetics of Cd/Pb adsorption in these soils. The soil profiles had a large retention capacity for Cd and Pb. The Cd and Pb adsorption isotherms for these soils conformed to the Freundlich isotherm, with maximum adsorption at 298 K of 2097-4504 mg ·kg-1 for Cd and 4376-10564 mg ·kg-1 for Pb, based on the Langmuir isotherm. The adsorption capacity of Cd and Pb increased with an increase in initial pH and temperature. The Cd and Pb adsorption process were a spontaneous physical and chemical process, and the soil profiles were ranked by their Cd and Pb adsorption capacities in the following order:completely weathered slate (S4)>miscellaneous fill (S1)>silty clay (S3)>plain fill (S2). The variation in adsorption capacities resulted from the differences in physical and chemical properties of the soil, mainly Fe/Al content and cation exchange capacity. Fourier transform infrared and SEM-EDS analysis showed that the main adsorption mechanism is the exchange of Cd and Pb with Fe/Al, while -OH/C＝O sites in soils were the predominant adsorption sites for Cd and Pb. In the study area, exogenous Cd and Pb discharged by smelting activity accumulated predominantly in surface soil, and their concentration gradually decreased with depth. These results provide a scientific basis for the prevention and control of heavy metal pollution in the soil and groundwater of a smelting site.

Pristine and Magnetic Kenaf Fiber Biochar for Cd2+ Adsorption from Aqueous Solution

Development of strategies for removing heavy metals from aquatic environments is in high demand. Cadmium is one of the most dangerous metals in the environment, even under extremely low quantities. In this study, kenaf and magnetic biochar composite were prepared for the adsorption of Cd2+. The synthesized biochar was characterized using (a vibrating-sample magnetometer VSM), Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The adsorption batch study was carried out to investigate the influence of pH, kinetics, isotherm, and thermodynamics on Cd2+ adsorption. The characterization results demonstrated that the biochar contained iron particles that help in improving the textural properties (i.e., surface area and pore volume), increasing the number of oxygen-containing groups, and forming inner-sphere complexes with oxygen-containing groups. The adsorption study results show that optimum adsorption was achieved under pH 5–6. An increase in initial ion concentration and solution temperature resulted in increased adsorption capacity. Surface modification of biochar using iron oxide for imposing magnetic property allowed for easy separation by external magnet and regeneration. The magnetic biochar composite also showed a higher affinity to Cd2+ than the pristine biochar. The adsorption data fit well with the pseudo-second-order and the Langmuir isotherm, with the maximum adsorption capacity of 47.90 mg/g.

Experimental investigation on minimum film boiling temperature during reflooding in multi-rectangular narrow channels

Determination of minimum film boiling temperature (Tmin) is significant in the nuclear reactor safety analysis. Tmin represents the start of quenching which is vital to mitigate the severity of the accident. In this paper, a bottom reflooding experiment is carried out to investigate Tmin and quench velocity in multi-rectangular narrow channels. Effects of working conditions, including inlet subcooling, reflooding velocity, initial wall temperature, and system pressure on Tmin and quench velocity, are analyzed in detail. It is found that Tmin and quench velocity distinctly increases with the increase of subcooling, system pressure, and reflooding velocity. However, the effect of reflooding velocity on Tmin and quench velocity is mild when the reflooding velocity is relatively high. Tmin increases with the increase of initial wall temperature, while quench velocity drops. Tmin at the upper position of the heating wall is lower than that at the lower position because the water subcooling changes when flowing along the heating channel. A prediction model of Tmin during reflooding in rectangular narrow channel is proposed, and very good agreement is achieved comparing with experimental data with ±10% uncertainty.

Study on associated gas combustion characteristics and inert gas influence rules in air-foam flooding process

Air-foam flooding technology is a potential tertiary oil recovery technology. However, enhancing oil recovery through air injection still indicates risks of explosion. In this study, the upper and lower flammability limit (UFL and LFL) and limiting oxygen concentration (LOC) of the associated gas during air-foam flooding are investigated. The change rules of these combustion characteristics are tested under different initial pressures and temperatures using a high-pressure experimental device. The measurement results indicate that with the increase of initial temperature and pressure, the LFL and LOC decrease, whereas the UFL increases. The flammability limits of the associated gas measured at 15 MPa and 80 ℃ are ranging from 1.14% to 56.67%, far exceeding the calculated value under the room temperature and pressure. The empirical formula of the associated gas combustion performance is also fitted to immediately identify the risk levels of associated gases with similar components. The change in initial pressure and temperature only slightly affects the LOC when CO2 is the inert gas. By contrast, it greatly reduces the LOC when N2 is the inert gas. The maximum difference value of 2.55% between the LOC of the two inert gases is observed at 4 MPa and 80 ℃. Overall, the findings of this study can serve as test data for the combustion limits and limiting oxygen content of associated gases in the process of air-foam flooding.

A Foreshock Bubble Driven by an IMF Tangential Discontinuity: 3D Global Hybrid Simulation

AbstractForeshock bubbles (FBs) have been observed upstream of solar wind tangential discontinuities (TDs). A hypothesized mechanism is that foreshock ions with gyroradii larger than the TD thickness may move to upstream side of TDs and generate FBs. In this study, we present the very first three‐dimensional global hybrid simulation of an FB driven by a TD. After the TD encounters the ion foreshock, plasma and magnetic field perturbations are generated upstream of the TD. These perturbations are characteristically consistent with the observed TD‐driven FBs, confirming that TDs can form FBs. We further analyze the initial perpendicular temperature increase initiating the FB and compare the temperature structure with that from tracing test‐particles in static TD electric and magnetic fields. The structure can be explained by the perpendicular velocity change of foreshock ions with large gyroradii as they encounter the magnetic field direction change across the TD, which supports the hypothesized mechanism.

Liquid spray modeling under sodium fire accidents

The Sodium-Cooled Fast Reactor (SFR) system, which features a fast-spectrum, sodium-cooled reactor and a closed fuel cycle for efficient management of actinides and conversion of fertile uranium, is rather prominent in the nuclear reactor design in Generation IV (Gen IV), and likely to be widespreadly used and well-constructed all over the world. However, molten sodium may be sprayed into the ambient or secondary side of steam generator, induced by the pressure drop, in case of an inevitable break in the primary system. This kind of leakage can result in sodium spray fire accident, as a result of the chemical activity of sodium, significantly damaging the equipment and working staffs nearby. Sodium spray fire, which occurs not only in the nuclear industry, but also in solar industry, is a complex process consisting of several specific phenomena, such as the spray dynamics (e.g. droplet particle size/velocity distribution, particle collision and agglomeration), droplets evaporation, sodium aerosol diffusion, thus being drawn many experts’ attention. Based on International Atomic Energy Agency (IAEA)’s effort on phenomena identification and ranking table (PIRT) for sodium spray fire, prediction of droplet size distribution and the mean diameter in particular, are supposed to be in the very first place at level 2, due to the lack of available experimental data for both of model development and validation, and code inadequacy, as well. In this paper, sodium droplet size distribution model is theoretically derived, regarding both of mass and momentum equations as constraints, based on the maximum entropy principle, which can quantitatively describe the effects of two main influencing factors, including initial injection velocity and thermophysical properties of molten sodium. This analytical model is implemented in three typical conditions, including two sodium droplets size distribution experiments and one water droplet experiment. Validations against both of the available test data and predictions by an empirical model, named of Nukiyama-Tanasawa correlation, are conducted with the relative error of median diameter ranging from 17.3% to 18.2%, which ensures the reliability and feasibility of the new model. Moreover, sensitivity analyses are carried out, in terms of typical test conditions of sodium spray fire, which demonstrates that the median diameter of droplets’ size decreases with both of the increase of initial injection velocity and sodium temperature, thus probable triggering positive effect on the propagation of the accident, due to rapid interaction of violent chemical reaction and sodium spray. Besides, the present work can provide a reliable analytical model for the development of safety analysis codes for SFRs.

Experimental and numerical study of a PV/T direct-driven refrigeration/heating system

A photovoltaic/thermal (PV/T) direct-driven refrigeration/heating system was proposed in this paper. This system had the functions of off-grid refrigeration and hot water supply without using batteries. The solar refrigeration efficiency could also be improved by means of PV cell cooling in PV/T modules and compressor speed controlling. In this paper, performance of this system was investigated by experiments and numerical simulations. The influences of the total capacity of PV cells and water temperature in the ice storage tank were also studied. When the number of PV cells increased, the daily cooling capacity per cell increased first, then decreased. This revealed that the capacities of the compressor and PV cells should be designed to improve the PV utilization efficiency. Total cooling capacity of the system increased with the increase of initial water temperature in the ice storage tank. This revealed that high initial water temperature was benefit for system cooling capacity.

Centrality dependence of kinetic freeze-out temperature and transverse flow velocity in high energy nuclear collisions

Centrality-dependent double-differential transverse momentum spectra of charged pions, kaons, and (anti)protons produced in mid-pseudorapidity interval in $\sqrt{s_{NN}}=200$ GeV gold-gold and deuteron-gold collisions with different centralities are analyzed by the blast-wave model with Boltzmann-Gibbs statistics. Meanwhile, the mentioned spectra in mid-rapidity interval in $\sqrt{s_{NN}}=2.76$ TeV lead-lead and $\sqrt{s_{NN}}=5.02$ TeV proton-lead collisions with different centralities are analyzed by the same model. The model results are approximately in agreement with the experimental data in special transverse momentum ranges. It is shown that with the increase of event centrality and energy, the kinetic freeze-out temperature of the emission source and the transverse flow velocity of the produced particles slightly increase in some cases but they do not give an obvious change in other cases. Meanwhile, the kinetic freeze-out temperature (transverse flow velocity) increases (decreases) with the increase of particle mass. The average transverse momentum and initial temperature increase with the increase of event centrality, collision energy, and particle mass. This work also confirms the maximum size dependent effect, which states that the main parameters such as the kinetic freeze-out temperature and transverse flow velocity are mainly determined by the heaviest nucleus from proton-nucleus to nucleus-nucleus collisions.

Formability enhancement in hot spinning of titanium alloy thin-walled tube via prediction and control of ductile fracture

The damage and fracture in hot spinning of titanium alloy is a very complex process under the combined effects of microstructure evolution and stress state. In this study, their dependences on processing parameters were investigated by an integrated FE model considering microstructure and damage evolution, and revealing the effects of microstructure and stress states on damage evolution. The results show that the inner surface of workpiece with the largest voids volume fraction is the place with the greatest potential of fracture. This is mainly attributed to the superposition effects of positive stress triaxiality and the smallest dynamic recrystallization (DRX) fraction and β phase fraction at the inner surface. The damage degree is decreased gradually with the increase of initial spinning temperature and roller fillet radius. Meanwhile, it is first decreased and then increased with the increases of spinning pass and roller feed rate, which can be explained based on the variations of β phase fraction, DRX fraction, stress state and tensile plastic strain with processing parameters. In addition, the dominant influencing mechanisms were identified and discussed. Finally, the thickness reduction without defect in the hot spinning of TA15 alloy tube is greatly increased by proposing an optimal processing scheme.

The Equivalent Effect of Initial Condition Coupling on the Laminar Burning Velocity of Natural Gas Diluted by CO2

Initial temperature has a promoting effect on laminar burning velocity, while initial pressure and dilution rate have an inhibitory effect on laminar burning velocity. Equal laminar burning velocities can be obtained by initial condition coupling with different temperatures, pressures and dilution rates. This paper analysed the equivalent distribution pattern of laminar burning velocity and the variation pattern of an equal weight curve using the coupling effect of the initial pressure (0.1–0.3 MPa), initial temperature (323–423 K) and dilution rate (0–16%). The results show that, as the initial temperature increases, the initial pressure decreases and the dilution rate decreases, the rate of change in laminar burning velocity increases. The equivalent effect of initial condition coupling can obtain equal laminar burning velocity with an dilution rate increase (or decrease) of 2% and an initial temperature increase (or decrease) of 29 K. Moreover, the increase in equivalence ratio leads to the rate of change in laminar burning velocity first increasing and then decreasing, while the increases in dilution rate and initial pressure make the rate of change in laminar burning velocity gradually decrease and the increase in initial temperature makes the rate of change in laminar burning velocity gradually increase. The area of the region, where the initial temperature influence weight is larger, gradually decreases as the dilution rate increases, and the rate of decrease gradually decreases.

Influence of sample temperature on nanosecond laser-induced Cu plasma spectra

There are many experimental methods to increase the emission intensity of laser-induced breakdown spectroscopy (LIBS). Among these methods, pre-heating the target is a simple and effective method to improve LIBS signal intensity. This study used Nd: YAG nanosecond laser pulse to ablate Cu target and produce Cu plasma, and time-resolved spectra of the Cu plasma were measured at different Cu temperatures. The measurement suggested that the higher the target temperature, the stronger the time-resolved spectra of the Cu plasma, and the higher the time-resolved electron temperature and density. Next, the morphology of ablation craters was observed by microscope at different target temperatures. As the Cu target was heated, the melting area in the center of ablation crater became larger, which indicated that more mass targets were ablated to produce plasma, thus producing stronger spectral signal. Finally, the thermal behavior of Cu at different target temperatures was simulated by one-dimensional heat conduction equation. The simulated results show that the temperature of the Cu under laser irradiation increased with the increase of initial temperature of the Cu, and the melting depth also increased, which was consistent with the observed results of Cu target morphology.

Thermal and viscoelastic behaviour of graphene nanoplatelets/flax fibre/epoxy composites

ABSTRACT The aim of this investigation is to enhance the thermal and viscoelastic performance of flax strengthened epoxy with graphene nanoplatelets (GNP). GNP was incorporated at various weight percentages with epoxy resin. Scanning Electron Microscopy (SEM) studies revealed a uniform and well-dispersed GNP with a few agglomerations and voids. Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Dynamic Mechanical Analysis (DMA) were used to evaluate the thermal degradation and viscoelastic properties. The flax strengthened epoxy with 0.1 wt-% GNP witnessed a 17% increase in initial degradation temperature and a 48% increase in char residue. Observations from the DSC revealed that GNP functioned as a thermal barrier due to its strong influence on the glass transition and crystallisation temperature of composites. The DMA findings indicated that the storage and loss modulus of GNP/flax strengthened epoxy increased by 18% and 25%, respectively.

Efficiency of zero emission cycles on the basis of their configuration

In this work, a study of the efficiency of carbon dioxide energy cycles of different architecture is carried out. The relevance of these technical solutions in modern conditions is shown. Basic options of zero emission thermodynamic cycles using CO2 as an cycle fluid are presented. It is shown that the efficiency of the analyzed CO2-cycles with an initial temperature of 1000 °C will be 54-58%, depending on their configuration. It is presented that the efficiency can be increased up to 65% with an initial temperature increase up to 1500 °C.

CHARACTERISTIC ANALYSIS OF HOT DRY ROCK DAMAGE AND FAILURE UNDER THERMAL SHOCK

Wave propagation and thermal conduction properties can indicate structural damage to hot dry rock (HDR) caused by thermal shocks. Granite from the central paleo-uplift belt in the Daqing area in the northern Songliao Basin is the focus of this research. Wave propagation tests and thermal conduction tests were conducted on high-temperature specimens after natural cooling and water cooling. The influence of the cooling process with water on the apparent temperature and thermal shock velocity of rock masses is discussed. Changes in the P- and S-wave velocities, specific heat capacity, thermal diffusion coefficient, and thermal conductivity coefficient of specimens under different heat treatment conditions are analyzed and compared. The relationships between the wave propagation characteristics and the thermal conductivity values are established. The results indicate the following: (1) The apparent temperature and thermal shock velocity values of high-temperature rock masses show nonconstant rates of change from fast to slow. Rock masses with higher initial temperatures exhibit a continuous and strong thermal shock effect, and water temperature differences have only a limited effect on the thermal shock velocity over 20 s of cooling with water. (2) As the initial temperature increases or water temperature decreases, the P-wave velocity, S-wave velocity, thermal diffusion coefficient, and thermal conductivity coefficient values of high-temperature rock masses decrease overall, while the specific heat capacity values increase. The amplitude of change after water cooling is higher than that after natural cooling. When the initial temperature is below 100° C, the free water content is the main factor influencing the wave propagation characteristics and changes in the thermal conduction characteristics. When the initial temperature is greater than 300° C, the changes in both properties depend on the amount of thermal damage done to the rock mass. (3) The fitting results suggest that the wave propagation and thermal characteristics are closely related, and the damage factors are strongly consistent. The deviation of fitting coefficients is mainly due to the limited development of fractures in the small-sized specimens. The research results provide a reference for studies on thermal damage in HDR in the geothermal development process, and a method to determine the in situ thermal conductivity of reservoirs is proposed.

Chromium and cadmium removal from synthetic wastewater by Electrocoagulation process

Electrocoagulation (EC) is one of the efficient electrochemical approaches for industrial wastewater treatment. The present work aims to reach optimum conditions for achieving simultaneous removal of chromium and cadmium ions from synthetic wastewater by EC through assessment of different parameters like electrodes material, electrode configuration, initial pH, current density, initial temperature, and initial contaminate concentration. In addition, a comparison between chemical coagulation and EC efficiency for Chromium and cadmium removal was presented. Results showed that the (Fe-Al), an anode and cathode, achieved better removal efficiency than other electrodes configurations (Fe-Fe / Al-Fe / Al- Al). Also, the increase of initial temperature and current density enhanced the removal efficiency. In contrast, the increase in the initial concentration reduced the removal efficiency. The complete removal of Chromium achieved through the use of Fe-Al electrodes and current density was 12.50 mA/cm2 with solution pH of 5.8, temperature was 25oC and an initial concentration of 280 mg/L. On the other hand, Cadmium’s complete removal was achieved through the use of Fe-Allectrodes, at pH of 5.8, applied current 1.4 A and 60oC. Therefore, EC was proved to be better approach than conventional coagulation in case of treatment of wastewater containing different types of heavy metals ions with high initial concentrations.