Local High Temperature Research Articles

Molecular dynamics of the spontaneous generation mechanism of natural gas hydrates during methane nanobubble rupture.

Natural gas hydrates have garnered significant attention as a potential new source of alternative energy, and understanding their formation mechanism is of paramount importance for efficient utilization and pipeline transportation. However, there is no consensus among academics on the formation mechanism of natural gas hydrates. In this paper, we propose a method for promoting the rapid formation of natural gas hydrates based on the rupture of methane nanobubbles, which creates local high temperature and pressure to facilitate the mixing of methane and water. The rapid decrease in system temperature and pressure during the process further enhances the formation of gas hydrates. Using molecular dynamics simulations, we theoretically verify the formation of natural gas hydrates. Our results indicate that the instantaneous rupture of methane nanobubbles induced by shock waves leads to a dramatic increase in the local molecular motion velocity around the bubbles. This results in extreme local high temperature and high pressure, leading to complete mixing of methane and water and rapid formation of gas hydrates during the cooling and pressure drop of the mixture. We confirm our findings by analyzing F3-order parameters, F4-order parameters, and water cage statistics.

Organic Waste Gasification by Ultra-Superheated Steam

The perspective of the emerging environmentally friendly and economically efficient detonation gun technology for the high-temperature gasification of organic wastes with ultra-superheated mixture of steam and carbon dioxide is discussed. The technology is readily scalable and allows the establishment of a highly reactive atmospheric-pressure environment in a compact water-cooled gasifier due to very high local temperature (above 2000 °C), intense in situ shock-induced fragmentation of feedstock, and high-speed vortical convective flows enhancing interphase exchange processes. These unique and distinctive features of the technology can potentially provide the complete conversion of solid and liquid wastes into syngas, consisting exclusively of hydrogen and carbon monoxide; microparticles, consisting of environmentally safe simple oxides and salts of mineral residues, as well as aqueous solutions of oxygen-free acids such as HCl, HF, H2S, etc., and ammonia NH3. A small part of the syngas product (ideally approximately 10%) can be used for replacing a starting fuel (e.g., natural gas) for the production of a detonation-born gasifying agent, while the rest can be utilized for the production of electricity, heat, and/or chemicals.

Insights to the microwave effect in formation and performance promotion of iron-based carbon nanofibrous composites for H2S removal

Iron-based carbon nanofibrous composites were synthesized as high-temperature coal gas desulfurization sorbents by electrospinning, pre-oxidation and conventional/microwave carbonizations. Compared with conventional method, microwave carbonization effectively promoted the nucleation and growth of zero-valent iron (ZVI) among nanofibers, which in turn expedited the carbonization process of carbon matrix via the catalytic graphitization. Desulfurization performance evaluations showed that the sorbent carbonized by microwave at 700 °C possessed the highest breakthrough sulfur capacity (3.81 g S 100 g−1 sorbent), which might be attributed to the porous structure and rich content of iron species on the surface of nanofibers. The local high temperature induced by the interaction of microwaves and ZVI imparted the sorbent with porous microstructure. In addition, the rapid and high-temperature carbonization of microwave greatly enhanced the diffusion of Fe to the fiber surface due to the difference in thermal expansion coefficients of Fe and carbon. As a consequence, microwave carbonization involves the advantages of high energy efficiency and structural strengthening effect, suggesting its potential for the preparation of desulfurization sorbent.

Impacts of Laser Power and Scan Speed on Temperature Field and Molten Pool of ZL104 Aluminum Alloy Selective Laser Melting

Selective laser melting (SLM), a significant branch of laser additive manufacturing (LAM) technology, has become a popular topic of research in engineering, materials and many other disciplines. SLM can transform metallic powders directly into 3D components, which allows SLM to offer the unique flexibility of manufacturing parts with complex structures. The quality of the product is closely related to the characteristics of the temperature field, as well as that of the molten pool. Because of the high localized temperatures and the rapid cycles of melting and solidification during SLM, it’s difficult to monitor the temperature field in real time. Hence, numerical simulation is often used to study the SLM process. In this work, the SLM process of ZL104 aluminum alloy was simulated using the CFD method, and the influences of processing parameters, including laser power and scan speed, on the temperature field and the characteristics of the molten pool have been investigated. Results showed that when the laser power increased, the peak temperature of the molten pool also mounted, however, the maximum temperature of the molten pool fell as the scan speed rose. The dimensions of heat affected zone (HAZ), including the width and depth, increased with growing laser power, but decreased with the increase of scan speed.

Failure analysis of the water-wall tube in once through Benson boiler

Failure analysis of a water wall tube of a once-through Benson boiler after 100,000 h of use of service is presented. A 15Mo3 material was used in the manufacture of the tube. In order to identify the root cause of the rupture, visual inspection, optical emission spectroscopy, microscopic examinations, mechanical strength measurements, and tube wall thickness measurements at various locations were performed on the failed tubes. Visual inspection revealed a fish mouth puncture opening with thin lips. As a result of optical spectroscopy, mechanical testing, and hardness measurements, the material was found to meet the requirements. Based on microstructure analysis, it appears that the pearlite spheroidized near the rupture site as a result of localized high temperatures. The failure mechanism of the tube was identified as a localized short-term overheating caused by high heat flux based on the results of all the tests and analyses conducted in this study.

Simulation research on thermal protection performance of firefighting robots and design of protection system

In response to manufacturing strategy demand, fire accidents in petroleum, chemical, forestry, and high-rise buildings are on the rise. Although the firefighting robot can replace fire rescue workers who come into the dangerous rescue site, electronic devices’ thermal failure problem caused by high temperatures in the whole electronic equipment problem is bigger. The proportion of electronic device thermal failure has a significant impact on the normal operation of electronic equipment. How to dissipate heat quickly and avoid local high temperatures becomes a key problem. Most domestic and foreign scholars only study the influence of thermal protection materials themselves on robot protection systems, and few study the influence of heat insulation materials and heat dissipation materials on robot protection systems through appropriate structure combinations. Therefore, the establishment of comprehensive high-temperature fire situations on the fire protection robot automatic detection of smoke concentration and temperature of heat insulation material and heat dissipation material composition of folded tensile structure and liquid nitrogen cooling system thermal protection model of robot thermal protection performance research is of great significance, at the same time through COMSOL Multiphysics software to simulate the proposed model, Select the best heat dissipation materials and heat insulation materials, protect the internal electronic components in the fire accident sustained high temperature, can adjust the temperature as soon as possible, make it adapt to the change of temperature field, for the rescue process to gain 2~15 minutes time duration.

Coupled Analysis of Thermofluid-Structure Field for Thermal Properties of Early-Age Concrete Influenced by Electric Heating System

When heat energy is transferred to concrete through energy conversion by an electric heating system, the overall thermal performance of the early-age concrete is affected by the local high temperature of the concrete. This, in turn, affects the accuracy of the prediction and calculation of concrete deformation. Concrete thermal physical parameter models considering the mutual influence of heat and humidity were established to clarify the influence of an electric heat tracing system on the heat transfer performance of concrete at an early age, based on the concepts of equivalent age and hydration degree. Additionally, the COMSOL numerical simulation software was used for realizing the numerical solution of concrete heat transfer. The research indicates that the degree of hydration is affected by the heating provided by the electric heat tracing system. When curing for 40 h, the degree of hydration approaches 0.82 and remains unchanged, which indicates that the hydration of cement was almost complete in less than 2 days. The specific heat value of concrete in the early stage was significantly affected by electric heat tracing. This value of concrete at a high initial temperature was larger than that at a low temperature, while the specific heat of each point in the later stage tended to be the same. The thermal conductivity was significantly affected by the local electrical heating. The higher the temperature was, the lower the thermal conductivity was, which remained stable for two days under the influence of temperature. The key contribution of this research is to provide a coupling model for concrete curing. The findings from the study also provide industry practitioners with a comprehensive guide regarding the specific applications of the electric heating system in early-age concrete curing.

Research on thermal vacuum reliability of pulse high-power solid-state power amplifier (SSPA) for satellite use

This paper investigates the abnormal phenomenon of local blackening of the internal circuit substrate caused by low-pressure discharge in the thermal vacuum test of an L-band high-power pulsed solid-state power amplifier for satellite use, i.e., the residual flux inside the product volatilizes under vacuum conditions. Thus, the low-pressure discharge causes a rise in local temperature, and under high local temperature, the silicone rubber is thermally decomposed. There are four proposed engineering improvements, which are proved to be feasible and effective through simulation and re-test verification. The blackening problem's observation, analysis, and resolution are crucial to improve the reliability of high-power microwave solid-state power amplifiers used in spacecraft in high orbit.

3D multi-phase simulation of metal bipolar plate proton exchange membrane fuel cell stack with cooling flow field

A three-dimensional (3D) multi-phase numerical model for a full scale proton exchange membrane fuel cell (PEMFC) stack is established, including inlet and outlet manifolds, cooling flow fields, membrane electrode assembly (MEA), and gas flow fields (including gas distribution zones). The performance of six-cell metal bipolar plate (BP) stack with isothermal boundary and cooling flow field is analyzed comprehensively, respectively. The simulation results indicate that the uniformity of oxygen distribution in the third fuel cell (FC) and fourth FC flow field is the worst, and the gas velocity in the flow field is directly proportional to the concentration and inversely proportional to the volume fraction of liquid water. The local high temperature in the stack leads to the decrease of liquid water, the increase of water vapor molar concentration and the dilution of oxygen concentration in the third FC and fourth FC flow fields. The cooling flow field reduces the overall temperature of stack, and the maximum oxygen concentration increases by 5.13 %. However, it causes a large temperature difference of stack, the maximum is 21.3 K, which increases the inconsistency of temperature distribution in the flow field. When the stack has cooling effect, the working voltage of each FC is higher. When the position is the same and the thermal boundary condition is different, the temperature difference of the stack is 6.2 K, and that of the single FC is only 4.5 K. High temperature leads to the decrease of hydration degree of proton exchange membrane (PEM) and uneven local current density. The hot spots zones of cooling flow fields in stack are concentrated in second FC, third FC and fourth FC. Temperature is an important factor causing the performance difference of each single FC, and the thermal management of stack is more significant than that of single FC.

Formation of subsurface Cu-O-Si system through laser-induced plasma-assisted copper penetration for fabricating robust adhesive copper wire on glass substrate

This study reports an approach, laser-induced plasma-assisted penetration (LIPAP), to facilitate copper diffusion to the glass interior using a femtosecond laser. TEM images and EDS analysis showed copper particles could diffuse into the glass up to 300 nm from the surface. The diffusion was driven by the local high temperatures generated by consecutively incident highly repetitive laser pulses. Furthermore, the HR-TEM images showed that, between the surface copper layer and the internal amorphous SiO2, there were crystalline regions of copper nanoparticles and copper oxides and an amorphous zone, belonging to the Cu-O-Si system, through which, the surface copper layer was firmly connected with the glass substrate. The LIPAPed copper layer then served as a patterning seed for electroless-plating of highly conductive copper wires. Consequently, copper wires with a resistivity of 9.9×10-8Ωm were obtained. Finally, a scratch adhesion test was performed to quantify the adhesion of the resulting copper films. Results showed that copper remained adhered to the surface before reaching the ultimate glass crush load of 30 N, corresponding to normal scratch stress of 240 MPa. Accordingly, based on the LIPAP-formed special subsurface nanostructures serving as the mechanical anchoring basis, highly conductive and adhesive electroless-plated copper wires were achieved.

Investigation on novel inertial minichannel to mitigate maldistribution induced high temperature zones

Axial conduction in channels depends on inlet velocity and thermal conductivity of the working fluid. In the case of parallel channels, axial conduction depends on heat sink configuration and inlet velocity. That at increased flow rates, the parallel channel generates flow maldistribution and develops localized high temperature zones in the heat sink. Effective use of heat sink configuration to mitigate axial conduction is found in the literature; however, the axial conduction effects are not suppressed in the parallel channels. Henceforth, the present study provides experimental and numerical insight to evaluate the potential of ribs and inertial based spillway channels to overcome the above mentioned problems in parallel channels. Especially, four different heat sink concepts were designed using copper material; normal channel, ribbed channel, ribbed inclined, and ribbed lifted. In which normal channel is experimented with and used as a reference, while the remaining channel types were investigated numerically. The factors such as maldistribution, thermal resistance, and pressure drop are considered to evaluate the impact of the ribs on inlet velocity. The ribbed inclined channel was found to perform better than other types and developed a 33 % lower center channel velocity than the normal channel. The temperature near the exit of the ribbed inclined channel was observed to be more even and the entire width of the minichannel was maintained at 47 °C, this trend was not noticed using other configurations.

Synergistic effect and mechanisms of ultrasound and AlOOH suspension on Al hydrolysis for hydrogen production

Ultrasound can accelerate and change the reaction process and is widely used in the field of hydrogen production and storage. In this study, ultrasound (US) and AlOOH suspension (AH) are used to promote hydrogen production from Al hydrolysis. The results indicate that both US and AH greatly shorten the induction time and enhance the hydrogen production rate and yield. The promoting effect of US and AH on Al hydrolysis originates from the acoustic cavitation effect and catalytic effect, respectively. When AH is used in combination with US, Al hydrolysis has the best hydrogen production performance and the hydrogen yield can reach 96.6 % within 1.2 h, because there is a synergistic effect on Al hydrolysis between AH and US. Mechanism analyses reveal that the micro-jets and local high temperature environment arising from acoustic cavitation improve the catalytic activity of AlOOH, while the suspended AlOOH particles enhance the cavitation effect of US. This work provides a novel and feasible method to promote hydrogen production from Al hydrolysis.

Causes for the Negative Scaling of Extreme Precipitation at High Temperatures

Abstract Although the intensity of extreme precipitation is predicted to increase with climate warming, at the weather scale precipitation extremes over most of the globe decrease when temperature exceeds a certain threshold, and the spatial extent of this negative scaling is projected to increase as the climate warms. The nature and cause of the negative scaling at high temperature and its implications remain poorly understood. Based on subdaily data from observations, a reanalysis product, and output from a coarse-resolution (∼200 km) global model and a fine-resolution (4 km) convection-permitting regional model, we show that the negative scaling is primarily a reflection of high temperature suppressing precipitation over land and storm-induced temperature variations over the ocean. We further identify the high temperature–induced increase of saturation deficit as a critical condition for the negative scaling of extreme precipitation over land. A large saturation deficit reduces precipitation intensity by slowing down the convective updraft condensation rate and accelerating condensate evaporation. The heat-induced suppression of precipitation, both for its mean and extremes, provides one mechanism for the co-occurrence of drought and heatwaves. As the saturation deficit over land is expected to increase in a warmer climate, our results imply a growing prevalence of negative scaling, potentially increasing the frequency of compound drought and heat events. Understanding the physical mechanisms underlying the negative scaling of precipitation at high temperature is, therefore, essential for assessing future risks of extreme events, including not only flood due to extreme precipitation but also drought and heatwaves. Significance Statement Negative scaling, a decrease of extreme precipitation at high local temperature, is a poorly understood phenomenon. It was suggested that the negative scaling may be a reflection of precipitation’s influence on temperature. Here we show based on observational data, a reanalysis product, and climate models that the negative scaling results primarily from the impact of the high temperature–induced saturation deficit on precipitation over land and from storm-induced temperature variations over the ocean. In hot weather when moisture is limited (as is over land), a large saturation deficit reduces precipitation intensity by slowing down the convective updraft condensation rate and accelerating condensate evaporation, leading to a negative scaling. The same mechanism can also contribute to increased compound drought and heat events.

Potent antibacterial fibers with the functional “triad” of photothermal, silver, and Dex for bone infections

Bacteria-induced bone infections disrupt the healing and repair ability of bone tissue, posing a serious challenge to the treatment of clinical bone defects. In this study, novel composite fibers (PLLA/Dex/Ag fibers) with light-responsive rapid antibiosis and osteogenesis were obtained by mixing the photothermal agent silver nanoparticles (Ag-NPs) and the osteogenic drug dexamethasone (Dex) in polylactic acid (PLLA) using electrospinning, which can simultaneously kill multidrug-resistant bacteria and accelerate bone tissue healing due to the photothermal effect and release of Dex. Ag-NPs can act as antimicrobial agents released from the fibers and as photothermal agents to generate local high temperature and singlet state oxygen (1O2) under 808 nm light radiation, thereby killing the bacteria. The antimicrobial tests in vitro showed that PLLA/Dex/Ag fibers had an excellent antimicrobial effect on Escherichia coli and Staphylococcus aureus under NIR light radiation, shortening the effective antimicrobial time from 24 h to 6 h and achieving light-responsive antibiosis rapidly. Meanwhile, the released Dex could induce the differentiation of bone marrow mesenchymal stem cells into osteoblasts, thus promoting the healing of bone defects. In conclusion, this study provided a simple and effective strategy for the clinical treatment of bone infections.

Pipeline safety monitoring technology based on FBG-ROTDR joint system and its case study of urban drainage pipeline monitoring

The damage of buried oil and gas pipeline has the characteristics of randomness and concealment. Pipeline damage monitoring and safety assessment is a research hotspot at present. Combined with the advantages of local high precision of fiber Bragg grating (FBG) and large-scale measurement of ROTDR, a FBG-ROTDR joint system is proposed and FBG-ROTDR based optical fiber sensor is developed to carry out Pipeline safety monitoring. In order to verify the joint system, one leakage model of PVC pipe is established, and multi-point fiber Bragg grating strings and optical fibers are arranged on the PVC pipe for corresponding strain and temperature measurement. Then the technology is used for urban drainage pipeline safety monitoring. The research results show that the FBG-ROTDR joint system can realize local high accuracy strain measurement and continuous temperature measurement of leakage area, and has the function of temperature compensation for local strain measurement.

Performance analyses and heat transfer optimization of parabolic trough receiver with a novel single conical strip insert

Parabolic trough collectors are the crucial component of the concentrated solar power plant, which can meet heat demand and mitigate energy shortages. However, their operation suffers from defects of high local temperature and poor wall temperature uniformity. To alleviate this issue, an enhanced parabolic trough receiver (PTR) with a novel single conical strip insert is proposed and numerically investigated in detail. Furthermore, the effects of structural parameters of the conical strip on the enhanced PTR are investigated, and multi-objective optimization is conducted to determine the optimal parameters. Finally, the performance of the optimal enhanced PTR is evaluated under different operating conditions. The results show two symmetrical longitudinal vortices are formed in the absorber tube due to the guidance of the conical strip, which is beneficial to enhancing fluid mixing and heat transfer. Accordingly, the temperature uniformity of the absorber tube and the actual efficiency are effectively improved. Compared to the smooth PTR, the tube wall temperature is dropped by up to 168 K, and the actual efficiency is improved by 3.3% at most. Moreover, the entropy generation and exergy destruction are reduced by 22.2%–49.3% and 30.6%–45.9%, respectively. This research may guide designing the PTR for efficient and safe operation.

Effect of structure parameters on low nitrogen performance of burner based on orthogonal experiment method

A flue gas internal and external double cycle low nitrogen burner was established. Using the method of orthogonal test, the number(n), inclination angle (i) and diameter (d) of the injection pipe, the end deflection angle(γ), overlap angle(β) and number (η) of the blade were set two levels respectively, and the maximum furnace temperature (Tmax), average furnace temperature (Tav) and NO emissions at the furnace outlet (MNO) were taken as experimental indexes. It is found (1) The influence degree of various factors of nozzle structure on the three indexes is n > d > i. The influence degree of cyclone structure factors on the three indexes is γ > β > η. The effects of factors i and η on the three indexes were negligible. However, the interaction of structural factors has different effects on the three indexes. (2) The size of the high temperature zone is the key reason for the formation of NOx. By adjusting the structural parameters, the fuel and oxidizer mixing process is enhanced, local high temperatures are avoided, and thermal NOx emissions are reduced. (3) In several of the cases studied, NO emissions from boilers were below 30 mg/Nm3, and in some cases below 10 mg/Nm3.

Microwave-induced steam distillation (MISD) remediation in petroleum hydrocarbon-contaminated sites: From process improvement to pilot application

The process improvement, a pilot remediation test and the decontamination mechanism of microwave-induced steam distillation (MISD) for petroleum hydrocarbons (PHs) removal were conducted. Processes of multistage steam distillation and carbon reinforcement were compared to determine the best remediation process. Pilot project was then carried out to explore the applicability of MISD in site-scale remediation. The remediation efficiency, procedures and influencing factors of site-scale MISD project were studied by monitoring variations of soil moisture, temperature and PHs concentrations. Furthermore, the decontamination mechanisms of PHs were clarified based on kinetic analysis. The results showed that the multistage steam distillation could improve 10%∼15% remediation efficiency, and the carbon reinforcement could shorten remediation duration of each steam distillation stage by 50%. Pilot MISD project adopted multistage steam distillation process and went through four (initial, rapid heating-up, gentle heating-up and quasi-equilibrium) remediation stages (overall temperature ≤100 °C). The final PHs removal rate was about 60%, which would get better with greater proportion of low boiling points components and stronger vapor extraction. Kinetic studies showed that PHs was removed by steam stripping and limited by intraparticle diffusion in the “steam distillation zone”, while local high temperature (＞100 °C) greatly improved PHs volatilization and provided activation energy for PHs desorbed and degraded in the “selective heating zone".

Numerical investigation of vibration-induced cavitation for gears considering thermal effect

In the lubrication of high-speed gears, cavitation can be induced by the strong vibration and high temperature, resulting in the insufficient lubrication and surface damage. For further understanding the lubrication mechanism between meshing teeth, the research in cavitation problem is essential, benefiting the design and optimization of high-speed gear transmissions. In this study, regarding a pair of spur gears with oil dip lubrication as the research objective, a computational fluid dynamics method coupled with cavitation model, thermal effect and gear dynamics is proposed for the theoretical study of cavitation mechanism, where the novelties are described as: (i) the gear dynamic responses from a finite element model are introduced for simulating the vibration effect; (ii) the cavitation vapor induced by local high temperature is included; (iii) the vapor distribution along tooth width is considered. Compared with the experiments from available researches, this method is validated. The results indicate that cavitation occurs easily at high speed, moreover, the decreased load and increased speed both intensify the fluctuation of cavitation vapor on meshing face, indicating the increased erosion risk. At high speed and heavy load, the local instantaneous temperature becomes very high, aggravating cavitation most significantly, so the thermal effect should not be ignored in this situation.

Research on arc root stagnation when small current is interrupted in self-excited circuit breaker

The self-excited DC air circuit breaker (SE-DCCB) has been widely used in urban rail transit due to its excellent stability. It can realize forward and reverse interruption, but has difficulty interrupting small currents due to the phenomenon of arc root sticking at the entrance of the arc chamber in the splitting process, which is known as arc root stagnation. A coupling model of the self-excited magnetic field and magnetohydrodynamics is established for the SE-DCCB with the traditional structure. The magnetic field, temperature and airflow distribution in the arc chamber are investigated with an interrupting current of 150 A. The simulation results show that the direction and magnitude of the magnetic blowout force are the dominant factors in the arc root stagnation. The local high temperature of the arc chamber due to arc root stagnation increases the obstruction effect of the airflow vortex on the arc root movement, which significantly increases the arc duration time of small current interruption. Based on the research, the structure of the magnetic conductance plate of the actual product is improved, which can improve the direction and magnitude of the magnetic blowout force at the arc root so as to restrain the development of the airflow vortex effectively and solve the problem of arc root stagnation when the small current is interrupted. The simulation results show that the circuit breaker with improved structure has a better performance for a small current interruption range from 100 A to 350 A.