Greater Temperature Difference Research Articles

Climate temperature and seasonal influences on the prevalence of temporomandibular disorders in South Korea

This study aimed to explore seasonal variations in temporomandibular disorder (TMD) prevalence in South Korea, utilizing nationwide population-based big data. Data corresponding to the Korean Standard Classification of Diseases code of K07.6, which identifies TMD, were extracted from the Health Insurance Review and Assessment Service online platform for the period from 2010 to 2022. Additionally, we integrated these data with climate temperature records from the Korean Meteorological Administration. We subsequently conducted a statistical analysis of TMD patient data on a monthly and seasonal basis over the past 13 years to assess prevalence. Over the past 13 years, the number of TMD patients in Korea has steadily increased. The prevalence of TMD rose from 0.48% (224,708 out of a total population of 50,515,666) in 2010 to 0.94% (482,241 out of a total population of 51,439,038) in 2022, marking a 1.96-fold increase. Among children under 10 years of age, no significant differences were observed in TMD prevalence between boys and girls. However, a distinct female predominance emerged after the age of 10, with an average female-to-male ratio of 1.51:1. The peak prevalence of TMD occurred in individuals in their 20 s, followed by adolescents in their late 10 s. The majority of TMD patients were concentrated in Seoul and Gyeonggi province, with metropolitan areas accounting for 50% of the total patient count. Seasonally, TMD patient numbers showed no significant increase in winter compared with spring or summer. The temperature difference, defined as the absolute difference between the highest and lowest temperatures for each month, showed a positive correlation with TMD patient counts. A greater temperature difference was associated with higher patient counts. The strongest correlation between temperature differences and TMD patient numbers was observed in winter (r = 0.480, p < 0.01), followed by summer (r = 0.443, p < 0.01), and spring (r = 0.366, p < 0.05). Temperature differences demonstrated a significantly stronger correlation with the increase in the number of TMD patients than absolute climate temperatures. This aspect should be a key consideration when examining seasonal trends in TMD prevalence in South Korea.

Heat transfer and temperature evolution in underground mining-induced overburden fracture and ground fissures: Optimal time window of UAV infrared monitoring

Heat transfer and temperature evolution in overburden fracture and ground fissures are one of the essential topics for the identification of ground fissures via unmanned aerial vehicle (UAV) infrared imager. In this study, discrete element software UDEC was employed to investigate the overburden fracture field under different mining conditions. Multiphysics software COMSOL were employed to investigate heat transfer and temperature evolution of overburden fracture and ground fissures under the influence of mining condition, fissure depth, fissure width, and month alternation. The UAV infrared field measurements also provided a calibration for numerical simulation. The results showed that for ground fissures connected to underground goaf (Fissure I), the temperature difference increased with larger mining height and shallow buried depth. In addition, Fissure I located in the boundary of the goaf have a greater temperature difference and is easier to be identified than fissures located above the mining goaf. For ground fissures having no connection to underground goaf (Fissure II), the heat transfer is affected by the internal resistance of the overlying strata fracture when the depth of Fissure II is greater than 10 m, the temperature of Fissure II gradually equals to the ground temperature as the fissures’ depth increases, and the fissures are difficult to be identified. The identification effect is most obvious for fissures larger than 16 cm under the same depth. In spring and summer, UAV infrared identification of mining fissures should be carried out during nighttime. This study provides the basis for the optimal time and season for the UAV infrared identification of different types of mining ground fissures.

Performance Zoning of Asphalt Pavement and Performance Grade (PG) of Asphalt Binder in Karamay: A Case Study of Xinjiang, China

Asphalt binder is a temperature-sensitive material with a performance that is greatly affected by changing climates. Improper selection of asphalt will cause a lot of damage and affect the durability of the road. The establishment of asphalt pavement performance zoning in Xinjiang, a vast area with great temperature differences, will provide a reference for the selection of asphalt suitability, the refinement of pavement design, and the sustainable development of road engineering. In this study, 11 years of temperature data in the Xinjiang region have been collected and analyzed, and 98% reliability of pavement design temperature has been used to draw a performance grading map of asphalt pavement in the Xinjiang region based on the ArcGIS platform. Finally, the Xinjiang region is divided into nine performance zones. At the same time, the performance grades (PG) of five kinds of asphalt binders in Karamay are explored. The result shows that there is little difference in continuous PG span between different matrix asphalt binders; the lower the penetration grade, the better the high-temperature performance, and the worse the low-temperature performance. After adding the SBS modifier, the continuous PG span can be about 20 °C higher than the matrix asphalt. The indoor test of asphalt mixture also shows that SBS-modified asphalt has better durability. All these provide the basis for a reasonable selection of asphalt binders in different areas of Xinjiang.

Experimental and Numerical Study of the Influence of Solar Radiation on the Surface Temperature Field of Low-Heat Concrete in a Pouring Block

With the influence of intense solar radiation heat and the greater temperature difference between day and night, surface concrete with a drastic temperature change can easily experience a great nonlinear temperature difference, which increases the risk of early-age concrete cracking. In this study, a distributed optical fiber temperature sensing (DTS) system is used to monitor the surface temperature gradient of concrete in real time, and a solar radiation heat monitoring test is also carried out based on the Baihetan project. Based on this, a solar radiation loading model and a finite element model of a typical pouring block considering solar radiation are established. Combined with the measured temperature data and different calculation conditions, the surface temperature changes of medium-heat and low-heat concrete experiencing solar radiation are analyzed, and the temperature control effect of surface concrete with different surface insulation measures is further analyzed. The results show that the temperature variation of medium-heat concrete at the same depth is more obvious than that of low-heat concrete. Additionally, the temperature variation of low-heat concrete is noticeable within 20 cm of the top surface. In addition, in an intense solar radiation environment, covering the concrete with a 4- or 5-centimeter-thick polyethylene coil can effectively control the surface temperature gradient and maximum daily amplitude of low-heat concrete, and surface concrete cured by running water has a significant temperature control effect. Therefore, it is suggested that 22–24 °C water temperatures be used for water curing during periods of intense solar radiation during the day and a 4-centimeter-thick polyethylene coil be used for coverage at night. These study results have been employed in the Baihetan project to optimize the temperature control scheme of the pouring blocks.

Analysis of Bearing Safety and Influencing Factors of Supporting Structures of Hydraulic Tunnels in Cold Regions Based on Frost Heave

In order to study the bearing safety and influencing factors of the support structures of hydraulic tunnels in cold regions under the action of low-temperature frost heave, a mechanical model of the support structure and surrounding rock was established. Taking a hydraulic tunnel of a hydropower station in Xinjiang as the research object, a combination of field measurement and a numerical simulation method was adopted to study the bearing safety of the support structure during a period of freezing weather. Based on this model, the effects of different thermal expansion coefficients, temperature differences, and surrounding rock porosity on the bearing safety of the support structure in the low-temperature region were studied. From the calculation results, it was concluded that the simulation results of the numerical model established by using the mechanical model in this paper were in good agreement with the actual measurement results of the project. The circumferential freezing and compressive stresses at the arch waist of the supporting structure of the project were the largest, and significant plastic strain was generated near the arch waist. The displacement at the arch of the supporting structure was the largest, while the weak points were at the arch waist and arch top of the supporting structure. The coefficient of thermal expansion, greater temperature difference, and increased porosity of the surrounding rock all led to an increase in the rock freezing and swelling force to varying degrees, thus reducing the load-bearing safety of the supporting structure. The research results could provide a theoretical basis and a reliable mechanical and numerical simulation model for establishing the bearing safety of tunnels in the cold region.

Large eddy simulation of highly compressible film cooling in transonic crossflow

Large eddy simulation is performed to study the thermal energy transport and mixing process of compressible film cooling in the fully-turbulent high-Mach-number crossflow. Three Mach numbers, 0.8, 1.2, and 1.4, based on the bulk crossflow velocity, are adopted. And the influence of both the compressibility and shock waves on the transverse jet from cylindrical orifices is discussed in detail. The results reveal that the effects of compressibility should be distinguished from shocks in supersonic flows. The compressibility effect strengthens the jet penetration and lateral spreading by increasing the energy contained in the large-scale coherent structures. The mixing of the jet is enhanced by the strong compressibility in the near field whether shocks exist or not. When the crossflow transits from the subsonic to the supersonic state, the effect of shock waves becomes more significant than that of the compressibility. Various interactions between shocks, coherent structures, and thermal energy transport are analyzed in this study. The results show that the appearance of the separation shock and bow shock reduces the jet penetration and strengthens its interaction with the bottom wall. The generation of this type of shock system suppresses the flow separation on the leeward side of the jet, which results in a higher cooling effectiveness in the jet near field. The incident oblique shock wave also induces lifting of the jet trajectory in the far-field region as a result of the intensified separation trend. In the highly compressible film cooling process with great temperature difference, the advection transport associated with turbulent motion, rather than the one associated with mean motion, turns out to dominate the thermal energy transfer in general. Moreover, the counter gradient behavior of this thermal energy transport in compressible turbulence is also shown.

Evaluating the utility of a CO2 surgical laser for piglet tail docking to reduce behavioral and physiological indicators of pain and to improve wound healing: A pilot study

In the U.S. millions of commercially raised piglets are routinely tail docked. Human and veterinary medical patients experienced reduced inflammation, healing time and post-procedural pain using a CO2 surgical laser compared to standard surgical instruments. Refinement of the tail docking procedure using a laser may improve piglet welfare by reducing tail docking-associated pain compared to cutting pliers. The objectives of this pilot study were to evaluate the ability of a CO2 surgical laser to 1) reduce pain and 2) improve wound healing of piglets after tail docking. Thirty piglets (male and female; 2 days old) were randomly allocated to one of three treatments (n = 10 piglets/treatment): tail docking with side pliers (SP), tail docking with a CO2 surgical laser (LA) or sham-tail docking (control; CON). Piglet vocalizations were recorded during the tail docking procedure and the maximum frequency, amplitude and energy were quantified. Piglet behavior was recorded for 30 min at baseline and at 0, 1, 2, 6, 7, 8, and 24 h post-procedure. Facial images were collected at the same time points to assess facial grimacing using the Piglet Grimace Scale (PGS). Digital images of the tail tip were taken at baseline and up to 168 h post-procedure for wound healing assessment. Infrared thermography (IRT) images of the tail tip and its surrounding tissues were taken at baseline, 0, 0.5, 8, and 24 h post-procedure to assess inflammation. Blood samples were collected from each piglet at baseline and 0.5 h and saliva samples at baseline, 0.5 and 8 h post-procedure for cortisol analysis. The LA and CON groups elicited calls of higher energy than the SP group (P < 0.0001). Across the assessment period, the SP group had higher grimace scores than the LA group (P = 0.03). Additionally, male piglets grimaced more than female piglets (P = 0.009). A treatment effect was observed for both wound scores and IRT (P < 0.0001). At 0 h the SP group had significantly higher wound scores than the LA and CON group (P < 0.0001). At 0 h, the SP group had a greater temperature difference between the tail tip and surrounding tissue compared to the LA group (P = 0.02). Behavioral indicators of pain were not different between the SP and LA piglets. In conclusion, LA piglets had less tail damage immediately post-procedure and lower facial grimace scores throughout the assessment period, suggesting it may have the utility as a less painful alternative to traditional tail docking with cutting pliers in piglets.

Microwave heating and fracturing of granite: Insights from infrared thermal imaging

Microwave heating has been considered as one of the promising rock breaking technologies. However, the non-uniform temperature distribution of microwave treated rocks has not been quantitatively studied and the microwave rock fracturing mechanisms have not been systematically revealed. In this paper, microwave heating tests were implemented using a 6 kW industrial microwave system. The ratio of maximum temperature to average temperature () was studied to characterize the non-uniformity of temperature. The temperature gradient and maximum temperature difference were calculated to quantitatively characterize the thermal stress. Experimental results indicate that the granite fracture temperature threshold is about 200 °C and cracking typically occurs at a minimum temperature gradient of 6 °C/mm. As either power level or irradiation time increases, the thermal gradient and temperature difference increase. For a fixed microwave energy, microwave heating at higher power levels for a shorter duration has a higher and a greater temperature difference and temperature gradient, which explains that the combination of high power and short heating time yields better rock weakening effects.

Thermal performance of double-layer porous-microchannel with phase change slurry

Combining porous media paved on sidewall and microencapsulated phase change material (MPCM) suspension as coolant is presented in double-layered microchannel heat sink (MCHS), in which more surface area of porous copper matrix with high thermal conductivity as well as greater temperature difference between the heating wall and working fluid during phase transition of MPCM will enhance heat transfer. The Forchheimer-Brinkman-Darcy model together with energy equation in local thermal equilibrium are employed to deal with fluid flow and heat transfer in porous ribs, and the equivalent heat capacity method is used to describe the phase change process of microcapsules under laminar flow. The influences of coolants, heat sink designs (including the thickness, height, porosity and pore size of porous medium as well as channel number) and working conditions (involving inlet velocity, heat flux and suspension concentration) on thermal and hydraulic characteristics are numerically investigated. The performance evaluation factor (PEF) is introduced to evaluate the comprehensive thermal–hydraulic performance of double-layered MCHS, and the effective performance evaluation factor (PEFeff) is used to compare the overall performance of porous-wall MCHS between conventional arrangements, different channel aspect ratio and channel height ratio configurations. The thickness and height of porous media paved on sidewall should be adjusted reasonably, especially for the arrangement of non-equal porous media, to obtain better overall performance. Different from the variable porosity configuration, the double-layered MCHS cannot rely on losing part of flow performance to obtain better thermal performance in smaller pore size mode, so a larger pore size can be selected to obtain better thermal–hydraulic performance according to actual working conditions. The PEF at larger flow velocity decreases due to higher pressure drop exceeding the benefit of more convection on heat transfer enhancement, in which case the phase change effect in porous-wall mode with MPCM suspension as coolant is suppressed and higher viscosity amplifies the effect of frictional resistance, resulting in a greater drop ratio of PEF than water. The greater PEF in porous-wall MCHS with suspension concentration increasing from 3% to 20% arises than that in non-porous mode, due to the larger surface area of copper matrix with high thermal conductivity and more MPCM particles available for phase transition. The larger aspect ratio configuration can achieve greater PEFeff rise and better overall performance by optimizing fluid velocity in the current mode due to greater thermal resistance drop and less pressure drop rise at lower flow rates, but the variable height ratio structure makes the comprehensive performance of porous-wall MCHS inferior to conventional arrangement due to larger pressure drop rise outweighing the benefits of heat transfer enhancement at the same total volume flux.

Dynamic spreading and interfacial reactions during the laser-induced wetting process of aluminum on stainless steel

Due to the difference in heating time, temperature distribution and environment, it is insufficient to explain the interfacial behavior under non-isothermal conditions relying on the isothermal wetting mechanism. In this study, the laser-induced dynamic wetting process of stainless steel by Al alloy was investigated. The wetting behavior was recorded by a self-built experimental setup. The mechanism for the spreading and metallurgical evolution was revealed by numerical simulation, spreading dynamics analysis and thermodynamic calculation. With continuous laser irradiation, the dominant factor for spreading changed from reaction product to adsorption. Induced by the laser, a great temperature difference was generated at the center and front zone of the droplet. Si atoms accumulated toward the Fe substrate at a faster rate than Al atoms and different Si-containing compounds were generated depending on the satisfaction of atomic concentration conditions and energy conditions. The formation of the thin τ5-Fe2Al8Si phase near the triple line was considered to be a vital role in the maintenance of the spreading process. The laser process could be guided by this study to reduce the equivalent heat input, thereby controlling the type and thickness of the compound and obtaining predictable wetting.

Insights into carbon production by CO2 reduction in molten salt electrolysis in coaxial-type reactor

With carbon capture and utilization (CCU) technologies, it is possible to take CO2 from air and transform it into valuable carbon products, such as graphene and nanotubes. In this study, CO2 was reduced to solid carbon by molten lithium carbonate salt electrolysis. The reactor used for the electrolysis was a coaxial-type unit, where a cylindrical nickel cathode was placed inside a cylindrical stainless steel vessel; such a coaxial-type reactor has not been used before for molten salt electrochemical reduction of CO2. This reactor design allows studies of voltage-current characteristics, which have previously not been conducted for this specific process. As a result, voltage efficiency of this process could be determined along with effect of temperature to cell voltage. Based on these results it is evident that accurate temperature control is crucial in terms of energy efficiency of the process. Data monitoring revealed a high accuracy of temporal temperature control. Great temperature differences were observed spatially. Thermoneutral voltage from the process was determined to be 1.02 V. For this electrochemical process studied, carbon nano-onions (CNOs) were obtained as a main product. Identification of the product was carried out based on Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) analyses. Results also showed that iron, chromium and nickel metals are released during electrolysis. Iron and chromium can only be released from the stainless steel anode, as nickel can come from anode or cathode.

Study on Annular Pressure Buildup in Offshore Heavy Oil Thermal Recovery Wells Considering Dissolved Gas Contained in Annuli

In the offshore industry, especially heavy oil thermal recovery wells, due to the great temperature difference between the low-temperature seawater and high-temperature heavy oil, it is easy to cause the temperature increase of annular fluid in the operation process which will result in the annular pressure buildup phenomenon (APB). The increase of annulus pressure may lead to the failure of the casing and wellbore integrity, which will seriously affect the normal production and lead to great economic loss. In order to study the formation of APB and provide a basis for the field operation design, a radial full-size physical experiment of APB was carried out in this work and an annular pressure prediction model in the presence of dissolved gas was proposed based on the experimental results. The verification and comparison analyses of the full-liquid model and the dissolved gas model were conducted with the experimental data. Furthermore, the sensitivity analysis of the influence of the dissolved gas volume fraction and casing deformation on APB was carried out. The results show that the prediction results calculated by the dissolved gas model are in good agreement with the experimental data and the prediction accuracy is higher than that of the full-liquid model. When the annular dissolved gas volume fraction is less than 0.1%, the full-liquid model can be used to simplify and approximate calculations. Ignoring casing deformation will produce prediction error in each annulus, which means this simplification should be used with extreme caution. This work provides a valuable experimental reference for the study of APB, as well as a novel model for APB prediction in the field.

Investigation of the in-situ gas cooling of carbon steel during wire and arc additive manufacturing

Wire and arc additive manufacturing (WAAM) is a promising technology for fabricating large-sized metal parts. However, to use this method efficiently, it is necessary to overcome the problem of severe heat accumulation that reduces manufacturing efficiency and deteriorates material properties. This paper proposes a new method using the in-situ gas cooling (ISGC) for reducing heat accumulation. Three parts were manufactured via the proposed method utilising CO 2 , N 2 , and air as cooling gases, respectively. A fourth part was fabricated with natural cooling (NC), without cooling gas. The temperature data measured by thermocouples and infrared pyrometers indicated that compared with NC, ISGC considerably reduced the temperature of the whole part and CO 2 had the best cooling effect. ISGC efficiently mitigated heat accumulation, due to the large heat transfer coefficient and the great temperature difference between the high-temperature region behind the torch and the cooling gas. Numerical simulations verified by the experimental data further denoted that in ISGC, high-temperature areas near the molten pool shrank sharply and heat dissipation conditions in the molten pool were improved markedly. ISGC not only improved the surface quality of the parts, but also strengthened the mechanical properties of the parts by obtained fine grains. The maximum ultimate tensile strength (UTS) and yield strength (YS) increased to 483 MPa and 358 MPa, respectively, which represented an increase of 4.1 % and 4.7 % respectively. The average hardness was enhanced to 161.3 HV, representing an improvement of 3.7 %.

Fluid-solid-thermal coupling analysis of rock failure under the joint action of cutting and jet impingement

Mechanical cutting assisted by high-pressure jet is a common and efficient drilling method in the exploration of hot dry rock (HDR). The drilling efficiency can be further improved with an in-depth understanding in the rock-breaking mechanism, which is a complex process involving the coupling of thermal stress, jet impact pressure and cutting force. To address such a multi-physics coupling issue, a loosely coupling method was adopted in this work to accomplish the exchange of data, including temperature, heat flux, nodes deformation and impinging pressure of jet in every time increment. In the fluid subdomain, the liquid nitrogen (LN2) jet and water jet were modeled and compared to demonstrate the potential of the novel jet in improving the drilling rate. In the solid subdomain, cutting force monitored in the experiment was loaded, and the concrete damage plastic model was employed to evaluate damage behaviors of the rock. Relative experiments were conducted to validate the reliability of simulation results. Results indicate that a great temperature difference develops on the coupling surface under the impingement of LN2 jet due to its cryogenic feature and lower heat transfer efficiency. Thereby, irreversible damage of the rock can be induced even at room temperature (298 K). As for the water jet, tensile damage is not observed until the rock temperature increases to 473 K. The assistance of jet impact on rock breaking is mainly reflected in two aspects: (1) the occurrence of tensile damage on the coupling surface facilitates the subsequent rock cutting; (2) the enhancement of tensile damage around the cutter promotes the initiation of cracks. Higher rock temperatures significantly improve the heat transfer rate and enhance the advantage of jet assistance. The present study can provide a new sight for the exploration of HDR.

Inclined Wellbore Stability in High Temperature Formations of Drilling

In recent years, exploring and developing oil and gas continuously expands into high-temperature environments, such as the Gulf of Mexico, North Sea, South China Sea, etc. Development of a high-temperature oil field from a platform always requires directional wells or extended reach wells (ERWs) departing from a central cluster to their targets at different depth of water in various azimuth. When drilling wells in high temperature formations, there is commonly associated with a suite of wellbore instability problems that are not normally encountered in onshore and normal temperature formations drilling. These problems are usually related to the presence of typically weak overburden sediments, unconsolidated formations, a small sedimentary coverage above the reservoir, and a great temperature difference between the drilling fluid and formation at the bottom hole In the past decades, a number of studies have been conducted to study the wellbore stability. However, few of the models are specific for wellbore stability of the inclined high temperature wellbores. In this work, an inclined wellbore stability model for high temperature formations is developed. The numerical method of the model is also provided. The study shows that drilling along the direction of minimum horizontal in-situ stress is safer than drilling in other directions, and the wellbore with a high inclination poses more risk of wellbore instability than the wellbore with a low inclination. It also shows that both of the wellbore collapse pressure gradients and wellbore fracture pressure gradients will increase as the temperature of borehole rises, and the fracture pressure is more sensitive to temperature. The model provides a practical tool to predict the stability of inclined wellbores for high temperature formations.

Investigation on waste heat recovery of a nearly kilowatt class thermoelectric generation system mainly based on radiation heat transfer

ABSTRACT Thermoelectric generation (TEG) is one of the most effective technologies converting heat directly into electric power. In this paper, a nearly kilowatt class TEG system mainly based on radiation heat transfer was designed and built. The open circuit voltage, the output power, the power density, and the conversion efficiency of the TEG system were investigated in detail at different temperature gradients. The maximum inverter power output of the TEG system assembled with 182 TEG devices can reach 684 W at a temperature difference around 125 K, and the corresponding power density can reach 845 W/m2. The inverter output power is almost proportional to the temperature difference between the hot and the cold side of TEG system. Our results confirmed that if the waste heat resource was sufficient to provide a greater temperature difference of 200 K in practical application, the output power and the power density of this TEG system would reach 1.23 kW and 1.51 kW/m2, respectively.

A New Method of Edge Crack Suppression in the Rolling Process of Magnesium Alloy Sheet and Study on the Method of Cathodic Protection

A new method is proposed to solve edge cracking and corrosion in rolling process of the magnesium alloy plate. Usually in the process, the edge cracking is caused by the great temperature difference between the edge and the center of the alloy plate and the corrosion is by water in air. The method uses hot air wrapped around the plate to perfectly prevent edge cracking and corrosion. The method also includes cathodic protection for the magnesium alloy based on electrochemistry. The suppression of cathodic protection on the chemical activity of the magnesium alloy was studied. The experiment shows that the new method of edge heating with hot air wrapping is effective to prevent edge cracking and corrosion. Also, the cathodic protection can effectively suppress the chemical activity of the magnesium alloy and improve the surface quality in the rolling process of the magnesium plate, which provides a new concept in rolling process of the magnesium alloy.

Heat and Mass Transfer in Porous Particle in Thermal Plasma Flow

The paper presents research into heat and mass transfer in agglomerated particles exposed to the thermal plasma flow. The dynamic motion, heating and melting are considered for agglomerated particles. It is shown that the surface temperature of porous particles rather rapidly reaches the value of Tsur&gt;Tmelt starting from the area of their introduction into the plasma flow. This effect is determined by the low conductivity of porous particles and indicates to a great temperature difference between the particle surface and its nucleus. It is shown that hollow particles can be obtained from silica sand treated by thermal plasma at 6700 K and 515 m/s velocity. The particle surface displays no clear defects. According to the analysis of X-ray diffraction patterns, the obtained hollow particles have no diffraction peaks.

The abnormal heat transfer behavior of supercritical n-decane flowing in a horizontal tube under regenerative cooling for scramjet engines

This paper aims to describe the reasons why abnormal heat transfer occurs under the condition of regenerative cooling applied in scramjet engines. Supercritical n-decane flowing in a horizontal tube under various mass flow rates (G = 0.001, 0.002, 0.003, 0.004 kg/s) and heat fluxes (qw = 100, 200, 300, 400 kW/m2) is investigated by numerical simulations. The mechanisms of the abnormal heat transfer were explained from the perspective of thermal diffusivity, velocity and the process of vortex evolution. The great temperature difference generated by the extreme operating condition (low mass flow rate and large heat flux) contributes to the higher buoyancy force inside the tube. Several interesting phenomena are found due to the existence of the vortices and a very special one is the slight downturn when the wall temperature reaches the first maximum point. In addition, the basic principles of the abnormal heat transfer are represented by the regularity of the distribution of thermal diffusivity, and mainstream velocity. An important conclusion is that the thinner boundary layer of the flow generated by the high velocity in the mainstream direction is benefit for restraining the abnormal heat transfer.

Predicting the fracture initiation pressure for perforated water injection wells in fossil energy development

Water injection is widely performed to enhance oil recovery in fossil energy development. The fracture initiation pressure (FIP) is a key parameter for designing the reasonable injection pressure for micro-fracturing water injection (MFWI). In this work, a modified method was presented to accurately predict the FIP, in which the thermal effect and plugging effect were considered; moreover, the stress around perforations was analyzed. To validate our method, the field tests, including a step rate test (SRT) and a well test, were conducted to obtain the actual FIP for perforated water injection wells, and then the FIP calculated by our method was compared with a low relative error of about 1.7%. Results show that (i) a greater temperature difference between the injected water and the formation forms a greater thermal stress around perforations, resulting in a greater change in the FIP; (ii) a larger skin factor causes a greater pressure drop for the injected water flowing through a plugged area, resulting in a stronger effective stress reduction around perforations and further producing a larger FIP. Therefore, our present work illustrates a better understanding of the stress distribution around a perforated wellbore, and paves a path for a more accurate prediction of the FIP in perforated water injection wells.