Uniform Temperature Research Articles

Sintering behavior of alumina by microwave hybrid sintering

Microwave sintering is considered an ideal sintering process due to its rapid heating rate, low energy consumption, and uniform temperature distribution between the interior and surface. However, the difficulty of using a dilatometer and the lack of systematic research have hindered the investigation of activation energy and grain growth kinetics during microwave sintering. In this study, we examined the internal heating mechanism of microwave hybrid sintering, its sintering behavior, and its applicability to commercial processes such as tape casting. The results demonstrated that microwave hybrid sintering reduces the activation energy for both shrinkage and grain growth, confirming the presence of the "microwave effect." This study underscores the potential of microwave hybrid sintering for commercial applications, especially for large ceramic components.

A comparative study of flow boiling performance in smooth and multi-stage enhanced open microchannels

Flow boiling in open microchannels is currently one of the research focuses in the field of phase-change heat transfer. The present paper described a comparative and experimental research on flow boiling heat transfer of SF-33, an environmentally friendly working fluid, in smooth surfaces open microchannels (SOM) and multi-stage enhanced open microchannels (MSEOM). The study investigated the flow boiling performance of SF-33 in two open microchannels with different mass fluxes, heat fluxes and inlet subcooling. The different boiling flow patterns in two open microchannels were analyzed with high-speed visualization. The results indicated that under different inlet cooling conditions, the MSEOM improved the flow boiling heat transfer performance significantly and improved the wall temperature uniformity. The visualization images indicated that the flow pattern transition was different due to the different surface structures of two open microchannels. The SOM experienced plug-stratified flow at high heat flux, while MSEOM transformed into churn flow due to its sintered copper powder and wire mesh micro-nanocomposite structures. The multi-stage enhanced structures exhibited excellent hydrophilicity and wicking capability, leading to a less pressure drop in the MSEOM compared with that in SOM. The pressure drops for both open microchannels decreased as inlet subcooling increased.

Design and Verification of Thermal Control System of Communication Satellite

The multiple working modes, complex working conditions, frequent changes in external heat flux, and high power consumption of communication satellites all pose great difficulties to their thermal design. This paper mainly describes the design of a thermal control system for high-power communication satellites. Firstly, new efficient heat transfer technologies and thermal control materials for spacecraft are introduced. Secondly, the structure and internal heat source of the satellite are introduced. Thirdly, the external heat fluxes are analyzed, and the position of the heat dissipation surface and extreme conditions are confirmed. Then, a thermal control system is designed around the difficulties of thermal control. With heat pipes, the temperature uniformity of +Y deck, −Y deck, and +Z deck increased by 8 °C, 9.9 °C, and 34.2 °C, respectively. Furthermore, the maximum temperature of the power controller, secondary power supply, bidirectional frequency converter, and solid discharge decreased by 32.5 °C, 22.0 °C, 14.0 °C, and 164 °C, respectively. Finally, a thermal balance test is performed. The test results show that the temperatures of the solid-state power amplifier, on-board computer, power controller, secondary power supply, and bidirectional frequency converter meet the requirements of the thermal control indices. In addition, the temperature of thermal-sensitive components such as batteries and the storage tank also meets the requirements. The thermal design scheme is reasonable and feasible, and the thermal balance test verifies the correctness of the thermal design.

Induction heating system of massive rings before rolling

The work examines an induction heating system for a large ring in a rectangular coil. The end surface of the workpiece is located horizontally. To form a uniform temperature distribution in the workpiece pushed into the inductor, a rotation mechanism is used. Conducted studies of the distribution of heat generation power and temperature in the workpiece showed the need to reduce the field strength in the hole area. A solution to the problem was found through the use of magnetic cores in the inductor design, displacing currents in the workpiece beyond areas prone to overheating. The obtained results of modeling electromagnetic and thermal fields in the workpiece confirm the correctness of the design solution.

A UAV Thermal Imaging Format Conversion System and Its Application in Mosaic Surface Microthermal Environment Analysis.

UAV thermal infrared remote sensing technology, with its high flexibility and high temporal and spatial resolution, is crucial for understanding surface microthermal environments. Despite DJI Drones' industry-leading position, the JPG format of their thermal images limits direct image stitching and further analysis, hindering their broad application. To address this, a format conversion system, ThermoSwitcher, was developed for DJI thermal JPG images, and this system was applied to surface microthermal environment analysis, taking two regions with various local zones in Nanjing as the research area. The results showed that ThermoSwitcher can quickly and losslessly convert thermal JPG images to the Geotiff format, which is further convenient for producing image mosaics and for local temperature extraction. The results also indicated significant heterogeneity in the study area's temperature distribution, with high temperatures concentrated on sunlit artificial surfaces, and low temperatures corresponding to building shadows, dense vegetation, and water areas. The temperature distribution and change rates in different local zones were significantly influenced by surface cover type, material thermal properties, vegetation coverage, and building layout. Higher temperature change rates were observed in high-rise building and subway station areas, while lower rates were noted in water and vegetation-covered areas. Additionally, comparing the temperature distribution before and after image stitching revealed that the stitching process affected the temperature uniformity to some extent. The described format conversion system significantly enhances preprocessing efficiency, promoting advancements in drone remote sensing and refined surface microthermal environment research.

In-pack radio frequency heating of liquid whole egg: Effect of agitation on heating rate and uniformity

In-pack radio frequency (RF) heating of liquid whole egg (LWE) was performed using a 27.12 MHz parallel-plate radio frequency (RF) system. To do this, 600 mL of LWE was subjected to RF heating in a RF-transparent plastic bag (140 mm×180 mm). Experiments were conducted at two different electrode gap settings (98 and 103 mm) with and without orbital movement in the horizontal plane. The effect of agitation on heating rate and uniformity was investigated for varying rpm’s (120 and 140 rpm) for a constant orbit diameter (35 mm). An orbital shaker was specially designed and coupled with the RF system for this purpose. Fiber optic probes were used to continuously measure the temperature of LWE at four different internal locations. Temperature uniformity index (TUI) was calculated to evaluate the uniformity of heating. Coagulation of LWE around the headspace was inevitable when the package was stationary during the treatment. Agitation brought about by orbital movement prevented the coagulation. Drastic improvement in heating rate and uniformity was observed upon orbital movement of LWE at all conditions.

Numerical investigation on the influence of swirl number to high-temperature zone evolution and outlet temperature distribution in multi-stage combustor

The outlet temperature distribution plays a crucial role in determining the lifespan and stability of downstream thermal components. It poses a significant challenge in the design and regulation of high-temperature combustors. This study aims to investigate the influence of swirl number on the outlet temperature distribution in multi-stage combustor. The impact of varying fourth-stage swirl numbers on flow structure, hot streaks, and temperature distribution is compared and analyzed. The results indicate that increasing the swirl number significantly improves the air–fuel mixing within the combustion zone, leading to the expansion of high-temperature regions. Additionally, the high-temperature region migrates upstream along the primary zone. With an increase in the swirl number, the relative area of hot spots within the combustor also increases. Remarkably, the swirler configuration with a swirl number of 1.5 exhibits the most minimal exit temperature gradient and the highest level of temperature distribution uniformity, quantified by an outlet temperature distribution factor (OTDF) of 0.26. Furthermore, changes in the swirl number affect the distribution of combustion modes within the combustor. Increasing the swirl number promotes the premixed combustion mode at the pilot stage exit and enhances temperature uniformity at the swirler exit. Thorough comprehension of the temperature distribution in the primary zone enables control of the outlet temperature distribution from its origin. Uniformity amplitude (UA) of HCO and primary temperature distribution factor (PTDF) are defined to describe the temperature distribution in primary zone. At a swirl number of 1.5, the UA and PTDF also shows the lowest values of 0.2754 and 0.3019, respectively. Overall, when improving the distribution of HCO under both premixed and non-premixed modes, a more uniform temperature distribution across the primary zone can be achieved, effectively optimize the exit temperature distribution.

Simulation of electrostatic particulate matter sensor regeneration based on the particulate deposition patterns

Purpose This study aims to establish a multi-physics-coupled model for an electrostatic particulate matter (PM) sensor. The focus lies on investigating the deposition patterns of particles within the sensor and the variation in the regeneration temperature field. Design/methodology/approach Computational simulations were initially conducted to analyse the distribution of particles under different temperature and airflow conditions. The study investigates how particles deposit within the sensor and explores methods to expedite the combustion of deposited particles for subsequent measurements. Findings The results indicate that a significant portion of the particles, approximately 61.8% of the total deposited particles, accumulates on the inside of the protective cover. To facilitate rapid combustion of these deposited particles, a ceramic heater was embedded within the metal shielding layer and tightly integrated with the high-voltage electrode. Silicon nitride ceramic, selected for its high strength, elevated temperature stability and excellent thermal conductivity, enables a relatively fast heating rate, ensuring a uniform temperature field distribution. Applying 27 W power to the silicon nitride heater rapidly raises the gas flow region's temperature within the sensor head to achieve a high-temperature regeneration state. Computational results demonstrate that within 200 s of heater operation, the sensor's internal temperature can exceed 600 °C, effectively ensuring thorough combustion of the deposited particles. Originality/value This study presents a novel approach to address the challenges associated with particle deposition in electrostatic PM sensors. By integrating a ceramic heater with specific material properties, the study proposes an effective method to expedite particle combustion for enhanced sensor performance.

Study on the flow and heat transfer characteristics of a hybrid nanofluid jet impingement microchannel heat sink with airfoil fins

AbstractDue to the continuously increasing power density of electronic devices, the improvement of the temperature uniformity and the reduction of the irreversible energy losses became crucial in these studies on enhanced cooling capacity of the heat sinks. In this paper, a jet impingement microchannel heat sink with airfoil fins (AF‐JIMHS) is proposed. The AF‐JIMHS with reversed fins arrangement has very high comprehensive heat transfer performance. The increase of the internal tangent circle radius and chord length of fin can improve the temperature uniformity of the AF‐JIMHS bottom surface and reduce the irreversible energy losses, at the expense of reducing its comprehensive heat transfer performance. Although the increase of the tangent arc length of fin reduces the temperature uniformity and increases the irreversible energy losses of the AF‐JIMHS, it improves the comprehensive heat transfer performance in a specific parameter range. The increase of fin height improves temperature uniformity of the AF‐JIMHS, while reducing its irreversible energy losses and improving its comprehensive heat transfer performance. Compared with the AF‐JIMHS with uniform height fins, the one with decreasing height fins has higher comprehensive heat transfer performance and lower irreversible energy losses. Moreover, the AF‐JIMHS with increasing height fins has better temperature uniformity.

Modeling temporal dynamics of a radiant Casson fluid near a steeped plate emitting heat and mass fluxes

AbstractIn today's rapidly advancing world, more deliberate development and implementation of energy‐efficient thermal management systems is emergent. In industrial and engineering contexts, the regulation of heat and mass transfer phenomena is heavily swayed by factors such as heat and mass fluxes, and wall temperature, and concentration levels. In cryogenic containers, understanding heat flux and wall temperature is essential for maintaining ultra‐low temperatures over extended periods. In this context, our paper embarks on modeling the transient dynamics of a radiant Casson fluid adjacent to a steeped plate, which is featured by its emission of both heat and mass fluxes. The plate is under two thermal conditions, namely uniform wall temperature (UWT) and uniform heat flux (UHF), which are crucial in modulating both upward and downward heat transport processes. The Laplace transform (LT) technique yields close‐form solutions for the model's governing equations. The distribution of flow and salient physical quantities are graphed and elucidated in response to intricate physical parameters. A comparative graphical analysis of UWT and UHF scenarios reveals stark differences. Notably, the fluid's flow rate appears considerably amplified in the UWT scenario compared to the UHF one. Furthermore, the UHF setting profoundly influences the heat and mass transportation within the fluid's flow realm. A pronounced Casson parameter tends to thin out the velocity profile. Concurrently, a heightened radiation parameter results in a reduction in fluid temperature. The theoretical framework explored in our study is not just an academic exercise but holds tangible applicability across varied sectors. This spans from rocket chamber cooling, where fine‐tuned heat flux conditions are paramount for safeguarding operations, to industries like cosmetics and food processing, which demand meticulous thermal regulation to ensure product excellence.

Simulation study on heat dissipation of a prismatic power battery considers anisotropic thermal conductivity in air cooling system

Heat accumulation could be occurred due to low thermal conductivity in one direction inside the power battery, which may lead to the decrease charging performance and potential thermal runaway. In this study, the impact of the anisotropic thermal conductivity (kx, ky, kz) on the temperature of the battery was analyzed. The anisotropic thermal conductivity was divided into the flow direction, thickness direction and spanwise conductivity. Then, the variation regularityof surface temperature distribution and heat flux are revealed by changing the anisotropic thermal conductivity. The results show that the increase of kx improves the heat dissipation efficiency of the upstream battery by 24 %. The higher thermal conductivity allows additional heat to be transferred from upstream to downstream along the direction of flow. The increase of kx makes the temperature difference only about 3 K, which improves the temperature uniformity of the battery. In addition, the impact of kx on the battery heat dissipation process is more dominant than ky and kz. However, there is an upper limit to the impact of ky on the battery temperature. When the ky exceeds 10 times the value of kx, the maximum temperature and temperature uniformity of the battery are almost unaffected by the change of ky. Meanwhile, the increase of kz has the minor effect on the temperature distribution of the battery surface. The anisotropic thermal conductivity is adjusted to reduce heat accumulation in the battery and improve the temperature uniformity. This work is beneficial to the engineering application of battery thermal management technology.

Numerical simulation and structural optimization of the diffusion furnace for crystal silicon solar cells

The diffusion furnace is an important device for crystalline silicon solar cell production. Given the rapid evolution of solar cell technology, large-scale, high-efficiency and mass-produced diffusion furnaces are required by the market. This puts forward higher requirements for the diffusion furnaces. In this study, a large-scale 3D model is established and validated by measured data in practical diffusion furnace. Its internal temperature, velocity and gas concentration fields are analyzed. The silicon wafer temperatures are found to be high at the top but low at the bottom. The temperature uniformity at both ends of silicon wafer groups is poor. To solve these problems, three structural optimization methods, namely the inlet pipe optimization, adding uniform-flow plates and the quartz boat optimization, are proposed and analyzed. The average mass fraction in the diffusion furnace is improved by 6.311% using the two-tube forked intake pipe. The uniform flow plates with evenly distributed pores on the lower half effectively improve the gas concentration uniformity on silicon wafer surfaces. The optimized quartz boat can improve the temperature uniformity of silicon wafers, though its deformation slightly increases by 0.338%. The silicon wafer temperature differences after quartz boat optimization are 13.77–50.27% smaller than those before optimization, which are conducive to reducing the thermal stress, the risk of thermal damage and the failure during manufacture and utilization of silicon wafers. Results in this study give guidelines for design and utilization of crystal silicon solar cell diffusion furnaces, some of which have been successfully used in Trina Solar Energy Co., China.

Stretchable, transparent and multifunctional PVC-gel heater: a novel approach to skin-mountable, wearable thermal devices

Electric heaters based on functional materials and innovative designs have been developed for various applications. In this paper, we propose a soft dielectric heater (SDH) using polyvinyl chloride-gel (PVC-gel) as the dielectric heater and hydrogel as stretchable electrodes. Under an AC voltage, the leakage current in the PVC-gel leads to continuous injection and discharge of charges, causing the polarized plasticizers and flexible PVC chains to vibrate and collide, thereby generating heat through dielectric heating. Furthermore, the SDH generates a uniform temperature distribution even under strains up to 400%. Besides, high transmittance over 86% across the visible range renders it suitable for wearable or skin-mountable heaters from an esthetic viewpoint. Its capacitor-like structure achieves a scalable design, enabling extension from a singular cell to a row/column addressable and pixelated array of heaters. The 5 × 5 SDH array can deliver varied thermal information and sensations while maintaining performance even when stretched.

Effect of turning conditions on the indirect liquid-cooled battery thermal management in the electric vehicle

There exist many kinds of turning situations for driving, and the turns would lead to additional forces on the liquid in the channel, which can affect the liquid-cooled battery pack thermal management of electric vehicles. However, few studies have investigated the cooling effect in battery packs during turns in electric vehicles. In view of this, the purpose of this paper is to study how the cooling effect of the battery pack varies under turning conditions and explain the mechanisms behind it. Based on an indirect liquid-cooled battery pack model and by applying turning conditions to the battery pack under different C-rate discharges, the cooling effect of the battery pack is investigated. It is found that the maximum temperature of the battery pack increases significantly under the turning motion condition and increases with vehicle speed. In addition, the temperature uniformity of the battery pack is also greatly deteriorated by the turning motion. Turning results in an increase of the inertial force, which acts on the cooling fluid and decreases the fluid mass flow, ultimately reducing the cooling effect of the battery pack.

Integrated neural network based simulation of thermo solutal radiative double-diffusive convection of ternary hybrid nanofluid flow in an inclined annulus with thermophoretic particle deposition

Numerical simulation of magnetohydrodynamic radiative double-diffusive convective heat and mass transfer of a ternary hybrid nanofluid with thermophoretic particle deposition in an inclined annulus is studied. Both sides of cylinders are preserved at uniform temperatures, while the remaining sides are thermally insulated. The coupled nonlinear partial differential equations are solved using a finite difference approach. The detailed computational results of heat and mass transfer rate, temperature, concentration and flow fields are presented and discussed for a distinct range of significant physical parameters. The results demonstrated that increasing the angle of the inclination factor increases fluid flow. In light of buoyancy, when the annular cavity is set downward, the enhanced shear velocity is transported upwards, where it reaches its optimal temperature. The higher temperature difference leads to augmented dynamic fluid motion, particularly in the radial direction, as the system seeks to balance the thermal energy through convective transfer. The Brownian motion parameter has abrupt mobility of nanoparticles in liquid, which promotes particle collisions with liquid molecules, yielding kinetic energy. Increased values of thermophoretic parameters augment the thermophoresis force. Thermophoretic particle deposition increases the concentration of nanoparticles in an annulus due to the migration of particles from hot to cold regions under the influence of temperature gradient. The heat and mass transfer characteristics of ternary hybrid nanofluid are forecasted through an artificial neural network-based Levenberg–Marquardt backpropagated algorithm. The built model shows the heat and mass transfer rate root mean squared values through the Levenberg–Marquardt algorithm as one and mean squared error values as 1e-07 and 1e-08 respectively.

Effects of ultrasonic vibration on residual stress distribution and local mechanical properties of AA6061/Ti6Al4V dissimilar joints by resistance spot welding

The joining of dissimilar titanium and aluminum alloys has potential applications in railway and aerospace industries, owing to substantial weight reduction and better economic viability. In this study, the residual stress distribution and local mechanical performance of ultrasonic-assisted resistance spot welding (UaRSW) welds were investigated. The welding current, welding time, and electrode force of the RSW process were set as 9.0 kA, 350 ms, and 1.0 kN respectively, and the frequency and power of ultrasonic vibration were 20 kHz and 800 W. The residual stress was evaluated by X-ray diffraction (XRD) method and numerical simulation, and these methods showed a reasonable match. There was tensile residual stress distributed on RSW welds and UaRSW welds, but the value of residual stress was reduced by about 30% at welding nugget and 20% at heat affected zone (HAZ) with the ultrasonic vibration, the reduction of residual stress in UaRSW welds was attributed to the more uniform temperature distribution and lower plastic deformation resistant of AA6061. The welding peak temperature was decreased from 1673.4 °C to 1584.2 °C with the ultrasonic vibration, resulted from the modified Al/Ti contact surface and reduced contact resistance. The miniature tensile test results showed the improvement of mechanical performance by ultrasonic vibration. The maximum load of welding nugget region increased from 19.6 N to 22.3 N, and the elongation obtained 10% increase. This hybrid welding technique shows a potential to improve the quality of welds with ensured efficiency, which is also simple to realize automation in the manufacturing industry.

Comparative investigation on heat transfer augmentation in a liquid cooling plate for rectangular Li-ion battery thermal management

This work conducted a numerical study with experimental validation to improve the performance of a rectangular multi-channel cooling plate utilised for cooling lithium batteries. Seven different designs on a cold plate for laminar flow conditions were evaluated using numerical modelling simulations in the 3D ANSYS program. Three cooling plate designs were proposed with channel arrangements: arc, convergent–divergent and different channel widths (narrow central channels and wide peripheral channels). The other four proposed cooling plate designs included representations of variable-sized pin fins with different shapes: oval, drop, rhombus and trapezoidal within different channel widths. Real experiments were conducted on a manufactured conventional cooling plate to verify the results of the numerical simulation. Results indicated that all proposed designs improved the heat transfer of the cooling plate. The percentage of enhancement in Nusselt number due to the presence of rhombus-shaped pin fins inside different channel widths is approximately 95.5 %, which is about three times the enhancement in pin fins that used only smooth different channel widths, which is approximately 33.5 %. Amongst the studied designs, incorporating different channel widths with the addition of rhombus-shaped pin fins exhibited the largest heat dissipation capacity and the best thermal–hydraulic performance. The highest temperature uniformity enhancement ratio and performance evaluation parameter for this case reached about 71.96 % and 1.68, respectively.

Numerical simulation and structural optimization of forced convection oven

Temperature uniformity is a fundamental parameter for a forced convection oven to guarantee food baking quality. In this study, computational fluid dynamics (CFD) simulation is employed to analyze the air flow and heat transfer within a forced convection oven. Subsequent experimental measurements were conducted to explore the temperature variations inside the oven. The maximum deviation between the numerical simulation results and the experimental data was 2.70%, demonstrating the high accuracy of the simulation model. Based on the established simulation model, we can meticulously investigate the impact of fan structures on the airflow and temperature fields. Carefully designing the fan structure can significantly enhance temperature uniformity across the oven’s baking racks, reducing the standard deviation of temperatures on the second and third baking racks from 5.46°C and 6.69°C to 2.26°C and 2.46°C, respectively. This study provides a robust design strategy for forced convection ovens, yielding tangible benefits for practical application and market competitiveness.

Simulation and optimization design of air distribution in a cigarette production factory

Air-conditioning energy consumption accounts for a significant proportion of the total energy usage in large commercial buildings. This study utilizes computational fluid dynamics (CFD) to examine the airflow distribution in a cigarette factory with a high ceiling. Numerical simulations were performed to assess the effectiveness of various air supply methods. Using FLUENT, the researchers analyzed the uniformity of airflow, temperature and humidity fields under summer conditions. The findings indicate that employing an upper supply and lower return air method can decrease air-conditioning energy consumption by 7.25%. Field measurements were carried out to validate the numerical simulations, with the measured values used as initial parameters. The average deviation between the measured and simulated temperature and humidity in critical work areas was within 2%. The comparative analysis of the simulation and measurement results confirms the reliability and effectiveness of airflow organization simulations in large commercial buildings. These results offer a scientific foundation and computational guidance for designing and implementing energy-efficient upgrades to air-conditioning systems in similar industrial facilities.

Novel design of a staggered-trap/block flow field for use in serpentine proton exchange membrane fuel cells

Enhancing the transverse velocity to the catalyst layer and exploiting the over-rib flow are two common methods of improving proton exchange membrane fuel cells (PEMFCs). The block flow field configuration significantly affects the augmentation of the transverse velocity to the catalyst layer, whereas the trap configuration significantly increases the molar concentration of O2 at the cathode catalyst layer without a pressure drop penalty. In this study, four-channel PEMFC models with different configurations were used, including the baseline and staggered-trap, -block, and -trap/block channels. The novel flow field with a combination of trap/block configurations exhibits a higher power output than those of the other designs. Furthermore, the novel staggered-trap/block channel induces a higher over-rib flow velocity than that of the baseline channel, leading to more uniform O2 and temperature distributions within the PEMFC. The optimal trap/block design increases the maximum net cell power by 8.04 % at V = 0.5 V.