Thermal Issues Research Articles

Thermally Conductive Shape-Stabilized Phase Change Materials Enabled by Paraffin Wax and Nanoporous Structural Expanded Graphite

Paraffin wax (PW) has significant potential for spacecraft thermal management, but low thermal conductivity and leakage issues make it no longer sufficient for the requirements of evolving spacecraft thermal control systems. Although free-state expanded graphite (EG) as a thermal conductivity enhancer can ameliorate the above problems, it remains challenging to achieve higher thermal conductivity (K) (>8 W/(m·K)) at filler contents below 10 wt.% and to mitigate the leakage problem. Two preparations of thermally conductive shape-stabilized PW/EG composites, using the pressure-induced method and prefabricated skeleton method, were designed in this paper. The expanded graphite formed a nanoscale porous structure by different methods, which enhanced the capillary action between the graphite flake layers, improved the adsorption and encapsulation of EG, and alleviated the leakage problem. The thermal conductivity and the latent heat of the phase-change materials (PCM) prepared by the two methods mentioned above are 9.99 W/(m·K), 10.70 W/(m·K) and 240.06 J/g, 231.67 J/g, respectively, at EG loading by 10 wt.%, and the residual mass fraction was greater than 99% after 50 cycles of high and low temperature. In addition, due to the excellent thermal management capability of PW/EG, the operating temperature of electronic components can be stably maintained at 68–71 °C for about 15 min and the peak temperature can be reduced by at least 23 °C when the heating power of the electronic components is 10 w. These provide novel and cost-effective methods to further improve the management capability of spacecraft thermal control systems.

Numerical study on the melting behavior of annular fuel under accident conditions

The use of annular fuel in nuclear power plants has been developed to improve their efficiency, safety, and economic viability. Therefore, studying the thermal hydraulic issues of annular fuel is crucial. The melting of annular fuel under accident conditions is equally important. This study uses a novel numerical technique called the Half Boundary Method (HBM) to tackle this issue. With new variables introduced, this method avoids the need for additional continuity equations at the boundary when solving multi-layer composite problems. First, the HBM is used to model a multi-layer composite ring and solve its transient thermal problems, which are then verified. Next, the temperature distribution of annular fuel under operational conditions is calculated, and the results are compared to validate HBM's accuracy. Based on these findings, simulations are conducted to model the melting phase transitions of annular fuel during Loss of Coolant Accidents (LOCAs) and Reactivity Insertion Accidents (RIAs).

Thermal Performance Enhancement of Serpentine Cooling Design Using Branch Modification for Lithium-Ion Batteries

Lithium iron phosphate (LiFePO4) batteries offer advantages such as low cost, safety, environmental compatibility, and stability over repeated cycles. However, when subjected to high currents, this battery generates thermal issues, particularly when arranged in packs. This study aims to maintain the LiFePO4 80Ah battery within an optimal temperature range (20 °C – 40 °C) while minimizing pumping power. The proposed research introduces a serpentine channel with additional branches. The design variations include a gradient in branch spacing and changes in channel width. Each design is evaluated using dimensionless parameters representing maximum temperature, temperature uniformity, pumping power, and cooling efficiency coefficient. The best design from each variation is then compared with the conventional serpentine (CS) channel design, which is well-known for its superior thermal performance. The gradient variation reduces 𝑇𝑚𝑎𝑥∗ and 𝑇𝜎 by 0.07 and by 0.42, respectively, compared to the non-gradient channel design, at a Re 400 and a C-rate 3 C. The design with the largest channel width reduces 𝑇𝑚𝑎𝑥∗ by 0.57 or 11.32 °C compared to the design with the smallest channel width. At a Re 1000 and C-rate 3 C, the reduction in 𝑇𝑚𝑎𝑥∗ for the proposed channel design compared to the CS design is 0.017. In terms of the friction factor (𝑓), the proposed design is 0.0149 lower than the CS design. The results indicate that the thermal performance of the proposed channel design is better than that of the CS design, with reduced pumping power.

LARES-2 contribution to global geodetic parameters from the combined LAGEOS-LARES solutions

LARES-2 is a new geodetic satellite designed for high-accuracy satellite laser ranging. The orbit altitude of LARES-2 is similar to that of LAGEOS-1, whereas the inclination angle of 70° complements the LAGEOS-1 inclination of 110°; hence, both satellites form the butterfly configuration for the verification of the Lense–Thirring effect. Although the major objective of LARES-2 is testing general relativity, LARES-2 substantially contributes to geodesy in terms of the realization of terrestrial reference frames, recovery of the geocenter motion, pole coordinates, length-of-day, and low-degree gravity field coefficients. We analyze the first 1.5 years of LARES-2 data and test different empirical orbit models for LARES-2 with and without co-estimating low-degree gravity field coefficients to find the best combination strategy with LAGEOS satellites. We found that LARES-2 orbit determination is more accurate than that of LAGEOS-1/2 due to a different satellite construction consisting of a solid sphere with no inner structure. Neither the correction for D0 nor the empirical once-per-revolution along-track accelerations SC/SS have to be estimated for LARES-2 when co-estimating gravity field coefficients. The only empirical parameter needed for LARES-2 is the constant along-track acceleration S0 to compensate for the Yarkovsky–Schach effect. On the contrary, for LAGEOS-1/2, the non-gravitational perturbations affect C30 and Z geocenter estimates when once-per-revolution parameters are not estimated. LARES-2 does not face this issue. LARES-2 improves the formal errors of the Z geocenter component by up to 59% and C20 by up to 40% compared to the combined LAGEOS-1/2 solutions and provides C30 estimates unaffected by thermal orbit modeling issues.

Chemical Competing Diffusion for Practical All-Solid-State Batteries.

The thermal safety issues of currently available Ni-rich cathode-based power supplies brought in the development of all-solid-state batteries, yet the cascade reactions in Ni-rich materials and the chemo-mechanical degradation between the cathode and solid electrolyte diminished the cycle life. Here, by introducing a new heteroatom chemical competing diffusion strategy, we successfully stabilize the Ni-rich cathode and the contact face with an solid electrolyte. Combining extensive explorations in theoretical calculation and multiscale in/ex situ characterization, we elucidate the atomic-level chemical competing diffusion upon the topological lithiation of layered materials. The heteroatoms with higher binding energy to the coordinated oxygen served as the "oxygen anchor" in the bulk and alleviated the excessive oxygen oxidation through charge compensation, thus easing the chemical aggression of the solid electrolyte by evolved oxygen. Comparably, others were enriched in the surface and formed an ionic "diffusion regulator" with residual lithium, and the special ionic transfer regulation mechanism of the piezoelectric layer validly improved the interface compatibility with the solid electrolyte and weakened the space-charge layer in solid-state batteries. This helped the designed Ni-rich cathode-based sulfide solid-state battery exhibit excellent cyclability under 4.5 V (97.3% after 120 cycles). Our findings unlocked the structure-function relationship between the polarization field generated by the piezoelectric material and the electrode.

Numerical and experimental study of a CO[formula omitted] multi-channel radiator used for space application

This article presents a novel multi-channel condenser/radiator designed for mechanically pumped two-phase cooling systems in space. A numerical model coupling two-phase condensation heat transfer with thermal radiation is proposed to design and accurately predict the performance of the radiator, taking into account both single-phase and two-phase heat transfer occurring within the fluid channels. The performance assessment of the radiator is carried out in a thermal vacuum chamber with CO2 circulating through a closed cooling loop. The validation of the numerical model is confirmed by comparing the predicted results with the experimental data obtained. The comparison demonstrates good agreement with the discrepancy of 10% between the predictions and the actual measurements. The numerical method presented here is simpler compared to Computational Fluid Dynamics (CFD), making calculations more accessible, particularly for those without access to CFD tools. Additionally, this paper explores ways to simplify complex thermal radiation issues using surface-to-surface radiation models and the Monte Carlo method to calculate the view factor.

Develop a Hybrid Thermal Simulation Method for EV Motor Performance Analysis, Optimization and Select Cooling Technology

The EV motor generates power losses during operations. The losses are dissipated as heat by motor cooling systems. The motor parts set thermal limits for safe and efficient operations. The motor go beyond these limits will have issues like performance reduction, lifetime, and insulation degradations. An optimized cooling system eliminate these thermal issues and ensure safe, efficient operation. The optimized cooling system achieved with hybrid simulation method proposed in this paper. The method combines the LPTN modelling technique with CFD Analysis results. The proposed method capable to optimize an EV motor with temperature distributions with safe hotspots, high efficiency & torque/power density, and overload time capability. The Motor LPTN model developed for passenger car requirements with PMSM motor as target motor topology. The motor heat transfers are modelled with analytical equations to capture the dominant heat paths. The motor endspace regions analyzed with CFD simulation to calculate wall heat transfer flux as complex windings, housings present here. The motor thermal model accuracy enhanced as CFD analysis used to calculate wall heat transfer flux at motor inner walls. The hybrid thermal model gives out the motor temperatures and performance as results. This hybrid simulation method eliminates error and high effort wasted during motor design iterations. The simulation method validated with measurements with accuracy around 90 to 95 %. The hybrid simulation method suitable for sensitivity analysis, cooling system study and optimization study.

Thermal and Power Management Challenges in High-Performance Mobile Processors

A significant computational capability to just a few cubic centimeters has been enabled by highperformance mobile processors that are rapidly evolving. Unfortunately, the increase in transistor density and clock speed, along with the integration of additional features, create prohibitive challenges with thermal output and power consumption. In this paper, we critically discuss key thermal and power management issues in modern mobile processors: thermal design power (TDP), energy efficiency tradeoffs, and the implications of thermal throttling on performance. Dynamic voltage and frequency scaling (DVFS), thermal aware task scheduling and sophisticated cooling mechanisms are reviewed. Emerging challenges posed by the integration of AI accelerators and 5G connectivity are also presented. Insights for future directions in sustainable processor design conclude the study

Grain Controlled Interlayer of Solid Oxide Fuel Cells Via Nitrogen Reactive Sputtering

Renewable energy conversion systems have been extensively studied and utilized due to increased environmental pollutions caused by fossil fuels. Among the various renewable energy sources, such as wind, solar, geothermal, and hydrogen, hydrogen is well known for its high energy density, non-toxicity, and easy transportation. Therefore, hydrogen production and utilization processes have been studied to enhance their efficiencies and lower costs for decades. To convert hydrogen into electricity, various types of fuel cells are frequently employed by chemical reactions between hydrogen and oxygen. Solid oxide fuel cells (SOFCs), one of the most promising energy conversion devices among the fuel cells, guarantee high conversion efficiency which is temperature dependent, thus the SOFCs are usually operate in high temperature regime (800 °C–1000 °C) to maximize their output. These high operating temperatures, however, induce thermal issues such as catalyst degradation, sealing, and cell durability which are needed to be concerned. Therefore, many researchers tried to mitigate these issues by lowering the working temperature (400 °C–600 °C). This strategy was successful, however, as abovementioned, the SOFCs are temperature dependent so that relatively low temperatures delay oxygen reduction reaction (ORR) resulted in increased polarization losses. To facilitate the SOFCs with high efficiency at this temperature regime, many studies inserted oxygen ion conducting materials between electrodes and electrolyte to promote transfer of oxygen ions. Further, researchers tried to control surface morphology of ion conductors to have large grain boundary density which is another approach to reduce polarization losses. In this study, yttria-stabilized zirconia (YSZ) was introduced between cathode and electrolyte via sputtering technique. During the sputtering processes with both argon and oxygen gases, nitrogen gas was further supplied to induce collision of YSZ atoms so that YSZ atoms with low kinetic energy will reach on substrates resulted in smaller grain sizes of YSZ interlayers.Silicon and YSZ substrates were utilized to analyze properties of YSZ interlayers and electrochemical characteristics of SOFCs, respectively. The YSZ interlayers were fabricated by sputtering of ZrY alloy target with argon, oxygen, and/ or nitrogen gases. While maintaining sputtering chamber pressure of 0.67 Pa, argon and oxygen gases were supplied with fixed amount of 40 sccm and 5 sccm, respectively. Furthermore, nitrogen gas was also introduced to sputtering chamber by 4 sccm differences from 0 to 16 sccm, hereafter, fabricated YSZ interlayers are denoted as N0, N4, N8, N12, and N16 with the meaning of applied nitrogen amount. All YSZ interlayers were deposited with RF power of 70 W and sputtering times were controlled to fabricate about 70 nm. To analyze the properties of fabricated YSZ interlayers, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were conducted. Electrochemical characteristics of SOFCs were evaluated by linear sweep voltammetry and electrochemical impedance spectroscopy.SEM images observed all the YSZ interlayers were about 70 nm thicknesses with various surface morphologies. This phenomenon is attributed to different adatom mobility of atoms due to flow rates of nitrogen during sputtering process. Further, XRD results shown that nitrogen influenced grain development of YSZ interlayers resulted in weaker and broaden peaks compared to N0. To calculate grain sizes of the YSZ interlayers, Williamson and Hall equation was utilized. Average grain sizes of YSZ interlayers were decreased from N0 to N12, and increased at nitrogen flow rate of 16 sccm. The electrochemical performances indicated that the smallest grain sizes of YSZ interlayers had the lowest polarization losses which means the highest ORR kinetics were found at the largest grain boundary density thus, the highest peak power density was observed.All the YSZ interlayers were fabricated by sputtering technique with constant flow rates of argon, oxygen, while nitrogen flow rate was varied. The SEM images and XRD patterns revealed that nitrogen successfully modified surface morphologies in terms of various grain sizes. The EIS analysis confirmed the smallest grain sizes of N12 had the lowest polarization losses resulted in the highest peak power density. As a result, we successfully modified surface morphologies of YSZ interlayers by nitrogen reactive sputtering. We expect that this one-step novel strategy can be utilized in other thin film fabrication fields by significantly reducing process times.AcknowledgementsThis work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No.2022R1C1C1006824) and the Basic Research Program through the National Research Foundation of Korea (NRF) funded by the MSIT (No.2022R1A4A3023960).

Vapor chamber thermal performance: Partially heated with different heating areas at the center and supported by numerical analysis for the experimental setup

This paper presents the design of a partially heated Vapor Chamber (VC) system utilizing a passive cooling technique, analyzed under various inclination angles. The Finite Volume Method (FVM) is utilized to compare the results with experimental measurements conducted. Additionally, all results obtained with the tested VC are compared to a copper plate of identical dimensions to demonstrate the VC’s impact on thermal management issues. The dimension of the copper VC is established as 56 × 56 mm2. Two distinct partial heating dimensions at the evaporator block, measuring 10 × 10 mm2 and 20 × 20 mm2, are evaluated under various heat flux loads. The study is further expanded to include varying temperatures between the evaporator block and the condenser block. While a chiller controls the temperature on the condenser block side, the power supply to the evaporator block is adjustable to facilitate heating. The inclination angle of the system is identified as an additional parameter for investigation, as it may influence the thermal performance of the vapor chamber due to gravitational effects. At the conclusion of the study, significant results indicated that a higher thermal resistance value was observed for a heating area of 10 × 10 mm2 for both VC and copper plate. The comparison between the copper plate and VC indicates a 7 % reduction in thermal resistance with VC across both selected heating areas. Furthermore, a higher temperature that increases proportionally with heat flux is observed in the case of the copper plate. The effect of inclination appears to be negligible for the parameters examined.

Enhancing Thermal Management of Graphene Devices by Self-Assembled Monolayers.

Two-dimensional graphene has emerged as a promising competitor to silicon in the post-Moore era due to its superior electrical, optical, and thermal properties. However, graphene undergoes a strong degradation in its in-plane thermal conductivity when it is coupled to an amorphous substrate. Meanwhile, the weak van der Waals interaction between graphene and the dielectric substrate leads to high interfacial thermal resistance. Severe challenges in the device's heat dissipation rise, resulting in elevated hotspot and deteriorated electrical performance. Here, we applied self-assembled monolayers (SAMs) to modify the interface between graphene and the oxide substrate and mitigate the thermal issues in the device. The -NH2 terminated SAM demonstrates enhanced interfacial coupling strength between graphene and substrate, increasing the interfacial thermal conductance. The -CH3 terminated SAM effectively suppresses the substrate phonon scattering, preserving the high in-plane thermal conductivity of graphene. Particularly, the -NH2 terminated SAM significantly enhances the heat dissipation efficacy of graphene field-effect transistors and alleviates the self-heating issues. Enhancements of 28.1% and 48.2% were observed in the devices' current-carrying capacity and maximum power density, respectively. Our research provides a highly attractive platform for incorporating SAMs to improve thermal management in two-dimensional electronic devices.

Optical performance and luminescence properties of Dy3+-doped LaMgB5O10 phosphors

Despite significant advancements in borate-based phosphors, improving luminescent efficiency and thermal stability, particularly at high temperatures, remains a persistent challenge. In this study, Dy3+-doped LaMgB5O10 (LMBO) phosphors were synthesized and characterized for their photoluminescent properties to address these issues. Under 344 nm excitation, the Dy3+-activated LMBO phosphors exhibited strong luminescence with characteristic peaks at 482 nm (blue), 578 nm (yellow), and 663 nm (red), corresponding to specific Dy3+ transitions. Optimal luminescence was achieved at a doping level of 2 wt% Dy3+, beyond which quenching effects reduced emission intensity. The critical quenching distance (Rc) was estimated at 24.66 Å, indicating predominant non-radiative energy transfer. Moreover, thermal quenching was reduced, with the activation energy for thermal quenching determined to be 0.1975 eV, demonstrating that the material can maintain reasonable luminescence efficiency at elevated temperatures. Time-resolved photoluminescence spectroscopy revealed multi-exponential decay behavior, indicating the presence of multiple decay processes. The average luminescence lifetimes were calculated as 632 µs for the 2 wt% Dy3+ sample and 539 µs for the 3 wt% Dy3+ sample, with a clear concentration quenching effect observed at higher dopant levels. Colorimetric analysis in the CIE 1931 color space revealed a shift toward yellow with increasing Dy3+ concentration, achieving a correlated color temperature (CCT) of 6595 K at 2 wt% Dy3+. This shift supports the material’s potential for photonic and lighting applications. These findings highlight a significant advancement in addressing the thermal stability issue in phosphor materials, making Dy3+-doped LMBO phosphors promising candidates for advanced photonic technologies.

Exploration on the liquid-based energy storage battery system from system design, parametric optimization, and control strategy

Lithium-ion batteries are increasingly employed for energy storage systems, yet their applications still face thermal instability and safety issues. This study aims to develop an efficient liquid-based thermal management system that optimizes heat transfer and minimizes system consumption under different operating conditions. A thermal-fluidic model which incorporates fifty-two 280 Ah batteries and a baffled cold plate is established. The reliability of battery heat generation is confirmed experimentally, with a maximum deviation of 14.8 %. Then, comparative studies are performed to evaluate the impacts of cold plate structure and attachment on thermal management performance. Results found that while side-attachment shows better heat transfer, bottom-attachment coupled with a baffled cold plate reduces the temperature gradient and power consumption at both cooling and preheating scenarios. Furthermore, the effects of flow rate and inlet temperature are studied systematically, and a decision making method is utilized to assist in multi-attribute optimization. Finally, a surrogate model is proposed to unveil the collaborative effects between these factors. Based on this, an optimal thermal management strategy with controllable flow rate and inlet temperature is obtained according to ambient temperatures. The proposed framework provides a feasible approach to improve the design and control of liquid-based battery thermal management.

Defect engineering of anchored on F-doped BNNR surface to enhance low-frequency microwave absorption and achieve exceptional thermal conductivity properties

The growing demand for AI and smart computing drives the development of compact, lightweight electronic products to mitigate electromagnetic wave (EMW) pollution and thermal management issues. This necessitates materials with enhanced microwave absorption (MA) and optimal thermal conductivity (TC). Herein, we designed and synthesized fluorinated boron nitride nanorods (F-BNNRs) in a single step via plasma ball milling. Ammonium fluoride (NH₄F) served as the fluorinating agent for hexagonal boron nitride nanorods (h-BNNRs). F-BNNR3, with a NH₄F to h-BNNR ratio of 10:1 and 5.84 % fluorine (F) content, exhibits excellent MA, achieving a minimum reflection loss (RLmin) of −68.56 dB at 5.14 GHz with a thickness of 4.32 mm. It also displays a broad MA frequency range (4.6–6.1 GHz, 15.4–17.2 GHz) with significant RL < −10 dB. Additionally, a 0.09 wt% F-BNNR3 solution achieves a thermal conductivity (TC) of 0.95 W m⁻1K⁻1, 134 % higher than that of a 0.09 wt% h-BNNR dispersion fluid. Following a post-static treatment, F-BNNR3 attains a TC of 0.86 W m⁻1K⁻1, 118 % higher than that of h-BNNR. The incorporation of F into h-BNNRs significantly enhances MA and TC performance, addressing EMW pollution and thermal management challenges in advanced communication technologies utilizing nanofluids.

Recent advances in LDO chip research

Abstract. With the rapid development of integrated circuit technology and the wide application of Internet of things devices, the demand for power management chips is increasing. Low-dropout regulators (LDO) play an important role in modern electronic devices. It provides a stable low output voltage while maintaining low power consumption. Recently some progress has been made in the research of LDO chips, focusing on improving power efficiency, reducing static current, and enhancing transient response. The study shows that the static current has been significantly reduced by using the subthreshold MOS tube and dynamic current bias technology. In terms of power supply rejection ratio (PSRR), by improving the circuit design, the PSRR of LDO can be maintained above -80 dB under various conditions. In addition, improvements to the transient response result in significantly optimized overshoot and recovery times of the output voltage, ensuring voltage stability when the load changes rapidly. These advances enable LDO chips to meet the demanding requirements of high-performance and Internet of things device applications. Future challenges include further reducing static current, improving PSRR performance in high-frequency environments, and effectively addressing thermal management issues.

Strain engineering for the interfacial thermal resistance of few-layer graphene with porous defects

As electronic devices continue to advance toward higher integration, thermal management issues have become a bottleneck, limiting device performance at the nanoscale. In this study, we reveal the bistable structural characteristics of circular hole defects in few-layer graphene, exhibiting both adhered and separated states, through molecular dynamics simulations. We propose a mechanical model that considers the interplay between the bending energy and cohesive energy to determine the critical size of the hole defect, at which the structure transits between the adhered and separated states. We further demonstrate that strain engineering can adjust the interfacial thermal resistance by more than fivefolds, which drives the structure transit between bistable states. The strain effect on the interfacial thermal resistance of the structure can be accurately described using analytical models. These findings illustrate that strain engineering is an effective method for precisely controlling the interfacial thermal resistance in few-layer graphene and provide new insights into possible thermal switch applications.

A Review on Friction Stir Welding of Copper: Tool Geometry, Process Parameters, and Joint Properties.

This paper comprehensively reviews friction stir welding (FSW) as applied to copper and its alloys. FSW is a solid-state joining process that offers significant advantages over traditional fusion welding methods, particularly for materials like copper that are difficult to weld conventionally due to their high thermal conductivity and oxidation issues. Over time, the FSW process has been developed for different industries. Copper structures joined through FSW are utilized for nuclear waste storage, electrical connectors, chemical and petrochemical storage, refrigeration systems, heat exchangers, and the aerospace industry. This covers recent advancements in FSW technology, the geometry of the tools used, the process parameters, and the microstructural characteristics and mechanical properties of the joints. It examines the shapes, sizes, and materials of the tools used for welding copper and its alloys, along with process parameters such as rotational speed and traverse speed, and their influence on the quality of the joints. Additionally, the paper presents syntheses of previously published results, highlighting the values of parameters that indicate the quality of the welds, including grain size, microhardness, mechanical strength, and elongation. The challenges and potential solutions in applying FSW to copper are also discussed, providing a starting point for future research and industrial applications.

Expansion force signal based rapid detection of early thermal runaway for pouch batteries

With the extensive application of lithium-ion batteries in electric vehicles and energy storage stations, thermal safety issues have increasingly become the focus of public attention. To alleviate the safety concerns, a qualified battery management system (BMS) must be able to detect and warn of thermal abuse before it develops into a thermal runaway (TR). For the first time, the expansion force characteristics of the pouch battery module during the early heating stage of TR under typical working conditions are analyzed, which proves that the expansion force signal can reflect the internal abnormal heating earlier than the terminal voltage and the surface temperature, and has better noise resistance. Furthermore, the electromechanical coupling model (EmCM) is improved for more accurate open-loop expansion force estimation. On this basis, an expansion force based early TR rapid detection framework is proposed with less 3 min expend in tests, in which the Kalman filter ensures the stability and convergence/divergence of the observer estimation error, and the reliability of fault judgment is ensured by the adaptive threshold designed by the model structure.

A Study on Ways to Expand the Speed Operation Range of Dental Laboratory Handpiece Motors Using Low-Cost Hall Sensors

In the dental prosthetics field, BLDC micro-motors are primarily used for implant procedures. As dental materials become increasingly harder, there is a growing demand for higher performance motors to precisely process these materials. However, difficulties in motor development arise due to price competitiveness. Dental motors require capabilities such as low-speed, high-torque for drilling operations and high-speed rotation for precise machining of high-strength dental materials. Additionally, there is a requirement to address thermal issues to prevent user burns due to motor-generated heat. Typically, motors requiring precision control utilize high-resolution position sensors like encoders or resolvers to acquire and control the rotor’s position. However, the high cost of these sensors and constraints such as increased device size pose challenges in maintaining price competitiveness. In this paper, we propose a control algorithm that satisfies the requirements for low-speed, high-torque and high-speed operation requirements for precision machining without hardware modifications using a BLDC micro-motor equipped with an inexpensive Hall sensor commonly used in the dental field. Furthermore, the algorithm is designed to ensure stable operation even in the event of Hall sensor failure or malfunction, and its effectiveness is validated through experiments.

Investigation of hydrothermal characteristics and entropy generation in a microchannel heat sink with elliptical fins

Abstract As the integration of microelectronic devices continues to increase, thermal management issues become increasingly prominent. Microchannel heat sinks are effective for heat dissipation in high heat flux microelectronic devices. This study designs five elliptical finned microchannel heat sinks with different aspect ratios (γ) while maintaining a constant elliptical area to enhance heat transfer performance. The values of γ are 0.74, 0.86, 1, 1.17, and 1.35, respectively. Over the Reynolds number (Re) range of 293 to 740, the hydrothermal characteristics and entropy generation of the microchannels with elliptical fins (MC-EFs) are investigated through numerical simulations. The thermal enhancement mechanism of MC-EFs is analyzed via flow, temperature, and pressure fields. The optimal γ value is determined by maximizing the overall performance factor (OPF) and minimizing the augmentation entropy generation number (N s,a). Results indicate that introducing elliptical fins in the straight microchannel (SMC) significantly improves heat dissipation. An increase in γ enhances thermal performance but also raises flow resistance. Specifically, when γ increases from 0.74 to 1.35, the Nusselt number (Nu) improves by 10.71%-25.64%, and the friction coefficient (f) increases by 30.92%-57.27%. Overall, at Re = 740, the OPF of the MC-EF with γ = 1.35 reaches a maximum of 1.285, and at Re = 597, the N s,a for this configuration is minimized to 0.578. These findings provide valuable insights for effective thermal management in microelectronic devices.