국외 저널

Designing latent heat thermal energy storage (LHTES) systems is computationally expensive due to the reliance on slow computational fluid dynamics (CFD) simulations. This study overcomes this bottleneck by developing a hybrid physics-informed neural network (PINN) framework. This PINN, governed by a 0D lumped-capacitance physical model, was trained on a sparse dataset of only 15 validated conjugated heat transfer (CFD) simulations. The resulting digital twin demonstrated exceptional fidelity, achieving a coefficient of determination (R2 ) greater than 0.999 against the ground truth data. This validated, instantaneous surrogate model was then coupled with a non-dominated sorting genetic algorithm II (NSGA-II) to perform a comprehensive multiobjective design optimization (MODO). The optimization autonomously navigated the fundamental thermohydraulic trade-off by simultaneously maximizing total discharged heat (Qtot) and average power (Pavg) while minimizing pumping power (Wpump). The balanced optimal designs on the global Pareto front matched the thermal performance of the best baseline (Flat-22), while reducing pumping power. This study demonstrates a powerful PINN-driven framework that transforms the LHTES design process from slow, manual evaluation to a rapid, autonomous exploration of the entire continuous design space, enabling the discovery of holistically optimized solutions.

Physics-informed neural network (PINN), Phase change material (PCM), Computational fluid dynamics (CFD), Multivariate thermal dynamics modeling, Latent heat thermal energy storage

Journal of Energy Storage

167

122514

2026.07.30

Thermochemical heat storage (TCHS) is a promising technology for long-duration thermal energy storage. However, TCHS reactors are often evaluated by discharging and charging as independent processes, even though the residual uptake field at the end of discharging sets the initial condition for regeneration. This study presents a cycle-consistent analysis of how discharging termination governs residual adsorption gradients, induces readsorption during charging, and degrades cycle-level performance in a zeolite 13X–water TCHS reactor. A labscale reactor was investigated using an experimentally validated three-dimensional transient model that captures cycle-coupled adsorption kinetics and residual uptake–dependent regeneration behavior in the bed. Discharging was terminated using three practical outlet-temperature thresholds, resulting in lower total uptake under earlier termination and leaving substantial unused adsorption capacity in the downstream region. During charging, the model revealed simultaneous upstream desorption and downstream adsorption at early times, and the effective cumulative desorbed mass exceeded the initially adsorbed water mass by up to 23.1%, confirming internal vapor recycling through re-adsorption and re-desorption. Energy classification further showed that 7.81% of the heat absorbed by the reactor during charging was expended to re-desorb water that had been temporarily readsorbed. This additional regeneration requirement explains a substantial portion of the gap between theoretical and actual cycle efficiencies and limits the benefit expected from simply reducing the initial uptake by earlier discharging termination. Therefore, robust efficiency gains require residual-state-aware termination criteria and reactor and flow-path designs that explicitly suppress re-adsorption.

Thermochemical heat storage, Discharging termination, Adsorption gradient, Re-adsorption, Zeolite 13X, Adsorption isotherm, Cycle efficiency

Applied Thermal Engineering

299

131195

2026.07.01

Underwater laser micromachining (ULMM) offers a promising alternative to conventional in‑air laser processing by mark‑ edly reducing thermal damage. Its industrial adoption, however, has been hindered by the adverse effects of laser‑induced cavitation bubbles and ejected debris, which cause severe optical shielding, process instability, and degraded machining quality. Here, we introduce and experimentally validate a hybrid bubble mitigation strategy designed to overcome these limitations by combining macroscopic advection through forced fluid flow with microscopic agitation by high‑frequency vibration. Using a 1064 nm pulsed fiber laser to machine single‑crystal silicon, we evaluate the performance of this approach. Experiments demonstrate a significant enhancement and clear synergy in the hybrid configuration, achieving meaningful improvements in groove depth and material removal efficiency compared with the baseline air machining con‑ dition. While negligible material removal was observed in still water and vibration‑only conditions, the forced flow and hybrid conditions yielded substantially greater removal. The hybrid method simultaneously broadened the kerf, enhanc‑ ing material removal, while reducing the heat-affected zone (HAZ), thereby demonstrating improved surface quality. We attribute this performance to a macro-micro multiscale mechanism in which bulk flow establishes a stable, optically transparent processing environment and high‑frequency acoustic agitation executes targeted, high‑energy cleaning at the laser‑material interface. The proposed hybrid technique therefore enables high‑efficiency, low‑damage micromachining of silicon and may be useful for materials other than silicon.

Underwater laser machining, Bubble, Water flow, Vibration

International Journal of Precision Engineering and Manufacturing

Accepted

14031417

2026.01.15

https://doi.org/10.1007/s12541-025-01431-2

Accurate control of high-temperature plasma is essential for realizing fusion energy. The in-vessel control coil of the Korea Superconducting Tokamak Advanced Research (KSTAR) device plays a vital role in plasma stabilization, yet its coil case exhibits a pronounced temperature rise during alternating-current operation, threatening long-pulse endurance. To address these issues, this study integrates full-scale experiments (<10⁻³ Torr; 0.5–1.8 kA, 60–160 Hz) with coupled electromagnetic–thermal–structural simulations to quantify eddy-current heating and its thermo-mechanical consequences. As the input increased from 0.5 kA–60 Hz to 1.8 kA–160 Hz, coil case eddy current loss rose from 1.2 W to 72.6 W and temperature from 37.4°C to 139.0 °C, following the power law I²fⁿ (n ≈ 1.6), indicating that the thermal response becomes increasingly governed by localized eddy-current concentration. Design variations further revealed a clear trade-off between heat spreading and electromagnetic susceptibility: a copper cap intensified induced currents and raised the temperature to 270.5°C, whereas a stainless-steel cooling pipe provided effective convective removal and reduced it to 89.5°C. These results highlight that, for high-conductivity design strategies, performance strongly depends on geometry-dependent optimization to interrupt eddy-current loops while retaining thermal advantages. Steep temperature gradients across the epoxy-glass insulation amplified local shear stress and accelerated mechanical degradation, underscoring the strong coupling between electromagnetic heating and structural reliability. These findings clarify how electromagnetic geometry governs localized heating and highlight the importance of an integrated EM–thermal design approach for mitigating eddy-current heating and improving the structural reliability of in-vessel coils in long-pulse fusion devices.

Eddy-current heating; in-vessel control coil (IVCC); Tokamak; KSTAR; coupled EM-thermal-structural modeling; thermal design, thermal management

Applied Thermal Engineering

286

129304

2026.02

https://doi.org/10.1016/j.applthermaleng.2025.129304

Poor length uniformity in nanowires synthesized by template-assisted electrodeposition remains a bottleneck to the development of nanowire-based energy and electronic devices. This fabrication method is inherently unstable, often amplifying non-uniform growth and making precise control difficult. In this work, we investigate how introducing a temperature gradient along individual Bi nanowires enables self-controlled growth that suppresses such instability and improves length uniformity. The temperature difference at the nanowire tips, induced by the fineffect, regulates the local growth rate of each nanowire, allowing the system to equilibrate toward uniform lengths. This approach not only enhances the feasibility of nanowire-based technologies but also provides fundamental insights into self regulating growth mechanisms, offering new opportunities in materials science

Nanowire, Electrodeposition, Length Uniformity, Temperature Gradient, Fin Effect

RSC Advances

15

42507 - 42512

2025.11.01

10.1039/d5ra07147j

Latent heat thermal energy storage systems can enhance energy flexibility and efficiency in applications such as renewable energy integration and industrial waste heat recovery. However, their performance is constrained by the low thermal conductivity of phase change materials, which limits heat transfer rates and slows thermal response. To address this limitation, this study investigates the influence of inner tube flatness on local thermal behavior and system-level performance in a shell-and-tube latent heat thermal energy storage system. A three-dimensional transient conjugated heat transfer model was developed and validated using experimental measurements from a laboratory-scale system filled with paraffin-based phase change material. To examine the influence of inner tube shape, three configurations were tested under the same phase change material volume. The configurations were a circular tube and two flattened tubes with long axes of 10 mm and 22 mm, called Flat-10 and Flat-22. The Flat-22 configuration enhanced melting and solidification by increasing the heat transfer area and rapidly growing the melted phase change material layer thickness, which intensified buoyancy-driven convection and improved conductive heat transfer. Despite a higher pressure drop, the Flat-22 design reduced pumping energy by approximately 55% in charging and 39% in discharging and shortened the phase-change duration by 55% and 44%, respectively, resulting in coefficient of performance improvements of 117% and 61% relative to the circular baseline. These results highlight tube flatness as a critical factor for enhancing phase-change rates and system efficiency, offering design insights for compact, scalable latent heat thermal energy storage systems.

latent heat thermal energy storage (LHTES); phase change material (PCM); tube flatness; conjugated heat transfer simulation; melting and solidification dynamics; system-level performance

Applied Thermal Engineering

280

128308

2025.12.01

https://doi.org/10.1016/j.applthermaleng.2025.128308

Boiling is a promising cooling strategy for systems with high thermal loads, and enhancing its performance is essential to ensure reliable thermal management to improve the performances of high-heat-flux systems. The use of surfactant additives as a passive enhancement method offers high fidelity because of its competitive cost, simplicity, and convenience in reducing the surface tension of the fluid to facilitate bubble detachment. While surfactant-enhanced boiling has been widely studied, its interaction with engineered surfaces possessing varying levels of cavity activation superheat remains insufficiently explored. In this study, we investigate the boiling characteristics of micropillar structures in surfactant solutions using a non-ionic surfactant, by employing surfaces with different nucleation sites density. Specifically, we compare a Si micropillar surface and a micropillar surface coated with reduced graphene oxide (rGO), which introduces a lower cavity activation superheat. Our results reveal that the combination of surfactants and surface engineering leads to significant improvements in boiling heat transfer, primarily due to modified bubble dynamics such as suppressed coalescence and enhanced nucleation activity. For the uncoated micropillar surface, the addition of surfactants increased the heat transfer coefficient and critical heat flux by up to 154 % and 41 %, respectively. Furthermore, we investigate the boiling-inversion effect of surfactant solutions on micropillar surfaces coated with a wide cavity size distribution. rGO-coated micropillar surface exhibited even greater enhancement, with maximum improvements of 493 % in heat transfer coefficient and 196 % in critical heat flux compared to the plain surface under DI water conditions, which highlight the synergistic effects of surfactant solutions and surface design.

Structured surface; Micropillar; Boiling heat transfer; Heat transfer coefficient; Surfactant

International Journal of Heat and Mass Transfer

251

127391

2025.11.15

https://doi.org/10.1016/j.ijheatmasstransfer.2025.127391

The successful application of thermochemical heat storage (TCHS) in real-world heating, ventilation, and air conditioning (HVAC) systems requires overcoming challenges related to low heat and mass transfer rates and high pressure drops. Also, as the system is scaled up, radial non-uniformities in temperature and mass transfer become more pronounced due to the mismatch between inlet duct and reactor diameters, which can significantly degrade zeolite utilization efficiency. This study investigates how reactor geometry influences heat and mass transfer efficiency, as well as fluid flow dynamics, in a TCHS system using zeolite 13X-water pair. We analyzed the effects of varying key geometric parameters, reactor inlet duct diameter (d), bed height (H), and bed diameter (D) on critical performance metrics including reactor outlet temperature, zeolite 13X consumption homogeneity (P(%)), and pressure drop. Our findings reveal that reducing the D/d ratio from 3 to 1 significantly enhanced the uniformity of zeolite consumption, leading to an 8.62% reduction in discharging time. Additionally, reducing the H/D ratio from 2 to 0.5 resulted in an 89.5% decrease in pressure drop, due to shorter flow paths and reduced flow resistance. While changes in reactor geometry did not alter the total heat released, they led to an 89.3% reduction in energy consumption, attributed to both shorter discharging times and reduced flow resistance. By quantitatively decoupling the geometric effects of the D/d ratio on flow uniformity and the H/D ratio on pressure drop, this study provides fundamental design guidelines essential for the successful scale-up of TCHS systems for practical applications.

Thermochemical heat storage; Reactor geometry; Zeolite 13X; Adsorption kinetics; Thermal discharge dynamics; Energy efficiency

Applied Thermal Engineering

279

127689

2025.11.15

https://doi.org/10.1016/j.applthermaleng.2025.127689

Maintenance of fusion experimental devices like KSTAR is challenging due to harsh conditions such as high vacuum and temperatures. Typically, long downtime is required to cool and reduce radiation levels before possible human access. To address this, we designed an articulated robotic arm to perform low-payload maintenance tasks inside the KSTAR device. This paper presents the design progress of an articulated robotic arm, including system configuration, hardware design, and structural analysis, as part of a stage-wise approach to developing the arm. The arm is connected to the shuttle device and stored in a cask, totaling 11 m and 13 DoF. We conduct a finite element method (FEM) analysis to ensure design reliability and safety under target load conditions. We use the proposed robot system to perform essential maintenance operations for KSTAR, including visual inspection, debris removal, and other simple tasks. Our robot arm system has the potential to reduce maintenance preparation time, minimize radiation exposure to personnel, and contribute to improving the fusion experiment’s operational uptime and efficiency.

Remote control; Inspection; Maintenance; Long reach robotic arm; Automation; Fusion energy

Fusion Engineering and Design

220

115343

2025.11.01

https://doi.org/10.1016/j.fusengdes.2025.115343

Flooding is one of the major obstacles to achieve stable performance in Proton exchange membrane fuel cells (PEMFCs). Here, we investigate cathodic flooding using a large-area single cell with in situ visualization. Multiphase flow dynamics are evaluated through synchronized measurements of pressure drop, voltage variation, and water behavior under varying output currents. We introduce a dimensionless parameter, the modified Euler number ( ), to quantify the onset and progression of flooding through the balance between air momentum and pressure resistance. enables distinction between channel flooding and gas diffusion layer (GDL) flooding, providing thresholds based on real-time hydrodynamic and electrochemical responses. At lower currents, water accumulation leads to increased pressure and voltage degradation, while at higher currents, enhanced airflow momentum mitigates blockage through effective droplet removal. Our results show that adjusting the output current indirectly regulates air supply, offering a practical strategy to suppress flooding under air-fed conditions. This airflow-driven mitigation becomes particularly relevant for PEMFCs operating with compressed air rather than pure oxygen. The application of enables a quantitative understanding of flooding transitions and their performance impact, informing the design and operational control of robust PEMFC systems for potentially advancing vehicle electrification.

Proton exchange membrane fuel cell; Cathodic flooding; Modified Euler number; Multiphase flow; Air-fed operation; Real-time diagnostics

Journal of Power Sources

649

237336

2025.09.01

https://doi.org/10.1016/j.jpowsour.2025.237336

We introduce a micro-electromechanical system (MEMS) energy harvester, designed for capturing flow energy. Moving beyond traditional vibration-based energy harvesting, our approach incorporates a cylindrical oscillator mounted on an MEMS chip, effectively harnessing wind energy through flow-induced vibration (FIV). A highlight of our research is the development of a comprehensive fabrication process, utilizing a 5.00 µm thick cantilever beam and piezoelectric film, optimized through advanced micromachining techniques. This process ensures the harvester’s alignment with theoretical predictions and enhances its operational efficiency. Our wind tunnel experiments confirmed the harvester’s capability to generate a notable electrical output, with a peak voltage of 2.56 mV at an 8.00 m/s wind speed. Furthermore, we observed a strong correlation between the experimentally measured voltage frequencies and the lift force frequency observed by CFD analysis, with dominant frequencies identified in the range of 830 Hz to 867 Hz, demonstrating the potential application in actual flow environments. By demonstrating the feasibility of efficient energy conversion from ambient wind, our research contributes to the development of sustainable energy solutions and low-power wireless electron devices.

Vibration-to-electricity conversion; MEMS energy harvester; Fluid-induced vibration (FIV); Karman vortex; Micro Electro Mechanical System (MEMS); Piezoelectric film

Micromachines

15(5)

581

2024.04.27

https://doi.org/10.3390/mi15050581

This study advances thermal management in flow boiling by investigating the synergy between nanoscale surface structures, hemi-wicking, and bubble dynamics during phase changes, with a particular focus on innovative surface morphology. Nanowires, known for enhancing heat transfer through surface roughening and interfacial wicking, play a crucial role. We highlight the importance of morphological roughening and its synergy with hemi-wicking in enhancing critical heat flux (CHF) in flow boiling. We demonstrate that surfaces functionalized with vertical silicon nanowires show a significant increase in CHF compared to smooth surfaces. This enhancement is attributed to improved liquid supply and prevention of bubble pinning, thus maximizing heat dissipation. However, the absence of hemi-wicking on nano-inspired surfaces unexpectedly leads to a substantial CHF reduction compared to smooth counterparts. By visualizing bubble dynamics under forced convection, we reveal the critical role of hemi-wicking in sustaining continuous liquid supply and postponing the onset of film boiling by ensuring an anti-pinning effect of bubbles. These findings offer valuable insights into interface functionalization and surface morphology design for efficient heat dissipation, emphasizing the often-overlooked role of hemi-wicking in preventing bubble pinning. This knowledge is pivotal for developing compact and high-efficiency cooling technologies.

Flow boiling heat transfer; Nanowires; Hemi-wicking; Surface roughening; Critical heat flux; Bubble pinning

International Journal of Mechanical Sciences

268

109021

2024.04.15

https://doi.org/10.1016/j.ijmecsci.2024.109021

Sorption thermal energy storage (STES) systems utilizing zeolite 13X present a promising solution to pressing global energy challenges. In this study, we explore the influence of absolute humidity and flow rate on the heat release process within a STES system, with a focus on local and overall performance considering temperature profile, degree of adsorption reaction, and average thermal power. A numerical model has been developed to investigate the adsorption kinetics of zeolite 13X and water, which is validated through experiments on pressure drop and transient temperature changes. In this study, we introduce P(%), a novel factor providing a holistic perspective of the adsorption process throughout the reactor. Through the analysis of P(%), we elucidate the link between the adsorption reaction, local heat transfer characteristics, and average thermal power within the reactor. Our findings reveal that increasing absolute humidity and flow rate accelerates the adsorption reaction of zeolite, leading to reduced discharge time. Our findings indicate that the adsorption reaction rate significantly decreases when P(%) approaches 95%. It is noteworthy, however, that the specific threshold of P(%) can vary based on the adsorbent type or reactor design. Despite this, P(%) can be utilized as a factor to establish the criteria for optimal control of STES. This research provides a guideline for optimum operational control and reactor design of STES systems.

Sorption thermal energy storage; Zeolite 13X; Heat discharging; Adsorption reaction; Adsorption kinetics; Reaction propagation dynamics

International Journal of Heat and Mass Transfer

221

125049

2024.04.01

https://doi.org/10.1016/j.ijheatmasstransfer.2023.125049

Nanowires (NWs) constitute a promising solution to the overheating of high-heat-load surfaces in multiphase heat transfer. Typical nanostructure fabrication methods such as complex photolithography and metal-assisted chemical etching (MACE) that utilize patterned templates are limited by high manufacturing costs and type of substrate materials. These limitations significantly hinder the industrial applicability of NW structures in high heat flux units. In this study, we first examine the effect of the morphology of Zinc oxide (ZnO) NW printed substrates, fabricated via microcontact printing (µCP) and solution based growing, on the heat transfer characteristics in pool boiling. Unlike advanced photolithography, µCP offers greater variability and convenience in terms of the substrate selection and large area creation for NW fabrication. Compared with the silicon substrate, the underlying mechanisms for enhancing both the critical heat flux and heat transfer coefficient of ZnO NW substrates are explored by analyzing the surface morphology, bubble, and wicking characteristics of the test surfaces, in order to determine the applicability of boiling heat transfer using ZnO NWs in industrial fields.

ZnO nanowires; Microcontact printing; Solution based growing; Wicking characteristics; Bubble visualization; Pool boiling

International Journal of Heat and Mass Transfer

212

124313

2023.09.15

https://doi.org/10.1016/j.ijheatmasstransfer.2023.124313

The boiling performance, represented by the heat transfer coefficient (HTC) and critical heat flux (CHF), must be enhanced because the energy demand of industrial processes that generate a lot of heat increases under extreme conditions. Surface manipulations have been used to improve boiling performance by controlling interfacial characteristics. Specifically, biphilic or superbiphilic patterned surfaces have been widely utilized to enhance HTC and CHF. However, it remains a challenging issue to improve CHF on superbiphilic surfaces with wicking phenomena due to the suppression of liquid supply in hydrophobic regions. In the present work, to investigate the mechanism and experimentally break through the limits of CHF enhancement, artificially patterned superbiphilic (SBPI) surfaces with different superhydrophobic (SHPO) area fractions were produced, and conducted pool boiling heat transfer. By artificially promoting nucleation, all SBPI surfaces demonstrated a higher HTC than homogeneous wettability surfaces. Considering dynamic wicking and bubble behaviors, the SBPI successfully broke through the CHF of homogeneous superhydrophilic surfaces. It is concluded that the non-dimensional liquid supply factor, which reflects both wicking and bubble behaviors, is essential to design structured surfaces during boiling. The results can contribute to a strategy for further improving boiling performance by controlling wettability on nanoscale interfaces.

Boiling heat transfer; Surface modification; Superbiphilic; Surface wettability; Surface wicking; Critical heat flux

International Journal of Mechanical Sciences

249

108280

2023.07.01

https://doi.org/10.1016/j.ijmecsci.2023.108280

The International Thermonuclear Experimental Reactor (ITER) vacuum vessel (VV) is one of the critical components of the ITER tokamak fusion reactor. The first sector of the ITER VV was delivered to ITER Organization in 2020, and it is ready to assemble into the tokamak system. After manufacturing the ITER VV, an evaluation should ensure that the components are designed and manufactured to meet the functional requirements, such as vacuum leak tightness and structural integrity. The factory acceptance test (FAT) is essential for confirming acceptance in engineering and manufacturing. This paper introduces the engineering process and technical method of the FAT, which is applied explicitly to the first-of-a-kind ITER VV. We establish a visual inspection, pre-pumping assessment, pressure test, helium (vacuum) leak test, and final dimensional inspection for the FAT. The visual inspection revealed no blockages in the cooling channels of the double walls. The pre-pumping assessment conducted to check the vacuum level and residual gas condition, concluded that the inside of the VV was flawless and thus met the leak test requirements of 1 × 10−8 Pa m3 s−1. We confirmed no leakage or deformation through the pressure test under reduced pressure. The helium leak test demonstrated engineering soundness with leak tightness of 6.08 × 10−9 Pa m3 s−1, which is more stringent than the allowable limit. Furthermore, three-dimensional metrology was utilized to determine the as-built dimensions of the manufactured sector. Due to unavoidable weld deformation and tight tolerances, the as-built result does not perfectly meet the assigned tolerance level. Nevertheless, it can be considered as advanced information for assembly with in-vessel components and other sectors. based on the conformance and suitability of the suggested FAT for the first ITER VV sector, we will determine the acceptability of the upcoming VV sectors, which will be manufactured and delivered by Korea shortly.

Tokamak fusion reactor; Vacuum vessel; Functional acceptance; Factory acceptance test; ITER

Nuclear Fusion

63

016003

2022.11.25

https://doi.org/10.1088/1741-4326/aca1d0

Boiling heat transfer is a favorable method for cooling high heat flux devices, and its performance is evaluated using critical heat flux (CHF), which indicates the maximum heat dissipation capacity. CHF occurs when a surface is covered with a vapor film due to bubble coalescence. Here, we propose a new nucleation patterning surface using rGO-coated micropillar-free cavities in order to enhance boiling heat transfer by suppressing bubble coalescence. Nucleation patterned surface is achieved by a sectored self-assembly on surfaces with artificial cavities embedded in micropillar array. The nucleation pattern is designed with spacings of 1.0 and 1.5 mm, with reference to the bubble departure diameter on the rGO-coated micropillar surface. The rGO particles deposited on the bottom of the micropillar-free cavity cause bubble formation in the cavities, and the micropillars around the cavities supply liquid to bubbles through wicking. Moreover, rGO deposition with varying heat flux schemes suggests the capability of constructing toned rGO layers on patterned micropillar surfaces. The results confirmed that high heat transfer performance can be obtained by applying denser bubble nucleation with a bubble generation spacing to bubble departure diameter ratio of 1, under the condition of preventing bubble coalescence. The heat transfer coefficient and critical heat flux were augmented by 340% and 203%, respectively, by preserving flow paths for water imbibition under the floating rGO layer and delaying bubble coalescence.

Nucleation patterning; Reduced graphene oxide; Self-assembly; Boiling heat transfer; Heat transfer coefficient

International Journal of Heat and Mass Transfer

197

123329

2022.11.15

https://doi.org/10.1016/j.ijheatmasstransfer.2022.123329

We open an avenue for discussing how we can pave the way for compliance with existing regulations is a far-reaching factor for settling nuclear fusion technology. based on a model of the Korean Fusion Demonstration Reactor (K-DEMO) with a target fusion power of 2.2 GW, we assess the intrinsic safety determinants of internal energy sources, the expected radioactive waste, and the tritium management. Regarding these safety factors, we scrutinize the compatibility of the current legislative environment in Korea with K-DEMO and envisage foreseeable obstacles, such as licensing of the nuclear facilities and acceptability of the radioactive waste. based on precedent licenses for the Korean Superconducting Tokamak Advanced Research (KSTAR) and lessons learned from the International Thermonuclear Experimental Reactor (ITER), we examine hazardous factors that would threaten regulatory compliance of K-DEMO. This approach can help shape a fusion-compatible framework for consolidating the necessary technical provisions and regulatory baselines reflecting social acceptance with a sense of safety. Fusion-compatible aspects in the regulatory environment are discussed, from fusion philosophy to subordinate administrative and technical guidelines, facility classification, and detailed methods guaranteeing integrity and safety. This paper will contribute to the timely settlement of fusion demonstration facilities and subsequent commercial plants.

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Scientific Reports

12

8276

2022.05.18

https://doi.org/10.1038/s41598-022-12389-w

Development of the Helium Cooled Ceramic Reflector (HCCR) breeding blanket is underway according to the development strategy of core technology for K-DEMO under the fusion energy development roadmap in Korea. The main goals are to validate integrated design tools and to develop core technologies in the field of materials, manufacturing and joining technologies, helium cooling and tritium technologies, system integration, and safety technologies. A unique graphite reflector concept was adopted to save cost by reducing the amount of beryllium neutron multiplier. The main functions and design concepts of the HCCR breeding blanket are to be verified in ITER through the HCCR Test Blanket Module (TBM) program. Not only breeder modules are to be tested in ITER but also the technologies of cooling, coolant purification, tritium extraction, etc. are to be tested or proved in ITER before employed in DEMO. This paper introduces the current updates of the design and R&D activities of the HCCR TBM systems in the preliminary design stage.

Helium Cooled Ceramic Reflector (HCCR); Test Blanket Module (TBM); Breeding blanket; Advanced Reduced Activation Alloy (ARAA); Test Blanket Systems (TBS)

Fusion Engineering and Design

171

112553

2021.10.01

https://doi.org/10.1016/j.fusengdes.2021.112553

Selective laser melting (SLM) is a promising additive manufacturing technique arising from glassy metal characteristics of treated medium. When creating novel compositions of materials and intricate workpieces, reliable thermal designs should be implemented based on well-understood heat transfer characteristics on matierlas to be used. Herein, we investigate local and overall heat transfer characteristics of SLM processes and investigate the principal parameters related to the magnituge of a radiative heating power and its exposure time. We present how to exert their influence upon local melting and sequential solidification of copper powder bed. The local solid media reach a quasi-equilibrium state in even 1 ms with the incident powers of 50, 100, and 200 W. The anisotropic expansion of the molten pool is governed by a thermally-induced Marangoni flow. As the power is increased, the Marangoni factor increases linearly up to 853.7%. Consequential heat transfer characteristics tell us that unconditional input power should be avoided to prohibit the detrimental effect; the radiative heating power should be confined for thermalization of a target domain and for that preventing the evaporation of a material. These approaches from material science to heat transfer can be used to develop a platform for SLM processes guaranteeing its feasibility and applicability.

Selective laser melting; Radiative heat absorption; Conductive heat dissipation; Thermal design; Additive manufacturing; Marangoni flow

Applied Surface Science

496

143594

2019.12.01

https://doi.org/10.1016/j.apsusc.2019.143594

Critical heat flux (CHF) enhancement is necessary in order to ensure a high operating limit for two-phase cooling applications. As the boiling is developed, formation of vapor film layer becomes vigorous, which causes CHF. Here, a graphene-coated micropillar structure (GMS) is proposed in order to enhance boiling heat transfer by suppressing vapor film formation on the surface. The GMS is designed to separate the bubble nucleation region from the liquid supply region in order to enhance CHF. By controlling the height of the micropillar, we obtained a structure in which the rGO layer is coated at the top of the micropillar array with high aspect ratio of the micropillar. In particular, the GMS consists of a reduced graphene oxide (rGO) porous mesh layer and a micropillar array layer. The rGO porous structure facilitated bubble nucleation by providing a suitably sized cavity. The micropillar array, which has excellent wicking performance, is located below the rGO porous layer in order to provide a capillary pumping to the vapor bubbles. Consequently, the GMS provides a significantly improved heat transfer coefficient and CHF of 288% and 152%, respectively, compared to the plain surface.

Reduced graphene oxide; Micropillar; Boiling heat transfer; Heat transfer coefficient; Critical heat flux

International Communications in Heat and Mass Transfer

109

104331

2019.12.01

https://doi.org/10.1016/j.icheatmasstransfer.2019.104331

Nuclear fusion energy is a solution to the substitution of fossil fuels and the global energy deficit. However, among the several problems encountered for realizing a nuclear fusion reactor, the divertor presents difficulties due to the tremendous heat flux (~10 MW/m2) from high-temperature plasma. Also, neutrons produce additional heat (~17.5 MW/m3) from collisions with the materials’ atoms. This may lead to unexpected effects such as thermal failure. Thus, a comprehensive investigation on the divertor module is needed to determine the heat-absorbing capacity of the divertor module so to maintain the effect of incident heat flux. In this study, using an analytical approach and a simulation, the quantitative effect of heat generation on the thermophysical behavior, such as temperature and thermal stress, was analyzed while maintaining the incident heat flux. Then, a correlated equation was derived from the thermal design criteria, namely, the maximum thimble temperature and the safety factor at the vulnerable point. Finally, on the basis of the thermal design criteria, the heat-absorbing capacity of a nuclear fusion reactor in operating conditions was determined. This study contributes to the understanding of the divertor’s effects in nuclear fusion reactors for high-heat-flux and high-temperature applications.

Heat transfer; Nuclear fusion; High-heat-flux component; Divertor

Energies

12(19)

3771

2019.10.03

https://doi.org/10.3390/en12193771

The radioactivation of in-vessel components due to the fusion neutrons is an unavoidable trade-off in a tokamak reactor. We investigate the radioactivity level of nuclides and decay heat of conceptual water-cooled ceramic breeder blanket and divertor modules in K-DEMO, and demonstrate that a cooling scheme related to the decay time is important to prevent thermal failure of those components due to decay heat during their maintenance. For K-DEMO with a fusion power of 2.2 GW, the activation levels of blankets and divertors are evaluated regarding a regulatory low level limit in Korea. Total decay heat from radioactivated blankets and divertors reaches 63.4 MW after the full power operation of two years. In an outboard module, immediately after the plasma shutdown, local maximum temperature reaches 1300°C with the temperature difference up to 840°C inside the module. Conservative natural convection was assumed to validate its integrity to remain within the allowable temperature range of the materials used, when provided that the cool-down time is secured at least a couple of days, the overall temperature of the module is reduced to about 200°C in 10 days. It is worth consideration that a forced convective scheme such an internal passage cooling can be tailored until a critical time corresponding to configurations of each module.

K-DEMO; Breeding blanket; Divertor; Radioactivity; Decay heat; Thermal analysis; Heat transfer; Cooling

Fusion Engineering and Design

146 Part B

2323-2327

2019.09.01

https://doi.org/10.1016/j.fusengdes.2019.03.181

We present a new concept of a structured surface for enhanced boiling heat transfer that is capable of self-adapting to the local thermal conditions. An array of freestanding nanoscale bimorphs, a structure that consists of two adjoining materials with a large thermal expansion mismatch, is able to deform under local temperature change. Such a surface gradually deforms as the nucleate boiling progresses due to the increase in the wall superheat. The deformation caused by the heated surface is shown to be favorable for boiling heat transfer, leading to about 10% of increase in the critical heat flux compared to a regular nanowire surface. A recently developed theoretical model that accounts for the critical instability wavelength of the vapor film and the capillary wicking force successfully describes the critical heat flux enhancement for the nanobimorph surface with a good quantitative agreement.

Nanowires; Bimorph; Phase-change; Boiling heat transfer; Critical heat flux

Nano Letters

18(10)

6392-6396

2018.10.01

https://doi.org/10.1021/acs.nanolett.8b02747

In boiling heat transfer, the emerging issues are the improvement of both the critical heat flux (CHF) and the thermal stability. Nanowire-forested (NF) surfaces and subcooled environments are favorable for improving CHF as well as the thermal stability owing to their distinctive morphology and consequential convection expedition, respectively. In this study, the improvement of CHF and temperature uniformity/stability are evaluated on NF surfaces immersed in de-ionized water with subcooling from 0 to 30 K using a resistance temperature detector (RTD) sensor with five measuring points. NF surfaces catalyze dispersed, confined and fast bubble ebullitions under subcooling conditions, resulting in the delayed bubble coalescences. This lead to the enhancement of CHF accompanying stabilized spatial/temporal temperature variations. We demonstrate that NF surfaces applying 30 K subcooled condition not only significantly improve the thermal stability by reducing spatial/temporal temperature variations to less than 1/5 but also enhance CHF by 4.3 folds, compared to the plain surfaces under the saturated condition. These remarkable enhancements show that NF surfaces can be effective solutions to secure the thermal stability under vigorous boiling conditions.

Boiling heat transfer; Nanowire-forested surfaces; Subcooling; Thermal stability; Critical heat flux; Nucleation

International Journal of Heat and Mass Transfer

120

1020-1030

2018.05.01

https://doi.org/10.1016/j.ijheatmasstransfer.2017.12.100

In two-phase heat transfer, promising issues include not only improving the boiling performance but also the surface temperature uniformity and stability, which indicate that how long the system maintains thermal stability without a failure on the surface. In this study, the merits of micro-nano hybrid surfaces (MNHS) are discussed for enhancing the thermal uniformity/stability and boiling heat transfer performance. Spatial/temporal heat transfer characteristics are evaluated on MNHS using a local temperature-measuring sensor of resistance temperature detector (RTD). We demonstrate that MNHS can enhance not only boiling performance but also thermal uniformity/stability by delaying bubble coalescence with an appropriate design of the location of the nucleation sites and the nucleated bubble size. The confining effects of nucleated bubbles on nanowire (NW) structures and of uniform bubble nucleation on uniformly distributed micro-cavity (MC) structures lead to the reliable enhancement of thermal uniformity/stability as well as critical heat flux (CHF) in pool boiling environments. These combined effects of the NW and MC structures could delay the bubble coalescence phenomenon by catalyzing bubble nucleation dispersedly and quickly at small bubble sizes. When the normalized pitch of the nucleation sites is 1, namely the pitch of the nucleation sites and the bubble departure size have the same dimension, CHF is significantly enhanced, by more than 170%, on an MNHS versus a plain surface by delaying bubble coalescence and maximizing bubble density. Boiling heat transfer using an MNHS represents a breakthrough reducing the spatial and temporal temperature variation at CHF to less than 1/3 and 1/4, respectively, compared with a plain surface.

Boiling heat transfer; Micro-nano hybrid surface; Thermal uniformity and stability; Critical heat flux; Bubble coalescence

Applied Thermal Engineering

130

710-721

2018.02.05

https://doi.org/10.1016/j.applthermaleng.2017.10.144

Enhancing the critical heat flux (CHF), which is the capacity of heat dissipation, is important to secure high stability in two-phase cooling systems. Coolant supply to a dry hot spot is a major mechanism to prevent surface burn-out for enhancing the CHF. Here, we demonstrate a more ready supply of coolant using aligned silicon nanowires (A-SiNWs), with a high aspect ratio (>10) compared to that of conventional random silicon nanowires (R-SiNWs), which have a disordered arrangement, for additional CHF improvement. We propose the volumetric wicking rate, which represents the coolant supply properties by considering both the liquid supply velocity and the amount of coolant (i.e., wicking coefficient and wetted volume, respectively). Through experimental approaches, we confirm that the CHF is enhanced as the volumetric wicking rate is increased. In good agreement with the fabrication hypothesis, A-SiNWs demonstrate higher coolant supply abilities than those of R-SiNWs. The longest (7 μm) A-SiNWs have the highest volumetric wicking rate (25.11 × 10–3 mm3/s) and increase the CHF to 245.6 W/cm2, which is the highest value obtained using nanowires among reported data (178 and 26% enhanced vs unmodulated plain surface and R-SiNWs, respectively). These well-aligned SiNWs can increase the CHF significantly with efficient coolant supply, and it can ensure high stability in extremely high thermal load systems. Moreover, our study provides nanoscale interfacial design strategies for further improvement of heat dissipation.

Surface modification; Aligned nanowires; Heat transfer enhancement; Interfacial wicking; Boiling heat transfer

ACS Applied Materials & Interfaces

9(20)

17595-17602

2017.05.04

https://doi.org/10.1021/acsami.7b01929

Interface-inspired convection is a key heat transfer scheme for hot spot cooling and thermal energy transfer. An unavoidable trade-off of the convective heat transfer is pressure loss caused by fluidic resistance on an interface. To overcome this limitation, we uncover that nano-inspired interfaces can trigger a peculiar fluidic interactivity, which can pursue all the two sides of the coin: heat transfer and fluidic friction. We demonstrate the validity of a quasi-fin effect of Si-based nanostructures based on conductive capability of heat dissipation valid under the interactivity with fluidic viscous sublayer. The exclusive fluid-interface friction is achieved when the height of the nanostructures is much less than the thickness of the viscous sublayers in the turbulent regime. The strategic nanostructures show an enhancement of heat transfer coefficients in the wall jet region by more than 21% without any significant macroscale pressure loss under single-phase impinging jet. Nanostructures guaranteeing fluid access via an equivalent vacancy larger than the diffusive path length of viscid flow lead to local heat transfer enhancement of more than 13% at a stagnation point. Functional nanostructures will give shape to possible breakthroughs in heat transfer and its optimization can be pursued for engineered systems.

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Scientific Reports

7

45323

2017.03.27

https://doi.org/10.1038/srep45323

Nuclear fusion is the promising energy sources because the fuels for power generation are abundant and by-products are eco-friendly rather than other power generations. However, there are several conundrums that must be solved for developing the nuclear fusion plants, including DEMO (DEMOnstration nuclear fusion reactors), such as superconducting system, blanket, cryostats and others. In particular, a divertor is one of essential components because of withstanding the excessive heat flux (∼10 MW/m2) from the high-temperature plasma. Therefore, it is necessary for thermal design of divertor module under tremendous heat flux to develop the nuclear fusion plants. We investigate thermophysical behavior by convective heat transfer and suggest principle operating variables to decide for appropriate thermal design for divertor module. based on the simplified thermal circuit, we demonstrate that the observed correlation can predict thermophysical characteristics of the divertor module and present the prerequisites for reliable thermal design based on the thermal design maps in terms of principle operating variables of divertor module. Finally, we reveal that the safety factor of thimble is primary concern to establish thermal design of divertor module. The present study will contribute to the development of divertor in nuclear fusion plants and the applications for high heat flux and temperature devices.

Thermal design; Divertor; Nuclear fusion; Heat transfer; Thermal stress

Applied Thermal Engineering

110

1578-1588

2017.01.05

https://doi.org/10.1016/j.applthermaleng.2016.09.062

Superhydrophilicity accompanying hemi-wicking driven by interfacial capillary force can be induced by constructing interfacial structures. We uncover the underlying mechanism for the morphologically driven hemi-wicking, and extend its impact into the practical heat transferring scheme of convective boiling system: the morphologically-driven hemi-wicking on a roughened interface can contribute greatly to the enhancement of boiling heat transfer performance of the convective heat dissipation capacity of critical heat flux (CHF). We present design prerequisites on controlling characteristic lengths of nanoscale interfacial structures that initiate hemi-wicking and consequently enhance boiling performance. Interfacial liquid refreshing through morphologically driven hemi-wicking leads to a greater than 100% increase in CHF by roughening surfaces using vertically aligned silicon nanowire structures (SiNWs). We confirm strong wicking characteristics are essential to increase CHF, however it must be differentiated from surface roughening. Even though the roughening is a prerequisite for leading to the wicking, it can even deteriorate CHF without involving advantage of the interfacial re-wetting. Dimensional prerequisites that initiate hemi-wicking by modulating the characteristic length of SiNWs can be design guidelines for pragmatic engineering applications to enhance feasibility and reliability. We use our findings to put forward a guideline to improve boiling performance, and suggest a way to make breakthrough in heat and energy transfer systems through the functionalized interface.

Hemi-wicking; Surface wetting; Surface roughness; Boiling heat transfer; Convective heat transfer

International Journal of Heat and Mass Transfer

102

1100-1107

2016.11.01

https://doi.org/10.1016/j.ijheatmasstransfer.2016.07.008

The enhancement of boiling heat transfer, the most powerful energy-transferring technology, will lead to milestones in the development of high-efficiency, next-generation energy systems. Perceiving nano-inspired interface functionalities from their rough morphologies, we demonstrate interface-induced liquid refreshing is essential to improve heat transfer by intrinsically avoiding Leidenfrost phenomenon. High liquid accessibility of hemi-wicking and catalytic nucleation, triggered by the morphological and hydrodynamic peculiarities of nano-inspired interfaces, contribute to the critical heat flux (CHF) and the heat transfer coefficient (HTC). Our experiments show CHF is a function of universal hydrodynamic characteristics involving interfacial liquid accessibility and HTC is improved with a higher probability of smaller nuclei with less superheat. Considering the interface-induced and bulk liquid accessibility at boiling, we discuss functionalizing the interactivity between an interface and a counteracting fluid seeking to create a novel interface, a so-called smart interface, for a breakthrough in boiling and its pragmatic application in energy systems.

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Scientific Reports

6

34348

2016.10.06

https://doi.org/10.1038/srep34348

The after-shell section, which is part of the gas turbine combustion liner, is exposed to the hottest combustion gas. Various cooling schemes have been applied to protect against severe thermal load. However, there is a significant discrepancy in the thermal expansion with large temperature differences, resulting in thermo-mechanical crack formation. In this study, to reduce combustion liner damage, thermo-mechanical analysis was conducted on three after-shell section configurations: inline-discrete divider wall, staggered divider wall, and swirler wall arrays. These array components are well-known heat-transfer enhancement structures in the duct. In the numerical analyses, the heat transfer characteristics, temperature and thermo-mechanical stress distribution were evaluated using finite volume method and finite element method commercial codes. As a result, we demonstrated that the temperature and the thermo-mechanical stress distribution were readily dependent on the structural array for cooling effectiveness and structural support in each modified cooling system. Compared with the reference model, the swirler wall array was most effective in diminishing the thermo-mechanical stress concentration, especially on the inner ring that is vulnerable to crack formation.

Thermal barrier coating; Average heat transfer coefficient; Impinge region; Heat transfer distribution; Divider wall

Heat and Mass Transfer

51(12)

1779-1790

2015.12.01

https://doi.org/10.1007/s00231-015-1532-4

Heat transfer based on radiative energy absorption and thermal dissipation is important in the design of energy conversion and transfer systems. We studied in the design of radiative energy absorber for efficient energy harvesting and transfer using a nanoscale interface modification technology. We presented that silver nanoclusters assisted silicon nanowires (SiNWs) forest could be feasible for radiative energy absorption in a broadband spectral region. A drastic increase of radiative energy absorption could be obtained in the near infrared wavelength region with accompanying quasi-perfect absorption (higher than 95%) of ultra-violet and visible range of the irradiation spectrum. All of surface manipulations were based on top-down metal-assisted chemical etching feasible under room-temperature conditions to synthesize SiNWs with silver nanoclusters. The spectral absorbance characteristics were elucidated for characteristic lengths of SiNWs, clustering of silver nanoparticles, orientation of the substrate, and single as well as double-sided silver nanoclusters orientations dominate in spectral absorbance characteristics. The results were also presented for guaranteeing efficient solar-thermal converting components with 92.4% solar absorption performance under AM1.5D condition. Surface modification and optimization will be helpful to improve the performances of solar energy conversion systems and various heat transfer systems.

Energy conversion; Heat transfer; Radiative absorbance; Surface modification; Silicon nanowires; Nanocluster

International Journal of Heat and Mass Transfer

82

267-272

2015.03.01

https://doi.org/10.1016/j.ijheatmasstransfer.2014.11.043

Convective boiling heat transfer is an efficient cooling mechanism to dissipate amount of thermal energy by accompanying the phase transition of the working fluids. Particularly, the amount of heat dissipation capacity can be readily extensible by increasing the degree of subcooling due to initial demands requiring for coolant saturation. Under severely subcooled condition of 60°, we investigate boiling heat transfer phenomena regarding spatial heat transfer uniformity and stability on a planar surface. Severe subcooling can induce locally concentrated thermal loads due to poor spatial uniformity of the heat transfer. For reliable cooling, a high degree of spatial uniformity of the heat transfer should be guaranteed with minimized spatial deviation of heat transfer characteristics. Under pre-requisite safeguards below CHF, we experimentally elucidate the principal factors affecting the spatial uniformity of the heat transfer for a flow/thermal boundary layer considering heat transfer domains from a single-phase regime to a fully-developed boiling regime. based on the local heat transfer evaluation, we demonstrate that full nucleation boiling over the entire heat transfer surface under subcooling conditions is favorable in terms of the uniformity of heat dissipation through the phase-change of the working fluid.

Heat transfer ;Heat transfer performance; Local heat transfer; Boiling heat transfer; Boiling regime

Heat and Mass Transfer

51(1)

1-9

2015.01.01

https://doi.org/10.1007/s00231-014-1379-0

International Journal of Heat and Fluid Flow

50(0)

378-385

2014.12.01

Applied Physics Letters

105(19)

191601

2014.11.10

Energy

76(0)

428-435

2014.11.01

Nano Letters

14(8)

4395-4399

2014.08.13

Journal of Materials Chemistry A

2(14)

5077-5086

2014.04.14

International Journal of Heat and Mass Transfer

70(0)

23-32

2014.03.01

641-650

641-650

641-650

2013.11.25

International Journal of Heat and Mass Transfer

62(1)

223-229

2013.07.01

http://dx.doi.org/10.1016/j.ijheatmasstransfer.2013.02.066

2012.12.17

Applied Physics Letters

101(25)

251909

2012.12.17

2012.09.03

Journal of Material Science & Engineering

1(4)

2012.09.03

2012.07.21

Lab on a Chip

12(14)

2568-2574

2012.07.21

2012.03.01

Microelectronic Engineering

91(0)

1-8

2012.03.01

2011.11.28

Journal of Materials Chemistry

21(44)

17967-17971

2011.11.28

2011.10.28

Journal of Materials Chemistry

21(40)

15935-15939

2011.10.28

2011.08.16

Langmuir

27(16)

10148-10156

2011.08.16

2011.07.23

Nanoscale Research Letters

6(1)

467

2011.07.23

2011.04.14

Nanoscale Research Letters

6(1)

333

2011.04.14

2011.01.15

International Journal of Heat and Mass Transfer

54(1-3)

118-125

2011.01.15

2010.09.01

Analyst

135(9)

2365-2371

2010.09.01

2010.06.01

Energy

35(6)

2400-2406

2010.06.01

2009.10.01

Heat and Mass Transfer

45(12)

1617-1625

2009.10.01

2008.11.28

Thin Solid Films

517(2)

933-936

2008.11.28

2008.08.01

Microfluidics and Nanofluidics

5(2)

255-262

2008.08.01