Spectral beam splitting technology offers a potential solution for limited solar conversion efficiency and local overheating of photovoltaic panels in centralized photovoltaic/thermal (CPV/T) system. In this work, an Ag@Al2O3 core-shell nanofluid-based spectral splitter is integrated into a thermally decoupled system equipped with a compound parabolic concentrator to address spectral mismatch and overheating in CPV/T. A numerical framework is constructed that couple finite-difference time-domain simulation for predicting the optical properties of nanoparticles, a radiative transfer model for the transmittance of nanofluids, and a three-dimensional conjugate heat transfer model coupled with photovoltaic electrical performance. With the spectral matching factor as the objective, a multi-parameter co-optimization is performed over the silver core diameter, shell thickness, particle mass fraction, and optical path length. The optimal nanofluid is selected, and its combined thermal and electrical performance is evaluated under 4 suns. Results indicate that the silver core diameter governs localized surface plasmon resonance, with absorption dominates below 40 nm, while scattering increases with rise of the diameter, accompanied by higher-order modes. The Al2O3 shell redshifts the resonance peak and provides chemical protection. Multi-parameter optimization yields an optimal design with 30 nm of silver core diameter, 5 nm shell thickness, 66 ppm mass fraction of nanofluid, and 19 mm optical path, yielding a spectral matching factor of 0.3916, achieving electrical efficiency of 12.82%, thermal efficiency of 67.76%, and total exergy efficiency of 17.76%. This work provides a systematic design framework for spectrally tunable, nanofluidbased CPV/T systems.

To address severe thermal accumulation and temperature non-uniformity of automotive lithium-ion batteries under high-rate charge–discharge cycles, this work proposes a high-performance hybrid battery thermal management system integrating dual-layer graded composite phase change materials with a wavy parallel liquid cooling plate. The composite PCM is prepared and characterized experimentally, and a three-dimensional coupled numerical model is established. The influence mechanism of key design parameters on system performance is clarified via single-factor analysis and response surface methodology, and multi-objective optimization is conducted using the Non-dominated Sorting Genetic Algorithm II. The validated numerical results indicate that the proposed system enables a reversible melting − solidification process and latent heat recovery of the graded composite PCM during the 5C discharge-1C charge cycle. The system reduces the maximum battery temperature by 11.1 °C and reduces the battery pack temperature difference and individual cell temperature difference by 2.82 °C and 22.06 °C, respectively, compared with the conventional liquid cooling system. The total thickness of the composite PCM and the outer-to-total gradient thickness ratio are the core regulatory parameters for the maximum battery temperature, while the coolant inlet velocity is the dominant factor governing the battery pack temperature difference and system energy consumption density. After multi-objective optimization, the maximum battery temperature, individual cell temperature difference, and energy consumption density of the system are reduced by 3.30%, 24.27%, and 51.45%, respectively, compared with the initial design, while the battery pack temperature difference is stably controlled below 2 °C, satisfying the thermal safety and temperature-uniformity constraints considered in this study.

The capillary structure within a heat pipe significantly influences the condensation heat transfer performance. In this study, an experimental setup was established under saturated atmospheric conditions to investigate the condensation behavior of water on vertically oriented sintered copper powder surfaces. The effects of subcooling, mesh count, and wick thickness on condensation mode, liquid coverage on the surface, and condensation heat transfer coefficient (HTC) were thoroughly investigated. Experimental results indicate that the surfaces of 100mesh copper powder wicks exhibit dropwise condensation, whereas those of 300-mesh wicks show filmwise condensation. On 200-mesh wick surfaces, both condensation modes are observed to coexist. As subcooling increases, the coverage ratio of liquid on the surface grows at different rates across the samples. For identical thickness and subcooling, larger mesh counts yield higher coverage ratios of liquid on the surface. Additionally, the sintered powder surfaces generally exhibit lower condensation HTC than smooth copper surfaces, with the degree of reduction varying under different subcooling conditions. Moreover, the variation in condensation HTC differs for different mesh counts as thickness changes. Droplet departure frequency also affects the condensation HTC differently for surfaces with different mesh counts. For surfaces with comparable mesh counts and thicknesses, sintered wire mesh and sintered copper powder wicks display varying HTCs under different subcooling conditions. Based on the experiments, a predictive correlation for the condensation HTC of vertically sintered copper powder porous structures is proposed, with an average MAE of 6.57 %. Compared to Nusselt's theory, the proposed correlation offers improved predictive accuracy for porous media condensation.

Concentrating photovoltaic (CPV) technology enhances energy flux density by focusing sunlight, offering potential for high-power generation coupled with heat recovery. However, it faces dual challenges in practical applications: significant increase in series resistance loss under high concentration and current mismatch caused by non-uniform radiation distribution. This study evaluates the performance and loss mechanisms of series-connected small-size sliced cells and innovatively proposes a non-equal-size cell series packaging scheme. The scheme aims to actively adapt to non-uniform radiation distribution through differentiated cell size design, thereby synergistically suppressing resistance loss and current mismatch. A high-precision three-dimensional optical-thermal-electrical multiphysics coupled simulation model is developed and validated with outdoor experiments. Results show that cutting conventional sized PV cells into equal-size units for series packaging can effectively reduce performance degradation from resistive loss, temperature rise, and non-uniform temperature distribution. However, this approach aggravates current mismatch loss due to radiance non-uniformity and lowers the fill ratio owing to increased inter-cell gaps. After non-equal-size optimization, current consistency among cells improves significantly, with the maximum current deviation in modules consisting of four and eight cells reduced to 0.03 A and 0.06 A, respectively. Maximum output power increases by 5.3% and 19.6% compared to the equal-size design. The study further clarifies the synergistic relationship among cell size, concentration ratio, and cable specification, providing guidance for optimal module selection. Under various cooling conditions, non-equal-size modules exhibit superior electrical and exergy efficiencies. A two-day outdoor experiment verifies the effectiveness of the proposed design: the average electrical and exergy efficiencies of a module with four equal-size cells increase by 51.2% and 33.3%, respectively, compared to a conventional full-size module, while thermal efficiency decreases by only 4.2%. After non-equal-size optimization, the average electrical and exergy efficiencies are further enhanced by 4.5% and 3.4%.

The Kubas interaction between H2 molecule and transition metal-modified storage materials has been considered an ideal adsorption mechanism and has been drawn great attention. In the study, the samples of hexagonal boron nitride decorated with Ti are successfully prepared by a wet chemical impregnation method, and its hydrogen adsorption ability is experimentally examined. The hydrogen adsorption enhancement mechanism, and the influence of Ti aggregation on hydrogen desorption ability are theoretically examined by combination of the Density Functional Theory and the Ab-initio Molecular Dynamics. The results show that Ti molecules have been relatively uniformly distributed on the h-BN surface with only minor aggregation observed. The decoration with Ti can significantly enhance the hydrogen storage capacity of h-BN from 0.10 wt% to 0.75 wt%. The adsorption of H2 on the h-BN surface occurs in two layers. The decoration with Ti not only introduces chemical and Kubastype adsorption in the first layer of adsorbed hydrogen molecules but also enhances the van der Waals forces throughout the entire system, thereby significantly improving the hydrogen adsorption capacity. The aggregation of Ti on the h-BN surface reduces the hydrogen adsorption capacity, however, it can enhance the reversible desorption capability and the kinetics of hydrogen desorption.

ObjectivesThermal energy storage technology can effectively mitigate the intermittency and volatility of renewable energy sources and holds great potential for enhancing the stability of energy systems. Solid particle packed beds, with their simple structure, low cost, and high thermal energy storage temperatures, offer broad prospects for development. To address the issue of optimal flow channel layout in solid particle packed beds, this study investigates flow channel configurations and thermal energy storage performance across a wide temperature range.MethodsUsing rock particles as the thermal storage medium, a computational fluid dynamics model of a solid particle packed bed is established. The performance of the packed bed is analyzed for different baffle configurations to determine the optimal flow channel layout. Based on this, the study systematically examines the effects of parameters such as the packed bed’s height-to-length ratio, inlet air flow rate, temperature, particle diameter, and porosity on the overall performance of the thermal energy storage system.ResultsThe double-baffle configuration with a parallel staggered layout effectively enhances thermal energy storage performance and improves the temperature distribution within the packed bed. The system’s overall performance is optimized when the height-to-length ratio of the packed bed is 0.557. Both the system’s thermal energy storage rate and pump power consumption increase with rising inlet air flow rate and temperature, while thermal energy storage efficiency and exergy efficiency decrease as the inlet air temperature rises but increase as the inlet air flow rate increases.ConclusionsInlet air flow rate, particle diameter, and porosity have the most significant regulatory effects on the overall thermal performance of the system. The research findings provide a basis for structural optimization of solid particle packed bed systems, matching of operating conditions, and multi-parameter co-optimization.

The power generation efficiency of concentrated photovoltaic (CPV) system is currently very low, which has severely limited its development and application. This study aims to enhance the power generation efficiency of CPV systems by series encapsulating of cut small size PV cells to effectively reduce resistance losses caused by current. An experimental test platform is established, and the Monte Carlo ray tracing method is used to assess the system performance under concentrated conditions. The effects of the distance between the lens and the PV cell, and the uniformity of the radiation distribution on the power generation performance of the PV modules are deeply examined experimentally. The results show that series encapsulation of PV cells cut into small sizes can effectively reduce resistance losses within the module, and power generation efficiency enhancement is more evident under concentrated than non-concentrated conditions. However, cutting photovoltaic cells into small sizes can cause edge damage, and too small cell size can also decrease power generation efficiency due to reduced cell fill ratio and reduced uniformity of cell-to-cell radiation flux. The module consisting of four small size cells exhibits the highest power generation efficiency at a Lens-to-PV module distance of 440 mm, with the average power generation efficiency of 16.4 % higher than that of the conventional size module. When cable losses are considered, the power generation efficiency gain will reach to 55.7 %.

Packed bed thermal energy storage technology offers a solution for mitigating the intermittency of renewable energy and enhancing the flexibility and stability of power systems. This paper constructs a model of a packed bed thermal storage tank using air as the heat transfer fluid and a mixture of 55% NaNO3 and 45% KNO3 molten salt as the phase change material. The dynamic and static characteristics of the thermal storage system are analyzed using numerical simulation methods, with a focus on the influence of parameters such as the inlet pore Reynolds number, Stefan number, packing porosity, and particle size on thermal storage performance. Building upon this, Response Surface Methodology (RSM) and the NSGA-II algorithm are employed to conduct single-objective and multi-objective matching optimization studies for the flow and structural parameters, respectively. The results show that, compared to the system without single-objective parameter matching optimization, the thermal storage capacity, thermal storage rate, energy utilization efficiency, and exergy storage efficiency are improved by 40.79%, 153.72%, 3.32%, and 9.23%, respectively, while the pump power consumption is reduced by 76.01%. The LINMAP and TOPSIS decision-making methods are used separately to search for the optimal solutions on the Pareto front. Taking the LINMAP decision as an example, the optimal comprehensive thermodynamic performance of the packed bed is achieved when the inlet pore Reynolds number, Stefan number, particle size, and porosity are 849.82, 0.898, 10.65 mm, and 0.60, respectively. Under these conditions, the pump power consumption is 47.98 kJ, with a deviation of only 1.052%. Under the optimal configuration, the perturbation effect of the initial temperature on the optimal solution is investigated. When the initial temperature increases to 330.15 K, the energy utilization efficiency decreases by 0.5%, while the exergy storage efficiency increases by 1.54%.

This study investigates the thermal performance of phase change material (PCM)-based heat sinks for portable electronic devices using ANSYS FLUENT. A novel multilayered PCM heat sink with pin fins is proposed, incorporating low melting point alloys (LMPA), paraffin, and both. The research compares single-layered and multilayered configurations, evaluating their performance under varying pin-fin volume fractions, heat sink orientations, PCM fill ratios, and heat flux values. The findings highlight significant thermal improvements, with multilayered PCM achieving an enhancement ratio of up to 1.12 compared to single-layered modules (1.03, 1.027, and 0.96). Increasing pin-fin volume fractions over fin thickness notably boosts performance, while a PCM fill ratio of 100 % at a high heat flux of 5000 W/m2 extends melting time by 2.97 times compared to 25 %. Inclination angles of 30 degrees deliver the lowest average temperatures and longest melting durations. Additionally, a 4 % fin volume fraction results in lower base temperatures than 16 % and 9 % at equivalent fin thickness. This research demonstrates the potential of multilayered PCM heat sinks with pin fins for enhancing thermal regulation in electronics, making them a promising solution for efficient heat dissipation under high-performance demands.

To enhance the operational flexibility of conventional coal-fired units, a novel power generation system that deeply couples adiabatic compressed air energy storage (AA-CAES) with a 600 MW coal-fired unit is proposed, achieving system efficiency improvement through cascade energy utilization. A bidirectional coupling mechanism of “condensate cooling + extraction steam heating” is established: during the energy storage phase, unit condensate is utilized to cool the compressed air; during the energy release phase, extraction steam from the fifth low-pressure heater of the steam turbine is employed to heat the stored compressed air, and energy recovery is realized by matching the heat-exchanged return water with the regenerative system. An analysis model for a new coal-fired power generation system based on compressed air energy storage is constructed based on Ebsilon software, focusing on the effects of storage tank pressure, inlet flow rate, and other parameters on heat rate, cycle efficiency, and exergy loss. The research results indicate that with the integration of the compressed air energy storage system and the coal-fired unit, as the storage tank pressure increases, the heat rate of the coupled system gradually rises, while the system cycle efficiency and energy utilization coefficient initially increase and then decrease, reaching optimal performance at a storage tank pressure of 10 MPa with a cycle efficiency of 50.66% and an energy utilization coefficient of 47.86%. As the inlet air flow rate of the compressor increases, the energy utilization coefficient and heat rate decrease, whereas the system cycle efficiency increases. Analysis is the most direct method to reflect system losses. Under rated conditions, the exergy efficiency is 77.39%, with the maximum exergy loss occurring at the throttle valve, accounting for 5.69%. When the load decreases, the system heat rate increases by 11%, the cycle efficiency decreases by 3.2%, and the energy utilization coefficient drops by 6%. The thermal and cold storage devices of the compressed air system are optimized, achieving dual benefits of enhanced unit peak-shaving capability and reduced investment costs. A new technical pathway is provided for the flexibility retrofitting of traditional coal-fired power, effectively lowering the investment cost of the coupled system and improving the economic performance of coal-fired units.

Phase change material heat sink can be used to effectively cool electronic device, and internal pin-fins can be utilized to improve heat transfer process. However, the latent heat storage capacity of phase change material will also be lowered due to inclusion of fins. In order to attain an ideal trade-off between two main objectives: maximizing the melting time and minimizing the base temperature of heat sink, a parametric study is conducted utilizing seven pin-fin geometries, which are analyzed numerically, followed by a multi-objective optimization of the grooved circular pin-fin heat sink aiming to maximize the phase change material melting time and minimize the base temperature of heat sink. To develop an optimal structure of pin-finned phase change material heat sink, the optimization design factors include fin diameter, orientation, thickness, and height in addition to the heater base thickness simultaneously with the thermophysical properties of the phase change material. The NSGA-II methodology, integrated with the Kriging interpolative model, is used as the optimization method in combination with ANSYS-FLUENT to decide the optimal parameters of the heat sink design. The results reveal that grooved pin fin is the best selection for phase change material heat sink in seven examined structures. The optimal grooved circular pin-finned phase change material heat sink with melting temperature of 44.28 degrees C, fin height of 16.67 mm and a fin rotation angle of 53.23 degrees, attaining 1.3 longer melting time and a lower base temperature than the referenced model. Findings highlight that the thermal conductivity of phase change material and the thickness of pin-fins serve as key determinants in improving thermal performance. By combining geometric and material properties, this study introduces a novel strategy for enhancing phase change materialbased heat sinks thermal management.

Coal-fired power units will play a crucial role in the integration of renewable energy sources and in the peak shaving of power grids in China. This can be realized through the coupling of thermal energy storage systems with coal-fired power units. In this study, an electric heater linked to four molten salt thermal energy storage systems are coupled to a coal-fired power unit. To evaluate the entire system performance, numerical simulation was performed using the EBSILON software, which uses realistic thermodynamic models for every system component. The simulation models were first verified based on different typical operating conditions of the coalfired power unit. Subsequently, a theoretical design of the coal-fired power unit coupled to the molten salt thermal storage system with an electric heater was developed for parametric evaluation. Various operating characteristics of the system are analyzed and evaluated by examining and comparing the overall thermal efficiency, overall exergy efficiency, local exergy loss, equivalent round-trip efficiency, and comprehensive coal consumption rate. The results show that the molten salt thermal energy storage system with an electric heater can flexibly adjust the load of the coal-fired power unit according to electricity demand, even achieving zero electricity output within a short time. The thermal release of the molten salt thermal energy storage system can increase the power output by a maximum of 27.5 %, and the thermal release duration of the system gradually shortens to a minimum of 1.43 h with increased thermal release power to maximum value. In addition, the coupled system overall thermal and exergy efficiency can achieve maximum values of 39.7 % and 38.4 %, respectively. The maximum equivalent round-trip efficiency of the system for the entire energy storage and release process is 50.2 %, with a minimum comprehensive coal consumption rate of 334.7 g/kWh.

Phase change materials (PCMs) have significant potential for utilization due to their high energy storage density and excellent safety in energy storage. In this research, a flexible heat storage device using the stable supercooling of sodium acetate trihydrate composite is developed, enabling on-demand heat release through controlled solidification initiation. The solidification and heat release characteristics are investigated in experiments. The results indicate that the heat release characteristics of this heat storage device are closely linked to the crystallization process of the PCM. During the experiment, based on whether external intervention was needed for the solidification process, the PCM manifested two separate solidification modes—specifically, spontaneous self-solidification and triggered-solidification. Meanwhile, the heat release rates, temperature changes, and crystal morphologies were observed in the two solidification modes. Compared with spontaneous self-solidification, triggered-solidification achieved a higher peak surface temperature (53.6 °C vs. 46.2 °C) and reached 45 °C significantly faster (5 min vs. 15 min). Spontaneous self-solidification exhibited slower, uncontrollable heat release with dendritic crystals, while triggered-solidification provided rapid, controllable heat release with dense filamentous crystals. This controllable switching between modes offers key practical advantages, allowing the device to provide either rapid, high-power heat discharge or slower, sustained release as required by the application. According to the crystal solidification theory, the different supercooling degrees are the main reasons for the two solidification modes exhibiting different solidification characteristics. During solidification, the growth rate of SAT crystals exhibits substantial disparities across diverse experiments. In this research, the maximum axial growth rate is 2564 μm/s, and the maximum radial growth rate is 167 μm/s.

Growing need for high-performance electronic devices has necessitate effective heat management solutions. This study conducts a three-dimensional numerical analysis of phase change material (PCM)-based heat sinks, examining single, double, and triple-layered structures with and without internal fins. The heat sinks are subjected to heat fluxes of 30,000 W/m2 and 100,000 W/m2 applied from both the bottom and side directions. The analysis evaluates the thermal performance of low-melting-point alloy (LMPA) PCM and paraffin-based PCM with comparable melting temperatures, while maintaining a constant PCM volume fraction (100 %) and under a set point temperature (SPT) of 100 degrees C. A cascading approach in the triple-layered module, where PCM layers are arranged in decreasing melting temperatures along the heat flux direction, is introduced. The results show that the cascaded PCM configuration in three layers are more effective to slow down the base temperature increase of the heat sink than the single and double ones. The presence of fins with triple layered LMPA PCM module shows a superior base temperature reduction, the complete melting time reach to about 1113 s under the temperature of 95.26 degrees C, remaining well below the SPT of 100 degrees C. This demonstrates the capability of LMPAs to sustain lower temperatures for extended periods, outperforming paraffin in terms of thermal shock resistance and faster melting under high heat flux. This work advances the design of PCM-based heat sinks by integrating cascaded configurations, metal PCM, and high-conductivity fins, offering an innovative holistic analysis of their combined effects on performance and providing a viable solution for cooling high-power electronic devices.

Metal hydrides used as hydrogen storage materials have the advantages of high storage density, low pressure and safety, and have been widely concerned. The application of phase change materials (PCMs) in thermal management of metal hydride reactors can effectively improve energy utilization and hydrogen absorption efficiency by absorbing and storing the heat generated during hydrogen absorption, and release to the reactor during hydrogen desorption process. A three-dimensional metal hydride reactor model based on thermal management of PCM is constructed in this study, and different fins are used for heat transfer enhancement. The hydrogen absorption and desorption performance of the reactor are numerically examined and compared for different models. The effects of thermophysical properties of PCM and inlet hydrogen pressure on the system performance are deeply analyzed. The results show that natural convection can shorten the time required for the reactor to reach 90% hydrogen absorption by 41.8%, but has almost no effect on the hydrogen desorption process. The effect of fins in PCM on hydrogen desorption is apparently larger than hydrogen absorption process, and longitudinal fin arrangement is obviously better than that of annular fin due to the natural convection effect in melted PCM. The metal hydride reactor with longitudinal fins can increase hydrogen absorption rate by 60.91%, and the hydrogen desorption rate by 72.07%. The ability of longitudinal fins to enhance hydrogen absorption performance is better than that of PCM after improving its thermal conductivity to 4 W/(m & sdot;K). The effect of thermal conductivity improvement of PCM on hydrogen desorption is more obvious than absorption process. The heat transfer performance and reaction rate of the reactor can be effectively improved by increasing the inlet hydrogen pressure and decreasing of outlet pressure.

Physical adsorption is one of the most promising methods for hydrogen storage currently under development. Enhancing the hydrogen storage capacity of physical adsorption materials through alkali metal modification is widely regarded as one of the most effective methods. In this study, one or two sodium (Na) metal atoms are decorated on the C2N unit cell, and first-principles in density functional theory (DFT) is used to evaluate the hydrogen storage capacity and thermal performance of the materials. The results indicate that the hydrogen storage capacity of the materials increases progressively with the number of Na atom decorations, which is attributed to varying degrees of hydrogen (H2) polarization under different conditions. The density of states (DOS) of the electrons near the conduction band decrease, while the electronic thermal conductivity gradually decreases as the number of Na metal decorations rises. Additionally, the decoration of Na atoms induces scattering and localization effects on phonons, resulting in a reduction of both phonon relaxation time and group velocity. As a result, the thermal conductivity of the materials decreases significantly. This reduction adversely affects the kinetic properties of the material during the H2 adsorption and desorption processes, thereby complicating the thermal management design of hydrogen storage vessels.

Noncovalent interaction-induced deformation is one of the most promising methods for tuning thermal conductivity because it does not alter the atomic structure and thus causes reversible changes in properties. Taking carbon nanotube (CNT) as a model, we found that by applying periodic van der Waals (vdW) forces based on C60 encapsulation, the thermal conductivity can be reduced by 58.64% compared with that without vdW force and by 34.09% compared with that with uniform vdW interactions (150 K). Physical insights are gained from both coherent and incoherent phonon transport. Due to the periodic distribution of Mises stress and Gaussian curvature in CNT with periodic vdW forces, the coherent interfaces between CNT parts with positive and zero Gaussian curvatures are formed, which help satisfy the Bragg condition. The phonon group velocities are found to decrease due to the reduced elastic modulus, Bragg scattering, and phonon localization. Additionally, the coherent interfaces induce phonon interface scattering and thus result in a further reduction in phonon relaxation time. With the magnitude of vdW interaction increasing, the thermal conductivity of CNT experiences a decrease followed by an increase. It is attributed to the dominant role of the coherent phonon transport. The periodically noncovalent interaction provides the possibility to control thermal conductivity without changing the pristine structure.

In order to achieve full-spectrum solar energy utilization, a spectral beam splitting photovoltaic/photothermal system based on secondary reflection is proposed and simulated through Monte Carlo ray tracing method (MCRT). The designed system concentrates solar radiation to a solar cell covered with a spectral beam splitter film through primary trough collector. After spectral beam splitting, the transmitted solar rays in wavelength of 380 nm-1100 nm are used for photovoltaic power generation, and with rest of light for photothermal recovery. The results show that the designed spectral beam splitter can achieve 93.77 % of transmittance in 380 nm-1100 nm wavelength for photovoltaic power generation and 93.14 % of reflectance for other wavelengths for photothermal recovery. The system can achieve 73.9 % of optical efficiency under the tracking error of 0.75 degrees. The PV photoelectric conversion efficiency of the spectral beam splitting solar cell is 7.3 % higher than the normal solar cell. The highest system thermal efficiencies and evacuated solar collector tube thermal efficiency is 49.8 % and 72.7 %, respectively, and the system electrical efficiency can reach to 15.05 % on a typical day in August of Beijing. The system can output 92.7 W/m2 electricity and 354.0 W/m2 thermal energy, simultaneously.

This study investigates the multi-objective optimization of cascaded phase change material (PCM)-based heat sinks integrated with rectangular fins for effective thermal management in high heat flux scenarios. Initially, a parametric analysis is carried out to determine the most effective cascading PCM arrangement, comparing configurations with single, double, and triple cascaded PCM layers at melting temperatures of 70 degrees C, 58 degrees C, and 44 degrees C. The Non-dominated Sorting Genetic Algorithm (NSGA-II) approach, in conjunction with the Kriging interpolative model, is employed as the optimization technique to adjust the design parameters of the heat sink. In combination with ANSYS-FLUENT, this approach optimizes five crucial design parameters: fin length, heat sink rotation angle, and the thicknesses of three PCM layers. The objective is to elevate the average Nusselt number for better heat transmission and thermal control with also reducing melting time. The triple-cascaded PCM design (HS6) is recognized as the most optimal configuration, decreasing the melting time to 3022 s and attaining an average Nusselt number of 10.9 at a high heat flux of 30,000 W/m2. The findings indicate that the optimized design attains homogeneous heat transmission, effective heat absorption, and substantial thermal regulation due to improved natural convection and stratified PCM melting. This work highlights the significance of PCM layer arrangement, fin design, and multi-objective optimization in attaining enhanced thermal performance for heat-intensive applications. By bridging important gaps between multi-objective optimization and parametric analysis in PCM-based thermal management, this study provides a solid technique for optimizing thermal solutions in high-performance applications.

Thermal conductivity modulations of amorphous silica through nanopore engineering are essential for performance improvement of many devices in practical applications. The physical insights behind the heat transport in nanoporous silica are still far from clear due to the disordered atomic arrangement and ultrafine structural features of the material. In this study, the effect of nanopores on the thermal conductivity of amorphous matrix was investigated based on the lattice dynamics for revealing the vibrational energy transfer mechanism and molecular dynamics for directly modeling the complex nanostructures. The thermal transport mechanism within the nanoporous amorphous silica was revealed from the perspective of atomic vibrational properties. Iterative optimization strategies for thermal performance were further elucidated by engineering the pore micromorphology. The results show that the phonon-like propagons in amorphous silica predominantly occupy the range below 0.82 THz and gradually transition to diffusons with increasing frequency. These heat carriers with different properties can also be clearly characterized in the nanoporous structure. The heat conduction in the nanoporous structure is inefficient due to the stronger localization of vibrational modes. Meanwhile, propagons and diffusons experience significant scattering effects as pore size increases, resulting in the suppression of thermal transport. The thermal conductivity of the material exhibits a negative correlation with porosity and a positive correlation with pore size. Heat conduction in nanoporous silica can also be modulated by pore topology, including the distribution, shape and orientation of channels.