Search Results (590)

A two-phase closed thermosyphon (TPCT), a gravity-assisted heat pipe, is a highly efficient heat transmitter involving liquid–vapor phase change. It is used in many applications, including heat spreading, thermal management and control, and energy saving. The main objective of this study is to investigate the effects of the operating conditions for a thermosyphon used in solar water heaters. The study particularly focuses on the influence of the inclination angle. Thus, a comprehensive simulation model is developed using the volume of fluid (VOF) approach. Complex and related phenomena, including two-phase flow, phase change, and heat exchange, are taken into account. To implement the model, an open-source CFD toolbox based on finite volume formulation, OpenFOAM, is used. The model is then validated by comparing numerical results to the experimental data from the literature. The obtained results show that the simulation model is reliable for investigating the effects of various operating conditions on the transient and steady-state behavior of the thermosyphon. In fact, bubble creation, growth, and advection can be tracked correctly in the liquid pool at the evaporator. The effects of the designed operating conditions on the heat transfer parameters are also discussed. In particular, the optimal tilt angle is shown to be 60° for the intermediate saturation temperature (<50 °C) and 90° for the larger saturation temperature (>60 °C). Full article

Transpiration cooling that utilizes the phase change of a liquid coolant is recognized as an effective thermal protection technique for extreme environments. However, the introduction of phase change within the porous structure brings about challenges, such as vapor blockage, pressure fluctuations, and temperature inversion, which critically influence system reliability. This study conducts numerical analyses of coupled processes of heat transfer, flow, and phase change in transpiration cooling using a Two-Phase Mixture Model. The simulation incorporates a Local Thermal Non-Equilibrium approach to capture the distinct temperature fields of the solid and fluid phases, enabling accurate prediction of the thermal response within two-phase and single-phase regions. The results reveal that under low heat flux, dominant capillary action suppresses dry-out and expands the two-phase region. Conversely, high heat flux causes vaporization to overwhelm the capillary supply, forming a superheated vapor layer and constricting the two-phase zone. The analysis also explains a paradoxical pressure drop, where an initial increase in flow rate reduces pressure loss by suppressing the high-viscosity vapor phase. Furthermore, a local temperature inversion, where the fluid becomes hotter than the solid matrix, is identified and attributed to vapor counterflow and its subsequent condensation. Full article

To address the reliability requirements for refrigerated container transport in the cold chain, this study established an experimental platform for phase change cold storage balls. A two-dimensional axisymmetric simplified heat transfer model of the three-dimensional cold storage ball was developed. The reliability of the model was verified through charging experiments. While ensuring a certain level of accuracy (average error less than 10%), the model significantly improved computational efficiency (completing calculations in only 49 s), offering a practical reference value. Based on the established 2D axisymmetric simplified heat transfer model, this study focused on the influence of secondary coolant (ethylene glycol solution) parameters on the charging performance. The results indicate that a smaller diameter of the cold storage ball and a higher flow rate lead to a higher freezing rate of the ball. Under the conditions set in this study, the optimal diameters were determined to be 80 mm and 60 mm, and the optimal inlet flow rate was 3.917 m³/h. This simplified model can provide a reference for the optimal design of phase change cold storage systems in refrigerated containers. Full article

The innovation in thermal storage systems for solar thermal power generation is crucial for achieving efficient utilization of new energy sources. Molten salt has been extensively studied as a phase change material (PCM) for latent heat thermal energy storage systems. In this study, a two-dimensional model of a vertical shell-and-tube heat exchanger is developed, utilizing water-steam as the heat transfer fluid (HTF) and phase change material for heat transfer analysis. Through numerical simulations, we explore the interplay between PCM solidification and HTF boiling. The transient results show that tube length affects water boiling duration and PCM solidification thickness. Higher heat transfer fluid flow rates lower solidified PCM temperatures, while lower heat transfer fluid inlet temperatures delay boiling and shorten durations, forming thicker PCM solidification layers. Adding fins to the tube wall boosts heat transfer efficiency by increasing contact area with the phase change material. This extension of boiling time facilitates greater PCM solidification, although it may not always optimize the alignment of bundles within the thermal energy storage system. Full article

Based on admirable porous media performance and the popularity of additive manufacturing technology, gradient porous media are progressively being applied in increasing fields. In this study, convection heat transfer within a square vented cavity, partially occupied by two copper metal foam layers of $10$ and $20$ PPI saturated with nanofluid, was assessed numerically. The left wall was heated uniformly and non-uniformly by applying multi-frequency spatial heating following a sinusoidal function. Governing equations, including continuity, the Darcy–Brinkmann–Forchheimer model, and local thermal non-equilibrium energy equations, were adopted and solved by employing the finite volume method. The influences of relevant parameters, including nanoparticle concentrations $\left(0\%\le \phi \le 10\%\right)$, Reynolds number ($1\le Re\le 100$), inlet and outlet port aspect ratios $\left(0.1\le D/H\le 0.4\right)$, three outlet vent opening locations ($\left(S_o=0\right)$ left, ($S_o=\left(H/2-D/2\right)$) middle, and ($S_o=\left(H-D\right)$) right), sinusoidal offset temperature (${\theta }_o=0.5$, $1$), frequency ($f=1, 3, 5$), and amplitude ($A=0-1$), were examined. The results demonstrate that flow and heat transfer fields are impacted mainly by these parameters. Streamlines are more intensified at the upper-left corner when the outlet opening vent is shifted towards the right-corner upper wall. Fluid- and solid-phase Nusselt number increases $Re$, $D/H$, ${\theta }_o$, $A$, and $f$ are raised, specifically when $A\ge 0.3$. The Nusselt number remains constant when the frequency is raised from $3$ to $5$, definitely when $D/H\ge 0.25$. In uniform and non-uniform heating cases, the Nusselt number of both phases remains constant as the outlet port is shifted right for $Re\le 10$ and slightly for higher $Re$ as the outlet vent location is translated from left to right. Full article

The spray evaporation process in the boiler desuperheater involves complex droplet behaviors and fluid–thermal coupling, and its temperature distribution characteristics greatly affect the performance and safety of industrial processes. To better understand the process characteristics and develop the optimal desuperheater design, computational fluid dynamics (CFDs) was applied to numerically investigate the flow and thermal characteristics. The Eulerian–Lagrangian approach was used to describe the two-phase flow characteristics. Both primary and secondary droplet breakup, the coupling effect of gas–liquid and stochastic collision and coalescence of droplets were considered in the model. The plain-orifice atomizer model was applied to simulate the atomization process. The numerical model was validated with the plant data. The spray tube structure was found to greatly affect the flow pattern, resulting in the uneven velocity distribution, significant temperature difference, and local reverse flow downstream of the orifices. The velocity and temperature distributions tend to be more uniform due to the complete evaporation and turbulent mixing. Smaller orifices are beneficial for generating smaller-sized droplets, thereby promoting the mass and heat transfer between the steam and droplets. Under the same operating conditions, the desuperheating range of cases with 21, 15, and 9 orifices is 33.7 K, 32.0 K, and 29.8 K, respectively, indicating that the desuperheater with more orifices (i.e., with smaller orifices) shows better desuperheating ability. Additionally, a venturi-type desuperheater was numerically studied and compared with the straight liner case. By contrast, discernible differences in velocity and temperature distribution characteristics can be observed in the venturi case. The desuperheating range of the venturi and straight liner cases is 38.1 K and 35.4 K, respectively. The velocity acceleration through the venturi throat facilitates the droplet breakup and improves mixing, thereby achieving better desuperheating ability and temperature uniformity. Based on the investigation of the spray evaporation process, the complex droplet behaviors and fluid–thermal coupling characteristics in an industrial boiler desuperheater under high temperature and high pressure can be better understood, and effective guidance for the process and design optimizations can be provided. Full article

Water, acetone, and TiO₂/nano-silver water (NSW) nanofluids were investigated as working fluids in loop thermosyphon battery thermal management systems (LTBMS) under simulated electric vehicle (EV) conditions to evaluate scalability and robustness across inclinations (0° to 60°) and ambient temperatures (−10 °C to 20 °C). Experimental conditions were established with 60 °C as the reference temperature, corresponding to the onset of battery thermal runaway, to ensure relevance to critical thermal management scenarios. Results indicate that LTBMS A maintained battery cell temperatures at 50.4 °C with water and 31.6 °C with acetone under a 50 W heat load. In contrast, LTBMS B achieved cell temperatures of 41.8 °C with water and 42.8 °C with 0.01 vol% TiO₂ nanofluid, however, performance deteriorated at higher nanofluid concentrations due to increased viscosity and related thermophysical constraints. In heating mode, LTBMS A elevated cell temperatures by 16 °C at an ambient temperature of −10 °C using acetone, while LTBMS B attained 52–55 °C at a 100 W heat load with nanofluids. The lightweight LTBMS design demonstrated superior thermal performance compared to conventional air-cooling systems and performance comparable to liquid-cooling systems. Pure water proved to be the most effective working fluid, while nanofluids require further optimization to enhance their practical applicability in EV thermal management. Full article

The Polish Free-Electron Laser (PolFEL), which is currently under construction in the National Centre for Nuclear Research in Świerk near Warsaw, will comprise an electron gun and from four to six cryomodules, each accommodating two nine-cell TESLA RF superconducting resonant cavities. To cool the superconducting resonant cavities, the cryomodules will be supplied with superfluid helium at a temperature of 2 K. Other requirements regarding the cooling power of PolFEL result from the need to cool the power couplers for the accelerating cryomodules (5 K) and thermal shields, which limit the heat inleaks due to radiation (40–80 K). The machine will utilize several thermodynamic states of helium, including two-phase superfluid helium, supercritical helium, and low-pressure helium vapours. Supercritical helium will be supplied from a cryoplant by a cryogenic distribution system (CDS)—transfer line and valve boxes—where it will be thermodynamically transformed into a superfluid state. This article presents the architecture of the CDS, discusses several design solutions that could have been decided on with the use of second law analysis, and presents the design methodology of the chosen CDS elements. Full article

The miniaturization of heat exchangers requires advanced manufacturing methods, as conventional techniques such as milling or casting are insufficient for producing complex microscale geometries. This study investigates the feasibility of using selective laser melting (SLM) with 316L stainless steel powder to fabricate compact heat exchangers with minichannels. The exchanger was designed using Autodesk Inventor 2023.3 software and produced under optimized process parameters. Measurements using a hydrostatic balance demonstrated that the applied process parameters resulted in a relative material density of 99.5%. The average microhardness in the core region of the SLM-fabricated samples was 255 HV, and the chemical composition of the final material differed only slightly from that of the feedstock material (stainless steel powder). Dimensional accuracy, surface quality, and internal structure integrity were assessed using computed tomography, optical microscopy, and contact profilometry. The fabricated component demonstrated high geometric fidelity and channel permeability, with local surface deformations associated with the absence of support structures. The average surface roughness (Ra) of the minichannels was 11.11 ± 1.63 µm. The results confirm that SLM technology enables the production of functionally viable heat exchangers with complex geometries. However, limitations remain regarding dimensional accuracy, powder removal, and surface roughness. These findings highlight the potential of metal additive manufacturing for heat transfer applications while emphasizing the need for further research on performance testing under real operating conditions, especially involving two-phase flow. Full article

Computational fluid dynamics became an essential tool for analyzing complex fluid behavior, with applications ranging from aerospace engineering to renewable energy systems. Recent advancements in artificial intelligence further enhanced computational fluid dynamics capabilities, improving computational efficiency and predictive accuracy. However, despite its widespread adoption, the integration of artificial intelligence in computational fluid dynamics for thermal energy storage remained an underexplored research area. This study presented a bibliometric analysis of the existing literature on artificial intelligence applications in computational fluid dynamics, with a specific focus on thermal energy storage systems. By comparing two research domains—artificial intelligence in computational fluid dynamics and artificial intelligence in computational fluid dynamics applied to thermal energy storage—this paper identified a significant gap in the latter, as reflected in the low number of publications, limited collaboration networks, and weak citation relationships. While artificial intelligence-driven computational fluid dynamics research expanded across multiple disciplines, its application in thermal energy storage is still in its early stages, highlighting the need for further investigations. The results indicated a growing interest in artificial intelligence-enhanced computational fluid dynamics models for thermal energy storage optimization, particularly in areas such as heat transfer, phase change materials, and system efficiency improvements. The results also included an analysis of leading contributors to this field, along with emerging countries’ contributions. A study of the key publication sources with a high impact in this domain was also included. Full article

Recently, studies on accelerator-based boron neutron capture therapy (AB-BNCT) systems for cancer treatment have attracted the attention of researchers around the world. A neutron source can be obtained through the impingement of high-intensity proton beams emitted from the accelerator onto the target. This process would deposit a large amount of heat within this target. A thermal management system design is needed for AB-BNCT systems to prevent the degradation of the target due to thermal/mechanical loading. However, there are few studies that investigate this topic. In this paper, a cooling channel with a boiling heat transfer mechanism is numerically designed for thermal management in order to remove heat deposited in the Be target of the AB-BNCT system of Heron Neutron Medical Corp. A three-dimensional (3D) CFD methodology with a two-fluid model and an RPI wall boiling model is developed to investigate its availability. Two subcooled boiling experiments from previous works are adopted to validate the present CFD boiling model. This validated model can be confidently applied to assist in thermal management design for the AB-BNCT system. Based on the simulation results under the typical operating conditions of the AB-BNCT system set by Heron Neutron Medical Corp., the present coolant channel employing the boiling heat transfer mechanism can efficiently remove the heat deposited in the Be target, as well as maintain its integrity during long-term operation. In addition, compared with the channel with the single-phase convection traditionally designed for an AB-BNCT system, the boiling heat transfer mechanism can result in a lower peak temperature in the Be target and its corresponding deformation. Full article

To enhance the steam parameters of steam injection boilers during the thermal recovery of heavy oil while ensuring the safe and stable operation of boiler pipelines, this study conducted two-phase flow boiling numerical simulations in a horizontal heated tube with an inner diameter of 65 mm, using water and water vapor as working fluids. The analysis focused on the gas–liquid phase distribution, temperature profiles, near-wall fluid velocity, and pressure drop along both the axial and radial directions of the tube. Furthermore, the effects of heat flux density, mass flow rate, and inlet subcooling on these parameters were systematically investigated. The results reveal that higher heat fluxes intensify the velocity difference between the upper and lower tube walls and enlarge the temperature gradient across the wall surface. A reduction in mass flow rate increases the gas phase fraction within the tube and causes the occurrence of identical flow patterns at earlier axial positions. Additionally, the onset of nucleate boiling shifts upstream, accompanied by an increase and upstream movement of the wall’s maximum temperature. An increase in inlet subcooling prolongs the time required for the working fluid mixture to reach saturation, thereby decreasing the gas phase fraction and delaying the appearance of the same flow patterns. Finally, preventive and control strategies for ensuring the safe operation of steam injection boiler pipelines during heavy oil recovery are proposed from the perspective of flow pattern regulation. Full article

The following study investigated the melting behavior of coconut oil as a phase-change material in shell-and-tube and shell-and-coil thermal energy storage systems. The primary objective was to deepen the understanding of PCM melting dynamics under varying boundary conditions, aiming to optimize TES designs for renewable energy applications. This research addresses a gap in understanding how different heat-transfer configurations and boundary conditions affect melting efficiency. Experimental setups included two distinct heat-transfer surfaces in a cylindrical shell—a copper tube and a copper coil—tested under constant wall temperatures (34 °C for the tube, 33 °C for the coil) and constant heat flux (597 W/m² for the coil). Findings reveal that melting under constant heat flux takes approximately twice as long as under constant wall temperatures, underscoring the critical role of heat-transfer conditions in TES performance. The liquid fraction was estimated using two approaches: image-based analysis and the volume-averaged temperature method. The former proved less reliable due to geometric limitations, particularly when the heat-transfer surface was distant from the shell wall. Conversely, the latter yielded higher accuracy, especially in the shell-and-tube setup. Due to the scarcity of correlations for constant heat-flux conditions, the novel contribution of this work is the development of a modified semi-empirical correlation for the shell-and-coil TES system. For this purpose, an existing model, which demonstrated strong alignment with experimental data, was adapted. The findings suggest that slower melting under constant heat flux could benefit applications needing sustained heat release, like solar energy systems. Future work could investigate additional PCMs or novel geometries to further improve TES efficiency and scalability. Full article

Two novel cyclometalated platinum(II) complexes based on 2-phenylpyridine (ppy) and 2,4-difluorophenylpyridine (dfppy) ligands in combination with a benzoylthiourea (4-(decyloxy)-N-((4-(decyloxy)phenyl)carbamothioyl)benzamide, BTU) functionalized with decyloxy alkyl chains as auxiliary ligands were synthesized and characterized for their mechanochromic and photophysical properties. Structural characterization was achieved through IR and NMR spectroscopy, single-crystal X-ray diffraction, and TD-DFT calculations. Both complexes exhibit significant photoluminescence with quantum yields up to 28.3% in a 1% PMMA film. The transitions in solution-phase spectra were assigned to mixed metal-to-ligand (MLCT) and intraligand (ILCT) charge–transfer characteristics. Temperature-dependent studies and thermal analyses confirm reversible phase transitions without mesomorphic behavior despite the presence of the two long alkyl chains. Both complexes displayed reversible mechanochromic and solvatochromic luminescence, with a change in emission color from green to red-orange emissions upon grinding and solvent treatment or heating at 80 °C. Full article

Efficient cooling is necessary for the reliability of phased-array radars for a longer life. With the miniaturization and functionalization of microchips, heat flux generated by these chips also rises sharply. Existing liquid cooling techniques are inadequate to meet the ever-increasing cooling requirements. The present paper examines the potential to enhance the convective heat transfer of minichannel heat sinks (MCHSs). Two types of double serpentine minichannel heat sinks are investigated and compared. The first one is a traditional-design MCHS with plate fins, while the second one is a performance-enhanced MCHS design. Three-dimensional conjugate heat transfer models are developed, and the equations governing flow and energy are solved numerically with ANSYS Icepak. The results indicate that the novel MCHS design is found to significantly reduce both the average pressure drop across the minichannels and the total thermal resistance by up to 51% and 8.5%, respectively. Meanwhile, heat transfer enhancement can be obtained for all the rib oblique angles from 13° to 163°, while lowest average pressure drop can be obtained near 90°. The present study provides a new choice for researchers to design more effective MCHSs for the cooling of modern phased-array radar high-heat-flux chips. Full article