Search Results (35)

Earthquake-induced soil liquefaction poses significant geotechnical hazards, including sand boiling, loss of foundation bearing capacity, lateral spreading, pipeline flotation, uneven settlement, and slope instability. While cyclic liquefaction constitutive models can effectively simulate and predict site liquefaction behavior, their reliability hinges on the accurate calibration of constitutive parameters. Traditional calibration methods often fail to capture the comprehensive material response, are labor-intensive, time-consuming, and susceptible to subjective judgment. To overcome these limitations, this study develops an intelligent calibration framework for a cyclic liquefaction constitutive model by integrating a numerical solver for unit tests with the genetic algorithm (GA)-based optimization framework. The proposed method is rigorously evaluated in terms of calibration accuracy, convergence, repeatability, uncertainty, and computational efficiency. Validation via a series of laboratory unit tests on materials from an extremely high earth-rock dam project confirms the method’s effectiveness. Results demonstrate that the intelligent calibration approach achieves a high accuracy of 91.84%, offering a reliable, efficient, and robust solution for parameter determination. Full article

This study addresses the characterization of two-phase flow phenomena in a microchannel heat sink designed to cool high-concentration photovoltaic cells. Two-phase flows can introduce instabilities that affect heat exchange efficiency, a challenge intensified by the small dimensions of microchannels. A single polydimethylsiloxane (PDMS) microchannel was fixed on a stainless steel sheet, heated by the Joule effect, which was cooled by the working fluid HFE 7100 as it undergoes phase change. Experiments were performed using two microchannel widths with a fixed height and length, testing two heat fluxes and three values of the Reynolds number, within the laminar flow regime. Temperature and pressure drop data were collected alongside high-speed and time- and space-resolved thermal images, enabling the observation of flow boiling patterns and the identification of instabilities. Enhanced surfaces with microcavities depict a positive effect of a regular pattern of microcavities on the surface, increasing the heat transfer coefficient by 34–279% and promoting a more stable flow with decreased pressure losses. Full article

Spacecraft and satellites are equipped with cryogenic storage systems to maintain instruments and engines at optimal operating temperatures. However, in cryogenic storage tanks, the steep temperature gradient along the pipeline (arising from sections inside and outside the tank) may induce instability in stored gases such as helium or hydrogen, leading to large-amplitude, self-excited thermoacoustic oscillations, known as Taconis oscillations. Taconis oscillations not only cause structural damage to pipelines, jeopardizing the safety of the cryogenic storage system, but also produce significant heat leakage and boil-off losses of cryogens. This study employs computational fluid dynamics (CFD) to simulate Taconis oscillations within a U-shaped cryogenic helium pipeline. The flow dynamics and acoustic field characteristics of the cryogenic helium pipeline are first analyzed. Fast Fourier transform and wavelet transform are employed to characterize the Taconis oscillations. A subsequent parametric study investigates the influence of the location and magnitude of temperature gradients on the dynamic behavior of Taconis oscillations. Simulation results reveal that the onset temperature gradient is at a minimum when the temperature gradient is applied at one-quarter of the cryogenic pipeline. To prevent the occurrence of Taconis oscillations, the transition between the warm and cold sections should be away from one-quarter of the cryogenic helium pipe. Moreover, increasing the temperature gradient leads to the emergence of multiple oscillation modes and an upward shift in their natural frequencies. This research gives deeper insights into the dynamics of thermally induced thermoacoustic oscillations in cryogenic pipelines, providing guidelines for improving the efficiency and safety of cryogenic storage systems in aerospace engineering. Full article

This work addresses enhancing flow boiling heat transfer via the use of engineered surfaces possessing specific novel geometries created via femtosecond laser texturing. Surface functionalization can result in improved, more controlled, and denser nucleation as well as controlled surface rewetting, leading to reduced incipient superheats, higher heat transfer coefficients, reduced flow instabilities, and increased critical heat fluxes with respect to a non-modified reference surface. Specifically, this study investigates how bubble dynamics and heat transfer performance are affected by three different surface textures fabricated on 200 µm thick 316L stainless steel foils using a femtosecond (fs) laser. The examined textures consist of inclined (=45°) microgrooves, inclined (=45°) conical microholes, and laser-induced periodic surface structures (LIPSSs). Each textured surface’s degree of heat transfer enhancement is assessed with respect to a plain reference surface in identical operating conditions. The working fluid is PP1, a replacement of 3M™ FC-72 in heat transfer applications. Among the tested surfaces, submicron-scale LIPSSs contribute to the rewetting of the surface but only show a slight improvement when not combined with bigger microscale structures. The inclined grooves result in the most gradual onset, showing almost no incipient overshoot. The inclined conical microholes achieve superior results, improving heat transfer coefficients up to 70% and reducing the incipient temperature up to 13.5 °C over a plain reference surface. Full article

The escalating thermal demands of high-power electronic devices and energy systems necessitate advanced thermal management solutions. Flow boiling in small/micro channels has emerged as a promising approach, yet its practical implementation is hindered by flow instabilities and heat transfer deterioration under high-heat fluxes. This study presents a systematic numerical investigation of subcooled boiling flow and heat transfer in a rectangular small channel under high-heat-flux conditions, employing the VOF method coupled with the Lee phase change model. The increasing heat flux accelerates bubble nucleation and coalescence while reduced mass flux promotes early local slug formation, shifting flow transitions upstream and degrading thermal performance. A local vapor volume fraction threshold of α_ν = 0.2 is identified for the bubbly-to-sweeping flow transition and α_ν = 0.4 for the sweeping-to-churn transition. Furthermore, a novel dimensionless parameter β is proposed to classify dominant flow regimes, with critical β ranges of 12–16 and 24–32 corresponding to the two transitions, respectively. These findings provide new quantitative tools for identifying flow regimes and improve the understanding and design of compact boiling-based thermal management systems under extreme heat- flux conditions. Full article

Marine transportation of liquefied carbon dioxide (LCO₂) is crucial for Carbon Capture, Transportation, Utilization, and Storage (CCTUS) technology, aiding in CO₂ emission reduction and greenhouse effect control. This study investigates the thermodynamic and fluid dynamic characteristics of LCO₂ in Type C storage tanks using numerical simulations, focusing on heat transfer, flow phenomena, and boil-off gas (BOG) generation under varying storage pressures. Results show that heated liquid rises along the tank wall, forming vortices, while gas-phase vortices are driven by central upward airflow. Over time, liquid velocity near the wall increases, enhancing flow field mixing. Gas-phase temperatures rise significantly, while liquid-phase temperature gradients remain minimal. Higher storage pressures reduce fluid velocity, vortex range, and thermal response speed. BOG generation is higher at low pressures and decreases as pressure rises, slowing beyond 1.5 MPa. Under sloshing conditions, interfacial fluctuations enhance heat and mass transfer, reducing thermal stratification. Resonance periods amplify interfacial disturbances, improving thermal mixing and minimizing temperature gradients (ΔT ≈ 0.1 K). Higher filling rates suppress surface rupture, while lower rates exhibit gas-dominated instabilities and larger thermal gradients (ΔT ≈ 0.3 K). Full article

The performance of lithium-ion batteries deteriorates significantly under extreme-cold conditions due to increased internal resistance and decreased electrochemical activity. This study presents an experimental analysis of a battery thermal management system (BTMS) incorporating electromagnetic induction heating and a fluid-based heat transfer mechanism to alleviate these problems. The experimental setup utilizes a closed-loop circulation system where ethylene glycol-based fluid flows through induction-heated copper tubes, ensuring efficient heat transfer to an 18650-cell battery. This study evaluates heating performance under varying ambient temperatures (−15 °C and −5 °C), fluid flow rates (0.22, 0.3, and 0.5 L/min), and induction power levels (150 W, 225 W, 275 W, and 400 W). The results indicate that lower flow rates (e.g., 0.22 L/min) provide faster heating due to longer thermal interaction time with the battery; however, localized boiling points were observed at these low flow rates, potentially leading to efficiency losses and thermal instability. At −15 °C and 400 W, the battery temperature reached 25 °C in 383 s at 0.22 L/min, while at 0.5 L/min, the same temperature was achieved in 463 s. Higher flow rates improved temperature uniformity but slightly reduced heating efficiency due to increased heat dissipation. Internal resistance measurements revealed a substantial decrease as battery temperature increased, further validating the effectiveness of the system. These findings present a viable alternative for heating electric vehicle batteries in sub-zero environments, thereby optimizing battery performance and extending operational lifespan. Full article

In the present study, to address the issue of flow rate instability in the flow boiling experimental system, a flow rate adaptive control system is developed using a single-neuron PID adaptive algorithm, enhanced with the whale optimization algorithm (WOA) for parameter tuning. A recursive least-squares online identification method is integrated to adapt to varying operating conditions. The simulation results demonstrate that in step response the WOA-improved single-neuron PID significantly mitigates the overshoot, with a mere 0.31% overshoot observed, marking a reduction of 98.27% compared to the traditional PID control. The output curve of the WOA-improved single-neuron PID closely aligns with the sinusoidal signal, exhibiting an average absolute error of 0.120, which is lower than that of the traditional PID (0.209) and fuzzy PID (0.296). The WOA-improved single-neuron PID (1.01 s) exhibited a faster return to a stable state compared to the traditional PID (2.46 s) and fuzzy PID (1.28 s). Finally, the effectiveness of the algorithm is validated through practical application. The results demonstrate that, compared to traditional PID and single-neuron PID algorithms, the WOA-improved single-neuron PID algorithm achieves an average flow stability of 9.9848 with a standard error of 0.0914394. It exhibits superior performance, including faster rise and settling times, and higher stability. Full article

The study of bubble growth and collapse is of great significance in the context of sustainability due to its influence on numerous energy-related processes and technologies. Understanding the dynamics of bubble behavior is vital for optimising heat transfer efficiency, which has an energetic role in improving the performance of sustainable systems such as nuclear reactors, thermal inkjet printing, and nucleate boiling. Indeed, researchers can progress strategies to enhance the efficiency of these technologies by analysing the parameters influencing bubble growth and collapse, which can lead to reduced energy consumption and environmental impact. Although several theoretical models and experimental investigations have been achieved in the past to inspect bubble growth and collapse, a thorough review and critical assessment of the studies conducted have not yet been achieved. This review aims to provide a comprehensive understanding of the relationship between bubble dynamics and sustainability, highlighting the potential for further research and development in this area. Specifically, the scope and limitations of past research on bubble growth and collapse is conducted to fill this gap in the open literature. The review covers both numerical and experimental studies of bubble growth and collapse in a wide set of innovative industrial applications including nuclear reactors, thermal inkjet printing, nucleate boiling, hydrodynamic erosion, and ultrasonic and medicinal therapy. The current review also attempts to illustrate and evaluate the numerical methods used and underlines the most relevant results from the studies that were looked at in order to provide researchers with a clear picture of the growth and collapse of bubbles in different applications. The results give a precise understanding of the dynamics of bubble growth and collapse and the related temperature change and cumulative heat transmission from the thermal boundary layer. Additionally, it has been demonstrated that simulation-based models can effectively predict transport coefficients. However, the review observes a number of limitations of the past research on bubble growth and collapse. Due to numerical instability, very little work with respect to dynamic modelling has been carried out on the mechanisms of bubble collapse. Accordingly, a number of recommendations are made for the improvement of heat transmission during bubble growth and collapse. Specifically, future criteria for the highest heat transmission will demand more precise experimental and numerical approaches. Full article

Thermal treatment has significant advantages in resource recovery for oily sludge (OS). However, the instability of heavy metals (HMs) within the residue poses a considerable risk of secondary pollution. This study explored the migration and transformation of HMs from OS under varying conditions (i.e., temperature, constant-temperature duration time, and different ratios of O₂ and CO₂). The elevation of the pyrolysis temperature augmented the decomposition of organic matter and total petroleum hydrocarbons (TPHs). However, the increased temperature also diminished the stabilization of HMs, and facilitating the HM’s transfer to oil and gas, particularly for HMs (i.e., As and Pb) with low boiling points. The constant-temperature duration time exhibited a weak impact on HM transformation, but the internal heating mechanism of microwave pyrolysis promoted the stabilization of HMs through vitrification. The existing O₂ with oxidizing properties facilitated the oxidation of organic matter and TPHs to CO₂ and H₂O, which also promoted the transformation of HMs into oxidized states for stabilization. Comparatively, CO₂ promoted the thermal cracking and disrupted the stability of HMs to a certain extent. Above all, this work revealed the migration and transformation of HMs in OS varied with the thermochemical methods and possessed an important significance for the immobilization and stabilization of HMs. Full article

In the pursuit of enhancing thermal management for miniaturized electronic devices, our study delves into the impact of entry effects on Ledinegg instability and flow maldistribution within parallel microchannels. Utilizing a coupled model that incorporates phase change and pressure drop dynamics in boiling flow, we examine microchannels characterized by a 50 length-to-diameter ratio and a 200 μm hydraulic diameter. Our findings unveil a significant influence of entry effects, which narrow the total flow excursion interval, thereby bolstering system stability. Specifically, as the heat flux escalates from 5 W/cm² to 120 W/cm², the entry effects increasingly mitigate flow instability and maldistribution in parallel channels, diminishing the total flow rate range susceptible to flow instability by 4.73% and 47.52%, while narrowing the total flow rate range corresponding to uneven flow distribution by 4.70% and 46.75%, respectively. Furthermore, entry effects expand the inlet subcooling range necessary for stabilizing the parallel channel system by 38.89% and 1000%. This research not only underscores the importance of considering entry effects in microchannel design but also opens avenues for further exploration into enhancing thermal management solutions. Full article

Interconnected microchannels (IMCs) in flow boiling have the advantages of optimized heat transfer performance, energy savings and high efficiency, compact size, and strong customizability. They provide new solutions for thermal management and heat transfer at the microscale and have broad application prospects. To further investigate the effect of microchannels with different numbers of transverse sections on the flow boiling heat transfer, we performed numerical simulations on a rectangular microchannel (RMC) and IMCs with 3, 5, and 7 transverse microchannels at high and low mass flux. It was found that fluid experiences similar bubble and slug flow in different numbers of IMCs and the RMC at low mass flux. At a heat flux of q = 90 W/cm², the downstream regions of the IMCs produce vapor films that span the channels, obstructing the cross-section and weakening the flow exchange between the channels, which lead the heat transfer performance factor of IMC-3, reaching 148.43%, 110.04%, and 116.92% of the RMC, IMC-5, and IMC-7. Under high-quality flux, as the heat flux increases, the heat transfer coefficient increases and the pressure drop decreases due to the existence of lateral microchannels introduced in the interconnected microchannels. Whether at high or low mass flux, structural reasons pertaining to the RMC can easily lead to the accumulation of bubbles and the occurrence of slugs, and the flow boiling instability increases with the increase of heat flux, which leads to a pressure drop and heat transfer performance generally lower than that of IMCs under the same conditions. At q = 120 W/cm², IMC-7 showed the best heat transfer enhancement. Its heat transfer performance factor was 129.37%, 120.594% and 107.98% of the RMC, IMC-3, and IMC-5, respectively. This article provides theoretical support for the design of interconnected microchannels in thermal management. Full article

The two-dimensional instability of a horizontal layer of boiling liquid with a finite height was experimentally studied. In this layer, “vapor columns” rose at the corners of a square rectangular grid, and the symmetry of “vapor column” location on the heating surface was considered. The model adopts an approach to the boiling crisis from the side of both developed nucleate boiling and transitional boiling (the Zuber problem). When dealing with developed nucleate boiling, the layer of boiling liquid is considered in calculations as an isotropic homogeneous system (foam). It is shown how the conditions on the heating surface (capillary-porous coating) affect the external hydrodynamics of the liquid layer and, ultimately, the value of the critical heat flux. The calculation ratio obtained by approaching the boiling crisis from the side of developed nucleate boiling takes into account the dependence of the critical heat flux on the void fraction of the boiling liquid layer. A new solution to the boiling crisis problem is proposed when approaching the crisis from the side of transitional boiling (the Zuber problem). This new solution eliminates some shortcomings of the classical problem (in particular, the void fraction of the layer corresponds to the experiments). Full article

Seepage erosion is one of the main reasons for the local collapse or instability of embankments. To investigate the characteristics and mechanism of seepage erosion for cohesionless soils, model tests using an independently developed seepage erosion device and numerical simulations based on a discrete element method-computational fluid dynamics (DEM-CFD) coupling model were carried out. The results show that the seepage erosion process of cohesionless soil could be characterized by four stages: stable seepage, upward migration of fine particles, boiling of sand samples, and erosion damage. The skeleton structure of a soil sample under seepage flow was continually changed due to the loss of fine soil particles, which resulted in a significant decrease in the sample strength and could, ultimately, lead to the failure of the sample. The results of this study can provide references and bases for the design, construction, and long-term service of embankments or earth dams under complex seepage conditions, reducing the risk of seepage erosion. Full article

The DNS of film boiling requires strong computational resources that are difficult to obtain for daily CFD use by expert practitioners of industrial R&D. On the other hand, film boiling experiments are associated with the usage of expensive and highly sophisticated apparatus, and research to this end is relatively difficult due to high heat flow rates that are present in the process itself. When combined with transient heat conduction in a solid, the problem becomes significantly difficult. Therefore, a novel method in computation of conjugate heat transfer during film boiling in a quiescent liquid is proposed in this paper. The method relies on the solution of mass, momentum and energy conservation equations in a two-fluid framework, supplemented with the appropriate closures. Furthermore, turbulent flow was determined as an important parameter in obtaining an accurate solution to temperature field evolution in a solid specimen, via the proper modeling of the turbulent kinetic energy (TKE) value, that was imposed as a constant value, i.e., the frozen turbulence approach. It was found, in addition, that the appropriate TKE value can be obtained by use of Kelvin–Helmholtz instability theory in conjunction with boundary layer theory. The obtained results show excellent agreement with the experimental data within the first 15 s of the experiment, i.e., the first ca. 10% of the total duration of the film boiling mode of heat transfer. Furthermore, the heat transfer coefficient matched the error bands prescribed by the authors of this paper, which presented the correlations, whilst the averaged values are far beyond this band, i.e., are slightly more than 30% higher. Further inspection revealed a measure of similarity between the computational result of the volume fraction field distribution and the experiment, thus confirming the capability of the method to obtain realistic interface evolution in time. The method shows full capability for further pursuing industrial-scale film boiling problems that involve turbulent flow and the conjugate heat transfer approach. Full article