Bubble rising near a heated vertical wall is a common scenario in industrial applications. However, the specific coupling between near-wall bubble migration patterns-governed by bubble-wall distances (S), Galilei number (Ga), and E & uml; otv & uml;os number (Eo)-and the resultant convective heat transfer characteristics remains less explored. To fill this gap, this study investigates the rise of an air bubble near a heated wall using the Volume of Fluid (VOF) method. By analyzing these factors, the study examines the migration patterns of rising bubbles and their effect on the wall-to-fluid heat transfer characteristics. The core of the heat transfer enhancement mechanism lies in the systematic disturbance of the fluid caused by the dynamic behavior of bubbles, including the rising trajectory of bubbles, bubble-induced agitation, and transition to turbulence. The results indicate that the Eo, Ga, and S are all critical factors influencing thermal performance. The heat transfer enhancement introduced by bubbles was analyzed by comparing the variation of the Nusselt number (Nu). A reduction in S has a clear enhancement effect on the heat transfer. Compared to the reference case of S = 4D (D represents the bubble diameter), configurations with S = 2D and S = D increased the instantaneous maximum local Nu on the heated wall by approximately 2.91% and 29.49%, respectively. Concurrently, the time-averaged, wall-averaged Nu increased by approximately 0.46% and 2.1%, respectively. The maximum relative enhancement in local Nu occurred in the oscillatory regime, approximately 376.22%, whereas the axisymmetric regime showed the minimum enhancement of only 27.14%.

Hydrothermal fluids, as significant carriers of marine renewable energy, hold importance for ocean resource utilization, and the efficient exploitation of the high temperature difference energy between them and the surrounding cold seawater is crucial. To address the technical limitations of traditional Organic Rankine Cycles and the low energy capture efficiency of thermoelectric effects, this study innovatively applies the supercritical CO2 Brayton cycle for power generation from deep-sea hydrothermal temperature differences. The design of key components, such as heat exchangers and expanders, is conducted. Consequently, a power generation system tailored for deep-sea high temperature difference energy is proposed. A thermodynamic model of the system was developed and solved using self-written Python code. Furthermore, a three-objective optimization framework for net electrical efficiency, power density and levelized cost of energy was established. To address the tendency of the Harris Hawks Optimization algorithm to be trapped in local optima, an improved algorithm, named MOHHO-SEIR, was developed by integrating multiple enhancement strategies. The Pareto optimal front was obtained within the multi-objective optimization framework. The results demonstrate that the optimization scheme derived from MOHHO-SEIR achieves superior overall performance. This study confirms the advantages of applying the supercritical CO2 Brayton cycle for power generation appled the high temperature differential of deep-sea hydrothermal vents.

Thermoeconomic diagnosis methods are designed to identify faulty components and evaluate the economic implications of these faults. However, these diagnostic techniques often struggle to filter out interference from induced factors during the diagnosis process. When multiple components malfunction simultaneously, these methods may fail to effectively identify all the faulty components. To address these challenges, this article introduces an improved thermoeconomic diagnosis method that integrates the traditional diagnosis method with the operational characteristic curves of the components. This improved method facilitates a more precise differentiation between the impacts of faults on each component, categorizing them into intrinsic and induced parts. The intrinsic part arises from the component’s inherent failure, while the induced part results from interactions among different components or adjustments made by the control system. The improved method generates fault diagnosis indicators and economic assessment indicators based on this classification, allowing for the identification of faulty components and the evaluation of the economic consequences of these faults. The proposed method was tested on a MAN 6S50 MC-C8 diesel engine and validated under two real operating conditions, where multiple faults were intentionally introduced in various components. The results demonstrated that the new method accurately identified all faulty components within the marine diesel engine and assessed the economic impacts of these faults.

The substantial thermal energy of two-phase NaCl-H2O hydrothermal fluids makes them a significant target for utilizing deep-sea energy. A fundamental understanding of the thermal performance of two-phase NaCl-H2O hydrothermal fluids during condensation is crucial for heat energy harnessing. It aims to obtain the flow and condensation heat transfer characteristics of two-phase NaCl-H2O fluids during the heat transfer process outside a spiral coil structure in this paper. The properties of the NaCl-H2O binary systems were adopted instead of pure water, and the salt transport equation was considered to reflect the impact of salinity change on heat transfer, making the simulation more representative of natural venting fluids. The results indicated a significant tangential velocity when the fluids externally swept the spiral coil. Secondly, the heat transfer area can be divided into the "normal region" and the "island region," of which convection and condensation contribute to the heat transfer mechanisms. The "island region" formation was attributed to both vapor condensation and the spoiler effect caused by the spiral structure. Moreover, the heat flux increased with decreasing salinity in the "island region," and a weak interaction was observed between heat flux and salinity in the "normal region." Finally, the spiral structure's heat transfer performance was superior to the straight structure's. This investigation may provide a basis for designing and optimizing the heat transfer equipment for deep-sea hydrothermal extraction.

The supercritical Organic Rankine Cycle (ORC) stands out as a promising technology for thermal power conversion due to its high thermal efficiency, straightforward equipment requirements, and compact footprint. Despite its potential, existing optimization design methods for supercritical ORC systems face several limitations, such as focusing on single-objective optimization, and relying on empirically when defined pinch point temperature differences. These limitations often result in a restricted operating parameter range, which may lead to suboptimal solutions or even render the optimization process infeasible under complex constraints. To overcome these limitations, this study proposes a novel multi-objective optimization design method that introduces variable pinch point temperature differences into the optimization process. The system performance was evaluated using three optimization objectives: net output power, heat exchange area, and specific investment cost, and the comprehensive performance for each evaluated case was calculated using the Entropy Weight Method. Compared to traditional methods, this approach eliminates the reliance on empirical assumptions for selecting the pinch point temperature, and expands the feasible matching range between turbine inlet temperature and turbine inlet pressure by over 50%, enabling more accurate and flexible optimization. As a result, the optimized system achieves a 3.1% increase in net output power, a 4.3% reduction in heat exchanger area, and a 9.3% improvement in the comprehensive performance. Finally, the proposed strategy is applied to low-temperature, medium-temperature, and high-temperature geothermal power systems, demonstrating its broad applicability and offering valuable insights for the optimal design and deployment of supercritical ORC systems in geothermal energy utilization.

Hydrate method to capture and store CO2 under sea floor as one of the most novel and promising methods to deal with the greenhouse effect and reduce carbon emission has gained increasing attention nowadays. But how to grow CO2 hydrate under promotion in confinement has rarely been exploited. Here the growth of CO2 hydrate with tetrahydrofuran (THF) promoter in confinement was systematically investigated by molecular dynamics simulations, with the counterpart growth but without promoter as a comparison. With promoter, an obviously more rapid growth of CO2 hydrate was observed and CO2 molecules went inside water cages along with the THF ones but not gathered into bubbles during the formation of clathrate. However, the gathering of CO2 bubbles in the system without promotion hindered the obvious formation of clathrate. The vivid movies and physical quantities were analyzed in detail in order to further unravel the physical mechanism of the growth process and the promotion effect of THF. The obtained simulation results proved that THF could indeed promote the confined growth of CO2 hydrate by preventing the formation of large CO2 bubbles, providing a theoretical foundation for the geological storage of CO2 hydrate in permafrost areas and marine sediments.

The shock resistance capability of ship power equipment is an important guarantee for the safe and stable operation of ships, and a reasonable evaluation method can be more convenient for obtaining the prediction results of power equipment shock resistance. First, the impact processes are divided into the low/high speed collision impact process and non-contact explosion impact process, and the non-integrated and integrated shock resistance methods of ship equipment are described in terms of the master-slave system. The research progress is then summarized and key research technologies in the field of shock resistance for ship power equipment are put forward. The non-integrated methods of ship equipment are divided into three categories, namely the equivalent static method, dynamic design analysis method and time-domain analysis method, and combined with the characteristics of integrated methods. It is concluded that the equivalent static method is only applicable to structurally simple power equipment with low frequency effects; the dynamic design analysis method neglects the effects of adjacent equipment, vibration isolation system and hull structure on impact input loads; and the time-domain analysis method is only applicable to specific scenarios or shock signal inputs such as explosive shocks. The integration of ship equipment takes into account the multi-degree-of-freedom system formed by the hull structure–base–vibration isolation system–equipment, and the calculation results are closer to the actual working condition data, but a large amount of resources is consumed in the modelling and calculation process. Finally, the author forecasts and summarizes important development directions for ship power equipment shock resistance, including the accurate selection of evaluation methods, reasonable improvement of shock resistance test rigs, extraction and analysis of impact response signals, analysis of the multi-field coupling effects of power equipment, simplification study of the physical models of power equipment, research on the equivalent substitution of internal flow media, and the combination of data mining and deep learning methods.

When a malfunction occurs in a marine main engine system, the impact of the anomaly will propagate through the system, affecting the performance of all relevant components in the system. The phenomenon of fault propagation in the system caused by induced factors can interfere with fault localization, making the latter a difficult task to solve. This paper aims at showing how the "characteristic curves method" is able to properly locate malfunctions also when more malfunctions appear simultaneously. To this end, starting from the working principle of each component of a real marine diesel engine system, comprehensive and reasonable thermal performance parameters are chosen to describe their characteristic curves and include them in a one-dimensional thermodynamic model. In particular, the model of a low-speed two stroke MAN 6S50 MC-C8.1 diesel engine is built using the AVL Boost software and obtaining errors lower than 5% between simulated values and test bench data. The behavior of the engine is simulated considering eight multi-fault concomitant phenomena. On this basis, the fault diagnosis method proposed in this paper is verified. The results show that this diagnosis method can effectively isolate the fault propagation phenomenon in the system and quantify the additional irreversibility caused by the Induced factors. The fault diagnosis index proposed in this paper can quickly locate the abnormal components.

The pioneering work on the newly experimentally synthesized biphenylene network C has triggered a worldwide tide of research on its family material counterparts. In this study, a biphenylene network BN structure was theoretically characterized by density functional theory (DFT) calculations. Initially, the structure's mechanical and thermal stabilities were evaluated. There were no imaginary frequencies in the phonon dispersion curve, indicating that the structure was mechanically stable. Additionally, the energy barrier for forming a biphenylene network BN structure from perfect pristine 2D h-BN is substantially less than that for forming a biphenylene network C from a perfect graphene sheet, as can be explained from the greater structure distortion in the biphenylene network BN with lower bond stress which thus caused lower energy. The electronic band structure and detailed projected density of states analysis indicated that the biphenylene network BN is a semiconductor with the valence band maximum (VBM) and the conduction band minimum (CBM) states from the pz orbitals of N and B atoms with sp2 hybridization. Finally, a bilayer structure was also proposed. Our obtained results provide more insights into two-dimensional biphenylene network BN based structures and those family materials which could be widely used in relevant nanoelectronic devices.

为探究在利用地热流体热能发电过程中流体的传热特性,对地热流体的换热过程进行了数值模拟研究.结果表明,有约23％的蒸汽冷凝成了盐水.壁面传热系数在起始位置最大,之后迅速衰减.大量蒸汽粘附在下端面上并在接近冷凝壁面位置逐渐脱离,这些脱离的蒸汽是导致传热系数在起始位置最大的主要原因.壁面处的传热量随壁温的降低而增大,传热系数随壁温的增加呈现出增大的趋势,但增加幅度较小.

利用Volume of Fluid(VOF)方法结合Lee相变模型对单气泡沸腾过程进行了模拟.通过控制加热面的尺寸,在压力为1.9 MPa、接触角为30°条件下对有机工质苯单个气泡的沸腾进行计算.分析了单个气泡的生长过程、速度场随时间变化的规律以及过热度对气泡直径及脱离频率的影响.模拟结果表明:通过观察单个气泡的速度场,发现在气泡长大过程中内部会形成环流.随着气泡脱离壁面,气泡底部的液体会形成涡流,涡流在气泡上升过程中会增大.对比不同过热度下的气泡脱离直径,发现过热度对气泡的脱离直径无影响,测得气泡直径均约为2.35 mm,过热度越大气泡生长脱离所需的时间越短,脱离频率越大,能有效的增强换热.

In this work, the numerical simulation study of the hydrothermal flow and heat transfer process in the porous rock under 30 MPa pressure was developed. The flow and heat transfer characteristics of hydrothermal in rocks with different porosities are studied by changing the porosity of the rock. The simulation results show that the average flow velocity decreases and the average temperature increases when the porosity decreases. The velocity field and temperature field are coupled due to the nonlinear thermophysical properties of hydrothermal. The velocity field and temperature field have strongly interacted in the range of 400-450 ℃ and the effect of temperature on velocity is gradually diminishing outside the range. Most of the fluid will be "squeezed" into the crevice and the average velocity is almost three times the no-creviced case when a crevice is present. The existence of the crevice makes the total heat flux decrease from an overall perspective, and the crevice makes a large temperature gradient at the entrance and export of the crevice from a local perspective. These results provide theoretical support for the utilization of submarine hydrothermal fluid shallow circulation heat energy.

To satisfy the requirements of low fuel consumption, low emission, and high efficiency of the shipping industry, marine diesel engines are developing in the direction of automation and energy-saving, which increases the possibility and complexity of marine diesel engine failures. A one-dimension thermodynamic model for the marine diesel engine is built with AVL Boost software. The model is applied to a low-speed two-stroke 6S50MC diesel engine, and the error between the main performance parameters obtained by simulation and the test bench data is less than 3% under 100% and 75% load. Based on the model, 6 typical single faults and many typical double faults concomitant phenomena of diesel are reproduced. Based on the second law of thermodynamics, the exergy flow among the components and the external environment is analyzed. The thermoeconomic model of a marine diesel engine is established where the "fuel" and "product" of the components are defined according to their function. The fault diagnosis results show that the effects of faults generally propagate through the diesel engine system and affect the behavior of several components, resulting in induced malfunction in normal components. Therefore the malfunction MFi of each component is the superposition of the intrinsic malfunction and the induced malfunction according to the malfunction and dysfunction analysis. The thermoeconomic fault diagnosis method can be used to narrow the search range of abnormal components though it cannot accurately locate the fault.

Despite the increasing interest in the physical properties of the newly synthesized three-dimensional (3D) nano-architectured graphene, there are still few studies on the thermal transport properties of this family of materials. In the present work, heat transport of 3D h-BN and its mechanical response are systematically explored through first principles calculations. It is fascinating to find that the thermal conductivity of the 3D h-BN honeycomb structure could be significantly modulated by mechanical tension. Its lattice thermal conductivity perpendicular to the hole axis increases by 7.2 times at 6% critical strain, compared to only 0.67 times for that of the strained 3D graphene counterpart. The structure's thermal conductivity versus mechanical tension differs quantitatively and qualitatively from the monotonic downward trend of traditional bulk diamond or silicon under tension. This deviation from the classic behavior could be attributed to the modification of the phonon lifetimes, together with the competition between group velocities of low- and high-lying phonons under strain. Finally, the phonon vibrational modes contribution analysis indicates that the BN ribbon atoms contribute mainly at a lower frequency range. Our results provide important insights into potential employment of nano-architectured 3D white graphene for thermal management in relevant industrial applications.

Considering organic inhibitor plays a great role in preventing hydrate formation in oil and gas industry by shifting the hydrate phase equilibrium conditions, it is necessary to study the effects of organic inhibitors on the phase behavior of gas hydrates. In this study, a thermodynamic consistency-based model was developed to predict the phase equilibria of gas hydrates in methanol (MeOH), ethanol (EtOH), monoethylene glycol (MEG), diethylene glycol (DEG), triethylene glycol (TEG) and glycerol (GLY) solutions with concentrations of 5.44 wt%~ 65 wt%, respectively. The Chen-Guo model was applied to hydrate system. Compared with the original Hu-Lee-Sum correlation, a modified HLS type correlation that additionally considers the slight effect of temperature on calculating the activity of water was proposed. The prediction accuracy was characterized by the average absolute deviation in temperature (AADT). Results show that for CH4 hydrate the Chen-Guo model coupled with HLS correlation performs as good as the original HLS correlation and PVTSim. The corresponding AADT for each organic inhibitor can be further decreased by at least 20.95% when using the Chen-Guo model coupled with the modified HLS type correlation. Besides, this modified model also shows a better performance in predicting the phase equilibria of C2H6 and CO2 hydrates in the presence of these organic inhibitors than the Chen-Guo model coupled with HLS correlation do.

Natural gas hydrate is an ice-like non-stoichiometric crystal compound which shows a series of advantages, such as large reserves and clean combustion. It is widely distributed in the permafrost and deep ocean sediments.

The mechanical properties play a vital role in the stability and behavior of clathrate hydrate. In this work, the structural and mechanical properties of some nitride gas (NH3, NO and N2O) hydrates were investigated using density functional theory calculations. The equilibrium lattice structures for these hydrates were obtained. The full second-order elastic constants were then determined by energy–strain analyses and the polycrystalline elastic properties were also predicted. It is found that these three gas hydrates have high elastic isotropy, but their shear properties are significantly different. This study may lay a theoretical foundation for future research on the structural evolution of clathrate hydrates under a mechanical field.

It is important to study the temperature stratification phenomenon in flash evaporation to well design the marine accumulator and some related industrial equipment. Therefore, a series of flash evaporation experiments with initial temperature of 65.0 °C ~ 84.4 °C and superheat degree of 5.0 °C ~ 30.0 °C are carried out to study the temperature variations at different water depths. Meanwhile, the functional analysis method is used to obtain the global and local digital characteristic of flash evaporation. Also, the application domain of this method is discussed in detail. Finally, the effects of initial temperature and superheat degree on the variation of non-equilibrium fraction are studied by the functional analysis method. Results show that the temperature of the deeper water drops earlier and faster than that of the shallower water, and the temperature stratification phenomenon is obvious at the beginning 20s of flash evaporation. This phenomenon gradually disappears as the flash evaporation proceeds. Increasing the initial temperature effectively accelerates the drop of water temperature. However, due to the large temperature decline, increasing the degree of superheat only increases the decreasing rate of temperature, but does not significantly reduce the duration time of flash evaporation.

Natural gas hydrate as a potential backup energy has very important scientific and social values. This paper aims at analyzing the gas production characteristic of methane hydrate sediment via depressurization. The physical model of 1 L cylindrical reactor is established and numerically simulated with the hydrate calculation software TOUGH + HYDRATE_v1.5. Based on the experiments, the cases in which ice formation are set to different initial reservoir pressures (2.0 MPa, 2.5 MPa, 3.0 MPa and 4.0 MPa) for numerical simulation to see the dissociation characteristics and heat and mass transfer during hydrate dissociation. The simulation results indicate that under the same driving force, the rate of hydrate dissociation increases with the initial pressure and the cumulative volumes of gas produced of the well and the sediment is the same due to the same initial hydrate saturation. The heat and mass transfer affected by ice formation plays an important role in hydrate dissociation and the temperature distribution in the sediment. When there is ice formation inside the sediment which inhibits the heat and mass transfer inside the sediment, the driving force should be carefully selected for different initial pressures to reduce the inhibitory effect of ice formation on hydrate dissociation.