bluuebunny/crossref_metadata_2025 huggingface dataset:
Sequentially Quadratic Surrogate Algorithm for Time-dependent Reliability and Reliability Sensitivity Analysis
Authors: Suting Zhou , Jie Liu , Lin Zhang , Zhenzhou Lu , Changhua Nie
Published: June 2024

Time-dependent reliability and reliability sensitivity analysis in presence of random uncertainty is widespread in equipment structures. To this end, this paper establishes a sequentially quadratic surrogate method. Firstly, the global reliability sensitivity analysis (GRS) is transformed into the classification problem of the time-dependent performance function outputs by means of conditional probability formula. Secondly, referring to the strategy of the Meta-IS method, the Kriging model of time-dependent performance function is employed to construct the importance sampling function to generate the importance sampling (IS) samples of failure domain efficiently. Furthermore, the Kriging model is updated in the IS samples set through the single-loop adaptive Kriging method to realize the accurate identification of the failure indicator function of IS samples, as well as simulation of time-dependent failure probability. Finally, utilize the information of the failure samples obtained by the estimation of time-dependent reliability to evaluate GRS. The proposed algorithm has excellent computational efficiency and applicability due to the conversion of the conditional probability formula, which enables the computational consumption of the time-dependent reliability and GRS analysis independent of the dimensions of the inputs, as well as the Meta-IS method, which improves the sampling efficiency and is applicable to the case of complex implicit performance function. The given examples fully verify the conclusions.
Study on fault characteristic of piezoelectric acceleration sensor
Authors: Guo Ziwen , Zhang Chengcheng , Zhang Xiangyu , Li Yongbo , Deng Zichen
Published: June 2024

In order to explore the fault characteristics and failure mechanism of the sensor, staring from the working principle and structural characteristics of the piezoelectric acceleration sensor, the problems affecting the quality of the collected signal due to the fault of the component of the sensor are systematically studied. Firstly, according to the application scenario and structural characteristics of this kind of sensor, the main fault forms are analyzed, including: insufficient preload, crystal plate damage, crystal plate side loading and crystal plate phase loading reverse four kinds of faults. Secondly, the signal of the exciter is used to test the above sensors. It is found that except the sensor with insufficient preload does not affect the signal, other fault sensors will make the collected signal amplitude smaller, but the signal frequency does not change. In order to verify the accuracy of the exciter test results, the sensor signal test on rotor bearing vibration was continued. The test results show that not only the signal amplitude decreases, but also the high frequency part of the signal is seriously distorted. Finally, the fault characteristics of various components of piezoelectric acceleration sensor are obtained by combining the test results of the two groups.
A prediction method for aircraft icing severity forecast based on probability model and meteorological observation data
Authors: Liu Huan , Wang Yi , Lei Li , Liu Zheyuan , He Xindang
Published: June 2024

Aircraft flight performance and safety are inevitably affected by adverse meteorological conditions, one such weather is icing. Aircraft icing can cause severe aerodynamic and flight mechanical effects, thus threatens aircraft flight safety. This study presents an aircraft icing severity prediction method with probabilistic model, in which meteorological observation data are described as random variables and the airplane icing severity level is defined as fuzzy variables with membership function. When the information of aircraft flying cloud type, altitude, speed, temperature, pressure and dew point temperature is known, the probability of aircraft icing severity during aircraft fly can be effectively predicted by a weighted icing forecasting method. Using the proposed method into two aircraft icing cases, the analysis results show that the proposed method is accurate and valid. It can provide technical support for aircraft icing forecasting.
Advancing UAV Sensor Fault Diagnosis based on Prior Knowledge and Graph Convolutional Network
Authors: Su Zhe , Zhang Yulong , Zhu Jun , Li Yongbo
Published: June 2024

Unmanned Aerial Vehicles (UAVs) are commonly equipped with multiple sensors to facilitate control and navigation. However, due to the complexity of the flight environment, the UAV sensors are prone to damage, which can cause serious accidents or even economic losses. Therefore, it is of great importance to propose an effective UAV sensor fault diagnosis method. The following weaknesses are obtained by the existing fault diagnosis methods: 1) The model-based methods, such as parameter estimation, state estimation, and equivalent space method, require introducing high-precision system models and expert knowledge. 2) Conventional graph convolutional network (GCN)-based methods fail to guarantee the accuracy of association graphs. To address the above two challenges, the dynamics model of quadrotor as prior knowledge is proposed in this paper to construct the association graph first. Then, a spatial-temporal difference graph convolutional network (STDGCN) consisting of a difference layer and multiple spatial-temporal graph convolutional modules is built. The difference layer enhances the feature extraction of the graph nodes, while the spatial-temporal graph convolutional modules extract the spatial-temporal dependencies of sensor data. Finally, the robustness and effectiveness of STDGCN are demonstrated in fault diagnosis compared with the commonly used data-driven methods. The experimental result shows that the proposed STDGCN method exhibits outstanding feature extraction ability with the highest diagnostic accuracy.
Method of aero-engine flight safety pre-warning based on support vector machine
Authors: Dong Jiang , Zhang Qiangbo , Guo Haidong
Published: June 2024

Engine vibration is a decisive factor in flight safety. Aiming at the problem that the current single vibration warning value of an aero-engine cannot reflect the vibration characteristics of the engine in flight, the estimated probability density of the measured vibration of the engine based on the support vector machine (SVM) method is established, and the aero-engine flight safety pre-warning research is carried out. Through the statistical analysis of the installed flight data of a engine, the probability density function estimation of the measured vibration data of the aero-engine flight was carried out by the support vector machine, and the vibration warning value of the installed engine in each state was determined according to the probability distribution and the general primary side determined by the vibration monitoring limit value of rotating machinery. Through the verification of actual flight data, the determined vibration warning value with the change trend of engine state is consistent with the actual flight data, and is more sensitive to engine failure, which is conducive to improving the early failure warning ability of aero-engine during flight.
Improvement of drilled holes quality by voice-activated ultrasonic vibration assisted drilling process of different orientation
Authors: Patwari Anayet U , Navid Wasib Ul , Morshed Rahman Maruf , Showkhin Sakib , Bhuiyan Shah Alam
Published: June 2024

Ultrasonic drilling enables drilling in difficult-to-machine materials, including ceramics and composites, with greater accuracy and precision. The localized and controlled energy application of ultrasonic frequency minimizes the risk of material fracture, cracks, or delamination. This capability ensures that the drilled hole maintains its intended dimensions, shape, and integrity, resulting in improved hole accuracy and overall drilled hole condition. Ultrasonic drilling is an advanced machining technique that utilizes high-frequency vibrations to improve the drilling process. In this designed voice-activated module, electrical energy has been converted into mechanical vibrations through piezoelectric transducers, generating ultrasonic waves in the range of 20 kHz to 80 kHz. Experiments has been conducted considering different process parameters with the changing different orientations of the emitters-horizontal and vertical positions and comparison was done with no vibration conditions. It has been observed that with the application ultrasonic vibration frequency the surface roughness improved by 45% in horizontal position, 28% in vertical position compared with no vibration conditions-conventional techniques. It has also been observed that the circularity index of the drilled holes also improved by 31% for horizontal and 7.6% for vertical position.
Dynamic Simulation Analysis and Research of Overhang Cold Launching System
Authors: Wang Yiwei , Li Jiasheng , Zhou Yuanchun , Yin Xiang , Liu Guang , Xu Bin
Published: June 2024

In order to study the structural dynamic response and the separation rule of launch tube and missile of the overhang cold launching system during launching, and provide a basis for the design of new overhang launching system, a dynamic model of the overhang cold launching system was established by using the rigid-flexible coupling method and multi-body dynamics according to the structural characteristics and ejection physical process of the overhang cold launching system. The accuracy and rationality of the modeling method proposed by this paper were validated against the test. Based on this, the dynamic response of ejection and outlet attitude were analysed. The results show that the dynamic model of overhang cold launching system can accurately reflect the vibration characteristics of the system. A large longitudinal displacement of the center of launch tube will occur during the ejection process. The oscillation frequency is relatively small, but the structural vibration caused by the ejection impact will have a great influence on the pitching attitude of the missile. The vibration response of the adjacent launch tube is small, which is beneficial for the continuous launching of the overhang launching system. The research results can provide a basis for the subsequent design of vibration reduction.
Instability Feature Extraction Method of Compressor Based on Sample Autocorrelation Function
Authors: Tian Lin , Tao Ye , Zhang Shaoli
Published: June 2024

The stability of aero-engine compressor is related to flight safety. Severe instability may lead to engine surge, parking or mechanical damage and even cause flight accidents. Aiming at this problem, a compressor instability feature extraction method based on sample autocorrelation function is proposed, and an autocorrelation analysis model of fluctuating pressure is established. The model is verified and analyzed by using the flight test data of an engine, which shows the feasibility of this method. It can provide technical support for real-time monitoring and quantitative evaluation of aero-engine compressor stability and improve safe flight efficiency.
Sparse Fast Fourier Transform Analysis of Aero-Engine Vibration Data
Authors: Jia Hao , Zhang Qiang , Wei Mengyuan , Sun Xiewen
Published: June 2024

Sparse fast Fourier transform is a new spectrum analysis method based on signal sparse characteristics in recent years. Sparse fast Fourier transform can quickly and accurately process large data by identifying and discarding frequency signals that have no effect on the analysis results. In order to explore the practicality of Sparse fast Fourier transform in aero-engine vibration data analysis, this paper combines the actual flight test vibration data, and studies the sparse fast Fourier transform method and the traditional fast Fourier transform method in terms of spectral characteristics, running time, algorithm stability. By comparison, it can be found that the sparse fast Fourier transform algorithm can greatly improve the efficiency of vibration data analysis while ensuring accuracy.
End-to-end Temporal Transformer with Autocorrelated Attention Mechanism Augmented for Remaining Useful Life Prediction of Turbopump Bearings
Authors: Chen Zhuohang , Chen Jinglong , Pan Tongyang , Luo Qinyuan
Published: June 2024

Accurately predicting the remaining useful life (RUL) has become crucial for ensuring stable and safe operations for rocket engines due to the extreme working environment. However, current RUL prediction approaches based on convolution and recurrent frameworks lack effective feature extraction methods to model long-term dependencies, resulting in limited accuracy and generalizability. To address this issue, we propose an end-to-end temporal Transformer with autocorrelated attention mechanism augmented for RUL prediction of turbopump bearings. The Transformer module is adopted as the backbone of proposed framework to model long-term dependencies from the raw signals. To further enhance predictive capability, we develop a self-attention mechanism based on autocorrelation calculation. This mechanism extracts and aggregates feature representations through similarity comparison at the sub-series level. Furthermore, we utilize convolutional layers with residual links to capture internal detail features, compensating for the limitations of capturing local information. The proposed framework is evaluated through a life-cycle rocket engine bearing dataset and the experimental results demonstrate the effectiveness and superiority on RUL prediction.
Research on transfer learning diagnosis method for planetary gearbox bearings based on variational embedding composite multiscale diversity entropy and manifold dynamic distribution adaptation
Authors: Guo Hang , Wang Xianzhi , Chen Gaige , Ma Hongbo
Published: June 2024

To improve the generalisation ability of traditional machine learning fault diagnosis model, this paper proposed a planetary gearbox bearing diagnosis method based on the variational embedded composite multiscale diversity entropy (veCMED) and manifold dynamic distribution adaptation (MDDA). Firstly, fault features are extracted using variational embedded composite multiscale diversity entropy (veCMDE). Secondly, the extracted entropy fault features are combined with manifold dynamic distribution adaptation (MDDA) of the flow shape to map the entropy values of different distributions to the space of the same distribution. Thirdly, the entropy value after feature mapping is input into the KNN classifier for fault identification. The final experimental results show that the proposed veCMDE and MDDA based transfer learning method has the best generalisation ability compared to seven transfer learning methods.
Autonomous Mission Planning for Spacecraft On-orbit Service Based on Hybrid Variant Particle Swarm Optimization
Authors: Wang Cheng , Lyu Yueyong , Zhao Xuebo , Hao Siqiang
Published: June 2024

For the complex on-orbit service (OOS) mission planning problem, an improved hybrid variant particle swarm optimization (PSO) method was proposed to improve the fuel utilization efficiency of spacecraft. Firstly, considering the time and fuel constraints, a model for OOS mission planning under the scenario of multiple target spacecrafts is established. The Lambert orbit maneuver method is used and the problem is transformed into a large-scale hybrid nonlinear integer programming problem. Next, an improved hybrid variant PSO algorithm is designed to optimize the fuel performance cost, and its simple structure and lightweight operation facilitate autonomous planning, considering the limited computing power of the onboard computer. The hybrid algorithm is composed of discrete particle swarm optimization (DPSO) and PSO, so it has a strong ability to search for the optimal service sequence and orbit maneuver time simultaneously. Moreover, the adaptive and variant operators are used to improve the searching ability and avoid falling into local optimal solutions. Finally, simulation experiments show that the proposed method can quickly give optimal results, reducing fuel consumption effectively in the OOS mission and improving the OOS capability of the spacecraft.
Close-range maneuver planning for uncontrolled rendezvous with multiple elliptical orbit targets based on genetic algorithm
Authors: Xiao Fuhong , Sun Yanhong , Wang Rixin
Published: June 2024

On-orbit debris removal is an important and challenging problem in space engineering. A low-cost method for this problem is to use uncontrolled rendezvous with a sub-spacecraft released by a service spacecraft. The sub-spacecraft do not carry any control system and are designed to rendezvous with the target debris to remove it. This paper presents a comprehensive study on the mission planning. First, we analyze and dynamically model the uncontrolled rendezvous process for elliptical orbit targets, and study various aspects such as maneuver, sub-spacecraft release parameter solution, and rendezvous accuracy estimation. Then, we use NSGA-II, a multi-objective optimization genetic algorithm, to establish the mission planning model, focusing on the design of decision variables, constraints and fitness functions. Finally, we apply our proposed method to two specific cases of Molniya orbit, and verify the effectiveness of the planning model. We also conduct a deep analysis of the planning results, and summarize the commonalities and differences of various effective strategies.
Defect Detection in Civil Structure Using Deep Learning Method
Authors: Zhou Xiaoling , Tiong Robert L. K.
Published: June 2024

With the usage time, undesirable defects like crack and spalling appeared in various types of civil structures including beam; wall and column. These defects have a great influence on the usage life of the structures and hence need attention and maintenance. Normally, defect detection in civil structures is the human visual inspection. The manual approach is time-consuming and has a low accuracy. In this paper, we use deep learning method to predict multiple defects in various types of civil structures. Crack and spalling are recognized using the convolutional neural network model in a pixel level. To build the inspection model, the U-net Plus Plus architecture is used for segmentation. In the dataset, 1300 images are taken for training and 600 images for validation. The obtained computer vison model is tested on a dataset of about 491 images. The recall for crack and spalling reach 0.89 and 0.85 respectively. This research work develops an automated approach for defects detection in civil structures. The results can provide helpful guidance for structure health monitoring and maintenance in civil engineering like buildings and bridges.
Deep LSTM-based autoencoder for CFRP damage imaging using Lamb wave and correlation factor weighted delay-and-sum algorithm
Authors: Ji Dingcheng , Lin Jing , Gao Fei
Published: June 2024

The ultrasonic Lamb wave testing (ULWT) has proven valuable in non-destructive testing (NDT) due to its high sensitivity and wide coverage. However, the classical post-processing algorithm, the delay-and-sum (DAS) technique, suffers from notable artifacts and inadequate accuracy in Lamb wave inspection due to the existence of reflection and superposition, especially on composite materials. In this study, we proposed a novel algorithm, the correlation factor weighted DAS imaging algorithm based on the Long short-term memory-autoencoder (LSTM-AE), to address these deterioration issues. The LSTM-AE demonstrates the capability to extract potential features and accurately reconstruct input signals. By incorporating the concept of anomaly detection, an LSTM-AE trained with intact signals produces a significantly distorted output when exposed to damaged signals as input. We formulated a novel damage index (DI) based on the Pearson Correlation Coefficient (PCC) between the output and input signals as the weighting factor. The proposed method has undergone experimental validation, confirming its effectiveness in Lamb wave inspection.
Simulation of Internal Flow Field in Pulse Thruster Unit
Authors: Sun Junli , Long Dafeng
Published: June 2024

Pulse thrusters are widely used in the attitude control and flight trajectory control of rotating ammunition and vertical launching ammunition, which use own pulse impulse to change the attitude and trajectory of the missile. This paper simulates the internal flow field of a double-layer pulse thruster unit (PTU). The internal flow field of the PTU is simulated at various temperatures based on the three-dimensional compressible N-S governing equations and k-ω SST turbulence model. In addition, the influence of nozzle throat length and divergence half-angle on the performance of pulse T-thruster is analyzed. The simulation results demonstrate that the thrust output error of the PTU is minimum, when the nozzle throat length of the internal pulse thruster is 38 mm. Moreover, the stability of the PTU is improved.
Study on the Corrosion Resistance Of Thermal Sprayed Aerospace Coatings Under The Action Of High Current Pulsed Electron Beam
Authors: Wang Hongbo , Ji Xiaolei , Jia Ben
Published: June 2024

Aluminum-based amorphous alloys have excellent mechanical properties and corrosion resistance and are currently used in the form of coating materials for the protection of aircraft surfaces. In this study, AlCoCe alloy and powder are prepared, and then AlCoCe alloy coating is prepared on Q235 substrate by supersonic flame thermal spraying technology, and finally, the surface remelting modification treatment is carried out on the coating by current pulsed electron beam, and the transformation behavior of microstructure of the coating and the change of the corrosion resistance in this process are analyzed by structural characterization and corrosion experiment, to make clear the relationship between the structure of the coating and its corrosion resistance performance. After 15 current pulsed electron beam pulses, the coating surface formed a layer of dense and homogeneous composition of the amorphous structure of the treatment layer, when the number of pulses is higher, due to the heat of the substrate leads to a decrease in the cooling rate, which in turn will lead to the emergence of a crystalline structure of the surface treatment layer.
Analysis of engineering structures and components created using the generative design
Authors: Tkachenko Arseny , Wang Chang Jiang
Published: June 2024

Generative design is an AI-driven process to explore all the possible design variants, it mimics nature’s evolutionary approach to create an optimised final design. Generative design and additive manufacturing are interlinked because additive manufacturing is able to fabricate complex geometries. Generative algorithms have demonstrated their effectiveness in reducing costs, weight and development time across various industries including automotive and aerospace. This paper analysed components and structures to show the advantages of using the generative design method, problems encountered and issues that could be addressed to improve the final designs. Loading conditions, stress concentrations and manufacturability of the generative-designed components were discussed in the paper.
A phase-splitting approach to describe macroscopically non-equilibrium transport in porous media
Authors: Quintard M. , Davit Y. , Wood B.
Published: June 2024

Classical macro-scale dispersion equation cannot correctly represent non-local, non-equilibrium effects, and alternatives had to be proposed to overcome these discrepancies. Two-equation models have been widely used and proved useful to incorporate, to some extent, local non-equilibrium effects. More accurate descriptions may be obtained through the introduction of additional complex terms in the one-equation dispersion equation, e.g. spatial and time convolutions. An alternative more practical route rely on the introduction of a N-equations description. For instance, instead of a two-temperature model, transfers in the solid and/or fluid phase maybe represented by several equations, each one defined by some splitting framework. Splitting of the solid phase has been proposed in the past (multi-rate models). Splitting of the flowing phase has a rustic illustration in the case of the Coats and Smith model, i.e., ”flowing” and ”stagnant” fluid equations. In this paper, we explore further the possibilities offered by N-equations splitting of the flowing phase. The N-equations macro-scale model is developed applying an averaging technique to N-pseudo phases obtained by splitting the flowing phase based on different criteria, e.g. the velocity histogram. Most important model properties are the matrices of dispersion tensors and exchange coefficients, which are provided by a system of specific ”closure” problems. To illustrate this approach, the methodology is applied to Taylor’s dispersion problem, in which non-local effects are produced by pore-scale spatially distributed inlet conditions. The proposed N-equations description was compared to estimates of the N-temperatures obtained from direct numerical simulations. The N-equations model was able to reproduce accurately the dynamic of pore-scale computations, for such reputedly non-homogenizable problems, with a relatively small number of equations.
Impact of one and two partial cooling ducts on temperature rise in transformer windings
Authors: Bulatovič Goran , Bokes Peter
Published: June 2024

We apply our quasi-1D model to the temperature rise in oil-filled transformer foil windings with two symmetric partial ducts. We compare the results with a two-dimensional FEM simulation. To compare the results to industrial tests we try to find a relationship between the effective values for heat transfer coefficients of different foil windings. Finally, we compare the effectiveness of adding one vs two partial cooling ducts to the winding.
Experimental investigation of phase change material (PCM) thermal energy storages with and without metal foam at different temperatures
Authors: Fareedi AR , Khoso AQ , Khan H , Buonomo B , Manca O , Nardini S
Published: June 2024

This paper presents an experimental investigation of phase change materials (PCM) thermal energy storage. The experimental unit consists of a square channel with a single flow stream having distilled water as a heat exchange fluid. RT-42 is used as a thermal energy storage and the overall system is designed in two configurations i.e. with and without aluminium metal foam having a porosity of 95%. Each configuration is analysed and compared for two temperature variations i.e. at 55 °C and 65 °C, respectively. The study reveals that the heat storage rate in metal foam (MF) integrated PCM thermal energy storage is enhanced to ~3-4 times as compared to the setup without metal foam. In metal foam PCM energy storage, the temperature distribution is uniform and heat transfer is due to conduction as well as convection, while in case of pure PCM, there exist a temperature gradient within the thermal storage and the heat transfer is slower due to convection phenomenon. It is also observed that the heat transfer rate for 65 °C is comparatively greater than that of 55 °C for both systems as the higher operating temperatures lead to higher heat flux. However, operating at high temperatures is less feasible as the setup is more prone to PCM leakages.
A 3D symmetry-preserving simulation of a concentrated photovoltaic thermal (CPVT) solar collector
Authors: Santos D , Rigola J , Castro J , Trias F X
Published: June 2024

In this work, a general collocated and unconditionally stable framework on unstructured meshes for solving Conjugate Heat Transfer (CHT) problems is presented by means of preserving the underlying symmetries of the continuous differential operators, thus not introducing uncontrolled artificial numerical dissipation to our system. Then, this framework is applied to solve a Concentrated PhotoVoltaic Thermal (CPVT) Solar Collector. Furthermore, a new boundary condition is implemented to consider the heat transfer between enclosed elements, including radiation. The model is validated using experimental data.
A coupled point particle two-phase heat and mass transfer model for dispersed flows based on Boundary Element Methods
Authors: Gomboc T , Zadravec M , Ravnik J , Hriberšek M
Published: June 2024

In dispersed multiphase flow processes we encounter coupled heat, mass and momentum transfer between the disoersed and the continuous phase. In the context of the subdomain Boundary Domain Integral Method (BDIM) solution of the Navier-Stokes equations a two-way coupling model is presented based on the use of the elliptic fundamental solution and the Dirac delta function properties which leads to accurate evaluation of the heat and mass point particle source impacts on the continuous (air) phase. In addition, the two-phase flow case under consideration is extended to the case of porous spherical particle drying with internal moving drying front, which is solved by the Boundary Element Method (BEM).
An experimental investigation of forced convective liquid immersion cooling of a 12-cell li-ion battery module
Authors: Salter D W , Bachelier G , Kumavat P S , Trimble D , O’Shaughnessy S M
Published: June 2024

This study details an experimental investigation of forced convective liquid immersion cooling of lithium-ion batteries. Twelve Samsung INR 18650 20S cylindrical cells, each with a nominal voltage of 4.2 V and nominal capacity of 2 Ah, are placed in a 4-in-series, 3-in-parallel arrangement inside a polycarbonate chamber. The cells are immersed in the dielectric fluid SF-33 and are discharged at C rates in the range of 1C to 4C. Temperature sensors placed along the body of each cell near the electrodes monitor their thermal behaviour during experiments. Results show that liquid immersion cooling is an effective method to maintain all cell temperatures within the desired temperature range of 15°C to 35°C for all cases tested, maintaining temperature differences within individual cells to ≤1.5°C, and those between cells to ≤3°C. This research contributes to the understanding of thermal management strategies for lithium-ion batteries, particularly in scenarios involving high discharge rate applications.
Thermal analysis of an integrated motor drive with a switching cell array power converter
Authors: Grespan M , Busquets-Monge S , De Les Valls E Mas , Jordà X , Di Francisco M Raya , Angeli D
Published: June 2024

In modern electric propulsion systems the electric motor is tightly integrated with the power converter and control unit. These so called Integrated Motor Drives can allow for vast improvements in efficiency and volume reduction, due to the elimination of redundant electric components, and the shared case and cooling system between the motor and the power converter. The cooling systems used in these applications must be carefully designed as the motor and power electronics components may feature greatly different temperature limits. This work discusses the development of a thermal model for an integrated motor drive composed by a six phase permanent magnet motor with hairpin windings and a switching-cell-array-based multilevel power converter. The system is modelled by means of a lumped parameter thermal network which includes an accurate model of the motor stator and rotor, as well as the arrangement of the power switches on the converter boards. The conductive resistances are simply obtained from geometric data and material properties. Instead, the convective resistances are evaluated by means of empirical models available in the literature and a CFD model for the cooling jacket. The developed model is employed to assess the feasibility of the presented arrangement of motor and power electronics components from the thermal point of view.
Improvement of the modelling of the conduction-radiation flash method by a fully stochastic approach. A numerical validation
Authors: Seyer L , Enguehard F , Rochais D
Published: June 2024

Three different numerical models for simulating the well-known experimental flash method are presented and compared. These models consider conduction-radiation coupling and are applied within a one-dimensional grey semi-transparent slab enclosed between two opaque surfaces. The first model (A) is deterministic, dating back to about a decade, and is based on three assumptions regarding radiation transfer: isotropic intensity within each of the two hemispheres, the scattering phenomenon is supposed to be isotropic, and linearization of terms involving differences of temperatures to the fourth power. The other two models are completely new and do not make these assumptions. While the first one (B) is purely deterministic and serves as a reference for validation, the other one (C) is fully stochastic, and is the focus of this paper. A comparison shows excellent agreement between (B) and (C), validating our new model of interest (C). On the other hand, (A) exhibits significant discrepancies with the other two, highlighting the importance of its limiting assumptions.
Numerical modeling of a confined falling liquid film sheared by a gas flow in a plate heat exchanger of an NH3/H20 absorption chiller
Authors: Sleiman J , Collignon R , Phan H T , Stutz B
Published: June 2024

In recent years, the demand for cooling has seen a substantial increase, primarily due to rising summertime temperatures. Conventional mechanical compression air conditioners have played a predominant role in fulfilling this demand, albeit at the cost of significant electricity consumption. In response, absorption chillers have emerged as an eco-friendly alternative, powered by sustainable heat sources like solar energy or industrial waste heat. The present work is conducted within the framework of developing compact absorption chillers incorporating plate heat exchangers. It builds upon prior research by improving an existing numerical model for falling film plate heat exchangers within an NH3/H2O absorption chiller. This former numerical model evaluates the coupled heat and mass transfer between the liquid film and the vapor flow while excluding hydrodynamic interactions at the liquid-vapor interface. The current investigation aims to address compactness and cost-efficiency limitations in absorption chillers. The consequences of operation within confined spaces were numerically evaluated. An innovative analytical model was developed to quantify the influence of the interactions at the liquid-vapor interface. Shear stress and interfacial perturbations were considered compared to the classical Nusselt model, enabling the evaluation of the changes in the average film thickness and the flooding phenomenon. This analytical model was then added to the previously developed heat and mass transfer model. The numerical model was applied to both the desorber and absorber units. The results show that increased confinement has minimal effects on the transfer coefficients. Additionally, an approach is suggested for estimating flooding in confined spaces and the results are compared with various correlations available in the literature.
Experimental investigation of the supercritical heat transfer of the low GWP refrigerant R1234ze(E): calibration and validation of test rig
Authors: Van Nieuwenhuyse J , Lecompte S , De Paepe M
Published: June 2024

Heat transfer of supercritical refrigerants is applied in practical systems such as the transcritical organic Rankine cycle or supercritical heat pump. The concept of supercritical heat transfer is not new and has already been studied and applied for decades in several applications. However, results on one fluid cannot be directly translated to another one. This is because the thermohydraulic behavior of fluids is heavily influenced in the near-supercritical region due to sudden variations in the thermophysical properties when the fluid is heated or cooled close to its critical point. For refrigerants under horizontal flow, the research is limited. Most studies in literature are on small diameter tubes and on R134a, which has a high global warming potential. Therefore, an experimental test rig has been built to measure the supercritical heat transfer of low global warming potential refrigerants over a large temperature and pressure range in the supercritical region. In this work, the calibration and validation of this test rig is presented using the refrigerant R1234ze(E). The test section consists of a 4 m long horizontal tube with an inner diameter of 22.9 mm, equipped with thermocouples at both the tube wall and in the bulk of the flow, and is heated by resistance wires wrapped around the tube. For the calibration, the temperature profiles under both non-heating and heating conditions are evaluated. For the validation, the average Nusselt numbers obtained through experiments under subcritical conditions are compared to the average Nusselt numbers calculated based on the Dittus-Boelter and Gnielinski correlation.
Improving virtual heat transfer description of developed and undeveloped annular gap flows at high Taylor numbers
Authors: Žnidarčič Anton , Katrašnik Tomaž
Published: June 2024

Increased power densities of electric machines are, amongst other factors, related also to the increase of the rotors’ rotating velocities. These can be combined with axial flow to improve the heat transfer in the annular gap. The resulting high rotating and axial velocities are characterized with high Taylor (Ta) and Reynolds (Re) numbers. Such flow regimes are currently not yet thoroughly described. The reasons are in the complex interactions between the operating conditions, annular gap geometry and the conditions at the gap inlet, which affect the flow development in the gap. Each of these impacts varies between different electric machines, adding to the complexity of description. To address this, a numerical study based on 3D CFD simulations is performed. The study accounts for the impacts of the flow conditioning at the entrance to the annular gap and the possibility that the small scale turbulent structures might not be well resolved at high Ta numbers. Thus, different inflow configurations are applied using both RANS and LES models. The results are compared with available experimental and numerical data and provide a valuable insight into the requirements for reliable heat transfer description in the increasingly interesting flow conditions.
On a proper tensorial subgrid heat flux model for LES
Authors: Trias F X , Gorobets A , Oliva A
Published: June 2024

In this work, we aim to shed light on the following research question: can we find a subgrid-scale (SGS) heat flux model with good physical and numerical properties, such that we can obtain satisfactory predictions for buoyancy-driven turbulence at high Rayleigh numbers? This is motivated by our previous findings showing the limitations of existing SGS heat flux models for LES. On one hand, the most popular models rely on the eddy-diffusivity assumption despite their well-known lack of accuracy in a priori studies. On the other hand, the gradient model, which is the leading term of the Taylor series of the SGS flux, is much more accurate a priori but cannot be used as a standalone model since it produces a finite-time blow-up. In this context, we firstly aim to reconcile accuracy and stability for the gradient model. To do so, it is expressed as a linear combination of regularized (smoother) forms of the convective operator. The new alternative form can indeed be viewed as an approximate deconvolution of the exact SGS flux. Moreover, it facilitates the mathematical analysis of the gradient model, neatly identifying those terms that may cause numerical instabilities, leading to a new unconditionally stable non-linear model that can indeed be viewed as a stabilized version of the gradient model. In this way, we expect to combine the good a priori accuracy of the gradient model with the stability required in practical numerical simulations.
Experimental and numerical pressure drop investigation of a protruding tube microchannel heat exchanger
Authors: Settati Mohamed , Oliet Carles , Sanmarti Oriol , Oliva Assensi
Published: June 2024

An experimental and numerical fluid flow study in a micro heat exchanger (microHEX) is conducted in this work to investigate its pressure drop characteristics. The microHEX sample presents a high degree of protrusion of the microchannels inside the inlet and outlet manifolds (Lprot
/Dm
=0.7), a large manifold-to-branch area aspect ratio (Am/As
=37), and a very small flow division in each microchannel (β=1/34). These features configure T-junctions that differ completely from the conventional ones in the literature. Experimental measurements of the microHEX pressure drop were performed for the Reynolds range of 300-2200. The numerical methodology combines a 1D model to evaluate the pressure drop of a single microchannel, adding minor entrance and exit losses due to the change of section and direction. A CFD numerical simulation evaluates the particular pressure loss associated with the dividing T-junction towards the protruded microchannel. The numerical simulation pressure drop results compared well with the experimental measurements, reporting a difference of 3.11% for an initial case. An extension of the work will soon cover all the collected experimental cases.
Experimental investigations of the potential of organic salt solutions for application in pressure-retarded osmosis
Authors: Dietrich F , Cieślikiewicz Ł , Furmański P , Łapka P
Published: June 2024

Pressure-retarded osmosis (PRO) is a process that enables useful work generation from the salinity difference of solutions. The literature most often considers using PRO with natural sodium chloride (NaCl) solutions such as seawater and river water or industrial solutions such as seawater desalination concentrate. Open cycle systems, which are dependent on the available source of streams feeding the system, are most often analyzed. In such systems, the full PRO potential as a power generation method cannot be explored due to the existing limitations of natural and industrial NaCl solutions. The second approach, found less frequently in scientific publications, is closed-cycle systems. They allow more extensive manipulation of the feed and draw stream parameters and the use of optimized synthetic solutions. This allows optimization of the process precisely for the intended applications. Furthermore, engineered solutions of various compositions can be used in closed-cycle systems, which opens new ways of increasing the system performance and application potential. The research described in this article is focused on the experimental evaluation of PRO potential for generating useful work by applying solutions of organic salts under varying conditions. The chemical compounds used were selected based on their theoretical performance, ease of use, and availability. The developed experimental stand allows full control over the temperature of the feed and draw solution streams. The studies were conducted without back-pressure, in a configuration typical of the forward osmosis process, with solution circulation on both sides of the membrane. As a result, the effect of solution temperature and concentration on water flow through the membrane was determined, and permeate flow is directly related to achievable work in the PRO process. The obtained results were compared to the system performance with NaCl solutions under the same conditions to evaluate potential gains.
Numerical simulation of drop impingement onto superheated textured walls
Authors: Sontheimer Henrik , Ho Anh Tu , Elsäßer Leon , Stephan Peter , Gambaryan-Roisman Tatiana
Published: June 2024

Spray cooling stands out as a suitable method for cooling of high-end electronic devices. Texturing of the surface can further increase the cooling performance. Understanding the flow dynamics and heat transport during the impingement of a single drop is crucial to gain an in-depth insight into complex phenomena governing spray cooling. In this study, the influence of textured walls on drop impingement dynamics and heat transfer is investigated. Numerical simulations are conducted within the OpenFOAM framework. Our solver accounts for evaporation, conjugate heat transfer and a dynamic contact angle. We study wall topographies comprised of cubes, rectangular grooves, pyramids and triangular grooves. Our results reveal that textured surfaces significantly increase both wetted area and contact line length compared to a smooth wall, with cubes demonstrating the best performance. Furthermore, we observe a significant increase in heat flow during the sessile drop phase. This study lays the foundation for designing surfaces that optimize heat transfer for drop impingement and spray cooling.
Ensemble averaging parallel-in-time approach for industrial LES
Authors: Plana-Riu Josep , Xavier Trias F , Alsalti-Baldellou Àdel , Colomer Guillem , Oliva Asensio
Published: June 2024

Computational Fluid Dynamics for industrial applications usually relies on RANS modeling instead of LES, as the latter is more expensive and requires much longer simulation times. In order to reduce the computational cost of the simulation, an ensemble averaging parallel-in-time approach is presented so that the simulation time of LES simulations can be reduced up to overnight lengths by exploting the benefits of using sparse matrix-matrix products, SpMM, instead of the classic sparse matrix-vector products, SpMV, or SpMV-like stencil-based kernels, as it might lead to a speed-up given the proper conditions. These conditions are tested for a classical differentially heated cavity benchmark, to apply later on to the simulation of a CSP collector, as it is a well-known academic case that resembles the final geometry.
State of the art of micro vapour-compression systems
Authors: Blatnik Mihael , Klinar Katja , Kitanovski Andrej
Published: June 2024

Thermal management is becoming more challenging due to the increasing compactness and computational power of appliances. Affordable and efficient solutions include active liquid cooling methods, thermoelectric cooling, and the use of heat pipes. From these, vapour-compression technologies achieve the highest power density. However, the downscaling of vapour-compression for cooling of personal computers or workstations is rather problematic from several different reasons. The first problem concerns the low second law efficiency of miniature vapour-compression systems. The second problem concerns the available space occupation of such a cooling system. Moreover, miniature and high-power density condensers and evaporators have not yet been adequately researched and developed to date. In this review, we present several vapour-compression refrigeration systems that are based in some way on the miniaturisation of systems or individual components – evaporators, condensers, and compressors. These are presented and compared in terms of cooling power, COP, and the second law efficiency. At the end of the manuscript, guidelines for future improvements and the implementation of miniature vapour-compression systems are presented.
Direct air capture with renewable heating based on the technical lime cycle
Authors: Klockow E , Linder M
Published: June 2024

The industry and space heating demand contributes significantly to the CO2 emissions in Germany, as it is mainly supplied by the combustion of fossil fuels. In this contribution a concept is presented that not only provides heat based on renewable sources, but is also able to actively capture CO2 from the atmosphere. Thereby, the reversible reaction of lime with water is utilised to store and provide heat on demand – all based on abundantly available resources. By closing the technical lime cycle this long-term energy storage could additionally be combined with a Direct Air Capture technology.