Non-uniform Conditions Research Articles

A two-dimensional method for radial turbine volute design - Part 2: Circumferentially non-uniform boundary condition

A two-dimensional method for radial turbine volute design - Part 2: Circumferentially non-uniform boundary condition

Numerical study on fluid flow and heat transfer characteristics of supercritical CO2 in horizontal tube under various non-uniform heating conditions

Supercritical CO2 (sCO2) is deemed the potential working medium for thermodynamic cycles in the next generation of power machinery. In this paper, the flow and heat transfer characteristics of highly buoyant turbulent sCO2 in horizontal tubes are numerical studied under the non-uniform heating conditions. The tube with a typical internal diameter of 10 mm is selected with mass flux equaling to 300 kg/(m2·s), effective heat fluxes ranging from 20 to 60 kW/m2, and pressure equaling to 8 MPa. The results confirmed that the heat transfer of sCO2 inside the horizontal tube in the circumferential or axial non-uniform heating conditions is greatly deteriorated by 13 %-68 % compared to the uniform heating. The overall heat transfer performance of semi-circumferential axial non-uniform heating is about 2.5 % higher than that of bottom semi-circumferential uniform heating, while the axial temperature difference of the bottom surface exceeds 150 K. Screening three representative heating positions, the bottom heating has the best temperature uniformity. The corresponding turbulent streamlines featured by unique helical structures can substantially improve the circumferential and radial heat transfer over 10 %, enhancing the heat transfer performance of the smooth tube close to that of rifled tubes. Based on the numerical data, viable correlations were developed for calculating the axial local Nusselt number of forced convection heat transfer of sCO2 in horizontal tubes considering the effects of cross-sectional vorticity, secondary flow intensity, and buoyancy-natural convection, and the prediction values are in good agreement with experimental data.

A general model for spin coating on a non-axisymmetric curved substrate

We derive a generalised asymptotic model for the flow of a thin fluid film over an arbitrarily parameterised non-axisymmetric curved substrate surface based on the lubrication approximation. In addition to surface tension, gravity and centrifugal force, our model incorporates the effects of the Coriolis force and disjoining pressure, together with a non-uniform initial condition, which have not been widely considered in existing literature. We use this model to investigate the impact of the Coriolis force and fingering instability on the spreading of a non-axisymmetric spin-coated film at a range of substrate angular velocities, first on a flat substrate, and then on parabolic cylinder- and saddle-shaped curved substrates. We show that, on flat substrates, the Coriolis force has a negligible impact at low angular velocities, and at high angular velocities results in a small deflection of fingers formed at the contact line against the direction of substrate rotation. On curved substrates, we demonstrate that, as the angular velocity is increased, spin-coated films transition from being dominated by gravitational drainage with no fingering to spreading and fingering in the direction with the greatest component of centrifugal force tangent to the substrate surface. For both curved substrates and all angular velocities considered, we show that the film thickness and total wetted substrate area remain similar over time to those on a flat substrate, with the key difference being the shape of the spreading droplet.

Characterizing surface pressure and wind fields of typhoons approaching Hong Kong

In this paper, 17 severe typhoons that have affected Hong Kong are simulated using an advanced numerical atmospheric simulation system - Weather Research and Forecasting model (WRF). The simulated surface pressure and wind fields of these typhoons are validated against a wide range of field observations. Then azimuth-dependent models for the radius of maximum winds and the Holland parameter are established statistically at the surface level. It is observed that the shape parameter of the Holland pressure model is smaller at the surface than that at the gradient level. And the Holland wind field model cannot well reproduce the simulated radial wind profiles due to the complexities of nonuniform surface conditions and typhoon dynamics. It is found that the modified Rankine model provides satisfactory estimates of typhoon wind speeds in Hong Kong. Additionally, wind field asymmetries of typhoons approaching Hong Kong are highly correlated with the typhoon track velocity, vertical wind shear and the angle between them. The proposed statistical models and identified characteristics of wind field asymmetries of typhoons will provide useful information for rapidly assessing typhoon wind hazards.

Enhancement of carbon nanotubes/kerosene nanofluids on mixed convective heat transfer in rectangular enclosures

With the objective of understanding how the mixed convective and the geometrical parameters together influence the nanofluid behavior (enhancement or deterioration) and finding the best configuration of the moving walls for engineering purposes, this paper investigates the single lid-driven mixed convective flow of carbon nanotubes/kerosene nanofluids confined in vertical and horizontal cavities with non-uniform boundary conditions applied to the vertical walls. The findings of this paper can provide crucial conclusions into the behavior and optimization of nanofluids in mixed convective flows in enclosed systems for engineering applications. The system of the governing equations is tackled by a validated in-house code, where we compared the code accuracy with previous experimental and numerical works. The governing parameters are -50 ≤ Pe ≤ 50, 0.5 ≤ A ≤ 4, and 0 ≤ φ ≤ 3%. The effective nanofluid properties are calculated using special experimental models. The outcomes revealed that the carbon nanotube effect on heat transfer depends on the aspect ratio. The greater the aspect ratio, the more pronounced the negative impact of the nanotube concentration where Nusselt number is reduced by 4.49% and 16.17% for φ = 0.01 and 0.03, respectively, in the case of Pe = 0 and A = 4. The Peclet number also has a significant impact on the heat transfer, especially for higher aspect ratios, and diminishes the critical aspect ratio where the nanofluid's behavior changes. An augmentation in the aspect ratio and Peclet number brings about an augmentation in the Nusselt number. Additionally, the Peclet number can reverse the conjugated effect of carbon nanotube volume fraction and aspect ratio on nanofluid enhancement. When Pe = 50 in C1, heat transfer rate is 1.75% and 1.11% enhanced for φ = 0.01 and 0.03, respectively, and A = 4. Moving horizontal walls exhibits higher heat transfer enhancement compared to vertical ones.

Underwater image restoration via attenuated incident optical model and background segmentation

Underwater images typically exhibit low quality due to complex imaging environments, which impede the development of the Space-Air-Ground-Sea Integrated Network (SAGSIN). Existing physical models often ignore the light absorption and attenuation properties of water, making them incapable of resolving details and resulting in low contrast. To address this issue, we propose the attenuated incident optical model and combine it with a background segmentation technique for underwater image restoration. Specifically, we first utilize the features to distinguish the foreground region of the image from the background region. Subsequently, we introduce a background light layer to improve the underwater imaging model and account for the effects of non-uniform incident light. Afterward, we employ a new maximum reflection prior in the estimation of the background light layer to achieve restoration of the foreground region. Meanwhile, the contrast of the background region is enhanced by stretching the saturation and brightness components. Extensive experiments conducted on four underwater image datasets, using both classical and state-of-the-art (SOTA) algorithms, demonstrate that our method not only successfully restores textures and details but is also beneficial for processing images under non-uniform lighting conditions.

An innovative subdivision collocation algorithm for heat conduction equation with non-uniform thermal diffusivity.

This paper presents a subdivision collocation algorithm for numerically solving the heat conduction equation with non-uniform thermal diffusivity, considering both initial and boundary conditions. The algorithm involves transforming the differential form of the heat conduction equation into a system of equations and discretizing the time variable using the finite difference formula. The numerical solution of the system of heat conduction equations is then obtained. The feasibility of the algorithm is verified through theoretical and numerical analyses. Additionally, numerical and graphical representations of the obtained numerical solutions are provided, along with a comparison to existing methods. The results demonstrate that our proposed method outperforms the existing methods in terms of accuracy.

Optimizing and investigating the charging time of phase change materials in a compact-latent heat storage using pareto front analysis, artificial neural networks, and numerical simulations

There's a growing emphasis on adopting eco-friendly energy sources to mitigate greenhouse gas emissions and foster sustainability. While renewable energy sources like solar power offer numerous benefits, they have some limitations. Additionally, storing electricity generated from solar panels can be costly and challenging due to limitations in battery technology and storage capacity. Therefore, phase change material-based thermal energy storage systems offer a promising solution to these challenges. These systems also play a crucial role in enhancing buildings' energy efficiency and sustainability. The dimensionality of these systems affects their performance. Traditional systems often rely on fixed dimensions, leading to non-uniform thermal conditions within the storage medium. To address these challenges, adopting a compact-latent heat storage (C-LHS) mechanism was recommended herein. Besides, some fins were inserted into the C-LHS system to alter the heat transfer dynamics within the device. Three of the critical parameters of the fins were changed to examine their impact on the charging time. Artificial neural networks and genetic algorithms were employed to determine the optimal positioning of fins to minimize the duration of material to get both part (melt fraction of 0.8) and full (melt fraction of 1) melting capacities. Here, the primary aim was to present a predictive model capable of accurately forecasting the charging time of the material. In all the presented finned samples, the entire PCM melted in less than 15,110 s (4 h and 12 min) and was able to fully utilize the energy absorption capacity in latent form, whereas in the non-finned system, only 68.6 % of the material managed to melt within the entire duration of the investigation (5 h). After analyzing the data, two optimal configurations of OS1 and OS2 with the minimum time for melt fractions of 0.8 and 1 were introduced. In the OS2 configuration, it took 16,200 s (4 h and 30 min) to absorb 4929 kJ of energy. The non-finned sample absorbed only 3250 kJ of energy during the same period. In General, OS2 achieved total energy absorption 51.6 % faster than the non-finned sample. Therefore, the introduced system has the potential to increase absorbed energy in the rest of the daylight hours to further amounts by increasing the number of units and employing a larger volume of material.

Pore Network Modeling of Intraparticle Transport Phenomena Accompanied by Chemical Reactions.

In this work, a 3D pore network model (PNM) is introduced for modeling reaction-diffusion phenomena, with and without coupled heat transfer, in a spherical porous catalyst particle. The particle geometry is generated by packing thousands of microspheres inside a large sphere to represent the 3D geometry, porosity, and tortuosity of a spherical catalyst particle. A pore-network representation is extracted from this geometry, and a PNM for diffusion-reaction and heat conduction is constructed. This newly proposed particle-scale PNM allows for the application of realistic 3D nonuniform boundary conditions on the particle's surface, which is commonly encountered in slender packed-bed reactors. Concentration profiles inside the particle, and effectiveness of the reactions, is analyzed.

Numerical investigation on the effects of non-uniform azimuthal heating in natural convection airflow within a vertical tube

Airflows established by buoyancy forces within vertical tubes with circular cross-section are analyzed. Obtained (finite-volume) numerical results cover the complete laminar-turbulent range (modified Rayleigh number from 10−3 to 109), through a low-Reynolds turbulence model. Both uniform and non-uniform heating conditions are regarded. Three different types of non-uniform heating along the azimuthal direction are considered, which constitutes an advance in the knowledge of the flow behavior, since it has not sufficiently addressed in the literature. Specifically, two modes of continuous non-uniform heating are proposed (temperature fixed at wall, and heat flux fixed at wall), and another mode through discrete heaters (for heat flux condition). The circumstances under which non-uniform azimuthal heating can be beneficial or detrimental with respect to thermal and dynamic performance are investigated. It is encountered that disrupting effect of discrete heat sources can induce, under given conditions, an improvement in the thermohydraulic performance.

Effects of the Operating Point of Photovoltaic Strings on Sizing of DC‐ and AC‐Connected Energy Storage Systems for Power Smoothing

Photovoltaic (PV) power generators are constantly exposed to operating condition variations. While the electrical characteristic of a PV generator has exactly one maximum power point (MPP) during homogeneous operating conditions, several MPPs may exist during nonuniform operating conditions. Since highly varying global MPP voltage causes large fluctuations in the inverter reference voltage, it would be beneficial to keep the operating point of the inverter all the time close to the nominal MPP voltage to secure more predictable and straightforward operation of the PV system. This article presents a study of the effects of the operating point on the operation of PV strings equipped with energy storage systems (ESS). A scenario in which the MPP closest to the nominal MPP voltage is used as the operating point is compared to operation in the global MPP. The effects of inverter sizing on the selection of the operating point are also studied. Moreover, DC and AC connections of the ESSs are compared. The study is based on measured current–voltage curves of a 23 module PV string. The results show that, in practice, there are no major differences in sizing of DC‐connected ESSs between the two MPPs.

UPT-Flow: Multi-scale transformer-guided normalizing flow for low-light image enhancement

Low-light images often suffer from information loss and RGB value degradation due to extremely low or nonuniform lighting conditions. Many existing methods primarily focus on optimizing the appearance distance between the enhanced image and the normal-light image, while neglecting the explicit modeling of information loss regions or incorrect information points in low-light images. To address this, this paper proposes an Unbalanced Points-guided multi-scale Transformer-based conditional normalizing Flow (UPT-Flow) for low-light image enhancement. We design an unbalanced point map prior based on the differences in the proportion of RGB values for each pixel in the image, which is used to modify traditional self-attention and mitigate the negative effects of areas with information distortion in the attention calculation. The Multi-Scale Transformer (MSFormer) is composed of several global-local transformer blocks, which encode rich global contextual information and local fine-grained details for conditional normalizing flow. In the invertible network of flow, we design cross-coupling conditional affine layers based on channel and spatial attention, enhancing the expressive power of a single flow step. Without bells and whistles, extensive experiments on low-light image enhancement, night traffic monitoring enhancement, low-light object detection, and nighttime image segmentation have demonstrated that our proposed method achieves state-of-the-art performance across a variety of real-world scenes. The code and pre-trained models will be available at https://github.com/NJUPT-IPR-XuLintao/UPT-Flow.

An Experimental Derivation of Transient Nonuniform External Boundary Conditions for the Solidification Process Modeling of Equiaxed Investment Castings

An Experimental Derivation of Transient Nonuniform External Boundary Conditions for the Solidification Process Modeling of Equiaxed Investment Castings

Examination of the Behavior of Double Cold-Formed Steel Columns with Σ-Shaped Sections Subjected to Non-Uniform Temperature Conditions

Examination of the Behavior of Double Cold-Formed Steel Columns with Σ-Shaped Sections Subjected to Non-Uniform Temperature Conditions

Two-dimensional heat transfer and thermoelastic analysis of temperature-dependent layered beams with nonuniform thermal boundary conditions

Two-dimensional heat transfer and thermoelastic analysis of temperature-dependent layered beams with nonuniform thermal boundary conditions

Configuration optimization of PV array for stratospheric airship under nonuniform radiation condition

The nonuniform solar irradiation on the stratospheric airship surface leads to overlooked mismatch losses in photovoltaic (PV) array. Proper configuration for PV array is crucial but frequently neglected in airship energy system research. In this paper, a mathematical model coupled with the layout of PV array on airship surface, radiation model, electrical model and energy balance model is established. The deployment of PV pack based on the distribution characteristics of solar radiation on airships surface is analyzed. Three maximum power point tracking configurations for the PV array are investigated in detail. The results indicate that mounting PV pack in axial series on stratospheric airships leads to higher power output compared to parallel-connected deployment, PV packs on stratospheric airships exhibit significant output power differences along the circumferential direction and minor differences along the axial direction, the peak of daily maximum output difference ratio is merely 0.4 % between the PV array under the distributed maximum power point tracking (DMPPT) and the partial distributed global maximum point tracking (PDMPPT) configuration, and PDMPPT configuration needs much fewer module, it emerges as the optimal choice for stratospheric airship PV array. This investigation can provide references for the further PV array configuration optimization under nonuniform radiation condition.

Hetero-associative Memory Based New Iraqi License Plate Recognition

نتيجة للتطورات الأخيرة في أبحاث الطرق السريعة بالإضافة إلى زيادة استخدام المركبات، كان هناك اهتمام كبير بنظام النقل الذكي الأكثر حداثة وفعالية ودقة (ITS) في مجال رؤية الكمبيوتر أو معالجة الصور الرقمية، يلعب تحديد كائنات معينة في صورة دورًا مهمًا في إنشاء صورة شاملة. هناك تحدٍ مرتبط بالتعرف على لوحة ترخيص السيارة (VLPR) بسبب الاختلاف في وجهة النظر، والتنسيقات المتعددة، وظروف الإضاءة غير الموحدة في وقت الحصول على الصورة والشكل واللون، بالإضافة إلى الصعوبات مثل ضعف دقة الصورة ، الصورة الباهتة ، الإضاءة السيئة، التباين المنخفض، يجب التغلب عليها. اقترحت هذه الورقة نموذجًا باستخدام تعديل الذاكرة الترابطية ثنائية الاتجاه (MBAM)، وهي نوع واحد من الذاكرة الترابطية غير المتجانسة، وتعمل MBAM على مرحلتين)مرحلتي التعلم والتقارب) للتعرف على اللوحة، ويمكن لهذا النموذج المقترح التغلب على تلك الصعوبات بسبب قدرة الذاكرة الترابطية لـ MBAM على قبول الضوضاء وتمييز الصور المشوهة، وكذلك سرعة عملية الحساب نظرًا لصغر حجم الشبكة. نتيجة دقة تحديد منطقة اللوحة هي 99.6٪، ودقة تجزئة الأحرف 98٪، والدقة المحققة للتعرف على الأحرف هي100 ٪ في ظروف مختلفة.

Improved PV module model for dynamic and nonuniform climatic conditions in ISIS-proteus

Improved PV module model for dynamic and nonuniform climatic conditions in ISIS-proteus

Experimental and numerical studies of the fuel concentration distribution within the near-wall area in a compact space for a gas turbine combustor

Interstage combustion is known for its small axial distance, high combustion efficiency and low lean blowout boundary. However, in a compact space, the distance between the fuel injection location and the wall is confined, and the high-temperature wall may affect the fuel distribution and in turn affect the combustion efficiency. In this study, an experiment of kerosene single-droplet evaporation was conducted, and the fuel distribution in an interstage combustor was numerically simulated. The experimental results showed that the evaporation rate of fuel droplets decreased with increasing distance from the high-temperature wall, and the influence of the lower wall on fuel evaporation was greater than that of the sidewall. The fuel evaporation rate at the high-temperature position within the nonuniform wall temperature field was relatively high. The numerical simulation results indicated that with increasing temperature, the effect of the wall on fuel evaporation increased, as did the uniformity of the fuel distribution. The direction of the temperature gradient imposed the greatest effect on the fuel distribution under nonuniform temperature conditions. This will facilitate the selection of the optimal ignition location within the cavity to achieve efficient combustion. Moreover, it's possible to control the fuel distribution by adjusting the wall temperature.

A gyroid TPMS heat sink for electronic cooling

The trend toward thinner and lighter electronic devices necessitates developing advanced thermal management solutions to address modern microprocessors’ escalating heat dissipation demands. This study introduces an advanced thermal solution incorporating a gyroid TPMS structure with remarkable physical properties for microprocessor cooling. Detailed investigations were conducted using a full-scale heat sink model to understand the inner geometric structure, flow, and heat transfer characteristics within a gyroid heat sink (GHS). The thermo-hydraulic performance of the GHS design was systematically assessed against that of a pinfin heat sink (PHS) across different porosities and flow rates. Both heat sinks were evaluated under non-uniform heating conditions, considering three heating schemes, each with eleven randomly distributed hotspots. The thermohydraulic performance was assessed by calculating temperature non-uniformity, thermal resistance, and pumping power. A correlation was established using the cell size and cell wall thickness of a unit cell of gyroid TPMS to calculate its hydraulic diameter. The analysis revealed that the enhanced thermal performance of the GHS design can be attributed to its intricate and convoluted flow structure, along with a significantly large heat transfer surface area. However, these same factors contribute to a notably high-pressure drop. Compared to the PHS design, the GHS design showed better thermal performance at all the selected porosities and flow rates, albeit with higher pumping powers. The GHS design showed improvement in the thermal performance as the porosity decreased. Investigation under heterogeneous heating conditions showed substantially lower temperatures at the hotspots in the GHS design, along with reduced temperature variation among them. The study’s findings provide valuable insight into the advantages and drawbacks of gyroid TPMS structure for their application in electronic cooling.