Non-uniform Temperature Research Articles

A review on magnetic permeability in heat and fluid flow characteristics: Applications in magnetized shielding

Magnetic permeability as a material property has a significant impact on the characteristics of a heated surface where induction heating or magneto-thermal systems are involved. In the heat and fluid flow mechanism where heat induction is used, magnetic permeability has a significant and crucial impact. Materials-like ferromagnetic materials with high magnetic permeability enhance the eddy current formation and can concentrate the magnetic field during the processes. These eddy currents lead to Joule heating in terms of electric current induced within the conductor by a changing magnetic field. Magnetic permeability also impacts the temperature profile within the material. Materials with extraordinary permeability due to the concentration of magnetic field can cause localized heating. The variable material properties in the presence of localized heating lead to non-uniform temperature distribution throughout the medium. In the magnetohydrodynamics heat and fluid flow region in the presence of magnetic permeability, some materials perform magnetostrictive impacts; therefore, they change shape or size under the influence of a magnetic field. The role of magnetic permeability along the heated surface is multifaceted in the system where an electromagnetic field is involved and affects how heat is generated, distributed, and dissipated. It is pertinent to mention that in the system where the electromagnetic field is involved, the magnetic permeability directly impacts the efficiency and uniform heating. Therefore, the understanding and controlling of magnetic permeability is important to design the systems that rely on exact thermal management, such as in magnetic shielding, magneto-thermal devices, and induction heating.

A prediction method of thermal deformation of near-zero warping sandwich structure under non-uniform temperature field

The thermal deformation of structure in non-uniform thermal environment in space is a critical factor affecting the imaging accuracy of remote sensing satellite. In this study, the thermal deformation theory of near-zero warping sandwich structure under non-uniform temperature field is established. A high-fidelity prediction method based on CT scanning and reconstruction of structural defects is proposed. Thermal deformation experiments show that this method can accurately characterize the ultra-low thermal deformation behavior of the near-zero warping sandwich metastructure, which is significant for the real-time correction of satellite imaging in orbit.

Intelligent decision-making approach for rapid optimization of double-wall cooling structures under varying cooling demands

Double-wall structures are widely employed for cooling turbine blades. When manufacturing materials and application conditions vary, the design of double-wall structures should be adapted to meet different cooling demands. However, because of inevitable repetitive iterations, conventional evolutionary algorithms exhibit low efficiency in optimizing double-wall structures when cooling demands change. This paper presents a reinforcement learning-based method to optimize double-wall cooling structures facing various cooling demands rapidly. A decision network established a forward mapping from cooling demands to optimized structural designs and was trained using historical decision-making experiences generated from numerical simulations. The historical experiences were quantified uniformly based on the cooling performance gains or losses resulting from changes in geometric parameters. The physical understanding that cooling performance evaluations differ with varying cooling demands was incorporated into the training dataset. The performance of the trained decision network was validated by varying the cooling optimization objectives. Results indicate that the decision network can achieve optimal double-wall cooling units that meet given objectives with a single decision. The decision process took 5 ms, nearly 90 times faster than traditional genetic algorithms. Moreover, a partitioning, multi-cycle application strategy for the decision network was employed to optimize double-wall cooling plates under non-uniform inlet temperature distributions, resulting in a 13.7K reduction in overall average temperature and improved radial temperature uniformity.

Thermal challenges in heterogeneous packaging: Experimental and machine learning approaches to liquid cooling

In recent years, electronic packaging has evolved significantly to meet demands for higher performance, lower costs, and smaller designs. This shift has led to heterogeneous packaging, which integrates chips of varying stack heights and results in non-uniform heat flux and temperature distributions. These conditions pose substantial thermal management challenges, as they can create large temperature gradients, which increase thermal stress and potentially compromise chip reliability. This study explores single-phase liquid cooling for multi-chip modules (MCMs) through a comprehensive experimental and machine learning approach. It investigates the impact of chip spacing, height, fluid flow rate, fluid inlet location, and heat flux uniformity on chip temperature and the thermohydraulic performance of a commercial cold plate. Results show that increasing coolant flow from 1 LPM to 2 LPM decreased thermal resistance by 26 %, with heat losses remaining below 5 %. The left inlet configuration improved temperature uniformity compared to the right, though both yielded comparable thermal performance. Adjusting heater spacing impacted temperature distribution based on inlet position, and lowering one heater by 1 mm raised its temperatures by 15 °C due to increased thermal resistance from thermal interface material. A transient test demonstrated the cold plate’s quick response to power surges, in which there is only a 1 °C spike above steady state. Complementing these findings, an Artificial Neural Network (ANN) model was developed with optimized architecture specifically for the unique challenges of this study. The ANN model was rigorously validated using an independent dataset, achieving highly accurate temperature predictions (R2 = 0.99) within 2.5 % of experimental values, which demonstrates this framework’s potential for optimizing MCM thermal performance.

Experimental investigation on combined flow and temperature non-uniformity for three-fluid compact heat exchanger with cross flow configuration

ABSTRACT Non-uniformities in flow and temperature are the most conspicuous reason behind diminishing efficacy in heat exchangers. Cross-flow three-fluid heat exchanger being a pivotal component in cryogenics, is experimentally investigated under imposed flow and temperature non-uniformities in central hot fluid. The interaction of combined flow and temperature non-uniformity invariably precipitates a degradation in the efficacy of both adjacent fluids. About 7.3% and 6.2% of efficacy degradation is encountered in fluid “a” (for C 2 configuration) and fluid “c” (for C 1 configuration), respectively, for F N 1 + T N III model. In many cases, C 1 configuration and T N III model is inimical to fluid “c” performance.

Improved numerical modeling of photovoltaic double skin façades with spectral considerations: Methods and investigations

Photovoltaic double skin façades are crucial tools for mitigating the escalating energy consumption in buildings. However, current simulation studies often neglect the variation in solar spectra and focus on only limited operational modes, resulting in incomplete and less accurate modeling. In response to these limitations, this study proposes an improved numerical model incorporating temporal spectral variations and non-uniform surface temperatures, which comprehensively encompasses all operational modes of photovoltaic double skin facades. Real-time solar spectra are acquired using specialized software and remote sensing data, while the transportation and conversion of radiation energy will be solely solved at individual wavelength steps, providing the model with spectrum resolution. Built on the fundamental principles of optics, thermodynamics, and hydromechanics, the proposed two-dimensional numerical model consistently demonstrates desirable accuracy across various airflow paths and mechanical ventilation conditions. Based on the proposed model, the feasibility of the previously proposed parameter-based control strategy is proved, which offers potential energy savings of 25.9–341.6 MJ compared to the radical strategy and 67.5–170.7 MJ compared to the conservative strategy. The photovoltaic efficiency drop due to spectral mismatch is also quantified as about 15–35 %. These results highlight the potential of the proposed model as an efficient tool for future research.

Novel design of centralized square array of pin-fins in microchannels heat sink for thermal management of high concentrator photovoltaic systems

High concentrations of direct normal irradiation on photovoltaic cells can cause a substantial rise in the cell’s temperature, leading to a decline in performance and potential damage to the cell. Therefore, maintaining low and uniform temperatures in solar cells is crucial for enhancing reliability and optimizing the performance of high concentrator photovoltaic systems. By placing the solar cell layer centrally and integrating a centralized square array of pin-fins within rectangular microchannels, cooling performance can be greatly improved. This study proposes a novel heat sink design incorporating a centralized square array of pin-fins in rectangular microchannels, specifically aimed at efficient active cooling of high concentrator photovoltaic systems. The investigation was conducted under a concentration ratio of 1000 suns and mass flow rates of water coolant ranging from 15 to 1000 g/min with the inlet temperature of 25 °C. The number of centralized square array of pin-fins were varied with the aim of obtaining the best design of square array of pin-fins that provides efficient cooling of solar cell with minimum temperature non-uniformity distribution. The results revealed that the number of square arrays of pin-fins have significant effect on the cell temperature, temperature uniformity, cell efficiency, net electrical power, thermal and exergy efficiency. For all design cases, the non-uniformity temperature of the cell declines with increase in mass flow rates, and the minimum value of 9.50 K for a design case 4 with 7-square array of pin-fins was achieved at the mass flow rate of 1000 g/min. The net electrical power peaks at 35.825 W for the design case 8 as the mass flow rate increases from 15 to 200 g/min. However, as the mass flow rate further increases from 200 to 1000 g/min, the net power decreases due to increased pumping power with design case 1 and 8 experiencing the minimum and maximum percentage reduction of 0.231 % and 6.606 % respectively. CFD code was utilized for the computations and validated with the available data in an open literature.

Nonuniform Temperature Compensation in Ultrasonic Guided Wave Pipeline Health Monitoring Using Local Phase Matching

Faced with a complex working environment, pipelines are prone to nonuniform temperature variations, which cause nonuniform phase changes in the guided wave signals during structural health monitoring, thereby increasing the difficulty of monitoring. To address this, a simulation model is established in this paper to analyze the effects of temperature on material parameters and the variation patterns of guided wave signals. A nonuniform temperature compensation method based on local phase matching is proposed. The algorithm first uses cosine similarity to find the locally best-matched signal segments between the monitoring signal and the baseline signal. Then, an indicator is introduced to quantify the differences between these best-matched signal segments, with the maximum difference considered to be the damage index. Three heating experiments on pipelines with nonuniform temperature fields ranging from 24 °C to 80 °C demonstrate that the proposed method can effectively overcome the resulting phase deviations while achieving high detection accuracy and a reduction false positives. Additionally, the method shows high resolution in detecting defects in both temperature-varying and non-temperature-varying regions.

Hydrogen and Solid Carbon Production via Methane Pyrolysis in a Rotating Gliding Arc Plasma Reactor.

Plasma-induced methane pyrolysis is a promising hydrogen production method. However, few studies have focused the decomposition of pure methane as a discharge gas. Herein, a rotating gliding arc reactor was used for the conversion of methane (discharge gas and feedstock) into hydrogen and solid carbon. Methane conversion, gaseous product selectivity, and energy usage efficiency(specific energy requirement for hydrogen production(SER)) were investigated as functions of operating parameters, e.g., specific energy input(SEI), residence time, and reactor design. SEI was positively(almost linearly)correlated with methane conversion and hydrogen yield and negatively correlated with SER. Conversion and efficiency of energy usage increased when reactor designs providing higher thermal densities were used. With the increasing flow rate of methane at constant SEI, the reaction volume and, hence, the residence time of the gas inside the reaction zone increased, which resulted in methane conversion and hydrogen selectivity enhancement. The solid carbon featured four distinct domains, namely graphitic carbon, turbostratic carbon, few-layer graphene, and amorphous carbon, which indicated a nonuniform temperature distribution in the reaction zone. But it seems that graphitic carbon dominates amorhphous one. This study highlights the potential of rotating gliding arc plasma systems for efficient methane conversion into hydrogen and valuable solid carbon products.

Lie-symmetry analysis of a three dimensional flow due to unsteady stretching of a flat surface with non-uniform temperature distribution

Various mathematical frameworks have been developed to study dynamics of the fluid flow in stretching films. In this work, a three–dimensional flow induced by an unsteady stretching of an infinite flat sheet is analyzed through the Lie symmetry approach. Twelve Lie point symmetries for the nonlinear partial differential equations describing the considered flow and heat transfer phenomena are derived. Invariants for these Lie symmetries are obtained to construct a new class of similarity transformations. With the deduced similarity transformations, the flow equations are converted to ordinary differential equations which are solved using the Homotopy analysis method. The deduced analytic solution enables an exploration of the effects of various parameters on the flow and heat transfer, which have not been revealed previously using the Lie method as per the authors’ knowledge. The influences of the stretching rate, parameters that maintain the non-uniformity and unsteadiness of sheet temperature, and the Prandtl number, are demonstrated with the help of graphs and tables. These results show that for certain values of the system parameters, heat transfer reverses its direction and occurs from the fluid to the sheet. At these values, maximum heat transfer does not occur at the sheet but rather slightly above it.

Investigation into the nonuniform temperature effect of a large-span stainless steel roof system under solar radiation

Metal roof systems have been widely used in various landmark buildings. The effect of the temperature of a large-span metal roof system under solar radiation is significant. As the latest roof form, the continuous welded stainless steel roof (CWSSR) system shows many unknown behaviors under the action of temperature. The purpose of this work is to analyse the temperature field and temperature effect of the CWSSR system under solar radiation and to select the appropriate support layouts to reduce the temperature effect of the CWSSR system. First, an experimental study on the temperature field of the CWSSR system was carried out. Finite element analysis of the temperature field distribution was then performed, and the validity of the finite element method was verified by comparing the experimental results. Finally, the influence of different support layouts on the temperature effect of the CWSSR system was researched. The results show that there is an obvious nonuniform distribution of the temperature field and temperature effect of the CWSSR system under solar radiation. The maximum temperature difference between the roof panel and the ambient temperature is 39.4 °C. By using arrangements of cross-support and segmented support, the stresses of the roof panel and support can be effectively reduced, and the maximum reductions are 14.4 % and 38.9 %, respectively. The investigation results contribute the most to the safe design of metal roof systems and are expected to provide guidelines for future applications of the CWSSR system.

The enhancement effects of internal convection on the heat transport of condensing droplets out of pure steam and moist air

In this work, the effect of internal convection on the heat transport of condensing droplets is theoretically and numerically focused on considering two typical working scenes (pure steam and moist air). A three-dimensional transient multiphysics model is first constructed by elaborately coupling time-dependent multiple physics during the dynamic growth of condensing droplets. Considering variable surface wettability and industrially universal applications, heat transport characteristics of condensing droplets in these two scenes are comparatively analyzed over a wide range of the droplet radius (500–1000 μm), contact angle (60–120°), and subcooling (1–50 K). It is found that internal convection resulting from the thermocapillary effect and curved vapor/liquid interface plays a progressively prominent role as the contact angle and subcooling increase, accordingly dominating heat transport within droplets. In the steam scene, internal convection is activated neighboring the triple-phase contact line at which the temperature gradient exists solely. In comparison, in the air case, the external vapor diffusion promotes a non-uniform temperature profile over the droplet surface, and the temperature gradient is extended toward the whole surface with stronger internal convection and heat transport enhancement. In general, the quantitative analysis demonstrates that driven by strong internal convection, the total heat flow rate through the droplet can be increased by several times for both two scenes. Furthermore, using the fundamental dimensionless groups governing internal convection, we put forward an empirical correlation of the droplet Nusselt number in two condensing scenes over wide working conditions.

Liquid hydrogen refuelling at HRS: Description of sLH2 concept, modelling approach and results of numerical simulations

The paper considers the concept of efficient liquid hydrogen (LH2) refuelling at hydrogen refuelling stations (HRS), presents modelling approach and 3D transient CFD simulation results. The concept is based on the advantages of transforming hydrogen from equilibrium to a non-equilibrium sub-cooled state (sLH2) during compression at pump. The modelling approach comprises a thermodynamic model of LH2 transfer from the HRS tank to the pump exit and a two-phase CFD model from the pump exit through the HRS equipment, i.e. pipes with bends, automatic valve, breakaway, nozzle, and manifold to onboard storage tanks. Due to the absence of published experimental data, the modelling approach and simulations are verified against conceptual LH2 refuelling process available in the literature. The CFD model reproduces key LH2 refuelling parameters: flow rate, pressure, temperature dynamics, including non-uniform temperature in onboard tanks and predicts pipe cooldown from 88K to allowable temperatures corridor of 23.9–26.5 K.

Numerical study on inter-particle effects for multiple reacting biomass and coal particles based on Micro-CT morphology

Co-firing of biomass with coal combines the environmental benefits of renewable biomass with the high energy content of coal. Although the common numerical simulation treats the biomass and coal particles with ideal morphology, real particles often demonstrate nonsmoothed surface and irregular shape. To understand the impact of particle morphology in a group of biomass and coal particles co-firing together and to inform simple models appropriate, this study investigated the interparticle effects among particles using realistic particle morphology, focusing on fluid dynamics such as temperature distribution, flow patterns and drag coefficients. Particle-scale computational fluid dynamics (CFD) simulations using micro-CT imaging showed that realistic particle shapes resulted in nonuniform flow fields and temperature distributions with different reaction intensities due to the species transportation. It is in contrast to traditional ideal shape models, which often rely on simplified spherical representations of particles and cannot capture the intricacies of real particle shapes. Realistic models revealed more complex surfaces, highly irregular particle structures, and varied reaction zones that affected the overall dynamics. In addition, changing the orientation of one particle affects the combustion characteristics of neighboring particles. This effect is also not captured while using the spherical structure. These differences underscore the critical impact of particle morphology on drag and heat transfer, thereby challenging conventional spherical models. The findings of this study advocate for a paradigm shift in CFD modeling approaches, emphasizing the importance of realistic particle representation to improve the accuracy of predictions and enhance the co-firing system efficiency.

Experimental study on boiling heat transfer and pressure drop characteristics of hybrid jet microchannel heat sink

Hybrid jet microchannel cooling can improve the non-uniform temperature distribution, significant pressure drop in microchannel, and the uneven heat transfer coefficient in jet impact. The heat transfer and pressure drop characteristics of a hybrid jet microchannel heat sink were investigated experimentally using deionized water as the working fluid. The experiments were carried out under the operating conditions of mass fluxes from 200 ∼ 600 kg/m2s, subcooling degrees from 20 ∼ 40 K, jet-to-target spacings from 1 ∼ 2.5 mm, and outlet pressure of 1 atm. The results show that increasing jet-to-target spacing and mass flux and decreasing subcooling can improve the heat transfer coefficient, and the maximum heat transfer coefficients increase by 58 %, 73 %, and 50 %, respectively. A heat transfer correlation for the hybrid jet microchannel is proposed with a mean absolute error of 6.5 % based on the experimental data. Since large jet-to-target spacing has more expansion space and is closer to the length of the potential core, increasing jet-to-target spacing results in higher critical heat flux at low mass flux. Compared to the heat sink with higher jet-to-target spacing, the pressure drop of the heat sink with the lower one is significantly affected by the mass flux due to the superposition of size effect of the channel and gas–liquid friction. In addition,the slope that pressure drop curves increase with the decrease of jet-to-target spacing rises with the mass flux, while it is not apparent with the subcooling. As the subcooling and jet-to-target spacing rise and the mass flux decreases, the coefficient of performance will increase.

Measurement of high-temperature absorption cross-sections using an optical cell with a non-uniform temperature distribution

A mathematical method to enable absorption cross-section measurements using an optical cell with a non-uniform temperature distribution is formulated, validated and experimentally demonstrated in this study. The motivation of the proposed method is to facilitate high-temperature spectroscopic studies in the long-wavelength mid-IR region, and to offer an alternative to highly engineered optical cells. The method is based on virtual segmentation of the non-uniform temperature field within an optical cell into bins, each having a sufficiently uniform temperature. By collecting a set of absorbance measurements corresponding to unique temperature profiles and expressing the temperature dependence of the absorption cross-section in terms of a model with limited number of unknowns, a closed-form system of equations is obtained which can be solved to evaluate absorption cross-sections. It is shown, through a set of simulated validation cases, that modeling the temperature dependence in terms of a third order polynomial results in accurate reconstruction of the cross-section spectra for a wide range of cases. Piece-wise polynomials and an alternative nonlinear model are proposed for improved accuracy and to model potentially complex temperature dependencies of the absorption cross-sections. To demonstrate the application of the proposed method, an optical cell with a non-uniform temperature profile was used to measure the cross-section spectra of methane over 1280 – 1330 cm-1 at temperatures up to 523 K. The proposed method is expected to be highly useful in collecting spectroscopic data at high temperatures particularly in the mid-infrared region.

Stabilization system for solar loading thermography applied on cultural heritage objects exposed outdoors: the contribution of advanced algorithms and dual-branch U-Net

AbstractThis study investigates the use of solar loading thermography (SLT) for thermal non-destructive testing (TNDT) and image stabilization of cultural heritage objects, specifically focusing on a century-old ancient book. The irregular contours and deteriorated areas of the book posed significant challenges for feature extraction due to non-uniform temperature variations. To address these challenges, a convolutional neural network (CNN) based dual-branch network of U-Net was used to stabilize the dataset across three degrees of freedom with the ancient book. The stabilization process involved tracking feature lines across each frame of the time-domain datasets, correcting for frame misalignment caused by sample movement during prolonged data acquisition. The effectiveness of this stabilization technique was evaluated by comparing the results of principal component analysis (PCA), fast Fourier transform (FFT), and fast iterative filtering (FIF) algorithms before and after stabilization. Significant improvements were observed, particularly in the clarity and accuracy of defect detection, indicating that this technique provides a robust foundation for further analysis and processing of SLT datasets in cultural heritage preservation. This research demonstrates the potential of combining advanced image processing techniques with SLT to enhance the quality and reliability of NDT in preserving valuable historical artifacts.

Effects of 910 MHz Solid-State Microwave Cooking on the Quality Properties of Broccoli (Brassica olearacea L. var. Italica Plenck), Carrots (Daucus carota subsp. Sativus), and Red Peppers (Capsicum annuum L. cv. Kapya).

Domestic microwave ovens offer rapid cooking but face challenges such as non-uniform temperature distribution and hot spots. A novel solid-state heating system, which precisely controls microwave frequency and power, provides a promising alternative to traditional microwave ovens utilizing magnetron systems. This study compared the effects of solid-state microwave cooking on the quality of broccoli, red peppers, and carrots with those of traditional microwave and conventional cooking. The traditional microwave cooking used in this study operated at 2450 MHz, while the solid-state system functioned between 902 and 928 MHz. Weight loss was highest for conventional cooking, reaching a maximum of 34%, whereas microwave cooking resulted in a maximum of 11.65% and solid-state microwave cooking in 17.04%. The total phenolic content obtained through conventional cooking ranged between 61.58 and 116.51 mg GAE (gallic acid equivalents)/100 g dry basis, while microwave cooking resulted in a range of 88.04-110.92 mg, and solid-state microwave cooking achieved values between 76.14 and 122.91 mg. Furthermore, reductions in chlorophyll content were observed to be 68.2%, 25.6%, and 35.7% for conventional, microwave, and solid-state microwave cooking, respectively. Lycopene content after conventional cooking decreased to 224.73 mg/100 g dry basis, compared to 289.55 mg after microwave cooking and 242.94 mg after solid-state microwave cooking. β-carotene content showed a decrease of 14.5% in conventional cooking, while both microwave methods showed an increase of 14.7%. These results suggest that solid-state microwave cooking may have promising positive effects on food quality.

Effect of Non-Uniform Temperature Distribution on the Natural Frequency of Concrete Girder Bridges

Structural dynamic properties like frequencies and mode shapes have been widely adopted for bridge condition assessment and damage identification. One of the main challenges lies in environmental factors, particularly the varying temperature, which significantly influences the bridge’s natural frequencies. In some cases, the effect of temperature changes can be comparable to, or even exceed, the effect caused by damage, rendering the damage identification methods ineffective. This study investigates the influence of the cross-sectional non-uniform temperature distribution, as a result of surrounding environmental factors, on the frequency of concrete girder bridges. A theoretical analysis is conducted to derive the bridge’s frequencies considering the cross-sectional non-uniform temperature distribution. The upper and lower bounds of the frequencies are developed by using only the environmental temperature and the largest temperature gradient defined by codes. More importantly, the damage to the bridge can be detected if the frequencies exceed the bounds for a certain period. This approach is convenient and practical in real applications without embedding thermocouples in the main girder. Numerical simulations, laboratory experimental tests, and field measurements are carried out to validate the derived frequency considering the cross-sectional non-uniform temperature distribution as well as the upper and lower bounds of the frequency. In particular, the results of the Z24 bridge show that when the bridge is damaged, the measured frequency exceeds the bound continuously, verifying the capability of the developed upper and lower bounds to evaluate bridge conditions.

Enhancing the sustainability of interfacial evaporation to mitigate solar intermittency via phase change thermal storage

Solar-driven interfacial water evaporation is a low-carbon footprint strategy for addressing global water scarcity. However, the operation of the evaporator requires continuity of solar radiation. Herein, the key to overcoming the intermittency of sunlight lies in utilizing the heat storage/release cycle of phase change materials. Additionally, the synergistic effect of high thermal conductivity materials and increased heat transfer area addresses the nonuniform spatial temperature within the heat storage device caused by the low thermal conductivity of molten paraffin. Although the heat transferred to the paraffin reduces the evaporation rate under illumination, the thermal storage/release capacity of paraffin increases the evaporation mass by 171.5% in darkness. Ultimately, after one light–dark cycle, the total evaporation mass over the entire period increased by 11.5%. Finally, although paraffin undergoes sensible and latent heat absorption and release across various temperature ranges during multiple light–dark cycles and prolonged operation, the phase change delays at different internal locations still ensure stable dark-state evaporation compensation for the evaporator, thereby enhancing the sustainability of the evaporation process.