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For the development of functional honeycomb plates (FHPs) and efficient resource utilization of straw, based on the measurement of the equivalent thermal conductivity (λE) of paper honeycomb plates (HPs) and FHPs, including straw-core paper honeycomb plates (SHPs), under cold-left and hot-right conditions, the influence mechanism of the system geometry parameters on the convective heat transfer of HPs and the heat insulation performance of FHPs by fillers are discussed. The results are as follows. 1) Compared with the case of hot-above and cold-below conditions, the convective heat transfer ratio of HP increases substantially under cold-left and hot-right conditions. 2) The main heat transfer modes of the FHPs are radiative heat transfer between the wall (including the panel and side) and filling material and solid heat conduction in the filling material, supplemented by a small amount of heat conduction through air or local convection heat transfer in the void. 3) The higher the temperature is, the greater the FHP equivalent thermal conductivity, with little influence from the heat transfer direction. 4) It is relatively conservative to use the heat transfer effect of HPs and FHPs to evaluate that of beetle elytron plates (BEPs) and functional beetle elytron plates (FBEPs). This study lays a foundation for the application of multifunctional BEPs and HPs in building envelopes. [ABSTRACT FROM AUTHOR]

Modeling of the dryer section of a paper machine is of high importance in both designing and operation points of view. In this research, a novel thermodynamic and heat and mass transfer model has been introduced. The model is based on empirical equations of the literature and does not need fine discretization techniques such as finite difference method. The method used for calculation of convective heat and mass transfer coefficients of the dryer is a modification of the methods utilized in the literature. The trend of paper and air temperature in the dryer, the steam consumption of each cylinder, as well as the trend of drying process throughout the dryer has been calculated. Overall results of the dryer such as the total evaporated water and the specific steam consumption of the dryer have been obtained too. The results have been validated with experimental data of a previous research in the literature and show a relatively good agreement with the experimental data. Finally, the sensitivity of the results to some main parameters has been analyzed. [ABSTRACT FROM AUTHOR]

Insulation paper is the primary inter-turn insulation material for transformer windings. However, insulation paper is a poor conductor of heat and seriously impacts the natural convective heat dissipation in the winding oil channels. In order to study the convective heat transfer performance of the transformer vertical oil channel, the heat transfer characteristics of the two-dimensional boundary layer of the insulation paper–oil contact surface were analysed, and a characteristic number equation with a roughness correction factor was established. Based on the similarity principle and modelling theory, an experimental apparatus was designed to determine the convective heat transfer coefficient of the insulation paper–oil contact surface. Coefficients were obtained for different qualitative temperatures and characteristic lengths. Parametric fitting of the experimental data was carried out to obtain the correction factors. The results show that the natural convective heat transfer coefficient h of the insulation paper–oil contact surface is positively and linearly related to qualitative temperature and inversely related to characteristic length. For temperatures of 312.9 K to 328.1 K and characteristic lengths of 3 cm, h ranges from 116.15 to 144.38 W/(m2 · K). For temperatures of 319.0 K to 337.9 K and lengths of 6 cm, h ranges from 103.79 to 131.14 W/(m2 · K). The correction factor of the characteristic equation coefficient is 1.067. The maximum deviation of h calculated with a coefficient of 0.63 and an exponent of 0.25 is 5.93%. The results are essential for modelling the transformer space thermal circuit and solving the hot-spot temperature problem. [ABSTRACT FROM AUTHOR]

The aim of this study was to find out what will happen to paper coating quality and material gradients if coating is dried in one air dryer at a high convection rate (150 kg/m2h). Different printing papers were coated, calendered and printed with pilot machines. The binder and pigment gradients of the coated, and also printed, samples were analyzed with LIPS (Laser Induced Plasma Spectrometry). It was found that drying affects the migration of starch, but not latex. Total air drying can be used to dry printing papers, if air temperature, velocity and moisture content can be separately controlled. The control of web temperature is more important for paper quality formation in a coater drying section than that of evaporation rate. [ABSTRACT FROM AUTHOR]

The fabrication of most current thermal insulation materials from polymeric foams has created an unfavorable impact on the environment. With the aim of reducing the use of foam plastic, this paper focuses on honeycomb paperboard, an alternative thermal insulation material which is recyclable and cost-effective, and evaluates its heat transfer performance under different conditions. The experimental results show the effective thermal conductivity of honeycomb paperboard increases as the honeycomb height or the side length increases. This paper also establishes a novel theoretical model based on a newly developed convective heat transfer correlation to predict the effective thermal conductivity under different conditions. The model's results conform well to the experimental results, and the effect of convective heat transfer is investigated quantitatively using this model. As the vertical adiabatic boundary surfaces are replaced by honeycomb walls, the convection heat transfer strictly depends on the thermal boundary condition of the honeycomb walls and highly depends on honeycomb height and side length. • The novel theoretical models involving convective heat transfer are established under different conditions. • The different heat transfer paths are quantitatively investigated based on the proposed models. • Under the condition of hot-above and cold-below, convective heat transfer in honeycomb paperboard increases as the honeycomb height increases, but decreases as the side lengths increases. • Under the condition of cold-above and hot-below, convection heat transfer in honeycomb paperboard increases as the honeycomb height or the side length increases. [ABSTRACT FROM AUTHOR]

Some errors exist in the above paper. [ABSTRACT FROM AUTHOR]

They found that this novel loop heat pipe can start up and run successfully under different working modes and the heat dissipation capacity of a set of loop heat pipes can reach 250 W at room temperature. The series of UK Heat Transfer Conference (UKHTC) has been organized under the auspices of the UK National Heat Transfer Committee since 1984. In the seventh paper, Ren et al. conducted the parametric analysis of a novel photovoltaic/thermal system using amorphous silicon cells and micro-channel loop heat pipes. [Extracted from the article]

The temperature distribution is vital to the lifetime and reliability of converter transformer bushings. However, the temperature distribution of epoxy impregnated paper converter bushings under a certain current has usually been calculated through the two dimensional model, without considering the heat convection and radiation effects. In this paper, using the computational fluid dynamics (CFD) and finite element method (FEM) analysis, a 3-D electromagnetic-fluid-thermal analysis method has been proposed. With the considering of heat conduction, heat convection and radiation, the temperature distribution of the converter transformer bushing has been simulated according to the actual operating environment. The temperature and velocity distribution of the converter transformer bushing has been obtained. Moreover, the simulation results have been compared with the experimental results to verify the accuracy of the simulation method. The simulation results, especially for the inner conductor, external conductor and the epoxy impregnated paper, are very close to the experimental results and the maximum temperature difference percentage is within 10 %, which indicates the accuracy and effectiveness of the electromagnetic-fluid-thermal analysis method proposed. [ABSTRACT FROM AUTHOR]

The present note presents some errors in the aforementioned paper published in Mathematical Methods in the Applied Sciences. Two errors are found in the definition of the non-dimensional parameters and correct results are presented for temperature profiles included in figure 10 of the previous paper. [ABSTRACT FROM AUTHOR]

In this study, conductive silver features using inkjet printing have been successfully prepared and their sintering studied. Regarding conductivity, metallic inks are the most efficient available conductive inks, even if important drawbacks regarding the use of such inks in inkjet still exist. Indeed, the sintering step is an important limiting factor for the productivity and the substrate choice. An infrared (IR) drying method was experimented to optimize the sintering treatment time. Trials with glass and paper substrates were performed and proved that IR drying is interesting to optimize sintering. Indeed a similar level of resistance was obtained for conventional heating (200 °C, 5 min) and for IR radiations within a shorter treatment time (3 min). Moreover, the substrate temperature during the IR sintering treatment was controlled. The substrate appears to be a relevant parameter to optimize sintering because its thermal behaviour directly impacts on the treatment duration. And for the first time a sheet resistance of 1.9 Ω sq was obtained on paper substrate after only 2 min of IR treatment without any observation of substrate degradation. The evaluation of an electrical treatment on the sintering of a nanoparticle film was also performed using a corona pre-treatment. This lead appears to be interesting because the study proves that an electrical treatment can initiate the sintering of silver nanoparticles. The current flow generated by the corona electrodes certainly generates a local heating by dissipation of the conductive pattern. Finally, the solutions presented in this article allow reducing the sintering time of silver conductive inkjet inks. However mainly, it proves that using paper as substrate for such inks is now possible. [ABSTRACT FROM AUTHOR]

The environment inside a spacecraft, or a space habitat, can greatly differ from those on earth, affecting the burning behavior of solid fuels. Because in a gravity field there is a flame-induced buoyancy, it is very difficult to reproduce on Earth the environmental conditions of a spacecraft, or a habitat in the Moon or Mars, thus making fire testing and burning predictions harder. A potential alternative approach to overcome this problem is to reduce buoyancy effects by using reduced ambient pressure in normal gravity. The objective of this work is to explore the possibility of simulating the effect of gravity, and in turn buoyancy, through changes in ambient pressure, on upward/concurrent flame spread over a thin combustible solid. Comparisons with available data at different gravity levels are used to determine the extent to which low-pressure can be used to replicate flame spread characteristics at different gravities. Experiments of the upward/concurrent flame spread over thin Kimwipe paper sheets were conducted in normal gravity inside a pressure chamber with ambient pressures ranging between 100 and 30 kPa and a forced flow velocity of 10 cm/s. Results show that reductions of pressure slow down the flame spread over the paper surface, and also reduces flame intensity. Comparison with published partial gravity data shows that as the pressure is reduced, the normal gravity flame spread rate approaches that observed at different gravity levels. The data presented is correlated in terms of a mixed convection non-dimensional number that describes the convective heat transferred from the flame to the solid, and that also describes the primary mechanism controlling the spread of the flame. The correlation provides information about the similitudes of the flame spread process in variable pressure, flow velocity and gravity environments, providing guidance for potential ground-based testing for fire safety design in spacecraft. [ABSTRACT FROM AUTHOR]

Abstract: In the finite volume approach for incompressible flow and heat transfer, the discretization of the convection term and the treatment of the coupling between velocity and pressure are the two major issues affecting solution stability, accuracy and convergence rate. In this review paper, some recent advances made in the CFD/NHT & Enhanced Heat Transfer Center of Xi''an Jiaotong University, China, are presented and their applications in the study of heat transfer enhancement are also briefly summarized. [Copyright &y& Elsevier]

This paper develops the mathematical apparatus of studying control problems for the stationary model of magnetic hydrodynamics of viscous heat-conducting fluid in the Boussinesq approximation. These problems are formulated as problems of conditional minimization of special cost functionals by weak solutions of the original boundary value problem. The model under consideration consists of the Navier–Stokes equations, the Maxwell equations without displacement currents, the generalized Ohm's law for a moving medium and the convection-diffusion equation for temperature. These relations are nonlinearly connected via the Lorentz force, buoyancy force in the Boussinesq approximation and convective heat transfer. Results concerning the existence and uniqueness of the solution of the original boundary value problem and of its generalized linear analog are presented. The global solvability of the control problem under study is proved and the optimality system is derived. Sufficient conditions on the data are established which ensure local uniqueness and stability of solutions of the control problems under study with respect to small perturbations of the cost functional to be minimized and one of the given functions. We stress that the unique stability estimates obtained in the paper have a clear mathematical structure and intrinsic beauty. [ABSTRACT FROM AUTHOR]

With the development of nuclear energy, microreactors have received increasing interest among researchers in recent years. In this paper, a megawatt heat pipe reactor with metal hydride moderators and burnable poisons is proposed. The hydrogen stability of the reactor under accident conditions, including reactivity insertion accidents, loss of power conversion unit heat sink accidents, and heat pipe failure accidents are analyzed. In this work, Gd2O3 is introduced as a burnable poison in the form of mixing with the UO2 fuel. According to the results of the burnable poison design, the 0.1% mass fraction of Gd[sub 2]O[sub 3] is selected as the burnable poison loaded in the core. Safety analysis indicates that the introduction of burnable poisons can be beneficial during the positive reactivity insertion accident as it can reduce the excessive reactivity at BOL, thus reducing power peak and preventing hydrogen dissociation in ZrH1.4 rods. However, during the loss of PCU heat sink accident, ZrH1.4 rods will dissociate regardless of the presence of burnable poisons, whereas YH1.7 rods show better hydrogen stability. Moreover, in the event of the heat pipe failure accident, ZrH1.4 rods aremore susceptible to dissociation than YH1.7 rods. As a result, the YH1.7+BP core is a better choice compared with other designs proposed in this paper as it provides a relatively high temperature margin. [ABSTRACT FROM AUTHOR]

The paper explores the application of Wilson plot method, and its modifications, as an alternative approach for determining convective heat transfer coefficients in heat exchangers with complex geometries. For achieving the delicate balance, one needs to introduce heat transfer augmentation techniques in devices, which results in intricate geometries of heat exchanger. For such geometries of heat exchanger, correlations are not available to estimate convective heat transfer coefficients. The Wilson plot method provides a robust tool for deriving correlation equations based on experimental data. The paper discusses the implementation of the Wilson plot and modified Wilson plot methods to establish correlations for tube-in-tube type heat exchangers with wire mesh inserts, and results are obtained for both methods. It is found that modified Wilson plot method provides correlation with great accuracy in the range of 94 to 97%. Furthermore, the paper presents the development of a computational tool using VB.net, designed to facilitate the iterative calculations required for Wilson plot methods. The paper also describes a roadmap for the proficient application of Wilson plot method and its modification in heat exchanger analysis. [ABSTRACT FROM AUTHOR]

In this paper, we study the temperature distribution of a body when the heat is transmitted only by radiation. The heat transmitted by convection and conduction is ignored. We consider the stationary radiative transfer equation in local thermodynamic equilibrium. We prove that the stationary radiative transfer equation coupled with the nonlocal temperature equation is well-posed in general geometries when emission-absorption or scattering of interacting radiation is considered. The emission-absorption and the scattering coefficients are assumed to be general, and they can depend on the frequency of radiation. We also establish an entropy production formula of the system which is used to prove the uniqueness of solutions for an incoming radiation with constant temperature. [ABSTRACT FROM AUTHOR]

The Brakes contact surface temperature rises sharply when vehicle braking by friction, so vehicles are generally equipped with ventilated brake discs for cooling. However, the recirculation zone in the ventilated brake disc passage severely blocks fluid flow. In order to improve the convective and heat dissipation performance of the ventilated brake disc, this paper aims to introduce an optimized slotted vane geometry to improve the heat dissipation performance of ventilated brake discs. Therefore, three structural parameters of slot width, slot inclination and number of vanes were selected as optimization variables, and the optimization objective was to maximize the mass flow rate and convection heat transfer coefficient. And then, combined with the RSM and NSGA-II for optimization. The results showed that the optimized slotted vanes effectively suppressed the recirculation zone in the flow passage and made the airflow distribution more uniform. The optimal characteristic parameters after optimization are N = 36,θ = 56.38°, H = 12.7 mm. The CFD calculation results are consistent with the experimental results, and the Nu error obtained is about 2.6%. Within the given speed range, compared with experimental data of the straight vane brake disc, the total heat dissipation rate of the optimized brake disc is increased by 9%, the heat dissipation rate in the channel was increased by 5.6%, and the pumping capacity is increased by 12%. [ABSTRACT FROM AUTHOR]

In this paper, the free convective flow and heat transfer in a porous rectangular enclosures filled with Cu-water nanofluid is studied and analyzed. The cavity sidewalls are exposed to a constant heat flux and the horizontal walls are assumed to be adiabatic. The governing equations describing the problem are solved using a finite difference method. The main parameters of our problem are: aspect ratio, volume fraction of nanoparticles, types of media, porosity of the medium, and Rayleigh number. The results indicate that an increase in aspect ratio from 0.1 to 0.7 leads to a significant increase of Nusselt number, which then reaches a maximum value. However, the heat transfer rate progressively decreases for aspect ratios greater than 0.7. Moreover, the addition of Cu-nanoparticles weakens the heat transfer. As a result, when the porous medium has low thermal conductivity, the solid matrix porosity becomes particularly more effective in improving heat transfer. Also, a correlation was established between the average Nusselt number and the influencing parameters. Results show that the governing parameters impact the flow regime. [ABSTRACT FROM AUTHOR]

Diapers with various sizes can provide a variety of options for babies of different ages and weights, but at the same time, their "many to many" diaper sizing system, which classifies diapers only according to the baby's growing stage and weight, also brings decision-making problems to consumers. As a kind of special clothing, diaper fit will affect its heat and moisture properties and microclimate to some extent, causing differences in the thermal and moisture comfort of babies. The aim of this paper was to investigate the effect of fit on heat and moisture transfer in the diaper under dry conditions by baby manikin tests. The following conclusions were drawn. (i) The influence of diaper fit on its thermal insulation depended on the combined effect of convective heat transfer in the waist air gap and conductive heat transfer in the crotch air gap, which was related to the waist ease allowance and the crotch length of the diaper. In particular, the waist ease allowance of tape diapers would be affected by the wearing operations of caregivers. (ii) Under dry conditions before urination, the standing posture was cooler and more comfortable than supine for babies, at approximately 0.9°C lower in microclimate temperature underneath the diaper. This was mainly due to a substantial decrease in thermal insulation of the back waist and buttocks, which were 70.86% and 79.46%, respectively. (iii) The microclimates underneath the regular pants type and loose tape type were closest to the ideal comfortable zone, and this advantage was more obvious when the baby was lying on its back. Meanwhile, the temperature and humidity inside these two types of diapers were more stable and least effected by posture changes of babies. [ABSTRACT FROM AUTHOR]

Fully 3-D numerical simulations of thermal convection in a spherical shell have become a standard for studying the dynamics of pattern formation and its stability under perturbations to various parameter values. The question arises as to how does the discretization of the governing equations affect the outcome and thus any physical interpretation. This work demonstrates the impact of numerical discretization on the observed patterns, the value at which symmetry is broken, and how stability and stationary behavior is dependent upon it. Motivated by numerical simulations of convection in the Earth's mantle, we consider isoviscous Rayleigh-Bénard convection at infinite Prandtl number, where the aspect ratio between the inner and outer shell is 0.55. We show that the subtleties involved in development mantle convection models are considerably more delicate than has been previously appreciated, due to the rich dynamical behavior of the system. Two codes with different numerical discretization schemes: an established, community-developed, and benchmarked finite element code (CitcomS) and a novel spectral method that combines Chebyshev polynomials with radial basis functions (RBF) are compared. A full numerical study is investigated for the following three cases. The first case is based on the cubic (or octahedral) initial condition (spherical harmonics of degree l = 4). How variations in the behavior of the cubic pattern to perturbations in the initial condition and Rayleigh number between the two numerical discrezations is studied. The second case investigates the stability of the dodecahedral (or icosahedral) initial condition (spherical harmonics of degree l = 6). Although both methods converge first to the same pattern, this structure is ultimately unstable and systematically degenerates to cubic or tetrahedral symmetries, depending on the code used. Lastly, a new steady state pattern is presented as a combination of order 3 and 4 spherical harmonics leading to a five cell or a hexahedral pattern and stable up to 70 times the critical Rayleigh number. This pattern can provide the basis for a new accuracy benchmark for 3-D spherical mantle convection codes. [ABSTRACT FROM AUTHOR]

The cross-wave primary surface recuperator (CW-PSR) is a dependable option as a recuperator for micro gas turbines (MGT). The micro CW-PSR studied in this paper is composed of 171 stacked curved plates, with each plate containing 33 micro heat transfer channels with equivalent diameters of less than 1 mm. In this study, the influence of bending curvature on the thermal performance of CW-PSR plates is investigated through three-dimensional numerical simulation with fluid–solid–thermal coupling. The results indicate that the variation in bending curvature studied can result in a noteworthy 8% difference in the total heat transfer coefficient of CW-PSR plates. A direct correlation between heat transfer capacity and secondary flow strength is derived mathematically, explaining the mechanism by which secondary flow enhances heat transfer. By employing this relationship, a comprehensive analysis of CW-PSR plates with diverse bending curvatures is conducted, effectively showcasing how curvature influences the secondary flow pattern and enhances the channel's heat transfer capacity. In addition, this paper considers the comprehensive influence of the size parameters of the heat transfer unit and the bending curvature of the heat transfer plate on the heat transfer and flow characteristics of the CW-PSR, and a dominant mathematical expression is obtained, which can be used for the design of similar heat exchangers of the same type. [ABSTRACT FROM AUTHOR]

Purpose: For a lightweight and accurate description of bearing temperature, this paper aims to present an efficient semi-empirical model with oil–air two-phase flow and gray-box model. Design/methodology/approach: First, the role of lubricant/coolant in bearing temperature was discussed separately, and the gray-box models on the heat convection inside a bearing cavity were also created. Next, the bearing node setting scheme was optimized. Consequently, a novel semi-empirical two-phase flow thermal grid for high-speed angular contact ball bearings was planned. With this model, the thermal network for the selected motored spindle was built, and the numerical solutions for bearing temperature rise were obtained and contrasted with the experimental values for validation. The polynomial interpolation on test data, meanwhile, was also performed to help us observe the temperature change trend. Finally, the simulations based on the current models of bearings were implemented, whose corresponding results were also compared with our research work. Findings: The validation result indicates that the thermal prediction is more accurate and efficient when the developed semi-empirical oil–air two-phase flow model is employed to assess the thermal change of bearings. Clearly, we provide a more proper model for the thermal assessment of bearing and even spindle heating. Originality/value: To the best of the authors' knowledge, this paper introduced the oil–air separation and gray-box model for the first time to describe the heat exchange inside bearing cavities and accordingly presents an efficient semi-empirical oil–air two-phase flow model to evaluate the bearing temperature variation by using thermal network method. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-06-2023-0180/ [ABSTRACT FROM AUTHOR]

Nuclear reactors are very complex units in which many physical processes occur simultaneously. Efficient heat removal from the reactor core is the most important of these processes. Heat is removed from the reactor core via heat conduction, radiation, and convection. Thus, convective heat transfer and its conditions play a crucial role in the operation and safety of nuclear reactors. Convective heat transfer in nuclear reactors is a very complex process, which is dependent on many conditions and is usually described by different correlations which combine together the most important criteria numbers, such as the Nusselt, Reynolds, and Prandtl numbers. The applicability of different correlations is limited by the conditions of heat transfer in nuclear reactors. The selection of the proper correlation is very important from the reactor design accuracy and safety points of view. The objective of this novel review is to conduct a comprehensive analysis of the models and correlations which may be applied for convective heat transfer description and modeling in various types of nuclear reactors. The authors review the most important research papers related to convective heat transfer correlations which were obtained by experimental or numerical research and applied calculations and heat transfer modeling in nuclear reactors. Special focus is placed on pressurized water reactors (PWRs), boiling water reactors (BWRs), CANDU reactors, small modular reactors (SMRs), and molten salt reactors (MSRs). For each type of studied reactor, the correlations are grouped and presented in tables with their application ranges and limitations. The review results give insights into the main research directions related to convective heat transfer in nuclear reactors and set a compendium of the correlations that can be applied by engineers and scientists focused on heat transfer in nuclear reactors. Prospective research directions are also identified and suggested to address the ongoing challenges in the heat transfer modeling of present and next-generation nuclear reactors. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation into the cooling performance of a rotor-stator cavity with liquid nitrogen spraying. The experiments were conducted under varying rotational Reynolds numbers ranging from 1.70 × 106 to 5.12 × 106. The effects of rotational speed on temperature drop rate are studied and compared in detail, as well as the heat transfer coefficient distribution. Sufficient data, such as heat flux, injection rate, and injection pressure, were collected to provide a basis for further study in explaining the spray and evaporation over the cavity. It was found that the cooling performance of the rotating disc is strongly affected by the rotational speed. The short-term period exhibits a peak cooling rate of 14°C/s, in contrast to the sustained cooling rate during the spray process at rotational speeds of 500r/min, which amounts to 0.9°C/s. The occurrence of cavitation and evaporation within the nozzle results in a reduction of flow coefficient and fluctuation of the injection differential pressure. The transient cooling performance is well-explained by the temperature changes and cooling-down time under different rotational speeds. The analysis of the heat transfer coefficient is further enhanced through an evaluation of the convective and conductive heat transfer rates using a one-dimensional theoretical approach. The average temperature of the disc is expected to decrease by 100°C within a time frame no longer than 120 s. Additionally, after a duration of 120 s, the average heat transfer rate on the cold side is anticipated to surpass 8000 W/(m · K). [ABSTRACT FROM AUTHOR]

In the present paper the high-frequency induction welding process is studied numerically. The mathematical model comprises a harmonic vector potential formulation of the Maxwell equations and a quasi-static, convection dominated heat equation coupled through the Joule heat term and nonlinear constitutive relations. Its main novelties are a new analytic approach which permits to compute a spatially varying feed velocity depending on the angle of the Vee-opening and additional spring-back effects. Moreover, a numerical stabilization approach for the finite element discretization allows to consider realistic weld-line speeds and thus a fairly comprehensive three-dimensional simulation of the tube welding process. [ABSTRACT FROM AUTHOR]

Wearable thermoelectric generators have great potential to provide power for smart electronic wearable devices and miniature sensors by harnessing the temperature difference between the human body and the environment. However, the Thomson effect, the Joule effect, and heat conduction can cause a decrease in the temperature difference across the thermoelectric generator during operation. In this paper, phase change materials (PCMs) were employed as the heat sink for the thermoelectric generator, and the COMSOL software 6.1 was utilized to simulate and optimize the power generation processes within the heat sink. The results indicated that with a PCM height of 40 mm, phase transition temperature of 293 K, latent heat of 200 kJ/kg, phase transition temperature interval of 5 K, thermal conductivity of 50 W/(m·K), isobaric heat capacity of 2000 J/(Kg·K), density of 1000 kg/m3, and convective heat transfer coefficient of 10 W/(m·K), the device can maintain a temperature difference of 18–10 K for 1930 s when the thermoelectric leg height is 1.6 mm, and 3760 s when the thermoelectric leg height is 2.7 mm. These results demonstrate the correlation between the device's output performance and the dimensions and performance parameters of the PCM heat sink, thereby validating the feasibility of employing the PCM heat sink and the necessity for systematic investigations. [ABSTRACT FROM AUTHOR]

Integrated circuits are being more and more extensively applied, and the reliability issues of devices are receiving increased attention from researchers. The study of electronic device performance is not limited to the device themselves; these studies also need to consider the operating environment, such as high temperature or high humidity, which requires fluid simulation. However, this approach inevitably increases the complexity of modeling and the difficulty of the equations to be solved. Aiming at the simulation of the thermal performance of a device under coupled humid air conditions, this paper proposes a surrogate model to quickly evaluate the multiphysical effects of humid air and a multiphysical solver based on it. In this research, the finite element method (FEM) is utilized to simulate the multiphysical problem, and the proposed method is verified as being efficient. [ABSTRACT FROM AUTHOR]

For wide-body all-electric aircraft (AEA), a high-power-delivery, low-system-mass electric power system (EPS) necessitates advanced cable technologies. Increasing voltage levels enhances power density yet poses challenges in aircraft cable design, including managing arc-related risks, partial discharges (PDs), and thermal management. Developing multilayer multifunctional electrical insulation (MMEI) systems for aircraft applications is a feasible option to tackle these challenges and reduce the size and mass of cable systems. This approach involves selecting layers of different materials to address specific challenges. Our prior research concentrated on the modeling and simulation-based design of MMEI systems for MVDC power cables. Experimental tests are essential for determining the behavior of PDs under varying pressure conditions. Also, the dielectric strength and time to failure of the designs need to be assessed. In this work, the fabrication process of a down-selected MMEI flat configuration is discussed and analyzed. This paper analyzes the fabrication process of power cables employing MMEI configurations and evaluates the PD characteristics of down-selected ARC-SC-T-MMEI cable samples. This study presents a detailed analysis of the characteristics of PD under atmospheric and low-pressure conditions, which will provide essential insights into the design of MVDC cables for future AEA applications. [ABSTRACT FROM AUTHOR]

The study of compressible flow plays a fundamental role in the design of heat exchangers at high temperature and pressure. Compressible flow is used to design the aerodynamic structure, engines, and high-speed vehicles. In view of these utilities, this paper is deliberated to acquire the analysis of the unsteady compressible flow of a viscous fluid through an inclined asymmetric channel with thermal effects. Special attention is paid to convective heat transfer with impact of viscous dissipation, source/sink, and joule heating effects. In addition, thermal flow is analyzed through slip boundary conditions. The current problem is modeled through the laws of energy, momentum, and mass with the help of a fluid’s response towards compression. As a result, the coupled nonlinear partial differential equations are obtained, which are investigated through a well-known numerical approach, the explicit finite difference method. The study examines impact of several parameters on the flow rate, velocity, and temperature with the help of graphical representations. The behavior of flow rate is intended to change with time. [ABSTRACT FROM AUTHOR]

This paper reports experimental investigations on cold plates made from Low-Temperature Co-fired Ceramic (LTCC) technology for liquid cooling of supercomputer microprocessors. LTCC, a ceramic substrate-based technology with lightweight and ease of fabrication for miniaturization of cooling devices, can be a potential alternative to the existing copper cold plates for future three-dimensional stacked chip architectures. LTCC cold plates were fabricated using ceramic substrates whose thermal conductivity was enhanced using thermal vias. They were embedded with microchannels for liquid with different flow configurations. Their thermal performance is compared against copper cold plates. Deionized (DI) water is used as a coolant. Pressure drop and thermal resistance across different cold plates are measured as per water-cooled data center standards (W3 and W4 class). Obtained experimental results show that the tested LTCC cold plates can be used to cool supercomputer processors. It is concluded that LTCC cold plates can be a potential alternative for existing copper cold plates. [ABSTRACT FROM AUTHOR]

Phase change materials (PCMs) have attracted greater attention in battery thermal management systems (BTMS) applications due to their compact structure and excellent thermal storage performance. This work developed a BTMS model based on composite phase change material (CPCM) for a cylindrical lithium-ion battery pack. The initial state of the CPCM was set as a liquid phase, and the insulating performance of the BTMS was investigated numerically, considering the CPCM solidifying from liquid phase to solid phase in a low-temperature environment. The numerical model was built, and calculations were performed using Ansys Fluent 19.2. The research results showed that a CPCM effectively can extend the time that the battery pack remains above 0°C by releasing a large amount of latent heat during the solidification process in a low-temperature environment. As the convective heat transfer coefficient increased, the insulation effect provided by CPCM to lithium-ion battery packs decreased, exacerbating the temperature inhomogeneity inside the low-temperature thermal management system. Increasing the thermal conductivity of the CPCM ensured that the maximum temperature difference of the battery pack during operation remained within a safe range. Finally, the simulation results indicated that adding different thicknesses of insulation materials at the periphery of the low-temperature thermal management system effectively can improve the insulation effect. However, it also is necessary to select the appropriate thickness of insulation materials in combination with the actual demand. This paper establishes a model based on CPCM for the low-temperature thermal management system of cylindrical lithium-ion batteries. The thermal insulation and temperature homogenization performance of the CPCM-based BTMS were analyzed under various conditions, including different ambient temperatures, convective heat transfer coefficients, and thermophysical properties of materials, as well as the addition of insulation layers, considering time-dependent variations. Based on this analysis, the physical requirements of CPCM and the package structure for BTMS under different operating conditions were determined. The simulation results demonstrate that the liquid-phase CPCM solidifies and releases the stored heat through latent heat to warm and insulate the battery when the discharging process is stopped at lower temperatures. This effectively extends the battery's holding time in the high-temperature domain and above 0°C. As the external convective heat transfer coefficient increases, the effectiveness of CPCM in insulating the battery decreases, exacerbating the temperature nonuniformity within the low-temperature thermal management system. Increasing the thermal conductivity of the CPCM ensures that the maximum temperature difference during battery operation remains within safe limits. In addition, the results indicate that the insulation effect can be improved significantly by adding an appropriate thickness of insulation material to the periphery of the thermal management system, based on specific requirements. This study provides a valuable reference for the design and optimization of thermal management systems for batteries operating in a wide temperature range. [ABSTRACT FROM AUTHOR]

In this paper, a comprehensive analysis of the combined effect of major influencing parameters on heat transfer in a single U-tube BHE (sBHE) and a double U-tube BHE (dBHE) with two independent circuits was performed by using a validated numerical heat transfer model. Geometrical parameters, such as shank spacing (with maximum, average, and minimum values), borehole diameter (large, medium, and small borehole sizes), and borehole depth (shallow, average, and deep borehole depths) as well as the thermal conductivity of soil and grout, which ranges from minimum to high values, were considered. The combined impact of these parameters was included under the following four major cases: (1) the combined effect of borehole depth, borehole size, and shank spacing; (2) the combined effect of borehole depth and soil and grout thermal conductivity; (3) the combined effect of soil and grout thermal conductivity and borehole size; and (4) the combined effect of soil thermal conductivity, borehole size, and shank spacing. Each of these major cases has nine different design options for both sBHEs and dBHEs. A series of results of heat transfer per unit borehole depth were generated for all the considered various cases. With the given parameters, the BHE case that provides the highest heat transfer among the various cases of sBHEs and dBHEs were obtained. [ABSTRACT FROM AUTHOR]

Worldwide energy requirements demand the functioning and formulating of thermal mechanisms and heat exchangers for the use and resuscitation of thermal energy. As a result, new heat transport liquids subject to improved heat transport characteristics are needed to enhance convection heat transport in nanoliquids. With that objective, the present work addresses the dynamical investigation for bioconvection effects containing gyrotactic motile microorganisms of Jeffery nanofluid over a stretching sheet, influenced by a magnetic dipole with ferromagnetic particles. Ferro nanofluids are used to develop a microtransformer which is mainly used in electronic products such as note books, e-paper, and mobile phones. Moreover, activation energy and thermal radiation are taken into account. The proposed model is based on flow rate, volumetric concentration of nanoparticle, motile microorganism, and nanomaterial temperature. The technical efficiency of nanofluids is explored by the evaluation of the Buongiorno process which helps us to determine the attractiveness of thermophoretic and Brownian diffusions. An appropriate transformation is established to transform the system of nonlinear partial differential equation (PDEs) into coupled nonlinear ODEs, which are numerically solved by a bvp4c solver in MATLAB. Results for various fundamental flow parameters are demonstrated through numeric results and graphical outcomes.. [ABSTRACT FROM AUTHOR]

This paper proposes a solution to address the challenges of high storage and transport costs associated with using hydrogen ( H 2 ) as an energy source. It suggests utilizing ammonia ( N H 3 ) as a hydrogen carrier to produce H 2 onsite for hydrogen gas turbines. N H 3 offers higher volumetric hydrogen density compared to liquid H 2 , potentially reducing shipping costs by 40%. The process involves N H 3 pyrolysis, which utilizes the heat waste from exhaust gas generated by gas turbines to produce H 2 and nitrogen ( N 2 ). Numerical simulations were conducted to design and understand the behaviour of the heat recapture N H 3 decomposition system. The design considerations included the concept of the number of transfer units and heat exchanger efficiency, achieving a heat recapture system efficiency of up to 91%. The simulation of N H 3 decomposition was performed using ANSYS, a commercial simulation software, considering wall surface reactions, turbulent flow, and chemical reaction. Parameters such as activation energy and pre-exponential factor were provided by a study utilizing a nickel wire for N H 3 decomposition experiments. The conversion of N H 3 reached up to 94% via a nickel-based catalyst within a temperature range of 823 K to 923 K which is the exhaust gas temperature range. Various factors were considered to compare the efficiency of the system, including the mass flow of N H 3 , operating gauge pressure, mass flow of exhaust gas, among others. Result showed that pressure would not affect the conversion of N H 3 at temperatures above 800 K, thus a lower amount of energy is required for a compression purpose in this approach. The conversion is maintained at 94% to 97% when lower activation energy is applied via a ruthenium-based catalyst. Overall, this study showed the feasibility of utilizing convective heat transfer from exhaust gas in hydrogen production by N H 3 pyrolysis, and this will further enhance the development of N H 3 as the potential H 2 carrier for onsite production in hydrogen power generation. [ABSTRACT FROM AUTHOR]

The presented paper focuses on a problem of heat transfer in periodic surface structures. The periodic structure surfaces are the compound structures described by mathematical formulas that represent areas similar to porous structures. The interest in them surged recently due to increased possibilities of their production using additive manufacturing technology. Elements designed with the use of periodic surface structures seem to have such advantages as decreased weight or good general mechanical properties. The most famous example of the periodic surface structure is gyroid. The main goal of this paper is to evaluate the impact of convective heat transfer on the temperature distribution in periodic surface structures. There are some papers with numerical simulations on this topic but they usually exclude heat exchange with the environment. The simulations of heat transfer in the periodic structure surfaces are important because of the high energy flux required for additive manufacturing to work properly. Importantly, high energy flux results in large temperature gradients that can affect the quality of the obtained part in properties like porosity or residual stresses. The heat transfer simulations in this paper are conducted by solving the heat transfer equation accompanied by the proper boundary conditions using our authorial software, which implements solution obtained by the finite element method together with the task of generation of the periodic surface structure domain. [ABSTRACT FROM AUTHOR]

In the present paper, recent advances in the application of nanofluids in heat transfer in porous materials are reviewed. Efforts have been made to take a positive step in this field by scrutinizing the top papers published between 2018 and 2020. For that purpose, the various analytical methods used to describe the flow and heat transfer in different types of porous media are first thoroughly reviewed. In addition, the various models used to model nanofluids are described in detail. After reviewing these analysis methods, papers concerned with the natural convection heat transfer of nanofluids in porous media are evaluated first, followed by papers on the subject of forced convection heat transfer. Finally, we discuss articles related to mixed convection. Statistical results from the reviewed research regarding the representation of various parameters, such as the nanofluid type and the flow domain geometry, are analyzed, and directions for future research are finally suggested. The results reveal some precious facts. For instance, a change in the height of the solid and porous medium results in a change in the flow regime within the chamber; as a dimensionless permeability, the effect of Darcy's number on heat transfer is direct; and the effect of the porosity coefficient has a direct relationship with heat transfer: when the porosity coefficient is increased or decreased, the heat transfer will also increase or decrease. Additionally, a comprehensive review of nanofluid heat transfer in porous media and the relevant statical analysis are presented for the first time. The results show that Al2O3 nanoparticles in a base fluid of water with a proportion of 33.9% have the highest representation in the papers. Regarding the geometries studied, a square geometry accounted for 54% of the studies. [ABSTRACT FROM AUTHOR]

With the increasing intelligence of automobiles, vehicle pre-ventilation can be better controlled. In summer, cars parked in the open air are directly exposed to sunlight; thus, a high-temperature environment is formed in the occupant cabin, which seriously affects the passengers and driver's riding and driving experience. Meanwhile, lowering the temperature of the passenger compartment from a very high temperature to a comfortable temperature consumes a lot of energy. Therefore, it is increasingly important to study the pre-ventilation of the cabin in order to improve the thermal comfort of the occupant cabin and reduce energy consumption. In this paper, a new theoretical model of a cabin temperature control system is proposed. To support the theoretical model, an outdoor parking temperature rise test was carried out. Environmental parameters were obtained and used as the boundary conditions of the subsequent simulation. Based on the mechanism of the cabin temperature rise, the convective heat transfer coefficient on the body surface, the equivalent heat transfer model of the cabin, the solar radiation model and the physical properties of the air, a computational simulation of the temperature rise in the occupant cabin was carried out, and a simulation of the temperature rise in the occupant cabin exposure was studied. The simulation results were compared with the experimental findings to verify the accuracy of the simulation, which provided a reference for the design of the pre-cooling function of the occupant cabin. This study revealed that the pre-ventilation model developed reduces the vehicle cabin temperature through optimal control of air supply volumes and air supply angles. Furthermore, the developed pre-ventilation model is capable of reducing energy consumption, thereby reducing greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

The main aim of this paper is to present the new design of an integrated planar spiral inductor with a new structure of an underpass to obtain a high inductance, high quality factor and minimum losses into winding and magnetic core. The performance of this structure dependent on the geometrical, electrical parameters and material properties. These parameters are calculated at 350 MHz and this is the high frequency used for MEMS applications. Furthermore, thermal analysis in inductor from finite difference method is described. The heat transfer model is based on heat conduction and heat convection. Moreover, the heat source is calculated by different losses. In addition, the simulation results from 3D finite element method using software also been presented in this paper. It is based on both the classical heat equation and certain condition limits. However, a new design of an underpass has been proposed where a via is fabricated with a circular layer. The input and output of the spiral are implanted in the same direction. In addition, the magnetic core is the solution to decrease the temperature. Finally, the results of the finite difference method are compared with simulation results from finite element method. The good agreement between the results is obtained. The proposed via and a core magnetic are responsible for enhancement the thermal behavior in integrated inductor. The result shows that the temperature of the air core inductor and magnetic core inductor could be 53 ℃ and 33 ℃, respectively. [ABSTRACT FROM AUTHOR]

This paper examines the heat transfer characteristics of magnetohydrodynamics (MHD), suction, and Marangoni convection under the stretching/shrinking Ag–Cu hybrid nanofluid surface flow. First, the governing partial differential equations (PDEs) were transformed into ordinary differential equations (ODEs), and the numerical result was obtained using the boundary value problem solver (bvp4c) in MATLAB. The development of the Nusselt number, the velocity profile and the temperature profile was plotted, discussed and inspected. Next, this paper undergoes stability analysis and heat transfer rate comparison between water, nanofluid and hybrid nanofluid. The dual solutions were observed, and the upper branch solution is determined to be stable. Compared to water, the heat transfer rates of Ag–Cu hybrid nanofluid and Cu nanofluid were accelerated by 2.84% and 2.75%, respectively. [ABSTRACT FROM AUTHOR]

Under the current background of high-speed continuous casting, it is essential to investigate the effect of casting speed on the stability of the solidification structure and quality of billets. In this paper, a three-dimensional transient numerical model was established to simulate the continuous casting process, and the model was verified through the temperature measurement data and the actual solidification structure characteristics of billets. On this basis, the effect of casting speed on columnar to equiaxed transition (CET) position fluctuation along the casting direction was investigated, and the corresponding control measures of CET position fluctuation were presented. The internal quality stability of billets will not always deteriorate with the increase of the casting speed, and there is an optimal casting speed. Meanwhile, the casting speed can affect the fluctuation of the heat transfer by changing the molten steel convection fluctuation in billets, and finally, resulting in the fluctuation of CET position and central quality along the casting direction. Under a certain specific water amount, the fluctuation of liquid convection and heat transfer at the CET region is relatively decreased, and the solidification structure along the casting direction is more uniform when the casting speed is controlled in the intermediate range. During the high-speed continuous casting process, the cooling intensity of the secondary cooling can be appropriately increased, when the optimal casting speed is undeterminable, to reduce the CET fluctuation and improve the uniformity of the billets central quality. This paper can provide methods and theoretical references for determining the optimal casting speed and improving the internal quality of billets under the background of high-speed continuous casting. [ABSTRACT FROM AUTHOR]

One of the major problems of using nanofluids in heat exchange applications is the forming and deposition of nanoparticles on the inner surface of the heat exchanger. In this paper, Water-Cmc fluid is used as a surfactant for nanoparticles to prevent deposition and congregation. The pressure drops and heat transfer in U-bend double pipe heat exchanger based on water-MgO-Cmc fluid, are examined. Nanoparticles of Magnesium Oxide (MgO) and Carboxymethyl Cellulose (Cmc) are used with pure water as a base fluid. The experimental rig and procedures are designed to facilitate various operational conditions such as flow rate, volume concentration of MgO particles and weight concentration of Cmc particles. Furthermore, convective heat transfer coefficient, heat exchanger effectiveness, pressure drop, friction factor, under different conditions, are measured. The results demonstrate convective heat transfer coefficient of U-bend double pipe heat exchangers is enhanced by 35% for 1 MgO vol.% and 0.2 Cmc wt.% compared to base fluid (Water-Cmc). It is concluded that pressure drops are directly proportion to the increase of MgO nanoparticles at same Cmc concentration by 23% at 0.2 wt.%. Whilst, friction factor of the system is inversely proportion to the increase of volumetric flow rate of water-MgO-Cmc fluid. An increase in MgO nanoparticle concentration increases the friction factor, hence maximum friction factor enhancement by 38% for MgO concentration of 1 vol.%. The effectiveness of heat exchanger is slightly increased by 8% with increase of MgO concentration and flow rate. Finally, thermo-physical characteristics of water-MgO-Cmc fluid at various temperatures, are measured [ABSTRACT FROM AUTHOR]

The performance of lithium-ion batteries is greatly influenced by various factors within their operating environment, which can significantly impact their overall efficiency and effectiveness. In this paper, a multi-physics field electrochemical thermal model is established to measure the physical parameters of a battery module during the charge/discharge process. The effects of working temperature, current rate, and convective heat transfer coefficient are investigated by establishing an electrochemical and thermal model. The results are obtained by conducting numerous parameterized scans to analyze the system's state across various operating conditions, enabling the determination of its temperature and the selection of appropriate cooling measures accordingly. Based on the internal and external conditions of battery operation, parameter selection corresponding to the operating range is divided into several stages, with thermal management strategies provided for each stage. The existing framework facilitates the design of battery packs equipped with efficient thermal management strategies, thereby enhancing the battery systems' reliability and performance. Furthermore, it aids in establishing optimal operational and safety boundaries for batteries. [ABSTRACT FROM AUTHOR]

In this paper, numerical simulations of a special energy pile, which constitutes a spiral-injected pipe and one straight discharge pile for Geothermal Heat Pump Systems (SGHEs-P(parallel)), were conducted by Fluent software. The effects of the spiral pitches on the heat transfer rate based on the G-function method and peripheral soil temperature of the pile were investigated under continuous and intermittent operation strategies. The impact of spiral tube sizing on the surface heat transfer coefficients was studied. The results indicated that SGHEs-P may be preferred for office buildings under intermittent operation conditions. For a short period, the temperature profiles and heat transfer efficiency of SGHEs-P were mainly influenced by the fluid type, length of the spiral tube, and spiral pitch. The smaller the spiral pitch, the more uniform the temperature distribution, and the better the heat transfer effect, but the heat transfer per unit depth of pile decreased. The average temperature variation curve of the soil around the energy pile with different spiral pitches was simulated and obtained over time. Meanwhile, the impact of spiral radius, spiral pitch, and spiral tube radius on the convective heat transfer coefficient was also presented. Through data fitting, the formulas for the correction coefficients of spiral radius, spiral pitch, and spiral tube radius on convective heat transfer coefficient were obtained, respectively. [ABSTRACT FROM AUTHOR]

The printed circuit heat exchanger (PCHE) is receiving wide attention as a new kind of compact heat exchanger and is considered as a promising vaporizer in the LNG process. In this paper, a PCHE straight channel in the length of 500 mm is established, with a semicircular cross section in a diameter of 1.2 mm. Numerical simulation is employed to investigate the flow and heat transfer performance of supercritical methane in the channel. The pseudo-boiling theory is adopted and the liquid-like, two-phase-like, and vapor-like regimes are divided for supercritical methane to analyze the heat transfer and flow features. The results are presented in micro segment to show the local convective heat transfer coefficient and pressure drop. It shows that the convective heat transfer coefficient in segments along the channel has a significant peak feature near the pseudo-critical point and a heat transfer deterioration when the average fluid temperature in the segment is higher than the pseudo-critical point. The reason is explained with the generation of vapor-like film near the channel wall that the peak feature related to a nucleateboiling- like state and heat transfer deterioration related to a film-boiling-like state. The effects of parameters, including mass flow rate, pressure, and wall heat flux on flow and heat transfer were analyzed. In calculating of the averaged heat transfer coefficient of the whole channel, the traditional method shows significant deviation and the micro segment weighted average method is adopted. The pressure drop can mainly be affected by the mass flux and pressure and little affected by the wall heat flux. The peak of the convective heat transfer coefficient can only form at high mass flux, low wall heat flux, and near critical pressure, in which condition the nucleate-boiling-like state is easier to appear. Moreover, heat transfer deterioration will always appear, since the supercritical flow will finally develop into a filmboiling- like state. So heat transfer deterioration should be taken seriously in the design and safe operation of vaporizer PCHE. The study of this work clarified the local heat transfer and flow feature of supercritical methane in microchannel and contributed to the deep understanding of supercritical methane flow of the vaporization process in PCHE. [ABSTRACT FROM AUTHOR]

A hydro-dynamic thermal fully developed forced convective heat transfer analysis of magneto-hydrodynamics fluid flow through an annular sector duct is presented in this paper. Two types of thermal boundary conditions i.e., axially uniform heat flux along with peripherally uniform temperature (known as H1-condition) and, axially and peripherally uniform temperature (known as T condition), have been considered to carry out the thermal analysis of fluid. The velocity components along r and θ direction are transformed into algebraic form by using power law discretized scheme, whereas cross-sectional pressure P (r , θ) is estimated with the help of well know technique S I M P L E R. The governing partial differential equations are solved by numerically with the help of M A T L A B code. Furthermore, simulated results have been compared with the existing results of literature to validate the results. From the results, it is noted that hydro-dynamically and thermally impacts relate directly by increasing the Hartman number, (M). It is further reported that the effect of magnetic field becomes insignificant for the higher number of fins, N. The findings of the present analysis will be applicable in various types of thermal systems. [ABSTRACT FROM AUTHOR]

Featured Application: The work specifically targets the enhancement of cooling mechanisms in high-power permanent magnet electrical machines, with a direct application in improving the thermal management of stator windings in such devices. This advancement can significantly benefit sectors like aerospace, where the efficiency, reliability, and longevity of electrical machines are critical. This paper investigates innovative methods for enhancing heat transfer efficiency in high-power permanent magnet electrical machines. The objectives are to quantify the effects of increasing the air speed, increasing the turbulence intensity, and introducing the spacing between windings on cooling performance. The cooling of stator windings is studied through experimental wind tunnel testing and Computational Fluid Dynamics (CFD) modelling. The CFD model is validated against wind tunnel measurements to within 4 Kelvin (K). The results demonstrate that each enhancement method significantly improves the cooling capability. Increasing the air speed from 10 m/s to 40 m/s reduces the winding hotspot temperature by 34%. Introducing a high turbulence intensity of 40% leads to a 21% lower hotspot temperature compared to 0.5% turbulence intensity. Creating a 1.5 mm spacing between coils also substantially improves convection and conduction heat transfer. Overall, combining these optimised design parameters yields over a 40% reduction in hotspot temperature compared to the original design. This research provides practical guidance for maximising heat transfer efficiency in high-power permanent magnet machines, without increasing complexity. The findings will lead to higher machine efficiency, reliability, and longevity for aerospace and other applications. [ABSTRACT FROM AUTHOR]

Measurement of the combustion temperature field is an extremely important issue in industrial production. Temperature is one of the key parameters in combustion studies. With the temperature field distribution of the combustion field obtained, heat transfer, heat convection, and heat radiation can be calculated directly and efficiently. Traditional background oriented Schlieren (BOS) is an effective method for non-axisymmetric temperature field measurements, but it requires simultaneous Schlieren imaging at multiple angles for tomographic reconstruction, which will greatly limit its application. In this paper, the compressive sensing algorithm is introduced into the temperature field reconstruction, which establishes the system of equations between the deflection angle and the refractive index gradient. Then, the reconstruction of the non-axisymmetric temperature field is realized by solving the underdetermined system of equations by the method of solving the sparse solution through the compressive sensing. First, light offsets across the non-axisymmetric temperature field are measured by the under-angled BOS system and image processing method. Second, the spatial refractive index field is reconstructed by the compressive sensing BOS method proposed in this paper. Finally, the spatial temperature field is obtained. The experimental results show that by comparing the iRadon reconstruction algorithm and the compressive sensing reconstruction algorithm, the temperature field reconstructed by the compressive sensing under the condition of the under-angled sampling of projection data had a higher accuracy than that reconstructed by the tomographic reconstruction algorithm under the same condition. The average error of the temperature field was reduced from 34.6 to 29.7 K under the same measurement conditions; however, the accuracy is better maintained by using the compressive sensing algorithm under the condition of undersampling projection. [ABSTRACT FROM AUTHOR]

Air-cooled heat exchangers in various industries enjoy an increasingly wider use thanks to their environmental friendliness and absence of the need for cooling water. Air-cooled heat exchangers from annular finned tubes are widely used in chemical, petrochemical, oil-refining, gas, and food industries, and also at automobile compressed natural gas filling stations (NGV gas stations), in heat power engineering, electric power engineering, refrigeration technology, and at nuclear power plants. The thermal capacity of air-cooled heat exchangers is largely determined by the characteristics of the motion of a flow of cooling air through them that can be organized with consumption of electric power by means of a ventilator or in an energy-saving regime by free convection. Unfortunately, the region of ambient air temperatures at which it is possible to use air-cooled heat exchangers under the conditions of free convection is limited. Low heat transfer intensity compared to forced convection is the main drawback of the free-convection regime which is usually compensated by an increase in a heat-emitting area, namely, by finning the heat transfer surface. By equipping air-cooled heat exchangers with additional devices making it possible to intensify free convection, the thermal performance of heat exchangers can be improved significantly. The paper provides an overview of experimental and numerical investigations of free-convection heat transfer in annular finned tube bundles with an exhaust shaft installed above them. [ABSTRACT FROM AUTHOR]