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IF=5.302; International audience; Microwave sintering (MW) allows fast heating (≤30 min) and densification of ceramic materials, like alumina Al2O3. In order to predict the final material properties (density, size and grain size) the mechanical SOVS (Skorohold Olevsky Viscous Sintering) model is adapted and validated for conventional sintering of alumina. The model is implemented on ABAQUS with UMAT subroutine. Secondly, the SOVS model is modified for the microwave sintering by adapting the shear viscosity Arrhenius type law. Pre-exponential and exponential coefficients are modified for MW sintering. The calculated relative densities are compared to experimental results from conventional and microwave sintering and the relative difference remains under 3%. The coefficients identified for the MW sintering reveal a decrease in the shear viscosity by around 10 and an increase by up to 50 times in the grain boundaries diffusion coefficient.

An original method of monolith impregnation in microsystem for the analysis of radionuclides in nitric acid is reported. Three microcolumns made of monolith poly(AMA-co-EDMA) were impregnated in COC microsystems. The robustness of the microsystems in nitric acid media until 8 M was demonstrated. High exchange capacity and affinity for tetravalent and hexavalent actinides in concentrated nitric media were obtained. The retention characteristics of the microcolumns impregnated by TBP, TBP-CMPO and DAAP were compared with those of the equivalent commercial particulate resins TBP™, TRU™ and UTEVA™ respectively. The separation of U, Th and Eu was validated in a classical microsystem and a procedure is proposed in a centrifugal microsystem.

Blackspot in potato is an internal tissue discoloration that occurs during handling and transport of potato tubers. Blackspot is cosmetically undesirable and represents a huge economic cost for the potato industry. The aim of this study was to test whether concentrations of certain metabolites in the potato tuber cortex could predict blackspot susceptibility.; Results: Seven russet potato varieties were stored for eight months at 8.8 °C. Stored tubers were subjected to mechanical impact and evaluated for blackspot susceptibility. A blackspot susceptibility index was calculated for each variety by determining an index for the percentage of the tuber cortex area that was covered with blackspot, and an index for the intensity of blackspot discoloration. Concentrations of tyrosine, chlorogenic acid, phenylalanine, and ascorbic acid, and blackspot biochemical potential of tubers to synthesize pigments were measured in the tuber cortex. Blackspot indices, metabolites concentrations and blackspot biochemical potential varied significantly between varieties. Tyrosine concentrations strongly, significantly, and positively correlated with blackspot biochemical potential. Phenylalanine concentrations showed good, significant, and positive correlation with blackspot biochemical potential and discoloration index. None of the analyzed metabolites correlated with blackspot susceptibility.; Conclusion: Concentrations of tyrosine and phenylalanine explained up to ∼80% of the variation in blackspot biochemical potential between varieties but did not correlate with blackspot susceptibility. © 2018 Society of Chemical Industry.; © 2018 Society of Chemical Industry.

International audience; The present study focuses on oil cooling for electric motors. A 40 kW test machine in which oil was introduced at each side of the machine to directly cool the stator coil end-windings was previously implemented. The lumped system analysis is used to model the thermal behavior of this test electric machine. An inverse method is applied to interpret the data obtained by the experimental setup. The inverse method leads to interior convection coefficients that help describe the heat transfer mechanisms.

Blackspot in potato is an internal tissue discoloration that occurs during handling and transport of potato tubers. Blackspot is cosmetically undesirable and represents a huge economic cost for the potato industry. The aim of this study was to test whether concentrations of certain metabolites in the potato tuber cortex could predict blackspot susceptibility.Seven russet potato varieties were stored for eight months at 8.8 °C. Stored tubers were subjected to mechanical impact and evaluated for blackspot susceptibility. A blackspot susceptibility index was calculated for each variety by determining an index for the percentage of the tuber cortex area that was covered with blackspot, and an index for the intensity of blackspot discoloration. Concentrations of tyrosine, chlorogenic acid, phenylalanine, and ascorbic acid, and blackspot biochemical potential of tubers to synthesize pigments were measured in the tuber cortex. Blackspot indices, metabolites concentrations and blackspot biochemical potential varied significantly between varieties. Tyrosine concentrations strongly, significantly, and positively correlated with blackspot biochemical potential. Phenylalanine concentrations showed good, significant, and positive correlation with blackspot biochemical potential and discoloration index. None of the analyzed metabolites correlated with blackspot susceptibility.Concentrations of tyrosine and phenylalanine explained up to ∼80% of the variation in blackspot biochemical potential between varieties but did not correlate with blackspot susceptibility. © 2018 Society of Chemical Industry.

International audience; Power transmission through power cables installed in ventilated tunnels is increasingly used worldwide and offers a complex thermal environment. Established correlations currently in use have been deduced from a nonfully developed turbulent flow and the effect of the proximity to a tunnel wall is not accounted for. This paper details the experimental and numerical investigations conducted on a mock-up of the heat transfer from a single cable in a fully developed turbulent airflow, with emphasis on the effect of the cable spacing from the tunnel wall. Nusselt numbers have been compared for different spacing and Reynolds numbers. The overall heat transfer is found to be meaningfully lower than in previous studies as only a third of the heat transfer is found, possible explanation of these differences are given in this paper. A threshold value is observed for the heat transfer while the cable rating depreciation is more gradual. The radiative heat exchange is found to be up to 30% of the total heat loss. An improved cooling law for the case of a single cable in tunnel taking into account the proximity of the wall has been developed from this study and confronted to the experimental and simulated data.

International audience; New calculations using an innovative Reynolds Stress Model are compared to velocity measurements performed by Particle Image Velocimetry technique and the predictions of a k-w SST model in the case of an impinging jet flow onto a rotating disk in a discoidal and unshrouded rotor-stator system. The cavity is characterized by a dimensionless spacing interval G=0.02 and a low aspect ratio for the jet e/D=0.25. Jet Reynolds numbers ranging from 17200 to 43000 and rotational Reynolds numbers between 33000 and 532000 are considered. Three flow regions have been identified: a jet-dominated flow area at low radii characterized by a zero tangential velocity, a mixed region at intermediate radii and rotation-dominated flow region outwards. For all parameters, turbulence, which tends to the isotropic limit in the core, is much intense in a region located after the impingement zone. A relative good agreement between the PIV measurements and the predictions of the RSM has been obtained in terms of the radial distributions of the core-swirl ratio and of the turbulence intensities. The k-wSST model overestimates these flow characteristics in the jet dominated area. For the thermal field, the heat transfers are enhanced in the jet dominated region and decreases towards the periphery of the cavity. The jet Reynolds number appears to have a preponderant effect compared to the rotational one on the heat transfer distribution. The two RANS modelings compare quite well with the heat transfer measurements for these ranges of parameters.

An optimization of the thermal behavior of a high-power salient-pole electrical machine is presented. Temperatures are calculated with the lumped method, which provides the thermal trends with relatively low computational cost. This model is used to define an aggregated objective function of our nonlinear thermal optimization problem by combining the mean solid temperature with the maximum temperature criteria. The 13 design variables correspond to the main volumetric flow rates in the electrical machine, which are bounded and subjected to a nonlinear constraint, assuming a fixed geometry. Two MATLAB optimization algorithms were tested: the Active-set (FMINCON solver) and the genetic algorithm (GA). Due to the strong nonlinearities of the model and the resulting nonconvex optimization problem, the GA is likely to give better results. Minimizing the mean solid temperature was demonstrated to be more important than the maximum temperature criterion. A strategic flow configuration is found to send fresh air to the second half of the cooling circuit, where air usually arrives heated. This optimal configuration provides better cooling than its current modeled configuration. This methodology should be of interest during the development phase.

International audience; Power transmission through power cables installed in ventilated tunnels has been increasingly used worldwide and offers a complex thermal environment. Established correlations currently in use have been deduced from a non-fully developed turbulent flow. This paper details the experimental investigation of the heat transfer from a single cable in a fully developed turbulent air flow, with emphasis on the effect of the cable spacing from the tunnel wall. Nusselt numbers have been compared for different spacing and velocities. The overall heat transfer is found to be meaningfully lower than in previous studies and no threshold spacing value for the average heat transfer to decrease is clearly found. Thermal radiation is found to greatly impact the cable cooling profile.

We present the thermal optimization study of a single inlet 90° T-junction. Head losses in association with the lumped method are used to calculate the 2D temperature field from a specific geometrical configuration, heat sources, boundary conditions and available ventilation power. This simple case is used as a benchmark to show a possible optimization methodology and to test 4 optimization algorithms suitable to non-linear problems; they are the Active-Set, Interior Point, Genetic Algorithm and Particle Swarm Optimization. The optimization problem is defined by an Aggregated Objective Function (AOF) that depends on three geometrical parameters which are subjected to linear and non-linear constraints. In order to consider not only the global thermal behavior, but also local hotspots, the AOF combines mean solid temperature pondered by its volume and the maximal temperature. Five weights for these criteria were tested. The physical interpretation of different points helped to identify the optimal geometrical characteristics. All optimization algorithms demonstrated to be able to avoid local minima with this benchmark, if properly used.

Discoidal rotor–stator systems are nowadays sometimes used in electrical wind generator. The cooling of such a system is a major problem due to the fact that high electrical losses are dissipated for relatively low rotational speed, responsible of the cooling. A new cooling solution is then investigated in this paper. So, this paper presents an experimental study of the local heat transfers on the rotor surface in the air-gap of a discoidal rotor–stator system, in which an air jet comes through the stator and impinges the rotor. To determine the surface temperatures, measurements were taken on the rotor, using an experimental technique based on infrared thermography. A thermal balance equation was used to identify the local convective heat transfer coefficient. The influence of the axial Reynolds number Re j and the rotational Reynolds number Re was measured and compared with the data available in the literature. Local convective heat transfer coefficients were obtained for an inter-disk dimensionless spacing interval G ranging from 0.01 to 0.16 for Re j between 0 and 41,666 and for Re between 20,000 and 516,000. The rotating disk can thus be divided into zones: one dominated by the air jet near the center of the rotor and one affected by both the air jet and rotation. Even though these two zones are not located in the same place on the disk, the heat transfers with non-zero impinging jets appear to be continuously improved compared to those with no jets. Critical radii over the rotor surface are identified and correlations are given.

The transient performance of a flat heat pipe (FHP) used to cool multiple electronics components, is presented in this paper. The fluid flows in both wick and vapor core were computed using a transient 2D hydrodynamic model (T2DHM). This model was coupled with a transient 3D thermal model (T3DTM) of the FHP wall, designed to calculate the heat transfer through the wall. An interesting procedure for solving the governing equations for the heat and mass transfers inside the FHP is proposed. The phase change mechanisms at the liquid–vapor interface are included in this procedure through the Clausius–Clapeyron law. During a start-up, the T2DHM is able to predict the velocity and pressure distribution of the liquid and the vapor, and thus the transient response of the FHP.

This article presents an experimental study of the local heat transfer on the rotor surface in a discoidal rotor–stator system air-gap in which an air jet comes through the stator and impinges the rotor. To determine the surface temperatures, measurements were taken on the rotor, using an experimental technique based on infrared thermography. A thermal balance was used to identify the local convective heat transfer coefficient. The influence of the dimensionless spacing interval G between the disks and of the rotational Reynolds number Re was measured and compared with the data available in bibliography. Local convective heat transfer coefficients were obtained for an axial Reynolds number Rej = 41.6 × 103, a rotational Reynolds number Re between 0.2 × 105 and 5.16 × 105, and a dimensionless spacing interval G ranging from 0.01 to 0.16.

This article presents an experimental study of the heat transfers in a discoidal rotor–stator system air-gap. Measurements are performed over the rotor, using an experimental technique based on infrared thermography, in order to determine the surface temperatures. Using a thermal balance, the local convective heat transfer coefficient is identified. The influences of the rotational Reynolds number Re and the dimensionless spacing between the two disks G are carried out and compared with literature data when available. Local convective heat transfer coefficients are obtained for Re ranging from 1.29 × 105 to 6.45 × 105 and for G between 0.01 and 0.16. Four heat transfer regimes are identified then correlated. Comparisons with our previous results concerning flow and heat transfers over a single rotating disk in still air are also carried out.

IF=2.624; International audience; The present study focuses on the use of lubricating oil as a coolant for electrical motors. Oil is introduced at each side of a 40 kW test machine to directly cool the stator coil end-windings. An experimental setup has been implemented to test different oil injection patterns. The influence of the oil flow rate, rotation speed and oil temperature has been investigated (40 L/h

International audience; Electrical machines are used in an ever-increasing number of applications, such as transportation systems and energy production, because of their high efficiency. The improvement of their cooling is of interest in order to increase the energy produced per unit volume. To that end, radial channels can be placed inside the stator, allowing the internal fluid to pass through, from the air gap where the mean flow is longitudinal to an external channel. To investigate both the flow between the air gap and the radial channels, and the induced convective heat transfer, an experimental set-up is used. Two fans, whose power can be adjusted, are used to create flows in the two longitudinal channels, which represent the air gap, and the external channel of the real machine. A thin heat foil is used to heat one channel face, and the temperature profiles are measured using an infrared camera. Convective heat transfer coefficients are determined along the radial centerline of each channel face by a conductive 1D model coupled with an inverse method. The inlet Reynolds number is kept constant at approximately 25000, and the mass flow rate ratio between the perpendicular channel and the inlet varies from 0.13 to 0.88. In particular, we will pay special attention to the heat transfers at channel entrances, where PIV measurements are also made. Recirculation areas, whose size are linked to the dynamic conditions, occur and have a direct influence on the local Nusselt numbers.

Cooling of electrical machines is nowadays of high interest in order to improve their efficiency. In railway applications, electrical motors can be shrouded in order to avoid particles to be deposited inside. To ensure a satisfactory cooling, pipes are placed inside the rotor and are thus rotating. Improvements in convective heat transfer inside the rotating pipes were numerically investigated. Model was first validated against experimental data and after that several geometry modifications were tested. Influence of the angle of attack of the fluid at the inlet to the pipe was discussed and it was shown that heat transfer can be significantly increased near the pipe inlet. In addition to that changing a circular pipe with an elliptical pipe was investigated in two ways: fixing the same hydraulic diameter or the same equivalent diameter. It was shown that the cooling efficiency can be significantly increased. The best overall heat transfer enhancement of about 45% exhibited elliptic pipes located orthogonal to the rotation radius and having the same cross-section as the reference circular pipes. Results can be used by designers of electrical machines in order to choose the best cooling strategy.

International audience; Fluid flow and convective heat transfer in rotor-stator configurations, which are of great importance in different engineering applications, are treated in details in this review. The review focuses on convective heat transfer in predominantly outward air flow in the rotor-stator geometries with and without impinging jets and incorporates two main parts, namely, experimental / theoretical methodologies and geometries/results. Experimental methodologies include naphthalene sublimation techniques, steadystate (thin layer) and transient (thermochromic liquid crystals) thermal measurements, thermocouples and infra-red cameras, hot-wire anemometry, laser Doppler and particle image velocimetry, laser plane and smoke generator. Theoretical approaches incorporate modern CFD computational tools (DNS, LES, RANS etc). Geometries and results part being mentioned starting from simple to complex elucidates cases of a free rotating disk, a single disk in the crossflow, single jets impinging onto stationary and rotating disk, rotor-stator systems without and with impinging single jets, as well as multiple jets. Conclusions to the review outline perspectives of the further extension of the investigations of different kinds of the rotor-stator systems and their applications in engineering practice.

The current work experimentally investigates the flow characteristics of an air jet impinging on an open rotor-stator system with a low non-dimensional spacing, G = 0.02, and with a very low aspect ratio, e/D = 0.25. The rotational Reynolds numbers varied from $$0.33\times10^5$$ to $$5.32\times10^5$$ , while the jet Reynolds numbers ranged from 17.2 × 103 to 43 × 103. Particle image velocimetry (PIV) measurements were taken along the entire disk diameter in three axial planes. From the obtained PIV velocity fields, the flow statistics were computed. A recirculation flow region, which was centered at the impingement point and possessed high turbulence intensities, was observed. Local peaks in root-mean-square fluctuating velocity distributions appeared in the recirculation region and near the periphery, respectively. Proper orthogonal decomposition analysis was applied to the cases of the jet impinging on the rotor with and without rotation to reveal the coherent structures in the jet region.

The present work relates to an experimental study of the local convective heat transfer over the rotor surface in the air-gap of a discoidal rotor–stator system. This configuration is of interest namely, in electrical machines or tubomachinery. Following precedent studies obtained for a single rotating disk or a closed (but unshrouded) rotor–stator system, an air suction comes through the stator and enters the air-gap in this particular work. Determination of Nusselt numbers is based on the use of infrared thermography. The influence of the suction is discussed for an interdisk dimensionless spacing interval, G ranging from 0.01 to 0.16 and for a rotational Reynolds number, Re between 30,000 and 5,16,000. Results shows that the suction could locally provide better cooling than in the closed rotor–stator and in the single disk configurations, even if the main influence is a decrease in the convective heat transfer.

The experimental work presented in this paper relates to the local convective heat transfer on the rotor surface in the airgap of a discoidal rotor stator system. The stator used in these experiments is a multiperforated disk in which an air suction due to the rotation of the rotor comes through and enters the airgap. A thermal balance equation was used to identify the local convective heat transfer coefficient, with temperatures as boundary conditions, which have been measured by infrared thermography. The influence of the suctions is discussed for an interdisk dimensionless spacing interval G ranging from 0.01 to 0.16 and for Re between 129,000 and 516,000. Results are compared with precedent studies in which we obtained Nusselt numbers with a closed rotor stator system in which stator is a full disk and a rotor stator system with one hole at the stator center. It is shown that multiperforated stator can or cannot improve the rotor cooling, depending on G and Re.

International audience; The design of electrical machines involves several fields of physics, such as electromagnetism, thermics, mechanics but also acoustics. This paper describes the analytical multi-physics models of a computer-aided design (CAD) software which is applied to inverter-fed traction induction machines. The electromagnetic model computes rotor and stator currents, the induction machine traction characteristics, and the radial air-gap flux density. The mechanical and acoustic model computes the motor audible magnetic noise level due to Maxwell forces. The thermal model based on 3D nodal network, computes the transient temperature of different parts of the motor. These fast models make it possible to couple the software with some optimization tools. Finally, some simulations are presented on a self-ventilated closed motor, and an example of multi-objective optimization is exposed.

The design of variable-speed electrical machines involves several fields of physics, such as electromagnetism, thermics, mechanics, and also acoustics. This paper describes the analytical multiphysics models of a computer-aided-design software which is applied to inverter-fed traction induction machines. The electromagnetic model computes rotor and stator currents, the induction-machine traction characteristics, and the radial air-gap flux density. The mechanical and acoustic models compute the motor's audible magnetic noise level due to Maxwell forces. The thermal model based on 3-D nodal network computes the transient temperature of different parts of the motor. These fast models make it possible to couple the software with some optimization tools. Some simulation results are presented on a self-ventilated closed motor and compared to experiments.

This work is aimed to simulate the transient performances of a flat heat pipe (FHP) used to cool electronics components in automotive applications. A transient 3D thermal model (T3DTM) of the FHP wall is performed to calculate the heat transfer through the wall of the FHP. This model is coupled with a transient 2D hydrodynamic model (T2DHM) which determines the flows both in wick and vapour core. An energy balance and Clausius-Clapeyron law permit to represent the phase change mechanisms at the liquid-vapour interface. The performed T2DHM model includes the solution of the complete governing equations in both wick and vapor core. The T2DHM is able to predict the velocity and pressure distributions of the FHP working fluid and then the FHP transient response. That analysis helps determine the maximum pore radius of the wick necessary to support the total pressure drop in the FHP. The heat removal capability of the FHP is highlighted through a comparison with a solid copper plate of the overall dimensions as the FHP.

This paper deals with flow structure and heat transfer modeling in a two coaxial disk air-gap. Numerical estimations for the local Nusselt number on the rotor, for the radial and tangential velocities are compared with experimental results obtained using PIV and infrared thermography. Models used for the numerical approach are then validated for a turbulent Reynolds Number.

National audience; La conductivité thermique effective de lits de poudres dépend d’un nombre important deparamètres. Dans cet article est présentée l’influence apparente de la taille des grains et de leursgéométries sur ce paramètre du milieu, en s’appuyant sur un modèle de conductivité thermique demilieux poreux non-connectés dans l’air à pression atmosphérique, que nous avons développé. Cemodèle se base sur la théorie de la percolation pour décrire le transfert thermique dans ce type dematériaux. Le milieu est décrit par les paramètres microstructuraux suivants: la porosité intra-granulaireet inter-granulaire, ainsi que des paramètres propres au matériau et à l’arrangement des particules. Lesdeux premiers paramètres sont mesurés pour certains échantillons grâce à une caractérisation de lamicrostructure du lit par un micro-tomographe à rayons X. Les valeurs de conductivités effectives du litprédites par ce modèle sont comparées avec des mesures effectuées à l’aide de la méthode du plan chaudinstationnaire. Les résultats montrent que la conductivité thermique d’un lit de poudre semble trèssensible à la répartition des porosités entre la porosité inter-granulaire et intra-granulaire.