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Downburst is a type of near-surface short-term destructive strong wind that significantly affects wind-sensitive flexible structures like transmission tower-line systems. The existence of the tower-line coupling effect complicates the wind-induced vibration response analysis. Firstly, the average wind speed time history is obtained using the impinging jet wind field model, the pulsating wind speed time history is simulated using the harmonic synthesis method, and then the total wind speed time history of the downburst is obtained by superposition. Then, the transmission tower-line finite element model is established to carry out the wind vibration response analysis under different wind attack angles. Based on the most unfavorable wind angle of attack, the wind-induced vibration response and the coupling effect of the tower-line system are investigated under different maximum wind speed heights (Z $_{\max }$ ) and span distances. Finally, the range of wind load reduction coefficients for the tower-line separation system is given. The results show that under the most unfavorable wind angle of attack angle, both the displacement and acceleration response of the tower-line separation system are more significant than that of the tower-line coupling system. At Z $_{\max }=70$ m, the difference in displacement response between the two systems reaches the maximum, indicating an apparent tower-line coupling effect. As the span distance increases, both the displacement response and the acceleration response of the tower-line separation system increase. In contrast, the displacement response of the tower-line coupling system increases, but the acceleration response decreases. For the proposed design reduction coefficient for the transmission tower-line coupling effect under the action of the downburst, it is considered more reasonable to take the value between 0.83-0.95. This study provides some references for further optimization of the transmission tower design.

High power-density electric machines present the benefits of high torque and speed. However, this generally comes with heating problems characterized by high temperatures that affect performance. Conventional approaches to address overheating are to include cooling fans or jackets within the stator core of the machine. This approach is challenging to implement in small-size high power-density machines. In this article, a cooling mechanism integrated in the rotor of a high power-density permanent magnet motor is proposed. It comprises a set of six holes, shrouded within a hollow shaft. The mechanism is based on conditioning air due to a centrifugal force that is produced by the rotational speed of the rotor from the inlet. A theoretical model based on flow resistance network is proposed to analyze the airflow rate. An analytical thermal model based on lumped parameter thermal network is developed to analyze the effect of the flow rate on the temperature distribution in the motor. Also, a simulation analysis model was conducted using computational fluid dynamics to analyze the effect of air flowing in the motor. An experimental prototype is developed to verify, validate, and evaluate the proposed cooling model. The cooling system is effective in reducing temperatures from speeds above 6000 min−1.

Quadcopters are widely used in military and civilian applications, but when flying near moving objects, they may encounter flight instability. This study investigates the flow aerodynamic interference of two drones' propellers when they hover near moving obstacles using CFD simulations. An unstructured mesh is used with frame motion to model the propeller's rotation. Different altitudes, rotational speeds, and obstacle velocities are tested to understand their aerodynamic effects on the propeller's performance. The results indicate that hovering 0.1 m above a fixed obstacle at 9550 rpm increased lift by 9.28%. This decreased by half when propellers were positioned adjacent to each other. Besides, a moving wall below the propellers at various velocities significantly affects the thrust and power variation of the propellers at low hovering speeds. For example, when hovering at 3000 rpm over a moving wall at 10 m/s, the thrust on one side of the UAV decreases by 8.51%, leading to flight instability. Different thrust control strategies and flight scenarios are performed to ensure flight stability and energy management. Finally, thrust control strategies prove crucial in stabilizing thrust and altitude, but power consumption increases by 12.8%, requiring 30% more energy required under specific flight scenarios near moving obstacles.

This paper proposes a computationally-efficient electromagnetic (EM)-computational fluid dynamics (CFD) coupling approach for a water-cooled Interior Permanent Magnet (IPM) motor. The numerical simulation of multiple fluids and their interaction with solid parts can be challenging. The proposed approach relies on the heat transfer coefficient (HTC) decomposition of different fluids/coolants inside the machine to generate an HTC look-up table (LUT) as a function of the coolant inlet flow rate. The HTC-LUT is then utilized as a surrogate model for the stationary coolant to decouple the fluid-to-fluid interaction and, hence, expedite the iterative approach. This reduces the computational time by almost two-thirds as compared to the multiple fluid approach while preserving the fidelity of the model. Additionally, the proposed approach formulates the correlation between the rotor speed, coolant flow rate, convective heat transfer coefficients, and the temperature rise, particularly for hot-spot locations in the end-windings. This approach uses a two-dimensional EM model coupled with a three-dimensional fractional CFD model. Thus, it reduces the computational cost and retains the model simplicity. The viability of the proposed coupling approach is also validated through lumped parameter thermal network (LPTN) analytical approach. The results from both approaches under different cooling conditions, flow rates, and current densities are in a good agreement.

This article proposes a computationally efficient thermal study method that substitutes computational fluid dynamics (CFDs) with a finite-element analysis (FEA) involving minimal loss of accuracy and omission of the increased computational load. The suggested technique contributes toward the realization of multiphysics optimization of high-speed electrical machines that effectively includes critical thermal evacuation phenomena. The strategy is regression-based and succeeds in constructing convection coefficient regression models that typically involve many variables and small training datasets. The proposed scheme is verified in high-loss density and high-speed outer rotor surface-mounted permanent magnet (SMPM) motor geometries that an optimization algorithm typically encounters during execution. The reference target specifications correspond to 20 kW output power, 15k r/min rotating speed, and 2 kHz electrical frequency. [ABSTRACT FROM AUTHOR]

Based on thermoelectric analogy method, a thermal network model coupled with electromagnetic loss is presented. According to the actual structure of dry-type transformer windings, an accurate thermal network is established. Considering the distribution characteristics of heat source along the cooling ducts inside the dry-type transformer, the thermal parameters such as heat flux and convective heat transfer coefficients are calculated by finite element method (FEM) analysis and computational fluid dynamics (CFD). Based on the temperature rise experiment, the hottest spot located at the top of the outmost high-voltage (HV) winding is 151.8 °C, which verified the correctness of thermal network model. [ABSTRACT FROM AUTHOR]

In this paper, a reduced computational fluid dynamics (CFD) model is proposed for determining the total heat dissipation and the oil temperature distribution of transformer radiators in oil natural air natural (ONAN) cooling mode. In the reduced radiator CFD model, the air flow simulation is replaced with an optimized air heat transfer coefficient (hair) equation. An experimentally verified full radiator CFD model, which includes the air flow simulation, has been introduced as a benchmark model for evaluating the validity of the reduced model. It was found that one ${{\boldsymbol{h}}_{{\boldsymbol{air}}}}$ can provide sufficient accuracy in simulating the air convection effect of transformer radiators. An ${{\boldsymbol{h}}_{{\boldsymbol{air}}}}$ equation was derived through a parametric study using the full radiator CFD model. The performance of the proposed ${{\boldsymbol{h}}_{{\boldsymbol{air}}}}$ equation was compared with the existing empirical equations, and its validities for different insulating liquids and different ambient temperatures were proven by additional CFD modelling. This ${{\boldsymbol{h}}_{{\boldsymbol{air}}}}$ equation can be transformed into a dimensionless form to help the radiator design and facilitate the complete-cooling-loop (CCL) based transformer CFD modelling. [ABSTRACT FROM AUTHOR]

In this work, the accuracy of row–column tensor velocity imaging (TVI), i.e., 3-D vector flow imaging (VFI) in 3-D space over time, is quantified on a complex, clinically relevant flow. The quantification is achieved by transferring the flow simulated using computational fluid dynamics (CFD) to a Field II simulation environment, and this allows for a direct comparison between the actual and estimated velocities. The carotid bifurcation flow simulations were performed with a peak inlet velocity of 80 cm/s, nonrigid vessel walls, and a flow cycle duration of 1.2 s. The flow was simulated from two observation angles, and it was acquired using a 3-MHz 62+62 row–column addressed array (RCA) at a pulse repetition frequency (${f}_{prf}$) of 10 and 20 kHz. The tensor velocities were obtained at a frame rate of 208.3 Hz, at ${f}_{prf} = {10} ~\mathrm{kHz}$ , and the results from two velocity estimators were compared. The two estimators were the directional transverse oscillation (TO) cross correlation estimator and the proposed autocorrelation estimator. Linear regression between the actual and estimated velocity components yielded, for the cross correlation estimator, an ${R}$ 2 value in the range of 0.89–0.91, 0.46–0.77, and 0.91–0.97 for the ${x}$ -, ${y}$ -, and ${z}$ -components, and 0.87–0.89, 0.40–0.83, and 0.91–0.96 when using the autocorrelation estimator. The results demonstrate that an RCA can, with just 62 receive channels, measure complex 3-D flow fields at a high volume rate. [ABSTRACT FROM AUTHOR]

Forced ventilated underground installations are challenging to design due to the complex mathematics of turbulent fluid flow. Previous methods have tackled this problem, but only recently, the effect of confinement on a single cable has been considered. In this paper, the effect of cable confinement on the practical case of ventilated trefoil installations is investigated. The complete Computational Fluid Dynamics (CFD) problem is solved using Finite Element Method (FEM) simulations and then validated by laboratory experiments using pipes. FEM simulations are then used to vary the current, the wind velocity, and the distance of the trefoil from the tunnel wall to get a comprehensive picture of the phenomena. This data is used to create a new empirical equation for the Nusselt number for a wide range of operating conditions. The principle of similitude is validated for a scaled-down model of a large tunnel and then used to analyze the thermal rating of tunnels. The new equation improves the IEC standard equations by accounting for the effect of cable confinement on trefoil installations. An important finding of this paper is that a lower maximum permissible current rating is obtained, which if ignored can present a serious risk for thermal damage. It was also found that the cables must be installed three cable diameters away from the wall to prevent the derating effect of confinement. [ABSTRACT FROM AUTHOR]

The devices for artificial flashover experiment should be constructed and the stability of the airflow field is the key to construct it. This work presents a methodology of constructing three models respectively without blades, with straight blades and with curved blades, coupled for artificial simulated fog-haze environment with computational fluid dynamics (CFD), to predict the impact of the rotating blades on the flow velocities in the enclosed environment by simulation. Atmospheric flow characteristics and variation of flow velocities were analyzed, and the influences of different rotating blades on flow velocities were compared to get the related simulation results in three models. It is showed that the flow velocities increase with the increase of device's Y coordinate. Compared with the variation of flow velocities in the model without blades, it is confirmed that the variation of flow velocities in two models with blades is reduced relatively, in which the variation of flow velocities in the model with straight blades is lower and more stable. Therefore, the designed model with straight blades will be developed for artificial flashover experiment.

Despite the importance of the desalination process in removal of water salinity to produce fresh drinking water, it is an energy-consuming process. Therefore, the use of solar energy as an alternative and free energy source has an important role in enhancing the efficiency of the desalination process. This paper presents an experimental investigation using solar chimney to enhance the desalination process, where a modification to the conventional solar stills has been made. A mathematical model describing air flow inside the solar chimney has been constructed using Computational Fluid Dynamics (CFD). The commercial CFD package fluent release 6.3 has been used in this paper to express the air flow and temperature distribution inside solar chimney. Furthermore, the process parameters such as seasonal temperature, salt concentration, water depth and type of solar desalination unit have been examined to find the best operating conditions. The desalination process has been recommended to be carried out under permissible operating conditions in sunny days, with water depths ranging from (1-2 cm) and low salt concentration ranging from (3.5-8%). The modeled data has been verified with experimental data and the verification results have been estimated at 14%. Simulation results showed that water desalination has been improved by 30%.

Background: Various computational models of the circle of Willis (CoW) have been developed to non-invasively estimate the blood flow and hemodynamic parameters in intracranial arteries for the assessment of clinical risks such as aneurysms, ischemia, and atherosclerotic plaque growth. This review aims to categorize the latest computational models of CoW and summarize the innovative techniques. Summary of Review: In traditional computational models of CoW, the computational complexity increased from zero-dimensional models to one-dimensional and three-dimensional models. The applications extend from estimating certain hemodynamic parameters to simulating local flow field. The innovative techniques include the combination of models with different dimensions, the extension of vascular structure including heart and veins, as well as the addition of distal fractality, cerebral autoregulation, and intracranial pressure. There are some nontraditional models based on fluid-solid-interaction, control theory, and in-vitro experiments. In all kinds of models, the in-vivo data and non-Newtonian rheological models of blood have been widely applied to improve the accuracy of hemodynamic simulation. Conclusion: Firstly, the selection of model depends on its application scenario. The balance between computational complexity and physiological accuracy deserves further investigation. Secondly, the improvement of CoW models relies on the large-scale validations and the combination of various innovative modeling techniques.

To address the growing energy use of data centers, waste heat recuperation offers a solution to better integrate these facilities into the broader energy system, thus facilitating a transition to the decarbonization of the energy system. The use of liquid coolants for full immersion cooling or local heat extraction from high power density components is considered for this purpose. However, heat can also be extracted by novel air cooling approaches, perhaps in combination with localized liquid cooling. To optimize heat extraction from air-cooled systems and maximize the heat grade, synthetic jets (SJs) can be used for targeted adaptive cooling in conjunction with air ducting to facilitate maximum heat recuperation potential in rack or server-mounted air-to-liquid heat exchangers. Internal server layouts can be optimized numerically, e.g., using a multiple objective genetic algorithm approach based on minimization of entropy generation rates. However, since SJs are inherently transient flow phenomena, this would require transient flow simulations, which forms a bottleneck in a numerical optimization loop. This research aims to develop a simplified steady-state representation of a synthetic jet actuator (SJA) with slot orifice using a localized body force to generate a similar time-averaged flow field to a real SJA, suitable for steady Reynolds-averaged Navier–Stokes simulations within a numerical optimization loop. Both flow fields are compared in terms of the mean flow field, jet spreading rate, and turbulence intensity distributions. [ABSTRACT FROM AUTHOR]

Under a given set of boundary conditions (BCs), the thermal performance of an electronic system is generally evaluated based on its steady-state response to constant power loads and thermal BCs that are time-averaged values of the actual transient or cyclic loads and BCs. Such analysis may produce accurate results if the time dependence of the power cycles and thermal BCs is small. Ideally, transient thermal analyses with actual time-dependent BCs and power cycles should be performed to determine the steady-state behavior. While being less overwhelming compared to laboratory experiments, fully time-dependent computational fluid dynamics (CFD) analysis still requires a large amount of CPU time. In order to overcome this large computational cost, several approximate models, such as resistor–capacitor (R – C) thermal network approaches, have been developed. Although reasonably accurate, these models require rigorous curve-fitting effort followed by an optimization process, which only makes them practical for relatively simple systems. The present study builds a state-space model applicable to heat transfer problems and makes comparisons with the R – C networks. The state-space model is later applied to determine the transient thermal behavior of a complex system, namely, a multidie SOIC chip over a printed circuit board (PCB), with a significant reduction in CPU time and no compromise on the accuracy. Finally, as a demonstration of systemic thermal design, an optimization exercise is performed on the above state-space model, in which the power cycles on individual die elements are controlled to limit the maximum temperature on the package die. [ABSTRACT FROM AUTHOR]

The aim of this article is to determine the contamination influence on the parameters of gas flow through multihole orifice (MHO) meter. The numerical investigations of the contamination influence for the MHO flow meters have not been reported in the previous researches. The air flow was steady, 3-D, and turbulent. The finite volume method was used for the purpose of numerical analyses. The main considered physical properties of air were density and dynamic viscosity. The standard $k-\varepsilon $ turbulence model was used. MHO meter with two different $\beta $ parameters was observed. Also, the influence of contamination formed in front of the MHO meter with the same $\beta $ parameters was analyzed. In order to qualitatively analyze the influence of the contamination, the 15 different combinations of contamination parameters for seven different Reynolds numbers were analyzed. The pressure drop, singular pressure loss coefficient, and discharge coefficient were analyzed. The grid sensitivity study was performed on four systematically refined numerical grids for MHO meter without contamination and the results were compared with the experimental results found in the literature. Also, the grid refinement was done for MHO meter with contamination for two different values of Reynolds number. It was found that for the same values of contamination angle, regardless of the contamination parameters ratio, the results were unchanged. Also, it was found that the contamination has an influence on the change of pressure drop values, which directly affects the change of other parameters. Pressure drop and singular pressure loss coefficient of the orifice with contamination are smaller compared to the values for a pure orifice, whereby the measurement accuracy was reduced. Also, for cases of contamination, the discharge coefficient was increased, leading to a negative measurement error. It was found that the same trend occurs regardless of the Reynolds number. It was found that the MHO meter was less sensitive to the pressure drop changes due to the increase of contamination angle in regard to the single-hole orifice meters. [ABSTRACT FROM AUTHOR]

This article presents an approach based on numerical reduced-order modeling to analyze the thermal behavior of electric traction motors. In this article, a single conjugate heat transfer analysis provides the possibility to accurately predict thermal performances by incorporating both computational fluid dynamic and heat transfer modules. Then, the developed model is used as the basis for deriving a fast reduced-order model of the traction motor enabling prediction of motor thermal behavior in duty cycles with a high number of operating points. All the results achieved are verified using flow and temperature measurements carried out on a traction motor designed and built for a traction application. A good agreement between the measured and estimated values of flows and temperatures is achieved while keeping the computation time within a reasonable range for both the full-order and reduced-order conjugate heat transfer models. The optimized full-order model can be run in minutes and the reduced-order model computation time is less than one second per operating point. The transient simulation based on the reduced-order model is conducted and both the learning phase and validation results are well illustrated. It is shown than the deviation of the reduced-order model in estimating the motor thermal performance is less than one celsius degree from the full-order model. [ABSTRACT FROM AUTHOR]

In order to determine the impact of various rotor structural elements on generation of windage losses, a computational fluid dynamics study on one salient pole generator has been performed. A fully predictive approach was employed in order to simulate airflow through the machine for five rotor configurations. The simulation results are compared with measurements and an agreement of −1.2% for losses and −2.4% for the flow rate is achieved. The analysis shows that between 84% and 90% of the overall windage losses can be attributed to centrifugal fans and poles. Regardless of the rotor configuration, the contribution of poles to the overall windage losses is always significant and ranges from 29% to 80%. A connection between the velocity field behind the fans and the losses generated by the poles is determined. An additional analysis was performed to study the causes of the vortex appearance at the fan impeller inlet. [ABSTRACT FROM AUTHOR]

This paper describes the application of computational fluid dynamics (CFD) in noise prevention of hyperbaric oxygen chambers. The flux vector splitting format and matrix transformation are used in the calculation of flow field in the hyperbaric oxygen chamber. At first, this paper simplifies the model of the hyperbaric oxygen chamber, and calculates the conservative state equation by flux vector splitting format. Being auxiliary to initial conditions, boundary conditions, meshing, time steps, and other computing elements, this paper gets the transient distribution of the parameters of each time step from flowing start to its near stop. Through displaying the data by graphic, we get the flow velocity variation, the location of the shock wave, the variational trend of pressure, and the variational trend of temperature. This paper compares the numerical and experimental results. Their similarity degree is high and this proves the feasibility to design Low-noise hyperbaric oxygen chamber by this numerical calculation method.

In continuous microfluidic processes, such as factory-on-chips, most valuable variables to be sensed for implementing an optimal control are usually not accessible. This is, for instance, the case of the shape and position tracking of the flow interfaces in a flow-focusing microdevice. In this context, virtual sensors are promising tools to improve the current control systems aiming at a zero-defect strategy. This article presents a methodology for building an accurate virtual sensor, based on computer-aided engineering simulations, both analytical and numerical, and model order reduction techniques. The methodology is applied to a given flow-focusing microchip. The outcome is a real-time model (virtual sensor) able to predict the shape and location of the multiphase fluid interfaces from the volumetric flow rate measured in the system. Results are successfully validated against the experimental data. The main challenge of this approach is to minimize uncertainties associated with the microfluidics setup. [ABSTRACT FROM AUTHOR]

We aimed to present an alternative method for calculating fractional flow reserve (FFR) from 3-D reconstruction of a coronary artery, based on coronary (X-ray) angiography and intravascular ultrasound (IVUS), to evaluate the ischemic-risk of stenosis and the relationship between FFR and geometrical features of the coronary lesion. The reconstruction of the 3-D catheter trajectory was obtained by the vertical intersection of spatial surfaces which were derived from the 2-D catheter curves in the angiography plane. Computational fluid dynamics was applied to calculate the hemodynamics in the coronary arteries and coronary flow-based FFR (fFFR) was obtained. Twenty-two stenotic coronary arteries were included in this paper for the evaluation of the proposed method. Good correlation between fFFR and the measured pressure wire-derived FFR was found (F = 0.916 and P

Optimization of liquid-cooled heatsinks (cold plates) is of critical importance due to their widespread application in high-performance electronic packages consisting of heterogeneous integrated systems, field programmable gate arrays (FPGAs), and on-chip hotspots. In this study, the thermo-hydraulic performance of a commercial microchannel impingement cold plate is analyzed in detail. Impingement cold plates are preferred over parallel flow cold plates due to their lower pressure drop where there is no restriction on space (i.e., where flow can enter perpendicular to the electronic board). Splitting the flow into two branches cuts the flow rate and the path into half, which leads to a lower pressure drop through the channels. Since the fins of the present commercial cold plate (considered as the baseline design) are tilted, the effect of the fin tilt angle on the hydraulic and thermal performance of the cold plate is also studied. The response surface method (RSM) is used to optimize the geometry of the fins and impinging inlet. The results of optimization show that hydraulic resistance can be reduced by 50% without a remarkable change in thermal resistance. The effect of the geometric parameters on the cold plate thermo-hydraulic performance is studied using the computational fluid dynamics results at the RSM design points. The variation in the cold plate coefficient of performance with the coolant flow rate and inlet temperature is compared for the baseline design and a selected optimal design. Finally, the effect of impinging inlet geometry on the chip temperature profile is also examined. [ABSTRACT FROM AUTHOR]

The thermal design process for electronic products often minimizes the use of computational fluid dynamics and heat transfer (CFD/HT) software in favor of quick prototyping and testing to determine the thermal characteristics of the product. For large-scale products with many thermal challenges, such a strategy can be impractical due to the high cost of prototyping cycles, time constraints, and inevitable iterations involved. In such cases, thorough CFD/HT models developed early in the design process are valuable for driving the product design. Based on this idea, the study examines thermal performance of 55” outdoor digital displays using CFD/HT tools and a prediction under hazardous outdoor condition is made for two different brightness outputs. The prediction is extrapolated and validated through the outdoor testing and simulation comparisons. It is shown that CFD/HT software can be used as a means of making conservative design choices. [ABSTRACT FROM AUTHOR]

The intended steady-state operation conditions of the International Fusion Materials Irradiation Facility—DEMO Oriented Neutron Source (IFMIF-DONES) target system are based on the D+ beam stationary running at full nominal power (5 MW). Nevertheless, critical situations can occur in the case of unavoidable sudden events like beam trips. The instantaneous variation in the heating power deposited in lithium when the beam is rapidly switched between ON- and OFF-states leads to thermal expansion, which is compensated by the compression of the target material, resulting in locally high pressures and a pressure wave propagating through the target toward the back wall. Besides the tensile stress of the back wall structure caused by shock pressure waves, undesirable cavitation may occur, when pressure waves are reflected leading to negative pressures. For this purpose, analytical and numerical thermohydraulic analyses of the effects generated in lithium during the beam-on/beam-off switches are performed. The pressure wave development inside the Li-target has been analyzed numerically with the computational fluid dynamics (CFD) code Star-CCM+. The simulation of the thermally induced pressure in the Li-target shows that for normal operation conditions, peak pressures of about 0, 3 MPa can be reached. In both “beam-on” and “beam-off” cases, a zone with a negative static pressure flow forms in the Li-target. The results obtained from the analytical and numerical analyses of the thermally induced pressure waves are discussed concerning potential cavitation and stability of the lithium free-surface flow. The simulation results served as input for the analysis of fatigue effects occurring in the target structure during sudden beam-on/beam-off events. [ABSTRACT FROM AUTHOR]

The convective heat transfer coefficient (CHTC) is a critical parameter that is required for developing an accurate and efficient thermal design of electrical machines. However, the existing empirical CHTC correlations are invalid for an oil-cooled hollow-shaft rotor. On this basis, a simplified numerical model based on computational fluid dynamics methods is developed in this paper to provide a qualitative understanding of the rotational effects on the convective heat transfer across a range of operation speeds. Then experiments are undertaken to validate the data obtained from numerical models and to estimate the impact parameters on the CHTC, such as the rotational velocity, coolant flow rate, and coolant temperature. On the basis of the numerical and the experimental results, it is concluded that the rotation can significantly increase the CHTC of the shaft inner wall surface above the level of the stationary condition. However, the axial flow rate and the viscosity of the coolant have less influence on convective heat transfer for the high rotational speeds. As a result of such analysis, a general correlation is defined by using Nusselt numbers as a function of rotational Reynolds numbers and Prandtl numbers. [ABSTRACT FROM AUTHOR]

This article presents the design, fabrication, experimental characterization, and modeling analysis of the chip-level hotspot targeted liquid impingement jet cooling for high-power electronics. The hotspot targeted jet impingement cooling concept is successfully demonstrated with a chip-level jet impingement cooler with a 1-mm nozzle pitch and 300- $\mu \text{m}$ nozzle diameter fabricated using high-resolution stereolithography (additive manufacturing). The computational fluid dynamics (CFD) modeling and experimental analysis show that the improved hotspot targeted cooler design with fully open outlets can reduce the on-chip temperature difference by 70% compared with the full array cooler at the same pumping power of 0.03 W. The local heat transfer coefficient can achieve 15 × 104 W/m2 K with a local flow rate per nozzle of 40 mL/min, requiring a pump power of 0.6 W. The benchmarking study proves that the hotspot targeted cooling is much more energy-efficient than uniform array cooling, with lower temperature difference and lower pump power. [ABSTRACT FROM AUTHOR]

This paper presents an accurate modeling method to investigate the thermal performance of the windings under steady state. The model considers the heat conduction of active windings and heat convection of end windings. To verify the validity of this model, a 20/24 poles/slots permanent magnet (PM) in-wheel motor is taken as an example. Firstly, the temperature distribution of the active windings in the slot is calculated by a multi-block 2-D temperature field model, which is verified by the model built according to the reality. The numerical results of blocks model agree well with those of the real model. Secondly, a 3-D temperature field model with the end windings is built on the 2-D blocks model. Furthermore, to include the air inside the motor, computational fluid dynamics (CFD) has been utilized, and the numerical results are experimentally verified. Finally, the distribution of the heat transfer coefficient (HTC) of the end windings and the influence of rotor speed on the HTC are investigated. These HTCs acquired from CFD results and empirical formulas are compared and analyzed carefully. [ABSTRACT FROM AUTHOR]

China Fusion Engineering Test Reactor (CFETR) will be a steady-state fusion power plant using a tritium blanket system. The current challenge is to develop a shielding blanket (SB) system which shields the components from nuclear heat impact. In this article, neutronics issues on the nuclear heat deposition induced by neutrons and photons are studied. It is found that the nuclear heat in the SB modules of breeding regions are 0.04–0.12 W/cc, and it is increased to 0.08–0.115 W/cc in the divertor region. This indicates that the SB concepts in different regions lead to the same effect on nuclear heat deposition. Moreover, it indicates that the nuclear heat trends on the two kinds of particles present a shrunken trumpet distribution in an SB interior and finally could be reduced to the minimum. In particular, the different nuclear heat levels are due to the different materials used in the components, while the steel zones absorb more photon heat than neutron heat and water zones absorb more energy from neutrons than steel. In addition, the thermal-hydraulics issues are discussed based on the computational fluid dynamics (CFD) technology. This article clarifies the nuclear heat distribution issues and also proposes an approach toward heat removal exploration, which would be beneficial to the SB design concepts in the blanket engineering phase later. [ABSTRACT FROM AUTHOR]

The chip-level bare die direct liquid impingement jet cooling is regarded as a highly efficient cooling solution for high-performance applications. Furthermore, it shows potential to be integrated inside the chip package. In previous studies, we demonstrated this cooling concept using a prototype fabricated with mechanical micromachining using polymers. With the improvement of fabrication resolution, additive manufacturing or 3-D printing technology enables the fabrication of low-cost polymer microjet coolers with complex internal 3-D geometries and allows easy customization of the cooler design. In this paper, a chip-level impingement jet cooler with a $4 \times 4$ jet array and 575- $\mu \text{m}$ nozzle diameter is fabricated with high-resolution stereolithography, and assembled directly on the top of the bare die. The modeling study shows that the pressure drop in the 3-D printed cooler is reduced by 24% compared to the micromachined (MM) cooler with the same nozzle dimensions thanks to an improved more complex internal geometry. The fabrication quality and tolerances of the printed cooler are evaluated using optical measurements, scanning acoustic microscope (SAM) inspection, and cross-sectional analysis, showing a measured average nozzle diameter of 575 $\mu \text{m}$ compared to the designed nozzle diameter of 600 $\mu \text{m}$. Moreover, the 3-D computational fluid dynamics (CFD) simulations used in this paper are experimentally validated by chip temperature measurements. The achieved minimal thermal resistance of 3-D printed $4 \times 4$ cooler is 0.16 cm $^{2}\cdot \text{K}$ /W for a flow rate of 1000 mL/min. The benchmarking study shows the cooler size can be reduced by a factor of 6.5 by using the 3-D printing technology compared to the MM cooler. [ABSTRACT FROM AUTHOR]

This paper proposes a novel power module concept specially designed for highly reliable silicon carbide (SiC) power devices for medium- and high-power applications. The concept consists of two clamped structures: 1) a press-pack power stage accommodating SiC power switch dies and 2) perpendicularly clamped press-pack heatsinks, in which the heatsinks are in contact with electrically insulated case plates of the power stage. The concept enables bondless package with symmetric double-sided cooling of the dies and allows for an order of magnitude higher clamping force on the heatsinks than what can be applied on the dies. The concept has been evaluated in a first demonstrator (half-bridge configuration with 10 paralleled SiC dies in each position). The experimental methodologies, setups, and procedures have been presented. The commutation loop inductance is approximately 9 nH at 78 kHz. The junction-to-case thermal resistance is approximately 0.028 K/W. Furthermore, a simplified 3-D finite-element thermomechanical model representing the center unit of the demonstrator has been established for the purpose of future optimization. The accuracy of the simulated temperatures is within 4% compared to the measurements. Finally, a 3-D thermomechanical stress distribution map has been obtained for the simplified model of the demonstrator. [ABSTRACT FROM AUTHOR]

This paper presents a practical approach to model and analyze transient thermal effects in air-cooled electric traction motors. The developed thermal modeling method enables accurate estimation of temperature in motor critical parts including winding and bearing. Advantages of both numerical and analytical modeling methods are exploited with the aim of realizing accurate estimation of hot spot temperatures in traction motors while keeping the computation time within a reasonable range. Computational fluid dynamics simulations are carried out to model air flow in the motor in order to provide heat transfer boundary inputs to the developed combined finite-element (FE) and lumped parameter (LP) thermal models. The combination of the FE and LP models keeps the size of the model relatively small and enables running transient calculations reasonably fast. Also, the developed model provides the possibility to study the influence of stator and rotor duct blockages on the motor thermal performance, which is a common root of failure in traction applications during operation in dirty environments. The proposed thermal model is verified using experimental results on a traction motor equipped with temperature sensors at different running conditions and a good agreement between the estimated and measured temperatures is achieved. [ABSTRACT FROM AUTHOR]

This paper addresses the heat transfer coefficient (HTC) associated with the hollow-shaft rotor cooling of a traction motor. In such a hollow-shaft cooling system, the coolant is made to flow through the shaft hole in order to cool the rotor. The HTC is estimated using computational fluid dynamics (CFD), where the effect of rotational velocity as well as the coolant flow rate has been accounted for. Experiments are then used to validate the accuracy of CFD models with the assistance of an analytical lumped-parameter thermal network approach. On the basis of CFD simulations and the experimental prototype testing, it is concluded that the rotational speed can significantly increase the convective heat transfer of the shaft hole about 3.8 times at 4500 r/min above the level of the stationary condition. As a result of such analysis, a new dimensionless correlation of the Nusselt number with the Reynolds number is derived. [ABSTRACT FROM AUTHOR]

In this paper, the response surface method (RSM) is exploited in the cooling system design optimization of oil-immersed transformers. To generate the training data for RSM, a 3-D computational fluid dynamic model for the transformer under study is constructed and solved, followed by verification on the solutions. Based on the simulation data, two types of RSMs, i.e., the second-order polynomial method and the Kriging method, are employed to evaluate their performance for this specific problem. The response surface with the best performance is used in the optimization process. The solution is compared with that found by the direct optimization method to showcase the effectiveness of applying RSM to oil-immersed transformer cooling system design. Details of implementation of the studied transformer are also presented. [ABSTRACT FROM AUTHOR]

CABRI is an experimental pulse reactor, funded by the French Nuclear Safety and Radioprotection Institute and operated by CEA at the Cadarache research center. It is designed to study fuel behavior under reactivity-initiated accident conditions. In order to produce the power transients, reactivity is injected by depressurization of a neutron absorber (3He) situated in transient rods inside the reactor core. The shapes of power transients depend on the total amount of reactivity injected and on the injection speed. The injected reactivity can be calculated by conversion of the 3He gas density into units of reactivity. So, it is of upmost importance to properly model gas density evolution in transient rods during a power transient. The 3He depressurization was studied by computational fluid dynamics (CFD) calculations validated by measurements using pressure transducers. The CFD calculations show that the density evolution is slower than the pressure drop. Studies also show that it is harder to predict the depressurization during the power transients because of neutron/3He capture reactions that induce a gas heating. Surrogate models were built based on CFD calculations and validated against preliminary tests in the CABRI transient system. Two methods were identified to evaluate the gas density evolution: CFD calculations and reverse point kinetics (PKs). The first one consists in adding a heat source in transient rods based on the experimental power conversion. The second one consists in using the measured power by boron ionization chambers to evaluate the net reactivity by a reverse PKs method and to subtract the reactivity feedbacks calculated with the DULCINEE multiphysics code. [ABSTRACT FROM AUTHOR]

During hypersonic flights of a space vehicle, shock heating ionizes the molecules of the surrounding air, which will create a plasma sheath that covers all or part of the vehicle. The plasma sheath absorbs and reflects electromagnetic (EM) waves, resulting in communication blackout of the installed electronic devices or systems. Moreover, when a high-power microwave (HPM) illuminates the moving vehicle, the constituent parameters of the plasma sheath will be altered since the plasma covering absorbs part of the energy of the HPM. In consequence, the transmission and scattering properties of the high-speed vehicle to the EM communication signals are changed. In order to investigate the complicated interactions among the plasma sheath, the HPM, and the low-power communication EM signals, a multiphysics model based on the computational fluid dynamics and the computational EMs is proposed, and the corresponding numerical solution is provided as well. Since the primary aim of the paper is to reveal the multiphysics method and relevant phenomenon, both the theoretical derivations and numerical examples are only presented in the 2-D space. [ABSTRACT FROM AUTHOR]

Plasma gasification of municipal solid waste (MSW) is one of the thermochemical technologies that convert waste into energy. The waste is exposed to high temperatures to transform the organic compounds into synthetic gas that could be used as power source, fuel substitute or reactive in the biofuel production. The inorganic compounds are melted completely and an inert environmentally friendly vitrified is obtained, that could be used as building material. Plasma gasifiers have some advantages against traditional gasifiers, for example, high temperature and heating rates lead to compact reactors, improving their performance and conversion rates. Moreover, all the inorganic residues are processed in a melting chamber, leaving a fully vitrified, strong, and resistant to chemical leaching material. On the other hand, this kind of technology has some disadvantages like high initial investment and high electric consumption of plasma torches. All these aspects, as well as others, are being studied at the Instituto Tecnológico de Costa Rica, through the development of computational fluid dynamics (CFD) models, defining a prototype reactor with a capacity of 1–2 metric tons of MSW per day and using DC nontransferred arc thermal plasma torch. Variations on composition within the MSW and process conditions will be studied in order to achieve high efficiency and economic feasibility. The CFD models include mechanical, thermal and chemical aspects of the turbulent reactive flows inside the gasification reactor, with 0-D, 2-D, as well 3-D considerations. The experimental phase of the project will be developed soon, taking into account the CFD models results, to implement the technology and eventually improve it. [ABSTRACT FROM AUTHOR]

In 2016, we have designed, built, and finally tested at the FE200 facility in Le Creusot, France, a planar mock-up mimicking the water-cooled cylindrical resonance cavity of the European 170-GHz, 1-MW gyrotron to be used for electron cyclotron plasma heating in ITER. The aim of the mock-up is the characterization of the cooling capability of the cavity. A Glidcop target is heated with an electron beam gun with resulting peak heat fluxes relevant for the full-size cavity. Underneath the target surface, whose temperature is monitored by means of a pyrometer, a set of parallel semicircular mini channels, with a diameter of 1.5 mm, allow the flow of pressurized water, entering the mock-up at ~9 bar and 40 °C. Several thermocouples measure the target temperature, at different distances from the heated target surface. The experimental results show that the mock-up is capable to withstand heat fluxes of 21 MW/m2, while the cooling system keeps the heated surface below ~400 °C, for flow conditions comparable to those of the full-size cavity. The test results are used to first calibrate the uncertain model parameters and then, with frozen parameters, to validate a previously developed computational fluid dynamics model, showing good agreement with the experiment. In view of its reliability, this model might eventually be a useful tool for the simulation of the full-size gyrotron cavity operation. [ABSTRACT FROM AUTHOR]

The design of the water-cooled ceramic breeder (WCCB) blanket includes beryllium multiplier layers. At elevated temperature, beryllium reacts with steam in an exothermic reaction producing beryllium oxide and hydrogen. Such situation may occur in WCCB in the case of the rupture of one of the cooling pipes in the blanket module. This process occurs locally in a complex 3-D geometry of the blanket containing several different granular levels and a network of cooling pipes and structural supports. The process is also inherently unsteady since reaction rate depends on concentration of steam and pure beryllium which changes in time. In order to perform the detailed analysis of the process, the model of the reacting flowthrough porous media was developed and introduced into 3-D computational fluid dynamics code. In this model, granular beds are introduced as porous solids simplifying the model geometry and reducing typical mesh size to manageable amount of tens of millions of elements. A reaction rate between solid beryllium and steam is obtained from experimental results, and depends on temperature and concentration of the reactants. The differential equation for beryllium oxide fraction is introduced, allowing obtaining distributions of beryllium oxide in space and time. Multicomponent flow consisting of a homogenous mixture of steam and hydrogen is considered flowing through the porous solid with variable properties. Sink and source terms for steam and hydrogen fractions are determined by local beryllium oxide mass fraction source according to the molar ratios of beryllium steam reaction. The conjugated heat transfer approach is applied to calculate heat transfer in support structures as well as coolant flow, simultaneously with the porous medium steam flow in a blanket’s granular beds. The model is validated using experimental data on beryllium steam reaction for granular bed samples. [ABSTRACT FROM AUTHOR]

Reducing the energy consumption of a data center has recently become more important because the data center market is rapidly expanding. We developed an “IT-facility linkage system” to deal with this energy saving requirement. This system reduces the amount of energy consumed in a data center by linking two systems. One is an optimized server load allocation system, and the other is an air conditioning optimization control system. One of the key technologies of the “IT-facility linkage system” is the precise prediction of the server inlet temperature. If we can comprehend future temperature distributions, we can reduce the amount of energy consumed in a data center by consolidating the IT load to more effectively cooled servers. Then, we carried out computational thermal fluid dynamics to predict the server inlet temperatures and evaluated the prediction precision by comparing the measured temperature data. As a result, we found that when we use a detailed rack model and reproduce the characteristic airflow of a data center such as the recirculation, we can predict the server inlet temperature to within less than 1.5°. Next, we carried out an experiment to verify the optimal server consolidation and confirmed that the effect of optimal consolidation can be predicted by simulation. [ABSTRACT FROM PUBLISHER]

Effective cooling of electronic equipment has emerged as a challenging and constraining problem of the 21st century. Jet impingement is a high-performance cooling technology for enhancing the heat transfer in thermal devices. This paper reports the experimental and numerical investigations carried out to study the heat transfer characteristics of multiple air jets impinging on a stationary flat copper plate. The software used for the numerical studies is a finite-volume-based software, ANSYS Fluent. An experimental setup was designed and fabricated. The results obtained from numerical studies were validated with that obtained from experimental studies. A copper plate, which is heated from the bottom, was used as the heat transfer surface of a simulated chip. The jets were produced by three sharp-edged circular orifices arranged in an in-line configuration. The nozzle-to-plate distance was varied as 1, 2, 4, 6, and 7 times the nozzle diameter ( $d$ ). The effects of Reynolds number (4000–8000) and jet-to-jet spacing on heat transfer characteristics were examined numerically. From the studies, it was found that for a Reynolds number of 5000, optimum cooling is obtained when nozzle-to-plate spacing ( $H$ ) is 6 times the orifice diameter. A correlation was proposed for Nusselt number in terms of Reynolds number, and it is valid for air as the cooling medium. [ABSTRACT FROM AUTHOR]

In this paper, we explore a novel modeling technique to investigate a parafoil flying in wind environments by using computational fluid dynamics. Further, we apply an eight-degree-of-freedom dynamic model of the parafoil in wind environment based on utilizing revised aerodynamic equations. Given that the traditional control methods cannot always tackle trajectory tracking effects properly, we propose an accurate trajectory tracking control method based on active disturbance rejection controller. Semiphysical simulation and airdrop experiments are conducted to evaluate the model as well as the control method. Results demonstrate that the proposed model is effective. Also, active disturbance rejection control outperforms the proportional-integral-derivative (PID) controller regarding the antidisturbance ability and control accuracy. [ABSTRACT FROM PUBLISHER]

Design optimization of an unmanned underwater vehicle (UUV) is a complex and a computationally expensive exercise that requires the identification of optimal vehicle dimensions offering the best tradeoffs between the objectives, while satisfying the set of design constraints. Although hull form optimization of marine vessels has long been an active area of research, limited attempts in the past have focused on the design optimization of UUVs and there are even fewer reports on the use of high-fidelity analysis methods within the course of optimization. While it is understood that the high-fidelity analysis is more accurate, they also tend to be far more computationally expensive. Thus, it is important to identify when a high-fidelity analysis is required as opposed to a low-fidelity estimate. The work reported in this paper is an extension of the authors previous work of a design optimization framework, where the design problem was solved using a low-fidelity model based on empirical estimates of drag. In this paper, the framework is extended to deal with high-fidelity estimates derived through seamless integration of computer-aided design, meshing and computational fluid dynamics analysis tools i.e., computer aided 3-D interactive application, ICEM, and FLUENT. The effects of using low-fidelity and high-fidelity analyses are studied in depth using a small-scale (length nominally less than 400 mm) and light-weight (less than 450 g) toy submarine. Useful insights on possible means to identify appropriateness of fidelity models via correlation measures are proposed. The term optimality used in this paper refers to optimal hull form shapes that satisfy placement of a set of prescribed internal components. [ABSTRACT FROM AUTHOR]

The converter transformer epoxy impregnated paper bushing is a multi-media electrical equipment, and the main materials include the internal conductor, the external conductor, transformer oil, SF6 gas, the air inside internal conductor, the main insulation material epoxy impregnated paper, sheath, and fittings. In actual operating, the converter transformer bushing is undertaken by the harmonic current with large number of high harmonics and the temperature distribution of the epoxy impregnated paper converter transformer bushings under actual current waveform needs to be researched. What's more, the temperature distribution of the epoxy impregnated paper converter transformer bushings is affected by several factors and to provide basis for the optimization of bushings it's necessary to research about the impact of these factors on the temperature distribution of the epoxy impregnated paper converter transformer bushings. In this paper, on the basis of our previous paper [8], the 3-D temperature distribution of the 400 kV epoxy impregnated paper converter transformer bushing under actual current waveform with large number of harmonics has been simulated by using the computational fluid dynamics (CFD) and finite element method (FEM) analysis. The temperature distribution regularity of the 400 kV converter transformer bushing under different influencing factors has been computed and analyzed. The dissipation structure of the bushing has been optimized and the DC steady-state electric field distribution of the 400 kV converter transformer bushing has been obtained considering the temperature gradient in epoxy impregnated paper. [ABSTRACT FROM PUBLISHER]

The analysis of many fusion applications such as liquid-metal blankets requires application of computational fluid dynamics (CFD) methods for electrically conductive liquids in geometrically complex regions and in the presence of a strong magnetic field. A current state of the art general purpose CFD code allows modeling of the flow in complex geometric regions, with simultaneous conjugated heat transfer analysis in liquid and surrounding solid parts. Together with a magnetohydrodynamics (MHD) capability, the general purpose CFD code will be a valuable tool for the design and optimization of fusion devices. This paper describes an introduction of MHD capability into the general purpose CFD code CFX, part of the ANSYS Workbench. The code was adapted for MHD problems using a magnetic induction approach. CFX allows introduction of user-defined variables using transport or Poisson equations. For MHD adaptation of the code three additional transport equations were introduced for the components of the magnetic field, in addition to the Poisson equation for electric potential. The Lorentz force is included in the momentum transport equation as a source term. Fusion applications usually involve very strong magnetic fields, with values of the Hartmann number of up to tens of thousands. In this situation a system of MHD equations become very rigid with very large source terms and very strong variable gradients. To increase system robustness, special measures were introduced during the iterative convergence process, such as linearization using source coefficient for momentum equations. The MHD implementation in general purpose CFD code was tested against benchmarks, specifically selected for liquid-metal blanket applications. Results of numerical simulations using present implementation closely match analytical solutions for a Hartmann number of up to 1500 for a 2-D laminar flow in the duct of square cross section, with conducting and nonconducting walls. Results for a 3-D test case are also included. [ABSTRACT FROM AUTHOR]

A novel modeling method, based on computational fluid dynamics (CFD) to simulate a parafoil flying in rain and wind environments, is proposed. Then, the dynamic model of the powered parafoil in the complex environment is established on the basis of revised aerodynamic equations. By introducing path-following controllers based on active disturbance rejection control (ADRC), horizontal and longitude trajectory tracking of the powered parafoil in realistic environments are simulated. Results verify the effectiveness of the model and control methods. [ABSTRACT FROM AUTHOR]

This paper presents coupled fluid-thermal analyses to improve the ventilation and thermal performance of radial forced air-cooled fractional-slot concentrated-winding (FSCW) permanent magnet synchronous wind generators (PMSWGs) using the computational fluid dynamics (CFD) method. Three-dimensional coupled fluid-thermal CFD models are established based on the governing conservation equations of the solved solid machine parts and the air domain. The losses are applied into the CFD models as the heat sources and the boundary conditions are determined. Based on the proposed method, the fluid and temperature field of the machines with different air cooling channel numbers and channel widths are calculated, and the ventilation and thermal performance are compared to determine the optimal channel number. Further, an alternative cooling structure with radial winding holes through the slot center to dissipate heat from the winding directly is proposed. The results show that it is a promising alternate, especially for the FSCW PMSWGs to decrease the winding temperature and ventilation losses. The proposed CFD method is validated by experiments implemented on a standard product of integral-slot distributed-winding (ISDW) PMSWGs with the same ventilation system. [ABSTRACT FROM AUTHOR]

The thermal management of an axial flux permanent magnet (AFPM) machine is essential because it determines the machine's continuous power output and reliability. In this paper, a secondary cooling method is proposed using rotor cooling, which allows better thermal management on the permanent magnets that are attached to the rotor. This will reduce the potential of the machine failing due to magnet demagnetization and degradation. Thermal analysis via lumped parameter networks is usually sufficient in predicting the motor's thermal behavior. However, the accuracy of the prediction can be increased, especially for the devices with complex flow regions by computational fluid dynamics. In this study, the fan blade was attached to the rotor of a yokeless and segmented armature machine for flow validation and then three different fan blade designs from other engineering applications were tested. The evaluation includes the flow characteristic, power requirement, and thermal characteristic for the AFPM's rotor cooling applications. Additionally, the rotor cooling performance index is introduced to assess each fan design performance. [ABSTRACT FROM AUTHOR]

The Coandă effect is a natural phenomenon, which is that flowing fluid on a certain surface is pulled to the surface due to the viscosity of the fluid. This phenomenon can be utilized to produce the lift force of a flying object. This paper presents a new type of unmanned aerial vehicle (UAV) lifted by the Coandă effect, called SCoandă. We introduce the empirical study of its design and implementations. The principle of the Coandă effect is briefly explained in the first section. The design optimization and control of the UAV, and implementation issues are explained. The structural design of SCoandă is devised to use the maximum lift force produced by the Coandă effect. Since there are a plenty of cases about the shape of SCoandă, it has been limited to oval. It is investigated through computational fluid dynamics. As the result, an optimized design is determined among several candidates and appropriate structural materials are selected via tests. Also, dynamic modeling is suggested under several conditions of SCoandă before simulations are conducted to build up a controller and determine gains according to the dynamic modeling. Finally, the UAV is manufactured and its performances are successfully demonstrated in the indoor and the outdoor environments. [ABSTRACT FROM PUBLISHER]

Previous works investigated particle trajectories in hard disk drives (HDDs) with the actuator arm and the head gimbals assembly at a fixed position. Actually, internal fluid field characteristics of HDDs can be greatly changed by the arm swing during track-seeking operations, which can affect particle trajectories and trapping status. In this paper, using the dynamic mesh method in a 2.5 in HDD for the first time considers the arm swing in the computational fluid dynamics (CFD) simulation. Al2O3 particle trajectories in this HDD are studied by the CFD solver FLUENT with user-defined functions. The trapping criterion for Al2O3 particles is used as a boundary condition for colliding surfaces. Simulation results reveal that the particle undergoes a larger number of collisions with the disk surface for the average seek time of 12 ms than for the average seek time of 6 ms. In addition, the faster the arm swings, the larger the number of particles that gather near the arm, and the shorter time it will take for particles to be trapped. Moreover, particle-surface collisions can successively take place many times in the helium flow. Furthermore, the particles are trapped slower in the helium-filled drive than in the air-filled drive. [ABSTRACT FROM AUTHOR]

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]

This paper presents an improved thermal design methodology for wind power converters. It combines analysis and experimental thermal design tools, including heat transfer correlations, flow network modeling (FNM), computational fluid dynamics (CFD), and experimental measurement techniques. Moreover, a systemic product development process is introduced and an effective combination between the product development process and the thermal design methodology is achieved. The draft CFDmodeling at the initial design stage is done. Furthermore, it uses the detailed CFD modeling and experimental measurement techniques to provide a higher degree of accuracy at latter design stages. The key advantage of the improved methodology is its emphasis on the use of varied design tools, each of which is actively applied at its optimal point in the proposed product development process. Thus, during the earlier stages of the product development process, the thermal risk is systematically reduced, and longterm reliability of products is maintained in a higher degree.