Since high-temperature superconducting (HTS) cables have attracted significant attention for their low losses (30% of normal power cable), large capacity, and small size, they can be used for ...electric power transmission for efficient use of energy in power systems. However, they are often subjected to overcurrent impact caused by a short-circuit fault when they are used in a transmission system. In this overcurrent impact, a large amount of Joule heat is generated, which can damage the stability of HTS cables and influence the efficiency of power transmission. A dynamic experimental test of a 110 kV/3 kA prototype HTS cable under a fault current impact has been carried out by China Electric Power Research Institute. A magnetothermal stability experimental system with a pulsed current power source (25 kA for 0-1 s) and a high-precision National Instruments digital data acquisition system have been set up. The transient current and temperature of each superconducting layer in the HTS cable have been tested and investigated considering the overcurrent impact of 25 kA for 1 s. Numerical simulations were also performed on the prototype cable using a computer program on the basis of a finite-element method and an electrical circuit model. The results have shown that the currents of the conducting layers decrease while the temperature increases in the HTS cable, and the former can withstand most of the fault current. Therefore, the proposed experimental system is proved to be effective for testing HTS cables with overcurrent impact.
An algorithm that combines a common source amplifier with the physics-based metal-oxidesemiconductor field effect transistor (MOSFET) model is proposed. By solving the coupled drift-diffusion model ...equations with spectral element time-domain (SETD) method, the distribution of electron quasi-Fermi potential, hole quasi-Fermi potential and the potential inside the MOSFET is obtained. The corresponding current densities and electric intensities distributed in the device can be used to couple the heat conduction equation. Furthermore, the Kirchhoff laws should be satisfied when the MOSFET device is inserted in the circuit. The Newton-Raphson method is used to solve the nonlinear circuit equations due to the existence of semiconductor devices. The transient electro-thermal characteristics of a common source amplifier circuit have been analyzed, and the numerical results demonstrate the validity of the proposed method.
In this paper, the thermal characteristics and air flow behavior over heated square plate of wavy configurations are assessed. Two cases of heated wavy configurations were considered, one having an ...elliptical and other with the sinusoidal cross‐sectional shape to augment heat transfer rate over the plate. To explore the impact of wavy configurations of plate on convective heat transfer, the Rayleigh numbers in the range of 104 to 1013 were considered. The steady‐state two‐dimensional momentum and energy equations were solved using a validated numerical model. The numerical results in terms of Nusselt numbers, Rayleigh numbers, aspect ratio (AR), and flow/temperature distribution over the plate are presented. The variations in the heat transfer coefficient and temperature contours with Rayleigh number and AR of waves were concentrated for both the elliptical and sinusoidal configurations of the plate. The results obtained indicate that the enhancement in heat transfer rate from the heated plate depends on the Rayleigh number, the AR of waves, plate configuration, and the Prandtl number.
This study presents a new hybrid and electric vehicle (HEV/EV) traction motor sizing strategy, an overcurrent-tolerant prediction model is used to estimate the dynamic and thermal characteristics of ...a motor operating in the overcurrent region. This can be used to determine if a prospective traction motor and powertrain configuration is able to fulfil the HEV/EVs target dynamic objectives. Since the prediction model only requires minimal motor torque–speed characteristics, it can be a useful tool during the early development stages of an HEV/EV when the detailed motor parameters used in analytical models cannot be obtained. Allowing the motor to operate in the overcurrent region could downsize the traction motor used in the final HEV/EV design to one that is smaller, easier to package and likely to run in a higher efficiency region. A case study is explored where this sizing strategy is used to convert an aeroplane pushback vehicle into a series HEV and tasked with following a rigorous duty cycle. The feasibility of two HEV configurations is then analysed further. The final HEV design reduces the fuel consumption and engine emissions by up to 52% from the original internal combustion engine powered vehicle.
Traditional Vojvodina house represents an important part of the building stock of the northern Serbian province of Vojvodina. The research examines the thermal transmittance of the walls of rammed ...earth, which is the basic structural and fa?ade element of traditional Vojvodina house, in two ways: by calculations in accordance with Serbian regulations and by measuring in situ. Parameters obtained from the measurements are compared with the calculated values for the three typical traditional Vojvodina rammed earth single family residential houses. The comparison between the values of the heat transfer coefficient, obtained by the calculation, and the results determined by in situ measurements show significant differences. It indicates that the thermal characteristics are better than calculated ones according to national regulations, but at the same time that, due to the complexity of the rammed earth walls and differences in the rammed earth structures, the results differ from case to case and can not be standardized.
nema
By means of the proposed thermal model and corresponding software, the thermal characteristics of high-precision spindles may be quickly assessed in the initial stages of design.
Nanofibers of polypropylene were produced by a modified melt-blowing method. The manufacturing method and thermal characteristics of fabricated nonwoven-fabric nanofibers were studied. Apparent ...thermal conductivity was measured as an evaluation of adiabatic properties, and a prediction model was developed with computational fluid dynamics (CFD) based on a one-dimensional computer-aided engineering method. In addition, we attempted to evaluate true thermal conductivity in consideration of lateral heat dissipation during measurement by thickness. Consequently, we determined the influence of the fiber diameter and thickness of the nonwoven fabric on the thermal conductivity and demonstrated that the proposed CFD model was effective for estimating the characteristics of the thermal conductivity of the nonwoven fabric.
Composite nanofibers of polyethylene oxide (PEO)/bacterial cellulose whisker nanoparticles (BCW NPs) and PEO/functionalized bacterial cellulose whisker nanoparticles (
f
-BCW NPs) were fabricated by ...an electrospinning process. BCW NPs were prepared using a blender in order to increase the filler density in composite nanofibers. Nitrogen functionalization of the
f
-BCW NPs was performed by plasma treatment using a microwave oven. The chemical bonding between the nitrogen functional groups of
f
-BCW NPs and the hydroxyl groups of the polymer chains in the PEO matrix was enhanced by the nitrogen functionalization. The average diameter of the PEO/f-BCW NP composite nanofibers was slightly larger than that of PEO nanofibers and PEO/BCW NP composite nanofibers at the same concentration. The melting temperature (
T
m
), crystallization temperature (
T
c
), and weight loss of PEO/
f
-BCW NP composite nanofibers decreased compared to those of the PEO nanofibers and PEO/BCW NP composite nanofibers. This was a result of the
f
-BCW NPs hindering the crystallization of the PEO nanofiber structures. The strong interfacial interactions between the
f
-BCW NP nanofillers and the polymer matrix increased the glass transition temperature (
T
g
) compared to PEO nanofibers and PEO/BCW NP composite nanofibers. These results demonstrated that N
2
plasma treatment of BCW NPs embedded in PEO nanofiber was a useful tool for improving their thermal characteristics for biological applications.
Taking the simplified airborne integrated thermal management system as the research object, the change characteristics of the system under different control modes are analyzed, which provides a ...theoretical basis for the study of system control schemes. Using a combination of mathematical models and computer models to establish an integrated airborne thermal management system model with fuel as the main heat sink, air/fuel heat exchanger, fuel/PAO heat exchanger and other main components, and A fuzzy self-tuning PID control method is proposed to analyze system characteristics such as fuel/PAO heat exchanger and electronic equipment thermal changes. The results show that compared to open-loop control under thermal extreme conditions, the fuzzy self-tuning PID control mode can not only effectively control a series of equipment such as fuel pumps to maintain proper speed, but also ensure the electronic cabin and fuel/PAO heat exchanger the outlet temperature is kept within a predetermined range to meet the design requirements of the onboard thermal management system.
This paper presents a study of the hot plate method with two simultaneous temperature measurements, on the heated and unheated faces of a sample to characterize. The thermal properties of polyvinyl ...chloride, plaster and laterite were considered to be a representative range of building materials. A 1D quadrupolar model was developed to represent the temperature evolution on the two faces over time. Three-dimensional numerical modeling of a quarter of the testing device with COMSOL software allowed defining the domain of the 1D hypothesis validity. The analysis of estimation possibilities of materials’ thermal characteristics, with the developed method, revealed that thermal effusivity can be accurately estimated by using the temperature of the heated face at the beginning of heating. We showed that the simultaneous use of two temperatures enables the estimation of the thermal conductivity with a greater accuracy and over a shorter time interval than using the temperature of the heated face alone. We also demonstrated that under certain conditions (samples with a high ratio of thickness to width) the method with two temperature measurements enabled the estimation of the thermal effusivity and conductivity, while the method with one temperature allowed only the thermal effusivity to be estimated, because of 3D effects. This conclusion was confirmed by experimental results obtained with a mortar sample.
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