十二相整流器二极管功耗和结壳温升仿真计算

为了在十二相整流器设计中,实现仿真计算二极管功耗和结壳温升,保证其在高温的环境中可靠地工作,对非常规小型散热器,选用大容量二极管在中小电流条件下工作,以降低功耗和热阻,充分保证整流器有较高的过载能力,实现高可靠性的设计,提出了特殊要求的整流器体积可以做得更小,为解决目前十二相整流器设计中功耗和结壳温升问题提出了新的思路。

电力半导体器件热阻及测量

介绍了电力半导体器件热阻的测试方法。

Strengthening pelletization of manganese ore fines containing high combined water by high pressure roll grinding and optimized temperature elevation system

Pelletization is one of useful processes for the agglomeration of iron ore or concentrates. However, manganese ore fines are mainly agglomerated by sintering due to its high combined water which adversely affects the roasting performance of pellets. In this work, high pressure roll grinding(HPRG) process and optimization of temperature elevation system were investigated to improve the strength of fired manganese ore pellets. It is shown that the manganese ore possesses good ballability after being pretreated by HPRG twice, and good green balls were produced under the conditions of blending 2.0% bentonite in the feed, balling for 7 min at 16.00% moisture. High quality roasted pellets with the compressive strength of 2711 N per pellet were manufactured through preheating at 1050 °C for 10 min and firing at 1335 °C for 15 min by controlling the cracks formation. The fired manganese pellets keep the strength by the solid interconnection of recrystallized pyrolusite grains and the binding of manganite liquid phase which filled the pores and clearance among minerals. The product pellets contain high Mn grade and low impurities, and can be used to smelt ferromanganese, which provides a possible way to use imported manganese ore fines containing high combined water to produce high value ferromanganese.

Contemporary and Historic Population Structure of Abies spectabilis at Treeline in Barun Valley,Eastern Nepal Himalaya

Treeline ecotone dynamics of Abies spectabilis （D. Don） Mirb. in the Barun valley, Makalu Barun National Park, eastern Nepal Himalaya were studied by establishing seven plots （20 m x variable length） from the foresfline to the tree species limit： three plots on the south- and north-facing slopes each （S1-S3, N1-N3）, and one plot on the east- facing slope （E） in the relatively undisturbed forests. A dendroecological method was used to study treeline advance rate and recruitment pattern. In all the plots, most trees established in the early 20th century, and establishment in the second half of the 20th century was confined to the foresfline area. Treeline position has not advanced substantially in the Barun valley, with 0nly 22 m average elevational shift in the last 13o years, and with average current shifting rate of 14 cm/yr. Moreover, no significant relationship was found between tree age and elevation on the south-, north-, and east-facing slopes. The number of seedlings and saplings in near the treeline area was negligible compared to that near the foresfline area. Therefore, A. spectabilis treeline response to the temperature change was slow, despite the increasing temperature trend in the region. Beside the temperature change, factors such as high inter-annual variability in temperature, dense shrub cover, and local topography also play an important role in treeline advance and controlling recruitment pattern above the treeline.

Thermal decomposition and mechanical properties of hydroxyapatite ceramic

Pure hydroxyapatite（HAP）ceramic and HAP composite ceramic with B2O3 were prepared by isostatic press forming and pressureless sintering.The relationships between thermal decomposition ratio and mechanical properties for pure HAP ceramic and the composite ceramic were investigated by means of FTIR,X-ray diffraction and three-point bending method.The results indicate that the decomposition ratio of pure HAP ceramic increases with ascending the sintering temperature and nearly reaches 80%at 1 350？殆or the HAP composite ceramic,the thermal decomposition is inhibited obviously due to the addition of B2O3.The added B atoms incorporate into the crystal lattice of HAP to form solid solution,resulting in an enlargement in the crystal spacing and an improvement in the binding strength of HAP crystal cell.Thermal decomposition ratio of HAP decreases but bending strength and fracture toughness are enhanced for HAP composite ceramics.However,when the added B2O3 is more than 5%（mass fraction）,HAP decomposition is promoted and a steady？-TCP is formed due to the fact that when B atoms with higher negative electricity are combined with O,sp2 and a full-air p are formed,and those voids have a strong trend to intake of the outer electrons.So,it is very possible to occupy the place where HAP loses OH - or PO4 3- .

IGBT逆变器——功率模块要求一种全面的热设计——

用恒定正向电流加热器件 ,可以判断电力器件开关损耗和导通损耗引起的结芯温升 ,这是简单的静态近似 ,它不能体现实际使用中器件的热状态。文章主要介绍一种动态近似法 ,它采用了实际的整流—逆变—异步电机系统的动态模式 ,通过热仿真导出计算 IGBT和二极管结芯温升的公式 ,最后给出了计算实例。

Effects of retrogression heating rate on microstructures and mechanical properties of aluminum alloy 7050

The effects of the retrogression heating rate(340℃/min,57℃/min,4.3℃/min)on the microstructures and mechanical properties of aluminum alloy 7050 were investigated by means of hardness measurement,tensile properties testing,differential scanning calorimetry(DSC)and transmission electron microscopy(TEM).The results show that the retrogression heating rate significantly affects the microstructures and mechanical properties of the alloys treated by retrogression and re-aging(RRA)process, and it is found that the medium rate(57℃/min)leads to the highest mechanical properties.The strengthening phases in the matrix are mainly the fine dispersed η′precipitates and GP zones,and the grain boundary precipitates are coarse and discontinuous η phases.

Pore structure formation and hydration characteristics of cement paste with temperature rising inhibitor

The early-age thermal cracking easily generates and severely impairs the durability of concrete.The temperature rising inhibitor(TRI)was utilized to regulate the temperature evolution by controlling the cement hydration process.This paper aimed to investigate the pore structure formation and hydration characteristics of cement paste containing TRI by low-field nuclear magnetic resonance.The experiment showed that the T_(2) peak of cement paste shifted from 7.32 ms to 0.23 ms regardless of TRI addition.But the pattern of pore structure formation was changed with TRI addition,that is,the pore structure formation was delayed,and the pore successively shifted to left in two parts.In addition,TRI addition significantly prolonged the duration of gel pore formation and greatly decreased the increase rate of gel water,which implied that TRI introduction hindered the growth of C-S-H,and subsequently decreased the hydration rates and delayed the main hydration peak.Meanwhile,TRI dissolved and diffused rapidly at 40℃,delaying the hydration of cement paste seriously.Moreover,TRI brought about the C-S-H nucleation homogeneous and the ion concentration uniform,which might reduce the localized curvature occurring on the sheet of C-S-H,and then decreased the T_(2) intensity of capillary water and gel water.

Low-temperature Properties of Biodiesel:Rheological Behavior and Crystallization Morphology

A soybean oil derived biodiesel was prepared and blended with a conventional No. 0 petrodiesel. The pour points （PP） and the cold filter plugging points （CFPP） of biodiesel blends were evaluated on a low-temperature flow tester. Dynamic viscosities of the blends at different temperatures and different shear rates were measured on a rotary rheometer. The crystal morphologies of biodiesel blends at low temperatures were analyzed using a polarizing microscope. The results indicated that blended fuels demonstrated slight decrease in PPs and CFPPs as compared with those of neat soybean oil derived biodiesel and pure petrodiesel. Below the temperatures of PPs or CFPPs, the dynamic viscosity of biodiesel blends dramatically increased with a decreasing temperature, but decreased with an increasing shear rate, so that biodiesel blends exhibited non-Newtonian behavior. At temperatures higher than PPs or CFPPs, a linear relationship appeared between the dynamic viscosity and shear rate and biodiesel blends became Newtonian fluids. At low temperatures, wax crystals of biodiesel blends grew and agglomerated rapidly. Loss of fluidity for biodiesel blends at low temperatures could therefore be attributed on one hand to the sharp increase of viscosity and on the other hand to the rapid growth and agglomeration of wax crystals.

Analysis of a Concrete Structure that Was Exposed to Fires in the Metropolitan Region of Recife

In large cities, news about fires in buildings are powered by problems such as old wiring and no maintenance. Accidents with chemicals and human error, which when added to the different characteristics of each fire and structures can generate the factors causing these disasters. The gradual rise in temperature causes a different effect in mortar and concrete parts, verifying the change in coloring provided to loss of mechanical strength and surface crumbling, cracking and disintegration of the structure itself. This paper presents a case study in which a building that is located in the metropolitan region of Recife was exposed to a fire situation. The metropolitan region of Recife is composed of several old buildings that by virtue of their age may have delayed construction methods, and may expose the fragility of the concrete used in its construction on a fire situation. The concrete structures are recognized by the good resistance to fire because of the thermal characteristics of the material, however, the temperature rise in the concrete elements in characteristic causes a reduction in strength and modulus of elasticity of the material, the loss in stiffness leading to polyphase degradation of reinforced concrete, structural parts can lead to ruin, but when properly sized and executed, the concrete can serve as a proactive agent to be exposed to high temperatures, as the same may be subjected to high temperatures accidentally or they may be part of their normal work.

Temperature rise and flow of Zr-based bulk metallic glasses under high shearing stress

Deformation of the bulk metallic glasses (BMGs) and the creation and propagation of the shear bands are closely interconnected.Shearing force was loaded on Zr 41.2 Ti 13.8 Cu 12.5 Ni 10.0 Be 22.5 (Vit.1) BMGs by cutting during the turning of the BMG rod.The temperature rise of alloy on the shear bands was calculated and the result showed that it could reach the temperature of the super-cooled liquid zone or exceed the melting point.The temperature rise caused viscous fluid flow and brought about the deformation of BMGs.This suggested that the deformation of BMGs was derived,at least to some extent,from the adiabatic shear temperature rise.

UH model considering temperature effects

The influences of temperature on the mechanical behavior of saturated clays are discussed first. Based on the concept of true strength and the revised calculation method of the potential failure stress ratio, the equation of the critical state stress ratio for saturated clays under different temperatures is deduced. Temperature is introduced as a variable into the UH model （3-dimensional elastoplastic model for overconsolidated clays adopting unified hardening parameter） proposed by Yao et al. and then the UH model considering temperature effects is proposed. By means of the transformed stress method proposed by Yao et al., the proposed model can be applied conveniently to 3-dimensional stress states. The strain-hardening, softening and dilatancy behavior of overconsolidated clays at a given temperature can be described using the proposed model, and the volume change behavior caused by heating can also be predicted. Compared with the modified Cam-clay model, the proposed model requires only one additional parameter to consider the behavior of the decrease of preconsolidation pressure with an increase of temperature. At room temperature, the proposed model can be changed into the original UH model and the modified Cam-clay model for overconsolidated clays and normally consolidated clays, respectively. The considered temperature range here is from the melting point to the boiling point of the pore water （e.g. the experimental temperatures （20℃-95℃） mentioned in this paper are within this range）. Comparison with existing test results shows that the model can reasonably describe the basic mechanical behavior of overconsolidated clays under various temperature paths.