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[en] The paper presents a press-pack package integrated with a microchannel cooling system, which is a new thermal solution for power devices, e.g. diodes. In comparison with conventional solutions enforcing the use of either an air cooling system or a liquid one, the novel package is characterised by considerably smaller dimensions, lower weight and significantly higher thermal performance. The conducted measurements of the manufactured model showed that a thermal resistance of 0.0182 K/W can be obtained for an allowable pressure drop for electronic applications.
[en] Thermal Analysis (TA) is the measurement of changes in a physical property of a material that is heated through a phase transformation temperature range. The temperature changes in the material are recorded as a function of the heating or cooling time in such a manner that allows for the detection of phase transformations. In order to increase accuracy, characteristic points on the cooling curve have been identified using the first derivative curve plotted versus time. In this paper, an alternative approach to the analysis of the cooling curve has been proposed. The first derivative curve has been plotted versus temperature and all characteristic points have been identified with the same accuracy achieved using the traditional method. The new cooling curve analysis also enables the Dendrite Coherency Point (DCP) to be detected using only one thermocouple. (author)
[en] Complete text of publication follows. Models for the thermoremanent magnetisation (TRM) acquisition of single-domain (SD) magnetic grains, include a time parameter (t), that defines the behaviour of an assemblage of magnetic grains for a given temperature in time t. This time t directly controls the blocking temperature and the intensity of the recorded TRM. However, in a cooling system, e.g., a lava, the temperature is constantly changing, making t ∼ 0 s for any given temperature. In the geophysical literature, previous studies looking at the effect of cooling rate on TRM acquisition [e.g., Dodson and McClelland-Brown, 1980; Halgedahl, et al., 1980] have circumnavigated this problem by taking discrete time intervals, i.e., steps with an equivalent time teq determined by the cooling rate. By numerically solving the master equation [Spinu, et al., 2001], it is possible to directly relate teq to ∂T/∂t without any need to use the step approximation. I investigate the effect of using the more robust definition of teq, and the implications for TRM acquisition and palaeointensity determination. For ∂T/∂t I have employed the standard Newtonian cooling rate equation.
[en] The equipment and technology of small bar tandem rolling line of Shijiazhuang Iron and Steel Co. in China has reached the 90's international advanced level in the 20th century, but products on the line are mostly of common carbon steel. Currently there are few steel plants in China to produce 45 steel bars for cold drawing, which is a kind of shortage product. Development of 45 steel for cold drawing has a wide market outlook in China. In this paper, continuous cooling transformation (CCT) curve of 45 steel for cold drawing used for rolling was set out first. According to the CCT curve, we determined some key temperature points such as Ac3 temperature and Ac1 temperature during the cooling procedure and discussed the precipitation microstructure at different cooling rate. Then by studying thermal treatment process of 45 steel bars for cold drawing, the influence of cooling time on microstructure was analyzed and the optimum cooling speed has been found. All results concluded from the above studies are the basis of regulating controlled cooling process of 45 steel bars for cold drawing. Finally, the feasible production process of 45 steel bars for cold drawing on common carbon steel production line combined with the field condition was recommended
[en] Highlights: → A procedure for deriving merit exponents when multiple property constraints are active is outlined. → The principles are illustrated for cooling systems (tube and plate). → Control area diagrams (CAD) for the active constraints for cooling systems are formulated. → The procedures do not require analytical solutions and are applied in FEM. -- Abstract: Merit indices are used to rank materials and are of fundamental importance in materials selection. Traditionally, merit indices have only been available for elementary design cases. In the present paper merit indices are generalised to cooling systems where heat flow and strength are design criteria in a materials optimisation framework. A cooling tube and a cooling plate are considered. A new concept, merit exponent is used that is related to the merit indices. A definition of the merit exponent is given also for cases with many design variables. In each design case a number of merit exponents are involved. It is a nontrivial task to identify which they are and when each of them is applicable. For this purpose control area diagrams (CAD) are used. A CAD is a diagram with the controlling properties on the axes, and areas where one or more constraints are active. For the cooling systems the controlling properties are heat conductivity and strength. The active constraints define the relevant merit exponent. The constraints involve the controlling properties and geometrical variables. Principles are established for how to set up the CAD and to derive the merit exponents.
[en] To achieve them, improved core structural materials with a potential to be applicable at elevated temperature under severe neutron exposure environment are required. Ferritic/martensitic (FM) steels are very attractive for the structural materials of fast fission reactors such as a sodium cooled fast reactor (SFR) owing to their excellent irradiation resistance to a void swelling, but are known to reveal an abrupt loss of their creep and tensile strengths at temperatures above 600 .deg. C. Accordingly, high temperature strength should be considerably improved for an application of the FM steel to the structural materials of SFR. Oxide dispersion strengthened (ODS) FM steels are considered to be promising candidate materials for high- temperature components operating in severe environments such as nuclear fusion and fission systems due to their excellent high temperature strength and radiation resistance stemming from the addition of extremely thermally stable oxide particles dispersed in the ferritic/martensitic matrix. In the present study, the effects of an intermediate heat treatment during a cold rolling on microstructures and mechanical properties of 10Cr-1Mo FM ODS steel were investigated. The FM ODS steels were manufactured by the MA, HIP and hot-extrusion processes. Intermediated heat treatments including furnace cooling, tempering, and normalizing-tempering with air cooling were performed after the cold rolling
[en] In this paper, experimental determination of dynamic viscosity of water based magnetite nanofluid (Fe_3O_4/water) was performed. The viscosity was measured in the temperature range of 20–55 °C for various samples with solid volume fractions of 0.1%, 0.2%, 0.4%, 1%, 2% and 3%. The results showed that the viscosity considerably decreases with increasing temperature. Moreover, the viscosity enhances with an increase in the solid volume fraction, remarkably. The calculated viscosity ratios showed that the maximum viscosity enhancement was 129.7%. Using experimental data, a new correlation has been proposed to predict the viscosity of magnetite nanofluid (Fe_3O_4/water). A comparison between the experimental results and the correlation outputs showed that the proposed model has a suitable accuracy. - Highlights: • Preparing Magnetite nanofluids with solid volume fractions up to 3%. • Measuring viscosity in temperature range of 20–55 °C using Brookfield Viscometer. • Maximum viscosity enhancement occurred at volume fraction of 3% and was 129.7%. • Proposing new correlation to predict the viscosity of Fe3O4/water nanofluid.
[en] Oxide growing on mild and low alloy steel components in the high pressure CO2 based coolant of UK gas cooled nuclear power stations can become porous and continue to grow at the interfaces of structural components even when any interfacial gap has filled with oxide. Because such growth gives rise to a net volume expansion, the adjacent components can be forced apart. Any fastening, such as a weld or bolt, holding them together can then become stressed as a result of growth of oxide alone, and may sustain mechanical damage. The phenomenon is now well understood and methods of predicting behaviour have been developed and refined over the years to ensure safe and continued plant operation. The basis of such methods is presented for bolted joints, and the way in which joint geometry, environment, and mechanical properties of component material can affect bolt strain is outlined with examples. (author)
[en] Highlights: • The size of two-phase atomized metal powder is smaller than that of gas atomized under the same atomization condition. • Two-phase atomized powders have a more concentrated powder size distribution and more irregular shape. • Two-phase atomized powders have larger cooling rate and finer microstructure. • Inexpensive atomization medium and simple facility make it a promising low-cost metal powder preparation technology. In this paper, the principle of gas-solid two-phase atomization methodology for metal powder is demonstrated. A cost-effective production technology for high-quality metal powder was proposed. The morphology, size distribution, microstructure and cooling rate of two-phase atomized 7055Al powder were examined. The experimental results have demonstrated a number of advantages and unique features of gas-solid two-phase atomization in the preparation of metal powders. When the Argon gas pressure P = 0.6 MPa and iron particle feed rate M′ = 235.6 g·min− 1, the mass median diameter (d50) of the 7055Al powder manufactured by two-phase atomization process was 22.8 μm, which is reduced by 52.7% compared with gas atomized powders with d50 = 48.2 μm under the same atomization parameters. Experimental results also showed that the gas-solid two-phase atomized powders exhibited more irregular shapes than gas atomized powders. The cooling rate of most powders was in the range of 104– 105 K/s, and for some extra checked fine powders the cooling rate can even reach 106 K/s. The two-phase atomized powders had larger cooling rate and presented obvious rapid solidification characteristics than gas atomized powder with the same diameter. Moreover, this study indicates that gas-solid two-phase atomization could be a promising high-quality and low-cost metal powder preparation technology.