Thermal conductivities of silicone matrix polymers including fillers of diamond particles and/or hexagonal boron nitride (h-BN) platelets were systematically investigated in an attempt to find a thermal interface material (TIM) having high isotropic thermal conductivity and high electrical insulating ability to enable efficient heat dissipation from the motor coil ends of electric vehicles. The TIM with mixed fillers of diamond particles and h-BN platelets had a maximum thermal conductivity of 6.1 W m−1 K−1 that was almost isotropic. This is the highest value among the thermal conductivities of TIMs with silicone matrix polymer reported to date. The mechanism behind the thermal conductivity of the TIMs was also examined from the viewpoint of the change in the number of thermally conductive networks and/or a decrease in the thermal resistivity of junctions of neighboring diamond particles through the incorporation of h-BN platelets. The TIMs developed in this study will make it possible to manage the heat of electric motors and will help to popularize electric vehicles.
A doublet flow is the circular free jet added the annular suction flow mounted on the same axis by using a double coaxial pipe. This flow was proposed for the purpose of diffusion control of a circular free jet. The doublet flow was examined experimentally with respect to time mean and unsteady characteristics over the full flow field by using PIV. It was found from the time mean analysis that as the suction velocity increases, the area average value of the fluctuating velocity increases. From the unsteady analysis, it was found that the vortex structures, which have the vorticity that is nearly equal to that of a jet, exist when the suction velocity is high. The vortex structure behaves intermittently, and exists randomly to the radial directions. Thus, the cause of the increase of the fluctuating velocity as described above is clarified by showing the behaviors of these vortex structures.
Transient Peltier effect was demonstrated for Al/Pt/PtSi x -coated single crystalline silicon (100) with a size of 10 mm × 10 mm × 0.625 mm sandwiched by a pair of gold blocks with a temperature gradient of 0.5 K. After an operation of Peltier device, maximum temperature decrease of ∼0.3 K was observed until t = 0.5-1.0 sec. Derivation of thermal parameters was performed by using a simple heat equivalent circuit. The derived response times of Peltier component τ P without SiC, approximately 0.1 sec, were much shorter than those reported for bulk Bi 2 Te 3 and other Si-related Peltier coolers. The Seebeck coefficient of the n-Si device in this work was −490 ± 20 μV/K, which is comparable to those reported previously. In addition, the insertion of a 4H-SiC substrate (thickness of 0.35 mm) substantially did not modify the thermal properties of the Si Peltier device. Simple simulation revealed that both high thermal conductance and high Seebeck coefficient are essential in order to minimize an increase of temperature of power devices with a short response time. Therefore, a real Si-based Peltier device integrated on a SiC-based power device would produce an effective heat transport with a sufficiently short response time. All of power devices emit a large amount of heat. For example, power waste of ∼1kW for an inverter corresponds to a heat generation of a few hundred W/cm 2 in a silicon carbide (SiC) power tip with a size of dozens of mm 2 . In addition, because the emitted heat fluctuates by time frequently, the amount of the thermal transport should be controllable in proportion to that relation. This controllable thermal transport allows us to flatten the time dependence of the temperature of SiC power chips, and should help to decrease the size of power modules. Therefore, we adopted Peltier devices for a thermal transport from 4H-SiC-based power devices.In a Peltier device, a flow of carriers enable an active heat transport. During an operation of the Peltier device with a current I P , the thermal flow in it consists of three terms: an active heat transport by Peltier effect, a Joule heat, and a passive thermal diffusion caused by a temperature gradient. If the device consists of n blocks of Peltier semiconductors with its Seebeck coefficient S, the first term is written as n|S|TI P . The value T denotes an average absolute temperature. The third term can be expressed as a product of thermal conductance K P and temperature difference between hot and cold sides ( T), namely,The expression of total thermal flow q all dependents on an application. Figure 1 shows a difference of the application of Peltier devices. Conventional Peltier devices have been applied for cooling systems including refrigerators, as shown in Fig. 1a. In this case, it is required to keep a lower temperature while to make a thermal isolation from the outside at a higher temperature. Because the direction of Peltier effect is opposite to that of thermal diffusion, the total thermal flow is written as q all = n|S|TI P − (1/2)R P I P 2 − K P T...
We propose 3-D integration of Peltier device onto a power device. In order to transport a heat from the power device, as a suitable material of the Peltier device, silicon was adopted because of its high Seebeck coefficient, high thermal conductivity, and applicability to semiconductor process. Bulk Si-based Peltier devices with conventional shape showed an active thermal transport over a Joule heat at the operation current less than 5 A. 3-D integration of 4H-SiC-based Schottky barrier diodes and Si-based film Peltier device, separated by intrinsic SiC layer, was realized by using conventional Si-based process flow.
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