Conjugate Model for Heat and Mass Transfer of Porous Wall in the High Temperature Gas Flow

Heat and mass transfer of a porous permeable wall in a high temperature gas dynamical flow is considered. Numerical simulation is conducted on the ground of the conjugate mathematical model which includes filtration and heat transfer equations in a porous body and boundary layer equations on its surface. Such an approach enables one to take into account complex interaction between heat and mass transfer in the gasdynamical flow and in the structure subjected to this flow. The main attention is given to the impact of the intraporous heat transfer intensity on the transpiration cooling efficiency.

Multi-field simulations and characterization of CMOS-MEMS high-temperature smart gas sensors based on SOI technology

This paper describes multiple field-coupled simulations and device characterization of fully CMOS-MEMS-compatible smart gas sensors. The sensor structure is designated for gas/vapour detection at high temperatures (>300 °C) with low power consumption, high sensitivity and competent mechanic robustness employing the silicon-on-insulator (SOI) wafer technology, CMOS process and micromachining techniques. The smart gas sensor features micro-heaters using p-type MOSFETs or polysilicon resistors and differentially transducing circuits for in situ temperature measurement. Physical models and 3D electro-thermo-mechanical simulations of the SOI micro-hotplate induced by Joule, self-heating, mechanic stress and piezoresistive effects are provided. The electro-thermal effect initiates and thus affects electronic and mechanical characteristics of the sensor devices at high temperatures. Experiments on variation and characterization of micro-heater resistance, power consumption, thermal imaging, deformation interferometry and dynamic thermal response of the SOI micro-hotplate have been presented and discussed. The full integration of the smart gas sensor with automatically temperature-reading ICs demonstrates the lowest power consumption of 57 mW at 300 °C and fast thermal response of 10 ms. © 2008 IOP Publishing Ltd.

Laboratory-scale fluidized bed rig for high-temperature tube wastage studies

As part of a study of the wear of candidate heat exchanger tube materials for use in fluidized bed combustors, two similar laboratory-scale rigs have been built and characterized. Specimens of selected alloys are carried on counter-rotating rotors immersed in a fluidized bed, and are exposed to particle impact velocities of up to approximately 3 ms-1 at temperatures up to 1000°C. The performance of this design of apparatus has been investigated in detail. The effects of several experimental variables have been studied, including angle of particle impact, specimen speed, position of the rotor within the fluidized bed, duration of exposure, bed material particle size, degradation of the bed material, degree of fluidization of the bed, and size of specimen. In many cases the results obtained with steel specimens at elevated temperatures are similar to those observed with polymeric specimens at low temperatures.

High temperature direct double side cooled inverter module for hybrid electric vehicle application

In this paper a novel approach to the design and fabrication of a high temperature inverter module for hybrid electrical vehicles is presented. Firstly, SiC power electronic devices are considered in place of the conventional Si devices. Use of SiC raises the maximum practical operating junction temperature to well over 200°C, giving much greater thermal headroom between the chips and the coolant. In the first fabrication, a SiC Schottky barrier diode (SBD) replaces the Si pin diode and is paired with a Si-IGBT. Secondly, double-sided cooling is employed, in which the semiconductor chips are sandwiched between two substrate tiles. The tiles provide electrical connections to the top and the bottom of the chips, thus replacing the conventional wire bonded interconnect. Each tile assembly supports two IGBTs and two SBDs in a half-bridge configuration. Both sides of the assembly are cooled directly using a high-performance liquid impingement system. Specific features of the design ensure that thermo-mechanical stresses are controlled so as to achieve long thermal cycling life. A prototype 10 kW inverter module is described incorporating three half-bridge sandwich assemblies, gate drives, dc-link capacitance and two heat-exchangers. This achieves a volumetric power density of 30W/cm3.

Microstructure and high-temperature wear and oxidation resistance of laser clad gamma/W2C/TiC composite coatings on gamma-TiAl intermetallic alloy

There are very strong interests in improving the high-temperature wear resistance of the y-TiAl intermetallic alloy, especially when applied as tribological moving components. In this paper, microstructure, high-temperature dry sliding wear at 600 degrees C and isothermal oxidation at 1000 degrees C on ambient air of laser clad gamma/W2C/TiC composite coatings with different constitution of Ni-Cr-W-C precursor mixed powders on TiAl alloy substrates have been investigated. The results show that microstructure of the laser fabricated composite coatings possess non-equilibrium microstructure consisting of the matrix of nickel-base solid solution gamma-NiCrAl and reinforcements of TiC, W2C and M23C6 carbides. Higher wear resistance than the original TiAl alloy is achieved in the composite coatings under high-temperature wear test conditions. However, the oxidation resistance of the laser clad gamma/W2C/TiC composite coatings is deceased. The corresponding mechanisms resulting in the above behaviors of the laser clad composite coatings are discussed. (c) 2006 Elsevier B.V. All rights reserved.

The positive floating potential of high-temperature particles in plasma

It has been predicted that the floating potential of particles in plasma may become positive when the particle surface temperature is high enough, but, to our knowledge, no positive floating potential has been obtained yet. In the present paper the floating potential theory of high-temperature particles in plasma is developed to cover the positive potential range for the first time, and a general approximate analytical formula for the positive floating potential with a thin plasma sheath and subsonic plasma flow is derived from the new model recently proposed by the authors. The results show that when the floating potential is positive, the net flux of charge incident on the particle approaches a constant similar to the 'electron saturation' phenomena in the case of the electric probes.