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Byline: M.C. Chaturvedi, N.L. Richards Optical, SEM/EDX and TEM/EDX techniques have been used to characterize the parent, weld and heat affected zone (HAZ) microstructures in electron beam welded (EBW) Incoloy 903. The as-forged microstructure showed a duplex grain size of large warm-worked grains decorated by finer grains. MX carbides, fine MC carbides and MNP phosphides were observed on grain boundaries. The weld metal solidified in a cellular-dendritic mode: with segregation of Nb and Ti to interdendritic regions; no micro-fissures were observed originating in the weld metal. The HAZ, however, showed extensive micro-fissuring, especially on the long warm-worked grain boundaries. The micro-fissuring was attributed to constitutional liquation of the MX carbides (partial), fine MC and MNP phosphides on the grain boundaries. Micro-fissuring was, however, absent on the fine grain boundaries, though the boundaries exhibited a thickened appearance attributed to liquid film migration (LFM). The LFM was found to influence the solidification mode of the grain boundary liquid phase. Liquid solidifying via a non-LFM mode, resulted in a terminal solidification products of γ + MC carbide. These carbides were in extensive sheets along the grain boundary. Areas associated with LFM solidified to a Nb rich austenite and exhibited no evidence of micro-fissuring. The LFM resulted in a smaller solidification temperature range for the grain boundary liquid and resulted in a less sensitive microstructure for the weld cycle thermal stress to act on. LFM was also concluded to be the reason for the beneficial effect of fine grains on minimizing HAZ micro-fissuring.

Byline: Ahmet Karakas, Unal Camdali, Murat Tunc Cooling of electronics by conduction with high thermal conductivity paths located in heat generating, low conductivity volumes are investigated using constructal theory. A new mathematical solution for the fundamental problem of how to collect and channel to one point the heat generated volumetrically in a low conductivity volume of a given size is developed using the Lagrange Multiplier Method. Additionally, at the fundamental step, the optimisation procedure is exact. No approximation has been made about the geometrical characteristics of the fundamental element. In solutions of the fundamental elements, the amount of high conductivity material (high conductivity paths) through the volume is fixed.

Byline: Huajiang Ouyang, Abd Rahim Abu-Bakar, Lijie Li This paper studies car disc brake squeal by transient analysis and details the first attempt to combine heat conduction analysis, contact analysis and transient analysis of disc brake squeal. The contact pressure at the disc/pads interface is first computed, and the information is used to define friction-induced heat flux. Its resultant heat conduction is then analysed. Finally, transient analysis is performed, considering the influence on squeal generation of contact pressure distribution affected by brake pad surface roughness and thermal deformation. A noticeable difference is found between the dynamic responses obtained with the thermal effect from those without the thermal effect.

Byline: Liang Ma, Hongzan Bin A 3D finite element model is used to analyse the non-linear behaviours of thermal conductivity and of specific heat due to temperature changes, phase transformations and powder-to-solid transitions. Compared to the traditional 'S' scanning pattern, the influences of three kinds of fractal scanning patterns on the evolution of sintering temperature are investigated by using the FE model. It is shown that different scanning patterns have strong influences on the temperature distribution and the fractal scanning patterns can make the temperature distribution much more symmetrical than that of the 'S' scanning pattern. In addition, powder-to-solid transition also has an obvious influence on the temperature distribution.

In this work, a coupled electromagnetic and thermal physical model has been implemented in order to analyse the thermal runaway development during the application of microwave energy. Both static and mode-stirred microwave ovens have been analysed and its influence on the electric field and temperature patterns compared. Additionally, the continuous and pulsed uses of the microwave power source are also compared. Results indicate that temperature permittivity dependence, thermal conductivity and the electric field deposition are mainly responsible for thermal avalanche and 'hot spot' development.

Assuming that the cooling rate of parts depends on thermal conductivity of the material and on the surface/volume ratio, a two-ways study has been carried out. Firstly, the isothermal surfaces have been calculated by a numerical method on parallelepipeds of constant cross section and varying height and weight. Microstructures, depending on isothermal surfaces predicted by the numerical model, agree with microhardness and mechanical properties. A maximum weight of about 200 grams has been observed to be apt to a full sinter-hardening process and the surface/volume ratio seems to be the critical driving factor. Numerical analysis and experimental tests show that the thermal diffusivity of sintered steels increases as porosity increases.

Byline: Frank Schafer, Annalisa Manera The test facility CIRCUS (CIRculation Under Start-up) was built to study the start-up phase of a natural-circulation BWR. During the start-up,so-called flashing-induced instabilities can arise. These instabilities are induced by flashing (i.e., steam production in adiabatic conditions) of the coolant in the long riser section, which is placed above the core to enhance the flow rate. The flashing that occurs in the riser causes an imbalance between driving force and pressure losses in the natural-circulation loop, giving rise to flow oscillations. Within the European-Union 5th Framework Programme, a project, NACUSP (Natural circulation and stability performance of BWRs), has been started in December 2000, having as one of its main aims the understanding of the physics of the phenomena involved during the start-up phase of natural-circulation-cooled BWRs, providing a large experimental database and validating state-of-the-art thermo-hydraulic codes in the low-pressure, low-power operational region of these reactors. One part of this project deals with the modelling of selected CIRCUS tests using the thermo-hydraulic code ATHLET (Analysis of THermal-hydraulics of LEaks and Transients). This paper gives an overview about experiments and simulations. The code ATHLET is used to investigate the dynamic behaviour of the CIRCUS test facility and the results of the calculations are compared with the experimental data.

Byline: Leticia R. Corral-Bustamante, Antonino Perez-Hernandez Motion of heat in work rolls used for hot rolling of steel strip is described by means of a model that take into account the Bessel-Thomson functions and La Theorie Analytique de la Chaleur of Fourier. This specific model is based on the Bessel's differential equation whose solutions are called Bessel functions of order n, which can be rewritten in the form of Kelvin functions. The heat transfer in hot rolling is carried out by means of conduction and free and forced convection. This model sets an important precedent for novel insight in computer modelling of industrial processes in the field of material sciences.

Byline: Rahim K. Jassim, Tahar Khir The purpose of this paper is to demonstrate the importance of the use of exergoeconomic analysis in the optimisation of the geometry of a rotary regenerator. The optimum geometry of a rotary regenerator is determined using the unit cost of the exergy of the warm air delivered as the objective function. The running cost is determined using different unit costs for the pressure component of exergy, EIP, and the thermal component of exergy, EIT, which are evaluated separately. A mathematical model using a finite difference technique of matrix thermal conductivity and heat transfer is presented and the governing differential equations have been formulated in terms of the characteristic dimensionless groups (I t, It and It) and the effect of two different materials is examined. The effect of variation of the regenerator geometry on the objective function is examined and recommendations are made for the selection of the most appropriate parameters for a rotary regenerator. The results show that the effect of thermal conductivity on the minimum exergoeconomic objective function is slightly over 1% for mild steel and 3.374% for aluminium.