We conducted thermal conductivity investigations by homogenization. This method can effectively model structural features such as pores within dispersed particle architectures via a finite element mesh. We investigated the factors that determine the effective thermal conductivity of porous structures and composites, such as the volume ratio of the continuous and dispersed phases, conductivity ratio, Biot number and particle packing model.


Keywords: homogenization method, effective thermal conductivity, multi-scale.

The robust and simple optimization method of functionally graded material (FGM) for combined cyclic thermal and mechanical loading with application to valve design is proposed. The optimization procedure starts from the homogeneous ceramic material distribution and after thermomechanical analysis of the whole process, the new distribution of material is determined by reducing concentration of the ceramic phase at places of high tensile stresses and by increasing ceramic contents at places of high effective stresses. The optimal distribution of ceramic phase is found through iterations. We have shown the numerical example of the proposed method for optimization of a composite exhaust valve of combustion engine. The example illustrates the optimal density distribution of ceramic phase of Al₂O₃ within NiAl matrix. In the design study we have used the transient analysis of stress and temperature fields. The proposed method shares merits of standard optimization and topology optimization, it allows for creating one phase of material inside the other. It can be especially useful to problems of structural elements subjected to thermomechanical loading histories.


Keywords: thermomechanical analysis, high frequency cyclic loading, coating, design, FGM, optimization.

In the paper, the thin metal film subjected to the ultrashort laser pulse has been analyzed. The heat conduction in the domain considered has been described by two-temperature model consisting of the system of two coupled parabolic equations determining the electron and lattice temperatures. The sensitivity analysis of electron and lattice temperatures with respect to the parameters appearing in mathematical description has been discussed. In particular, the changes of temperatures due to the changes of coupling factor G and the film thickness L have been estimated. At the stage of numerical computations in a case of basic as well as sensitivity problems solutions the explicit scheme of finite difference method has been used. In the final part of the paper the results of computations have been shown.


Keywords: microscale heat transfer, two-temperature model, sensitivity analysis, finite difference method.

The paper concerns the modelling of artificial hyperthermia. The 3D domain including healthy tissue and tumor region is considered. Heat transfer processes proceeding in this domain are described by the Pennes model and next by the porous one. The external heating of tissue is taken into account by the introduction of internal source function to the equation considered. Both models are supplemented by the same geometrical, physical, boundary and initial conditions. At the stage of numerical simulation the explicit scheme of finite difference method is used. The examples of computations show the similarities and differences of solutions and allow to formulate the conclusions connected with the applications of the results obtained in the hyperthermia therapy.


Keywords: bioheat transfer, heating of tissue, hyperthermia therapy, porous model, Pennes' equation.

This paper describes results of the mathematical modelling of the steady-state thermal phenomena taking place in a Fracmo 240 W DC electric motor. The model of the motor was defined in the ANSYS Fluent software to predict flow and temperature fields inside the machine. The thermal model was coupled with an electromagnetic solver to determine power losses occurring in different parts of the unit. In order to validate the proposed numerical model, a test rig was set up to measure temperatures at points located inside the motor housing and on its external wall. Additionally, the temperature field was captured by an infrared camera. The results obtained from the coupled analysis are comparable with the measurement data.


Keywords: computational fluid dynamics, coupled thermal problems, electric motor, validation.

In the paper, the numerical model of the flow phenomena in the flotation machine is presented. The process of flotation consists of a number of phenomena which provide serious numerical difficulties. One can enumerate rotation, two phase flow, foam formation etc. To the knowledge of authors there is no complete numerical model available for the flotation machine. The long-term task of the project is to create a complete model of the machine. Such a model would be very helpful in the process of construction and modernization of the flotation machine. As it was mentioned, due to difficulties connected with modelling the flotation phenomena, only a few aspects of the process were taken under consideration. In the paper, a single phase flow of water is considered. The efficiency of the flotation process strongly depends on the fluid flow field in the machine. The level of mixing the fractions and air bubbles strongly depends on the velocity field of the water, so the proper model of fluid flow is of great practical importance. This paper presents preliminary results of mathematical modelling. The commercial package ANSYS Fluent was utilized for the analysis. The results were compared with the measurements performed on the small scale model of the machine. Obtained results are satisfying and encouraging for further development.


Keywords: flotation, multiphase flow, numerical analysis, CFD, experiments, PIV measurements.