Search

The paper reports on development of a Boundary Element Method (BEM) based two phase dispersed flow model, that allows an accurate and efficient heat and mass transfer coupling by using a moving point source model to account for particle–fluid interaction. The two-way coupling model highlights the efficient use of the elliptic fundamental solution and the Dirac delta distribution properties to accurately evaluate the heat and mass point particle source impact on the continuous phase, solved by the Boundary Domain Integral Method (BDIM). In addition to the BDIM model of the particle–fluid heat and mass transfer interaction, the two-phase flow case under consideration is extended to the case of porous spherical particle drying with internal moving drying front, which is solved by the Boundary Element Method. As the two-phase flow is considered to be dilute, the particle–fluid momentum exchange is covered by a one-way coupling algorithm, with Lagrangian particle tracking used for determination of particle positions and velocities in the flow. Two computational cases are presented, where 1000 and 10000 particles are dried in a stream of hot air. Comparison between the obtained drying times for the cases of the one-way and the two-way heat and mass transfer coupling results shows, that the developed two-way coupling model accurately captures the effect of moisture accumulation and temperature decrease in the fluid phase, leading to realistic computations of drying rates of particles in the flow. [ABSTRACT FROM AUTHOR]

• Constant temperature cooling device for skin tumour screening by dynamic thermography, to achieve thick penetration and high temperature resolution. • Constant cooling device composed from metal disc and Peltier module to achieve active cooling. • Investigation of temperature measurement position, disc thickness, regulation coefficient and lesion size on achieved cooling temperature of the skin. • Analysis id the cooling device is made based on the more realistic skin tissue model using thermoregulation response to the cooling process, which affects the blood perfusion of skin and tumour. • The most important device parameter is disc thickness and regulation coefficient to achieve preset cooling temperature and homogeneity of the cooling skin area. Dynamic thermography is a promising new non-invasive diagnostic technique for melanoma screening. This paper proposes a novel experimental setup of an active cooling device for dynamic thermography using a metal disc and a Peltier module. The aim is to achieve constant cooling temperature that induce deep cooling penetration and, therefore, better thermal contrast. The paper covers the numerical analysis of the device design parameters like thermocouple position, disc thickness and regulation coefficient prior to building it. Simulation is based on a numerical model of skin tissue with melanoma and the metal disc. The Peltier module has been modeled indirectly through a boundary condition simulating the device active cooling. For effective solving of the direct problem, the BEM has been used. Results showed that the thermocouple position for cooling regulation is not as important as the value of the regulation coefficient or disc thickness. A thicker disc improves the initial cooling due to higher thermal capacity. However, a thinner disc is recommended due to the faster regulation and more constant cooling temperature. Results also showed that lesion size did not affect the cooling temperature, meaning that it can be used for investigation in any tumour stage. [ABSTRACT FROM AUTHOR]

The paper covers a porous particle drying problem, which can be divided into two or three stages. The first stage is drying of surface moisture, the second stage is drying inside the particle, and the third, one which is relevant only to hygroscopic material, represents the change of particle moisture due to the change of environmental moisture. The second stage is the most relevant for the porous materials, and is, therefore, covered in more detail in this paper, with the main focus on the heat transfer inside the particle which affects the drying kinetics. The heat transfer problem inside the spherical particle has been solved using BEM, by transforming a 3D problem into a quasi 1D case by assuming uniform boundary conditions all around the particle, resulting in the solution depending only on the radial direction. The solution of the heat transfer needs to be calculated accurately as it directly affects the evaporation rate of the liquid on the interface between the dry crust and the wet core, which dictates the drying speed and affects the drying time. An in-depth analysis of space and time discretisation was performed on a typical spray drying example, where it is shown that a choice of a correct time step is cruicial for achieving good computational accuracy of the drying kinetics. The proposed numerical approach has also been tested on various drying conditions, with changing the particle size and the temperature of the drying gas, which have a largest effect on the drying kinetics. Finally, an analysis of the computed drying times is made as this is the most important parameter from the practical point of view, especially when designing the drying chambers. [ABSTRACT FROM AUTHOR]