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EN
Purpose: The purpose of the present study was to demonstrate the procedure for determining the thermal conductivity of a solid material with relatively high thermal conductivity, using an original self-designed apparatus. Design/methodology/approach: The thermal conductivity measurements have been performed according to the ASTM D5470 standard. The thermal conductivity was calculated from the recorded temperature values in steady-state heat transfer conditions and determined heat flux. Findings: It has been found from the obtained experimental results that the applied standard test method, which was initially introduced for thermal conductivity measurements of thermal interface materials (TIMs), is also suitable for materials with high thermal conductivity, giving reliable results. Research limitations/implications: The ASTM D5470 standard test method for measurement of thermal conductivity usually gives poor results for high conductive materials having thermal conductivity above 100 W/mK, due to problems with measuring heat flux and temperature drop across the investigated sample with reasonably high accuracy. Practical implications: The results obtained for the tested material show that the presented standard test method can also be used for materials with high thermal conductivity, which is of importance either for the industrial or laboratory applications. Originality/value: The thermal conductivity measurements have been carried out using an original self-designed apparatus, which was developed for testing broad range of engineering materials with high accuracy.
EN
In this paper, the velocity field and turbulence effects that occur inside a crucible of a typical induction furnace were investigated. In the first part of this work, a free surface shape of the liquid metal was measured in a ceramic crucible. Then a numerical model of aluminium melting process was developed. It took into account coupling of electromagnetic and thermofluid fields that was performed using commercial codes. In the next step, the sensitivity analysis of turbulence modelling in the liquid domain was performed. The obtained numerical results were compared with the measurement data. The performed analysis can be treated as a preliminary approach for more complex mathematical modelling for the melting process optimisation in crucible induction furnaces of different types.
PL
W tej pracy przeprowadzono analizę pola prędkości i tworzących się wirów w tyglu typowego pieca indukcyjnego. W pierwszym etapie pracy zostały przeprowadzone pomiary kształtu powierzchni swobodnej ciekłego metalu na stanowisku z tyglem ceramicznym. Następnie został stworzony model numeryczny badanego tygla opisujący proces topienia aluminium. Model uwzględniał sprzężenie pola elektromagnetycznego oraz cieplnoprzepływowego, które przeprowadzono za pomocą komercyjnych programów. Następnie przeprowadzono analizę wrażliwości ze względu na sposób modelowania turbulencji w ciekłym metalu. Wyniki numeryczne zostały porównane z danymi z eksperymentu. Przeprowadzona analiza pozwoli na stworzenie dokładniejszych modeli numerycznych umożliwiających odtworzenie pola prędkości ciekłego metalu i optymalizację procesu topienia w piecach indukcyjnych.
PL
W pracy przedstawiono popularne podejścia wykorzystywane do modelowania hydrodynamiki złóż fluidalnych. Omówiono w skrócie modele ujmujące skale zjawisk na poziomie pojedynczych ziaren oraz modele globalne pół-empiryczne i niskowymiarowe operujące często w skalach rzędu całego układu i często w stanie ustalonym. Szczególną uwagę poświęcono modelom mezoskalowym, opartym na zastosowaniu oprogramowania numerycznej mechaniki płynów. W tym przypadku omówiono podejście Euler-Euler oraz Euler-Lagrange o akronimie DDPM. Szczegółowo omówiono równania rozwiązywane w tych przypadkach oraz modele domykające pozwalające na uwzględnienie oddziaływań międzyfazowych oraz odziaływań pomiędzy ziarnami w fazie rozproszonej. Przedstawiono wyłącznie popularne modele interakcji międzyziarnowych bazujące na kinetycznej teorii przepływu materii granularnej (KTGF). Istnieje szereg zalet modelu hybrydowego Euler-Lagrange DDPM, które, wraz ze wzrostem liczby zastosowań tego ciągle rozwijanego podejścia, mogą spowodować, że stanie się on narzędziem w modelowaniu złóż fluidalnych w skali mezo.
EN
Popular approaches frequently used in modeling of fluidized beds’ hydrodynamics are presented in this paper. Micro scale models, taking into account scales smaller than the particles and global semi-empirical, low-dimensional and frequently steady state approaches have been briefly discussed. Meso-scale, CFD models bases on Eulerian-Eulerian (multi-fluid) and Eulerian-Lagrangian (DDPM) models have been discussed in more detail. Governing equations of the approaches have been presented and discussed and closing models describing allowing for taking the account of the inter-phase interactions as well as particle-particle interactions in scattered phase. Only the popular models of inter – grain relations have been presented based on the kinetic theory of granular flow (KTGF) have been discussed. There are several advantages of the hybrid Euler-Lagrange DDPM which, together with an increase in continuous application of the approach, can cause that it will become a tool in modeling of fluidized beds in a meso-scale.
EN
The paper deals with a solution of radiation heat transfer problems in enclosures filled with nonparticipating medium using ray tracing on hierarchical ortho-Cartesian meshes. The idea behind the approach is that radiative heat transfer problems can be solved on much coarser grids than their counterparts from computational fluid dynamics (CFD). The resulting code is designed as an add-on to OpenFOAM, an open-source CFD program. Ortho-Cartesian mesh involving boundary elements is created based upon CFD mesh. Parametric non-uniform rational basis spline (NURBS) surfaces are used to define boundaries of the enclosure, allowing for dealing with domains of complex shapes. Algorithm for determining random, uniformly distributed locations of rays leaving NURBS surfaces is described. The paper presents results of test cases assuming gray diffusive walls. In the current version of the model the radiation is not absorbed within gases. However, the ultimate aim of the work is to upgrade the functionality of the model, to problems in absorbing, emitting and scattering medium projecting iteratively the results of radiative analysis on CFD mesh and CFD solution on radiative mesh.
5
Content available remote CFD estimation of heat losses in thermal conductivity measurements
EN
Knowledge of a material thermal conductivity is essential in several engineering applications. This material property serves also as a measure of the quality of manufactured materials. Nowadays, a lot of effort is directed into development of non-destructive, fast and reliable measurement techniques. In the works of Adamczyk et al. [1] and Kruczek et al. [10], a new in situ conductivity measurement technique for an anisotropic material was developed. This method, due to its rapidity and nondestructive character, can be embedded in a manufacturing process. However, despite many advantages, the developed measuring technique has some drawbacks corresponding to the applied mathematical model, which is used for determining the material thermal conductivities. It neglects the effect of heat losses due to radiation and convection phenomena on the calculated values of thermal conductivities. In this work, the computational fluid dynamic (CFD) modeling was applied to estimate heat losses due to radiation and convection. The influence of omitting the radiative and convective heat transfer on the predicted temperature field and calculated thermal conductivities was investigated. Evaluated numerical results were compared against experimental data by using the developed in situ measurement technique for the thermal conductivity of anisotropic materials.
6
Content available remote A 3D CFD model of a natural draft wet-cooling tower
EN
A 3D CFD model of a natural draft wet-cooling tower is presented in this paper. The model encompasses both the interior of the tower as well as the surrounding air. The developed CFD model is supplied with a low dimensional representation of the heat and mass exchanger, whose purpose is to determine the heat and mass rejected from the cooled water to the air. The representation is based on an original technique called the proper orthogonal decomposition. Due to the large scale differences, application of a low-dimensional heat and mass transfer model allowed reducing the computational time and accurately predict the heat and mass rejection effects. The Euler-Euler multiphase model was used to calculate the flow, heat and mass transfer in the rain zone. The model can be used in both, design computations as well as performance tests of natural draft wet-cooling towers. The effects of wind on the cooling tower can be taken into account. The CFD model was developed using the commercial code Fluent.
7
Content available remote On a numerical model of a natural draught wet-cooling tower
EN
In this paper the numerical model of a natural draught wet-cooling tower is presented. The model encompasses the tower and the surrounding environment. The analysis was performed using a commercial CFD code. The most important region of the heat and mass transfer is the fill. The process of heat and mass transfer is described by four ordinary differential equations that are solved by an external program. An original method called the Proper Orthogonal Decomposition (POD) has been applied to represent the heat and mass transfer in the fill. This technique allowed substantial reduction of computational time in the external program. The Euler-Euler model was used to calculate the multiphase flow in the rain zone. Results of the simulation are compared with data obtained experimentally and from other computational method. The comparison comprises a successful validation of the model.
PL
Praca dotyczy optymalizacji kształtu ciała sprężystego i przewodzącego ciepło. Ciało to wymienia ciepło z otoczeniem na drodze promieniowania i konwekcji, może być wieło-spójne a jego powierzchnie mogą się wzajemnie opromieniowywać. Zadanie promieniowania uwzględnienia występowanie stref zacienionych. W zadaniu termospręźystości uwzględnia się tytko wpływ poła temperatury na połę naprężeń. Zarówno zadanie przewodzenia ciepła, sprzężone z rozwiązaniem problemu promieniowania, jak i zadanie sprężystości są rozwiązywane metodą elementów brzegowych. Do rozwiązywania zadania optymalizacji kształtu użyto algorytmu ewolucyjnego. Łatwość modyfikacji siatek w MEB pozwała na prostą automatyzację obliczeń ewolucyjnych. Sama procedura optymalizacyjna cechuje się dużą elastycznością i odpornością na obecność łokałnych ekstremów.
EN
Shape optimization of heat conducting, elastic bodies subjected to thermal and standard loads is considered. Interaction of stress and temperature fields is modelled using the formulation of uncoupled steady state thermoelasticity. The presence of heat radiation with mutual irradiation of the boundaries and the presence of shadow zones is taken into account. To find the optimal shape evolutionary algorithm is used. The boundary element method is applied to discretize the thermoelasticity, conduction and radiation problems.
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