No description available.

No description available.

M.Tech. / Due to electric (E) and magnetic (H) fields that vary with space (r) and time (t) in the microwave cavity, and due to the inhomogeneous nature of the minerals, heating a mineral in a microwave oven gives an inherently non-uniform temperature distribution. The objective of the project is to introduce a mathematical model that will demonstrate the thermal interaction between ilmenite mineral (FeTiO3) and microwaves. The simulation presents the temperature distribution in the sample based on the conditions imposed on its boundaries. The field distribution in the cavity is simulated, and then the thermal analysis is performed using the lumped thermal capacity model. The temperature distribution in the sample is also simulated using the general heat conduction equation. Finite difference method is used two solve the two-dimensional unsteady heat conduction equation. The simulation of the field distribution in the cavity reveals that there are position of intense electric and magnetic field in the oven. This is demonstrated by experiment 6, where samples are heated at different positions in the oven for the same duration and different temperatures in the samples were measured. Electromagnetic wave propagation was also studied. It became apparent that the electric and magnetic field can not be treated independently from each other, because the changing electric field produces a changing magnetic field and the newly produced changing magnetic field produces a changing electric field, which is an electromagnetic wave. It is also proved that, considering the relationship given by Maxwell's equations, the electric and magnetic fields are not only space out of phase but they are also time out of phase, meaning that the one quantity is leading while the other is lagging. Based on the available mathematical evidence it was suggested to fit the conventional representation of the electromagnetic field, which show the electric field and the magnetic field at right angle to each other and in time phase, to the new representation which would highlight the fact that the electric and magnetic fields are time out of phase. The study of electromagnetic wave propagation has proved that the one-dimensional conventional representation of electromagnetic waves is inadequate. It does not support the fact that there are a number of resonant modes that exists in the cavity which has long been proved and accepted by authors in the field of electromagnetism. This is very much clear when dealing with electromagnetic waves in three dimensional space.

No description available.

No description available.

Dissertation (PhD)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: A mathematical model is presented which conceptualises fluid flow and heat transfer in cellular metallic foams completely saturated with a fluid in motion. The model consists of a set of elliptic partial differential governing equations describing, firstly, a momentum balance in the fluid by the spatial distribution of its locally mean velocity, and secondly, an energy balance in the fluid and in the solid matrix of the metallic foam, by the spatial and temporal distribution of their locally mean temperatures. The separate energy balance descriptions for the fluid and the solid matrix extend the application of the model to conditions of thermal equilibrium and thermal non-equilibrium between the fluid and the solid matrix. A computational solution algorithm is presented which allows the universal application of the model to porous domains of arbitrary shape, with spatially and temporally variable heat loads in a variety of forms. / AFRIKAANSE OPSOMMING: 'n Wiskundige model word voorgestel wat vloei en warmteoordrag voorspel in sellulêre metaalsponse wat in geheel gevul is deur 'n bewegende vloeier. Die vloeier kan in gasof vloeistoffase verkeer. Die model bestaan uit 'n stel elliptiese parsiële differensiaalvergelykings wat in die eerste plek 'n momentum-ewewig in die vloeier beskryf in terme van 'n ruimtelike, lokaal-gemiddelde snelheidsveld, en wat tweedens 'n energie-ewewig in die vloeier en in die soliede matriks van die metaalspons beskryf in terme van ruimtelike en tydelike lokaal-gemiddelde temperatuur verspreidings. Die aparte energie-ewewig beskrywings vir die vloeier en vir die soliede matriks van die metaalspons brei die aanwending van die model uit na gevalle waar die vloeier en die soliede matriks in termiese ewewig of in termiese onewewig verkeer. 'n Numeriese oplossingsalgoritme word ook voorgestel vir die universele toepassing van die model op ruimtelik-arbitrêre metaalspons geometrië wat onderwerp word aan 'n aantal verskillende ruimtelik-en tydveranderlike termiese laste.

The behavior of gas-solid reactors known as compact-fixed and moving beds, is analyzed from a theoretical viewpoint. For a compact fixed-bed the solution of the energy balance equations is obtained for the cases of a uniform temperature inside the solid pellets (i.e., the Biot number is zero) and for the case in which there are temperature gradients within the pellets (Bi > 0). For short contact times, beds with Bi > 0 have gas- and solid- temperatures which are greater than the temperatures within beds with Bi = 0. For long times, the situation is reversed. For a compact-moving bed the solution of the mass balance equations is obtained for the cases of a feed-solid with constant concentration and a feed solid with an oscillating concentration. In both cases the steady states obtained are unique, and internal recycling is observed only for a feed-solid with an oscillating concentration. Recycling is that situation when the concentration of the solid falls below that of the gas for a bed in which the feed-solid is greater than the feed-gas. This occurred when the period of oscillation was smaller than the residence time of the solid provided that the residence time of the solid was not very short (i.e., provided that B(,s) > 0.1). For both types of beds there is an equivalence between mass transfer and energy transfer so that the solutions can be interchanged with suitable definitions of dimensionless variables.

Tam Wai Shing = 穩態環流的熱傳送與縱橫比之關係及其與湍流狀態的瑞利-伯纳德對流之聯繫 / 譚偉誠. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 59-61). / Text in English; abstracts in English and Chinese. / Tam Wai Shing = Wen tai huan liu de re chuan song yu zong heng bi zhi guan xi ji qi yu tuan liu zhuang tai de Ruili-Bonade dui liu zhi lian xi / Tan Weicheng. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Review of the theoretical studies of heat transport by turbulent convection --- p.5 / Chapter 2.1 --- The marginal stability arguments --- p.7 / Chapter 2.2 --- Chicago mixing zone model --- p.7 / Chapter 2.3 --- Shraiman and Siggia theory --- p.10 / Chapter 2.4 --- Grossmann and Lohse Theory --- p.12 / Chapter 2.4.1 --- Estimation of the kinetic dissipation --- p.13 / Chapter 2.4.2 --- Estimation of the thermal dissipation --- p.14 / Chapter 2.4.3 --- The four regimes --- p.15 / Chapter 3 --- Aspect-ratio dependence: The problem studied --- p.19 / Chapter 3.1 --- The velocity field --- p.21 / Chapter 3.1.1 --- Incompressible flow --- p.21 / Chapter 3.1.2 --- Large-scale circulating flow --- p.21 / Chapter 3.1.3 --- No-slip boundary conditions --- p.22 / Chapter 3.2 --- The functions f(x) and g(y) --- p.23 / Chapter 3.3 --- Boundary conditions for the temperature field --- p.23 / Chapter 3.4 --- Important parameters in the numerical calculation --- p.24 / Chapter 4 --- The numerical calculations --- p.31 / Chapter 5 --- Results and discussions --- p.34 / Chapter 5.1 --- Nu-Г Relationship --- p.38 / Chapter 5.2 --- Nu - Pe Relationship --- p.41 / Chapter 6 --- Implications for heat transport by Rayleigh-Benard convection --- p.49 / Chapter 6.1 --- Nu-Ra relationship --- p.50 / Chapter 6.2 --- Comparison with recent experimental results --- p.52 / Chapter 7 --- Conclusions --- p.57 / Bibliography --- p.59

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / M.S.