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Browsing by Author "Thomas, J. R."

Now showing 1 - 4 of 4
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    Control of thermal runaway in microwave resonant cavities
    Wu, X.; Thomas, J. R.; Davis, William A. (American Institute of Physics, 2002-09-15)
    This article reports direct experimental evidence of the so-called "S curve" of temperature versus electrical field strength when materials with positive temperature dependence of dielectric loss are heated in a microwave resonant cavity applicator. A complete discussion of how the experimental results were achieved is presented. From the experimental results, we believe the S curve theory provides an incomplete explanation of thermal runaway in microwave heating. To understand microwave heating in a resonant cavity, cavity effects must be considered. To explain the experimental results, a theoretical model based on single-mode waveguide theory is developed. Finally, a method to control thermal runaway is described. (C) 2002 American Institute of Physics.
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    Exact Numerical Results for Poiseuille And Thermal Creep Flow in a Cylindrical Tube
    Valougeorgis, D.; Thomas, J. R. (AIP Publishing, 1986-02-01)
    The F N method is used, in the field of rarefied gas dynamics, to develop a complete solution for the cylindrical Poiseuille flow and thermal creep problems. The linearized Bhatnagar–Gross–Krook (BGK) model and purely diffuse reflection at the surface are used to describe the physical problem. The derived set of singular integral equations is solved by polynomial expansion and collocation. By choosing suitable F N approximations, the solution of both problems under consideration is accomplished with a single matrix inversion, minimizing computational time and effort. The converged numerical results for the flow rates and the velocity profiles are correct to four significant figures, thus supporting the results of previous authors achieved by other methods.
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    Heat Transfer in a Rarefied Gas Enclosed Between Parallel Plates: Role of Boundary Conditions
    Loyalka, S. K.; Thomas, J. R. (AIP Publishing, 1982)
    The influence of boundary conditions of accomodation coefficients and Maxwellian diffuse specular reflection on heat transfer through a rarefied gas enclosed between two parallel plates is examined. An exact expression for heat transfer for accomodation coefficient boundary conditions and the Bhatnagar–Gross–Krook (BGK) model is constructed by using results of Cercignani and Pagani and Thomas, Chang, and Siewert. These results are compared with some variational results of Cipolla and Cercignani and some exact results of Thomas, Chang, and Siewert and Thomas for the BGK model and Maxwellian diffuse specular reflection boundary conditions. It is concluded that the two boundary conditions provide results that agree within about 3% for a range of Knudsen numbers and boundary parameters. It is found that the variational results are remarkably accurate for the BGK model and both types of boundary conditions. Further, it is noted that the heat transfer between parallel plates with different accommodation coefficients at the two surfaces can be calculated exactly by using a harmonic mean for each surface.
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    Temperature-Jump Problem with Arbitrary Accommodation
    Loyalka, S. K.; Siewert, C. E.; Thomas, J. R. (AIP Publishing, 1978)
    A concise and accurate result for the temperature‐jump coefficient based on the linearized BGK model and arbitrary accommodation is reported. The jump coefficient is expressed as a power series in (1‐α), and values of the expansion coefficients are given.