Browsing by Author "Trevas, David Alexander"

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    The effect of shear on the thermal conductivity of non-Newtonian fluids
    (1994) Trevas, David Alexander; Chapman, Alan J.
    This work considers the effect of shear on the thermal conductivity of non-Newtonian fluids. These fluids display a variation of viscosity as a function of shear rate, and this study determines whether the thermal conductivity has a similar variation for these fluids. The experimental apparatus consisted of concentric cylinders immersed in a temperature-controlled water bath with the sample fluid situated in the gap between the cylinders. The outer cylinder was allowed to rotate to impart shear on the sample. The experimental method involved measuring the transient, temperature rise in the inner cylinder as heat is applied from the center of the cylinder. An interactive, transient, one-dimensional, finite-volume computer program was used to determine thermal conductivity from the experimental data. One of the non-Newtonian fluids tested, a mixture of bentonite clay in water, displayed a rise in thermal conductivity under shear that appeared to be a function of the square of the shear rate. The maximum rise was 6.8% above the zero-shear value at 100 s$\sp{-1}$. The other fluid, a mixture of carboxymethyl cellulose (CMC) in water, showed the same 1.9% decrease in thermal conductivity at both non-zero shear rates (50 and 100 s$\sp{-1}$). This work demonstrates that there is an effect of shear on the thermal conductivity of non-Newtonian fluids and that it is a different function for different types of fluids.
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    The Method of Exergy Multipliers: A new approach to exergy analysis of thermal systems
    (1989) Trevas, David Alexander; Chapman, Alan J.
    This work introduces the Method of Exergy Multipliers. Having asserted the utility of the exergy concept, this method aims to streamline the calculation procedures used in exergy analysis and its study. The method defines the exergy multipliers of a given process in terms of ratios of the work, heat transfer, irreversibility, and exergy output of the process with its incoming exergy. Algebraic properties of these multipliers aid in reducing the number of calculations. Many exergy and traditional concepts can be expressed in terms of the multipliers. Examples for a simple, closed Brayton cycle follow: the first optimizes the distribution of heat exchanger resources, the second optimizes the distribution of turbomachinery efficiency, and the third shows how to decide whether to improve the boiler or the turbine. The role of irreversibility in cycle performance is called into question and further study is recommended. Finally, limitations of the method are explained.