This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or "nanofluids," was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band ͑Ϯ10% or less͒ about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are ͑small͒ systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. ͓J. Appl. Phys. 81, 6692 ͑1997͔͒, was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

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In boiler combustion processes, the goals of the operation are to keep the combustor in the optimal condition and alleviate instabilities and their severe consequences. However, control systems based on the oxygen content usually have responses with certain delay. Most flames are turbulent and are affected by several unmeasured disturbances and continuous variation due to several types of fuels burned simultaneously. In this work, cascade control based on flame images, and oxygen is developed to prevent fast disturbances. One loop controls the feature of the flame image by correcting feed disturbance and throughput changes. The other loop controls the outlet oxygen content by eliminating the disturbance, which cannot be identified in the inner control loop. The designable performance bound and the corresponding optimal parameters of the PID controller structure computed from the closed loop operating data are also proposed. Finally, the proposed method is applied to a pilot scale experiment to evaluate the performance of the controller structure and to demonstrate its effectiveness in obtaining higher quality of the boiler combustion control system.

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