Jon L. Ebert

Chemical composition and size distributions for fly ashes

Abstract Inter-particle variations in particle diameter and chemical composition in coal fly ashes are significant, and can be quantitatively studied using currently available microanalytical techniques. One such technique, computer controlled scanning electron microscopy (CCSEM), is now routinely used to determine chemical compositions and diameters of individual fly ash particles, using statistically significant sample sizes. This paper proposes simple mathematical formulae for expressing the inter-particle variations. Additionally, these formulae can be used for economically storing the large amount of data generated by CCSEM. Two apparent limitations of the CCSEM technique are discussed — one relating to the measurement of size distribution, and the other to determining the iron oxide distribution in the ash. These limitations are imposed by statistical considerations, and by artifacts of sample preparation techniques.

Run-to-run control of static systems

Run-to-run control using static linear models is examined. Conditions are presented for stability, (statistical) performance, and robustness using the standard control theory. A simulation example shows the usefulness of the method applied to a rapid thermal oxidation process.

Active Control of Flow Over a Backward-Facing Step

We describe a control-oriented model reduction process from partial differential equation (PDE) descriptions of aerodynamic flow systems, and the design of low-order feedback controllers using these procedures. An effective approach for flow model reduction for active control using balanced truncation approaches was developed. The techniques were applied to a flow control problem representative of aerospace problems: active control of flow over a modified 2D backward-facing step, which can be handled by most commercial finite element packages. Although the geometry is rather simple, the richness of the flow field is well documented. Feedback controllers were developed for disturbance rejection and tracking of the reattachment point for both high and low Reynolds numbers.

Model-based temperature control of heated plates

Many modern thermal processing systems involve temperature control of heated plates, where the plate can be a single wafer, heated by an array of tungsten halogen lamps from one or both sides, or thicker carriers or susceptors on which one or more wafers are placed, heated by radiation from hot filaments. The plates temperature is typically measured using pyrometers. These types of systems can be accurately described by a mathematical model of the physics. However, some of the system properties vary over time and/or from wafer-to-wafer and cannot be predicted in practice, although their range of values may be known. In many cases, the plates temperature is controlled using a proportional-integral-derivative (PID) controller, which may not be able to meet the desired temperature tracking performance (e.g. settling time, overshoot, repeatability) over a broad range of operating conditions. In this paper, an alternative model-based control approach is discussed that can achieve good performance for a wide range of operating conditions. In our approach, the mathematical system model is directly incorporated into the feedback controller. Simulation studies show that this approach yields significantly better performance and exhibits a much smaller sensitivity to system properties variation than a gain-scheduled PID controller.

The infrared refractive indices of CHBr3, CCl4 and CS2

Abstract Spectrally resolved data for the real part, n(λ) of the complex refractive index, n = n + i k , of bromoform (tribromomethane, CHBr3) at room temperature (298 K) in the wavelength range 1–13 μm are presented. The measurements were made using the near-normal reflectance technique. The accuracy of the method was confirmed by comparing measured values of n(λ) of water with available data in the literature. For bromoform, n(λ) is found to decrease gradually from 1.58 to 1.51 over this wavelength range, except in the region of anomalous dispersion near absorption bands at 3.3 and 8.7 μm. A complete infrared window for extinction measurements on suspended particulates can be obtained using CCl4 in the spectral range 1–6 μm, CHBr3 in the ranges 6.0–7.4 μm and 11–13 μm, and CS2 in the range 7.4–11.0 μm. The data for n(λ) of CCl4 in the range 1–9 μm, and those for CS2 in the range 7.4–11.0 μm, obtained from reflectance measurements, compare favorably with data available in the literature.

A radiation source for both the visible and the infrared

Abstract A radiation source with high output in both the visible and infrared spectral ranges has been developed, and its operating parameters are described. The hot element, a carbon composite board, is simple to fabricate as well as to operate. The source has been compared to both a tungsten strip lamp and a Nernst glower. For applications where both the visible and infrared ranges are of interest, this source allows for simplified experimental design.