Introducing Systems and Control

Auslander, David M.; Takahashi, Y.; Rabins, Michael J.; Garrard, William L.

doi:10.1115/1.3423285

Cited by 26 publications

(3 citation statements)

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“…This leads to a very rapid reaction and a vigorous rate of heat release, which causes a transient temperature rise. The behavior resembles the well known inverse response of lumped-parameter systems, in which an output variable moves initially in the opposite direction of where it eventually ends up (Luyben 1973;Auslander et al, 1974).…”

mentioning

confidence: 62%

Wrong‐way behavior of packed‐bed reactors: 1. The pseudo‐homogeneous model

1981

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A sudden reduction in the feed temperature to a packed-bed reactor leads to a transient temperature rise, which is referred to as the wrong-way behavior. A pseudo-homogeneous plug-flow model is used to analyze the structure of this transient behavior. The key parameters which determine the magnitude of this response are the dimensionless adiabatic temperature rise, activation energy, heat transfer capacity, coolant temperature, magnitude of temperature drop and length of the reactor. A simple expression is derived for predicing the maximum transient temperature rise. SCOPEWhen the temperature of the feed to a packed-bed reactor is suddenly decreased a transient temperature rise may occur. This surprising dynamic feature is caused by the difference in the speed of propagation of the concentration and temperature disturbances and is referred to as the wrong-way behavior. This response was predicted originally by Boreskov and Slinko (1965) and Crider and Foss (1966), and was observed by many investigators (Hoiberg et al., 1971; Van Doesberg and DeJong, 1976a, 1976b; Hansen and Jorgensen, 1977;Sharma and Hughes, 1979).The wrong-way behavior may damage the catalyst and initiate undesired side reactions. The need to avoid it complicates the control policies and start-up and shut-down procedures of packed-bed reactors. At present lengthy numerical simulations are required to determine when this behavior may be encountered and its magnitude.The purpose of this work is to identify the key rate processes and parameters which cause this behavior and to develop a simple technique for a priori prediction of the highest transient temperature without solving the transient equations. This is accomplished by analyzing the dynamic response of a plug-flow pseudo-homogeneous model of a packed-bed reactor using the method of characteristics. First, we determine the structure of the solution and the conditions for which a wrong-way behavior occurs for a zeroth-order reaction in either a cooled or an adiabatic reactor. We examine then how this behavior is modified by a rate expression for which the reactants are not completely consumed and by intraparticle diffusional resistances. CONCLUSIONS AND SIGNIFICANCEThe analysis indicates that for a zeroth-order reaction the wrong-way behavior occurs only if the reactor is longer than a critical length of z,i. The highest transient temperature increases with reactor length until the reactor is of length z~,~. For 1981.downstream of zrfl.any reactor shorter than z,,, and longer than zri the highest transient temperature is encountered at the exit of the reactor. For a cooled reactor longer than zc.fl the limiting transient-peak temperature occurs at z,,,. For an adiabatic reactor the limiting transient-peak temperature is encountered at all points

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confidence: 62%

Wrong‐way behavior of packed‐bed reactors: 1. The pseudo‐homogeneous model

1981

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“…Consequently a strong non-linearity is introduced. If this is so, and bearing in mind that above the threshold the oscillation frequency and amplitude vary little with either time or cadmium concentration, the oscillations may well be interpreted as limit cycling (Auslander et al, 1974).…”

Section: A Mechanism For Inhibitory Thresholdsmentioning

confidence: 99%

Dynamics of Growth Control in a Marine Yeast Subjected to Perturbation

Stebbing¹,

Norton²,

Brinsley³

1984

Microbiology

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Normalized specific growth rates of cultures of the yeast Rhodotorula rubra apparently indicate the activity of a growth control mechanism, when growth is perturbed with low concentrations of a toxic inhibitor (cadmium). Data from a number of experiments, in which different cadmium concentrations were used, indicate non-linear growth control dynamics and some features of a model structure, but do not permit it to be defined. Interpretation of the oscillatory behaviour as the response of a control mechanism to perturbation suggests that inhibition of mean growth rates, indicated by a threshold on dose-response curves, is due to overloading of the control mechanism or 'saturation'. Hormesis, the tendency of subinhibitory levels of typically toxic agents to stimulate growth, is a consequence of transient or sustained overcorrections by the control mechanism to low levels of an inhibitory stimulus.

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“…A very common methodology of modeling a hydraulic system can be found in [10]. If we assume that the flow is linear (since the variations in the liquid level are bounded and the rate not arbitrarily fast) the hydraulic system equations are:…”

Section: Hydraulic System Modelingmentioning

confidence: 99%

Robust control of a MIMO thermal-hidraulic process with sensor compensation in real time

López-Moralès

Valdés-Asiain²

2005

JART

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The main goal of this paper is twofold: To show a kind of robustness in a nonlinear multivariable (NL MIMO) system with feedback control, by employing some linearization and observation techniques well known in reference kind of model; and at the same time it is a proposal to immunize the measurements of a level capacitance-based sensor when there are changes in the measured variables properties, by employing an on-line compensation. The MIMO thermal-hydraulic nonlinear system is stabilized when some linearizing conditions are met and a design methodology for using a state feedback scheme is established. In order to assign poles to the control system, the Jacobian linearization is transformed to the controllable canonical form. This is accomplished by the Brunovsky similarity transformation, and by a static state feedback. A Luenberger observer is added to the control system in order to improve its stability. Illustrations of these techniques are shown via numerical and practical simulations carried out directly in the inexpensive physical process.

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Introducing Systems and Control

Cited by 26 publications

References 0 publications

Wrong‐way behavior of packed‐bed reactors: 1. The pseudo‐homogeneous model

Wrong‐way behavior of packed‐bed reactors: 1. The pseudo‐homogeneous model

Dynamics of Growth Control in a Marine Yeast Subjected to Perturbation

Robust control of a MIMO thermal-hidraulic process with sensor compensation in real time

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