摘要:

The nonlinear dynamics of two-phase flow in heated channels has been studied numerically. Parallel channel density-wave stability analysis has been extended to the case of a simplified loop which includes the heated channel and pump characteristics. A set of two nonlinear functional ODEs obtained for the dynamics of the simplified heated loop with two-phase flow was integrated numerically for parameter values in different regions of the parameter space and various initial conditions. Stable limit cycles exist for parameter values in the region in which the two-phase flow fixed point is unstable, close to the density-wave MSB, and the oscillation amplitude grows monotonically with the distance from the MSB. Delicate dependence upon certain initial histories (t < 0) and initial conditions (f = 0) is found for parameter values for which there exist more than one attracting set-stable fixed points, stable limit cycle.

ISSN:0098-6445    

DOI:10.1080/00986449008940681

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This paper provides a review of the mathematical models to predict heat transfer coefficient in both batch and continuous systems with/without particulates and those related to the thermal process calculation. Heat transfer coefficient based on penetration theory, dimensional analysis and empirical models are also presented. In addition, residence time distribution of product in a scraped-surface heat exchanger (SSHE) and a holding tube with/without particulates is discussed.

ISSN:0098-6445    

DOI:10.1080/00986449008940682

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Combined conduction, convection and radiation heat transfer in a gray fluid-saturated sparsely packed porous medium is examined analytically for marginal convection using linear stability analysis. The effects of boundary and inertia which were absent in the usual Darcy model are considered. The Milne-Eddington approximation is employed to determine the solutions valid for transparent and opaque media which absorbs and emits thermal radiation. It is shown that the nature of the bounding surfaces and radiation significantly influence the critical Rayleigh and wave numbers. The mechanism for suppressing or augmenting convection is discussed in detail. The results obtained using Galerkin technique are compared with the existing results of Darcy model and of non-radiating systems and agreement is found.

ISSN:0098-6445    

DOI:10.1080/00986449008940683

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

In this paper, we shall deal with the control of fedbatch fermentation processes exhibiting substrate inhibition phenumenons. A simple adaptive control scheme based on the nonlinear structure of the system is proposed. It is shown how this adaptive controller can contribute to optimize the process yield without the knowledge of the process kinetics being necessary.

ISSN:0098-6445    

DOI:10.1080/00986449008940684

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The problem of acid deposition and its effects on the environment is receiving increasing attention in North America and Europe. The interaction between

ISSN:0098-6445    

DOI:10.1080/00986449008940685

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A computer model has been developed for the simulation of nucleation, drop growth and deposition processes during the supersonic flow of a gas mixture in a convergent-divergent nozzle and a magnetogasdynamic duct. The analysis is based on quasi-one dimensional magnetogasdynamics and on the assumption that the size of the droplets remains small.

ISSN:0098-6445    

DOI:10.1080/00986449008940686

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Nonlinear Model Predictive Control (NMPC), a strategy for constrained, feedback control of nonlinear processes, has been developed. The algorithm uses a simultaneous solution and optimization approach to determine the open-loop optimal manipulated variable trajectory at each sampling instant. Feedback is incorporated via an estimator, which uses process measurements to infer unmeasured state and disturbance values. These are used by the controller to determine the future optimal control policy. This scheme can be used to control processes described by different kinds of models, such as nonlinear ordinary differential/algebraic equations, partial differential/algebraic equations, integra-differential equations and delay equations. The advantages of the proposed NMPC scheme are demonstrated with the start-up of a non-isothermal, non-adiabatic CSTR with an irreversible, first-order reaction. The set-point corresponds to an open-loop unstable steady state. Comparisons have been made with controllers designed using (1) nonlinear variable transformations, (2) a linear controller tuned using the internal model control approach, and (3) open-loop optimal control. NMPC was able to bring the controlled variable to its set-point quickly and smoothly from a wide variety of initial conditions. Unlike the other controllers, NMPC dealt with constraints in an explicit manner without any degradation in the quality of control. NMPC also demonstrated superior performance in the presence of a moderate amount of error in the model parameters, and the process was brought to its set-point without steady-state offset.

ISSN:0098-6445    

DOI:10.1080/00986449008940687

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The purpose of this paper is to evaluate the effective viscosity of a concentrated Newtonian suspension via spatially periodic approximation and to clarify the results from previously published articies. It is found that singular characteristic of the effective viscosity expression does not disappear. This approximation is then extended to investigate the system of a concentrated non-Newtonian suspension fluid. The results obtained by using the spatially periodic approximation are similar to that of a quasi-steady approximation in terms of the first order of e−1urthermore, the singular behavior also appears in the expression of the effective viscosity both for a second-order-Rivlin-Ericksen fluid at low shear rate and a Harnoy fluid at high shear rate, except that the viscoelastic effect in the low shear rate is depressed by spatially periodic approximation as compared with those orders obtained by quasi-steady approximation.

ISSN:0098-6445    

DOI:10.1080/00986449008940688

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The generality of a pioneering correlation, proposed by Lynch (1) to predict the number of cycles to reach invariant cycling in periodically forced reactors, is evaluated using a model for the methanol synthesis reaction. Results show that Lynch's correlation needs to be modified to include elementary-step kinetics if it is to be generally applicable.

ISSN:0098-6445    

DOI:10.1080/00986449008940689

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Experimental data are presented concerning heat transfer to a sphere immersed into an argon plasma flow. Transient method has been employed to measure the heat flux to the sphere. The temperature and velocity of the thermal plasma flow are about 104K and 102m/s, respectively, while the sphere diameter is 0.68 or 1.0 mm. In preliminary tests, the applicability of the transient method has been demonstrated, and a series of complicated factors which may affect the heat flux measurement have been studied including the diameter and the length exposed to the plasma flow of the thermocouple wires, radiation heat loss from the probe to the surroundings, etc. Experimental results show that the Nusselt number defined based on the LTE (local thermodynamic equilibrium) heat-conduction-potential always assumes a value greater than 2.0. Main error source of the experimental Nusselt numbers is the: plasma temperature measurement.

ISSN:0098-6445    

DOI:10.1080/00986449008940690

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor