Unsteady processes

Uxbridge, June 28-29, 1984 edited by M. Die and G.C.Bond Volume 22 Unsteady Processes in Catalytic Reactors by u.Sh. Matrox... 

Matros, Yu. Sh., Unsteady Processes in Catalytic Reactors. Elsevier Science Publishers, Amsterdam, 1985. 

It has been found that atomization is a pulsating, unsteady process, even if the emerging liquid jet and atomization gas are initially free of oscillation and vibration. 

First of all, the conversion system can be operated in batch or continuous mode [32]. In general, a batch operation is analogous with an unsteady process, whereas a continuous mode is synonymous with a steady state process. A batch bed can therefore be referred to as an unsteady bed in the literature.[9,33]... 

First, it is of common interest to unsteady processes and their models. Chemical unsteadiness must be taken into account in many cases. For example, studies with variations in catalyst activity, calculations of fluidized catalyst bed processes (when the catalyst grain "is shaking in a flow of the reaction mixture and has no time to attain its steady state), analyses of relaxational non-stationary processes and problems of control. Unsteady state technology is currently under development [14,15], i.e. the technology involving programmed variation of the process parameters (temperature, flow rate, concentration). The development of this technology is impossible without distinct interpretation of the unsteady reaction behaviour. 

D. Tondeur and M. Bailly, Unifying concepts in non-linear unsteady processes. Part II Multicomponent waves, competition and diffusion. Chem. Eng. Process., 1987, 22, 91-105. 

In addition to the spatial model dimensions described above, time may be a key factor in the case of an unsteady processes, e.g., when starting up a screw. Co-rotating screws are generally operated continuously, however, so the focus of modeling is on steady processes. The development of a temperature field is described in Section 6.8 as an example of an unsteady starting process. 

During the extraction an unsteady process prevails. The present paper presents an unsteady state mathematical model for a fixed bed extractor (model 1). The overall mass transfer coefficients were calculated by matching the calculated and experimental values of oil loading in CO2. The results are compared with those obtained by the model developed by Catchpole et al, 1994 (model II). Good agreement between both models results and our experimental measurements were obtained, although the model II allows the best fit over the entire extraction curve. 

Steps 1, 2, and 3 The process can be viewed as an unsteady process without reaction in a tank as shown in Fig. E2.16. We first must calculate all the compositions for which data are given. 

In this approach, the unsteady processes occurring in turbulent flows are visualized as a combination of some mean process and small-scale fluctuations around it. The typical time variation of fluid velocity at a point in a turbulent flow is shown in Fig. 3.1. In the statistical approach, an instantaneous velocity, U, is visualized as a mean velocity, U (shown by a horizontal line in Fig. 3.1) and fluctuations around it, u. Based on such an approach, the statistical theory of turbulence flows has been developed (see Hinze, 1975 and references cited therein). It has been the basis for most of the engineering modeling of turbulent flow processes. Some of the key concepts of the statistical approach are discussed below. 

This chapter illustrates heat transfer, diffusion, diffusion with reaction, and flow in pipes, considering steady and unsteady processes. These problems are all solved using FEMLAB , which is easy to use for these applications. Details of the finite element... 

The existence of a kinetic model is a prerequisite for scale-up and simulation calculations. Kinetic modeling of the unsteady process is possible by coupling gas phase and catalyst phase. Calculated and experimental data show good agreement. 

Problem 3-30. A Model for Cell Migration. Cells proliferate and migrate along surfaces in a variety of processes, including healing and the cultivation of tissue on artificial scaffolds. The following mathematical model has been put forward to describe the ID, unsteady process ... 

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