摘要:

The two-dimensional Benard convection process is numerically simulated using a modified Marker and Cell finite difference method where the temperature equation is solved implicitly at every time step. Effects of the initial conditions, end-wall boundary conditions, Rayleigh number, Prandtl number, and aspect ratio on the development of the convection process and steady-state solution have been investigated. It is found that the Benard convection process is an initial value problem in the sense that the steady-state solution depends on the initial perturbation. If small scale perturbations are added in the initial temperatures, flow development and steady-state convergence is quicker. It is also found that when an appropriate aspect ratio is chosen, an infinite horizontal extent Benard system can be successfully and economically simulated using a small computational domain with periodic end-wall boundary conditions. The critical Rayleigh numbers are also predicted which agree closely with other published values. The critical Rayleigh number for infinite horizontal extent system is found to be independent of the fluid Prandtl number. The Row behavior and patterns at higher Rayleigh numbers are also investigated.

ISSN:0098-6445    

DOI:10.1080/00986449408936222

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Bubble column reactors are widely used in many industrial applications due to their simplicity of operation. Although simple to operate, bubble columns are difficult to scale-up due to the uncertainties in the estimation of some non-adjustable design parameters. One of these design parameters is the liquid phase backmixing.

ISSN:0098-6445    

DOI:10.1080/00986449408936223

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Colloidal Gas Aphrons (CGA) are finding increasing application in wastewater processing, bioseparations,etc. This article describes effect of various operating conditions such as pH, power input, impeller location, surfactant type and its concentration and viscosity of liquid on half life of CGA generated. Further, effects of various additives like, polymer, enzyme, solvents, salt, etc. are also investigated. A procedure for predicting the drainage rate of CGA has been proposed.

ISSN:0098-6445    

DOI:10.1080/00986449408936224

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A novel method for designing Kalman Predictor (KP) based multivariable self-tuning controllers for Multi Input Multi Output (MIMO) systems has been proposed, and also applied to the control of two distillation columns. The objective is to maintain constant terminal compositions despite disturbances entering the system even when the controlled variables are not measured at the same sampling rate. The KP generates minimum variance estimates of the output variables. Simulation results show that KP based multirate multivariable self-tuning controller exhibits better performance than the earlier reported multirate controller for set point tracking, even in the presence of nonstationary disturbances. KP based self-tuning controller is, therefore, suitable for industrial applications.

ISSN:0098-6445    

DOI:10.1080/00986449408936225

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0098-6445    

DOI:10.1080/00986449408936226

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this work, visual observation as well as the probability density function and the standard deviation of the pressure drop fluctuation were used for determination of the boundary of trickling-to-pulsing flow transition. Extensive experimental work was carried out with air and three liquid media on four kinds of packings. Experimental results indicate the transition depends on the physical properties of liquid (viscosity and surface tension), gas and liquid flow rates as well as the size and shape of packing particles. The Baker coordinates (Baker, 1954) used in the flow map as proposed by Charpentier and Favier (1975) was examined. It is found that application of the flow pattern map in this form is of rather limited universality. Two new correlations were proposed with satisfactory prediction of the liquid flow rates for the transition of trickling-to-pulsing flow.

ISSN:0098-6445    

DOI:10.1080/00986449408936227

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An analytical study is made into the process of heat transfer with the vapor condensation on a horizontal tube embedded in porous media. As in classical film condensation problems, it is assumed that (1) the condensate and the vapor are separated by a distinct boundary with no two-phase zone in between, and (2) the condensate has constant properties. Within boundary layer approximation as in Nusselt-type condensation theory, analytical expressions for both local condensate film thickness and heat transfer coefficient around the elliptical periphery have been derived under the effects of gravity and surface tension for various values of ellipticity. The dimension less mean heat transfer coefficient— Nu for various ellipticitieseand Bond numbersBohas been obtained; however, it is nearly unaffected by surface tension force due to surface curvature varying.

ISSN:0098-6445    

DOI:10.1080/00986449408936228

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The effect of square-wave concentration-forcing operation on the rate of methanol production over two industrial catalysts was studied at 513 K and 2.86 MPa total pressure. Improvements as high as 25 percent relative to the optimal steady-state methanol production rate, in moles per gram catalyst per unit time, were obtained over BASF's S 3-85 catalyst. This occurred in a laboratory-scale fixed-bed reactor with gas mixing for a cycling time of τ = 12 seconds and for a cycle split relative to carbon monoxide of γCO= 0.20, the rest of the cycle being hydrogen. Improvements as high as 15 percent were also obtained over Imperial Chemical Industries ICI 51-2 catalyst, in a differential plug-flow reactor for τ = 24 seconds and γCO= 0.15. These improvements were obtained for pure-component steady cycling between carbon monoxide and hydrogen with a constant carbon dioxide molar concentration of 2 per cent (BASF catalyst) or 3 percent (ICI catalyst) present in both parts of the cycle. On the other hand, no improvement over the optimal steady state was found for cycling between carbon monoxide and carbon dioxide with a constant molar concentration of 61 % hydrogen nor between hydrogen and mixtures of carbon monoxide and hydrogen such as 19.6/78.4 mole percent mixture of CO/H2.

ISSN:0098-6445    

DOI:10.1080/00986449408936229

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the present paper a comparative consideration is given for the physico-chemical phenomena involved in homogeneously and heterogeneously catalyzed reactive distillation processes (RDP). The processes are classified qualitatively by dimensionless parameter groups derived from the balances for vapor, liquid and solid phases according to the principles of irreversible thermodynamics. The groups are applied to analyze industrial processes and experimental data for esterification, etherification and alkylation regarding different catalysts, operating conditions and configurations of plants. The mathematical models published until today and the experimental results are contrasted taking the parameter groups as a basis. This gives a discrimination of the models and some recommendations for their applicability.

ISSN:0098-6445    

DOI:10.1080/00986449408936230

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An experimental program has been initiated to evaluate the performance of a reciprocating plate bioreactor for its use in viscous fermentations. The investigation is divided into three parts: (1) to study the hydrodynamics within the bioreactor, (2) to determine the axial dispersion coefficient and the overall oxygen mass transfer coefficient as a function of the operating conditions, and (3) the evaluation of a reciprocating plate column as a bioreactor for viscous fermentations. This paper reports on the determination of the axial dispersion coefficient and on the measurement of the overall oxygen transfer coefficient. Experiments were done in water on a semi batch scheme (no water flow) in a 1.26m high and 101.6mm internal diameter column.

ISSN:0098-6445    

DOI:10.1080/00986449408936231

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor