Quasi-steady State Model Research Articles

Heat and Mass Transfer in the Process of EB Penetration

The incident energy flux impinged on the free surface of liquid layer was considered to be balanced with the latent heat in evaporation and the heat in directional conduction but neglecting convective heat transfer due to a small Peclet number at the cavity base. The quasi-steady state model was developed in this study to analyze the effect of the energy density during the penetration process and an exponential expression for penetration velocity as a function of liquid-thickness and temperature was also derived. The penetration velocity versus energy density calculated by the present model showed good agreements with the experimental data for drilling copper, which the relative errors between the calculated and the experimental data are less than 15%. By the setup of non-uniform grids distribution in numerical method, this work had successfully predicted the variation of the penetration velocity with energy density distribution. The effects of the energy density on flow rate, thickness of liquid layer, base temperature of fusion zone had also been discussed in this study.

Indirect Cooling Crystallization Process Analysis

A quasi-steady state model is developed for the analysis of cyclically operated continuous cooling crystallization processes used in the recovery of hydrated salts from brines. When reliable correlations for the progressive deterioration of the clean heat transfer coefficients and for salt solubility under the prevailing industrial conditions are available, the model provides for a rational approach towards the optimization of the design and operation of cooling crystallizers. The numerical solution of the model equations enables the quantitative investigation of the effects of various design and operating variables such as brine feed flow rate, coolant flow rate, available heat transfer surface and total cycle time on crystals yield and fractional recovery, as well as the effects of constraints on the availability of refrigerated coolant on the overall system performance. The systematic application of the model is illustrated by considering a two stage crystallization train for Glauber salt recovery from lake brine using experimentally generated data on the evolution of the heat transfer coefficient and on Na 2SO 4 solubility in the lake brine. Extensive results illustrate the trade offs associated with alternative operating policies.

Assessment of building cooling energy need through a quasi-steady state model: Simplified correlation for gain-loss mismatch

The objective of this work is to implement a simplified calculation procedure for building net energy need, based on a quasi-steady state model and on a monthly data set. In particular, it is intended to supply a formulation of the dynamic parameters and to adapt them to Italian climatic, typological, constructive and user data. The method was validated by determining the numerical correlations of the gain/loss utilization factor, through a comparison with a detailed building energy simulation software (EnergyPlus). The simulation was run on some test rooms defined by CEN (European Committee for Standardization) and on some real buildings that are representative of the Italian building stock, assuming weather data from different Italian locations (Torino, Roma, Palermo). The work shows that the accuracy of results is greatly affected by nonlinearities in the determination of the heat transfer and that the dynamic parameters are sensitive to some building features which are not taken into account in the CEN correlations.

Simulation of active tectonic processes for a convecting mantle with moving continents

Numerical models are presented that simulate several active tectonic processes. These models include a continent that is thermally and mechanically coupled with viscous mantle flow. The assumption of rigid continents allows use of solid body equations to describe the continents' motion and to calculate their velocities. The starting point is a quasi-steady state model of mantle convection with temperature/pressure-dependent viscosity. After placing a continent on top of the mantle, the convection pattern changes. The mantle flow subsequently passes through several stages, eventually resembling the mantle structure under present-day continents: (a) Extension tectonics and marginal basins form on boundary of a continent approaching to subduction zone, roll back of subduction takes place in front of moving continent; (b) The continent reaches the subduction zone, the extension regime at the continental edge is replaced by strong compression. The roll back of the subduction zone still continues after closure of the marginal basin and the continent moves towards the upwelling. As a result the ocean becomes non-symmetric and (c) The continent overrides the upwelling and subduction in its classical form stops. The third stage appears only in the upper mantle model with localized upwellings.

A Comparative Study of the Mass and Heat Transfer Dynamics of Evaporating Ethanol/Water, Methanol/Water, and 1-Propanol/Water Aerosol Droplets

The mass and heat transfer dynamics of evaporating multicomponent alcohol/water droplets have been probed experimentally by examining changes in the near surface droplet composition and average droplet temperature using cavity-enhanced Raman scattering (CERS) and laser-induced fluorescence (LIF). The CERS technique provides a sensitive measure of the concentration of the volatile alcohol component in the outer shell of the droplet, due to the exponential relationship between CERS intensity and species concentration. Such volatile droplets, which are probed on a millisecond time scale, evaporate nonisothermally, resulting in both temperature and concentration gradients, as confirmed by comparisons between experimental measurements and quasi-steady state model calculations. An excellent agreement between the experimental evaporation trends and quasi-steady state model predictions is observed. An unexpectedly slow evaporation rate is observed for the evaporation of 1-propanol from a multicomponent droplet when compared to the model; possible explanations for this observation are discussed. In addition, the propagation depth of the CERS signal, and, therefore, the region of the droplet from which compositional measurements are made, can be estimated. Such measurements, when considered in conjunction with quasi-steady state theory, can allow droplet temperature gradients to be measured and vapor pressures and activity coefficients of components within the droplet to be determined.

Dynamic behavior of a direct expansion evaporator under frosting condition. Part I. Distributed model

A general distributed model with two-phase flow for refrigerant coupled with a frost model is developed for studying the dynamic behavior of an evaporator. The equations are derived in non-steady-state manner for the refrigerant and a quasi-steady state model with permeation for the frost. The complex flow and geometry of the finned tube evaporator lead to uneven wall and air temperature distributions, which in turn affect the rate of frost growth and densification along the coil depth. Results include frost accumulation and its effect on energy transfer, air off-coil temperature, refrigerant liquid dry-out position and propagation of frost formation along the coil.

Extraction of sunflower oil with supercritical CO 2: Experiments and modeling

Extraction of sunflower oil from sunflower seeds ( Heliantus annuus L.) using supercritical CO 2 was studied. The shrinking core model was applied to the modeling of the packed-bed extraction process. The experimental data were obtained for extraction conducted at the pressures of 20, 30, 40, 50 and 60 MPa; the temperatures of 313, 333 and 353 K, the CO 2 flow rates of 1–4, and 6 cm 3 CO 2 min −1; the mean particle diameters of 0.23, 0.55, 1.09, 2.18 mm. The supercritical CO 2 extraction process was modeled by a quasi steady state model as a function of extraction time, pressure, temperature, CO 2 flow rate, and particle diameter. The supercritical CO 2 extraction process. The intraparticle diffusion coefficient (effective diffusivity) D e was used as adjustable parameter. The model using the best fit of D e was correlated the data satisfactorily.

Study on Vibrational Distribution of D2 Molecules in Edge Plasmas

The molecules's behavior in edge plasma is very important in understanding the phenomena near plasma-facing materials. In this paper, various processes of deuterium molecules are discussed and most recent data are applied in the evaluation of molecules' vibrational excitation. For the excitation of the molecules to triplet states, complete sets of vibrationally-resolved cross sections are not available from the literatures. Semi-classical Gryzinski method is used to calculate these cross sections and rate coefficients. Finally, The vibrational distribution of deuterium molecules is calculated by applying a quasi-steady state model for the balance of the vibrational populations. The dependence on the plasma parameters is discussed.

Application of Quasi Steady-State Model to Slow Mode Periodic Pulsation of the Liquid in Trickle Bed Reactors

ABSTRACT Many published studies show the benefits of forced pulsation of the liquid flow rate in a trickle bed reactor, especially when mass transfer phenomena are rate controlling. Two types of periodic liquid pulsation, the slow and fast mode, are examined in the literature, depending on the period of the pulsation. The aim of this work is to show that, when slow mode pulsation occurs, the quasi steady-state model can be applied. The model assumes that the mean conversion rate in pulsed mode is the weighted mean of the two steady conversion rates at the minimum and maximum liquid flow rates. In fact, the period of the liquid pulsation is long enough to allow the reactor to reach the quasi steady-state conditions at every level of the liquid flow rate. The validity of the model is checked with experimental data concerning α-methylstyrene hydrogenation to cumene.

QSSC RE-EXAMINED FOR THE NEWLY DISCOVERED SNeIa

We examine the possible consistency of the quasi-steady state model with the newly discovered SNe Ia . The model assumes the existence of metallic dust ejected from the SNe explosions, which extinguishes light travelling over long distances. We find that the model shows a reasonable fit to the data, which improves if one take account of the weak gravitational lensing effect of the SNe which have been observed on the brighter side.

On rotationally driven meridional flows in stars

A quasi-steady state model of the consequences of rotation on the hydrodynamical structure of a stellar radiative zone is derived, by studying in particular the role of centrifugal and baroclinic driving of meridional motions in angular-momentum transport. This nonlinear problem is solved numerically assuming axisymmetry of the system, and within some limits, it is shown that there exist simple analytical solutions. The limit of slow rotation recovers Eddington-Sweet theory, whereas it is shown that in the limit of rapid rotation, the system settles into a geostrophic equilibrium. The behaviour of the system is found to be controlled by one parameter only, linked to the Prantl number, the stratification and the rotation rate of the star.

Consequences for some dark energy candidates from the type Ia supernova SN 1997ff

We examine the status of various dark energy models in light of the recently observed SN 1997ff at z≈1.7. The modified data still fit a pure cosmological constant Λ or a quintessence with an equation of state similar to that of Λ. The kinematical Λ models, Λ∼S−2 and Λ∼H2, also fit the data reasonably well and require less dark energy density (hence more matter energy density) than is required by the constant Λ model. However, the model Λ∼S−2 with low energy density becomes unphysical as it cannot accommodate higher redshift objects. We also examine an alternative explanation of the data, namely the absorption by the intervening whisker-like dust, and find that the quasi-steady state (QSS) model and the Friedmann-Robertson-Walker (FRW) model Ωm0=0.33without any dark energy also fit the data reasonably well. We notice that the addition of SN 1997ff to the old data has worsened the fit to most of the models, except a closed FRW model with a constant Λ and a closed quintessence model with ω=-0.82, and the models have started departing from each other as we go above z=1. However, to make a clear discrimination possible, a few more supernovae with z>1 are required. We have also calculated the age of the Universe in these models and find that, in the models with a constant Λ, the expansion age is uncomfortably close to the age of the globular clusters. Quintessence models show even lower age. The kinematical Λ models are, however, interesting in this connection (especially the model Λ∼H2), as they give a remarkably large age of the Universe.

Reaction Kinetics of Immobilized-Cell Denitrification. II: Experimental Study

Laboratory experiments were conducted to characterize the performance of an immobilized-cell denitrification process treating nitrate-contaminated groundwater and to provide supporting data for the validation of a quasi-steady state model based on half-order reaction kinetics. The treatment process consists of laboratory-scale, plug-flow reactors packed with biocatalyst particles. Pseudomonas denitrificans (American Type Culture Collection 13867), a heterotrophic denitrifier, was cultured and immobilized in calcium alginate particles. Ethanol was used as the source of organic carbon. Thirty concentration profiles were obtained at four levels of nitrate concentration and at three ranges of flow rate. An analysis of the nitrate and nitrite concentration profiles suggested that a half-order reaction rate model could be used to describe the reduction of both nitrate and nitrite. The half-order reaction rate constants for nitrate and nitrite reduction were dependent on the age of the biocatalyst particles and ...

A Different Approach to Cosmology: From a Static Universe Through the Big Bang Towards Reality

Preface 1. Introduction 2. Early relativistic cosmology 3. The observational revolution 4. The observational trail 1931, the determination of H0 and the age dilemma 5. Changing times 1945-1965: New techniques and new people 6. The extension of the redshift apparent magnitude diagram to faint galaxies 1956-1995 7. The classical steady state cosmological model and its observational tests 8. The cosmic microwave background, an historical account 9. The origin of the light elements 10. A new primordial calculation of Y and D/H 11. The new observational evidence and its interpretation: (a) quasi-stellar objects and redshifts 12. The new observational evidence and its interpretation: (b) ejection phenomena and energetics 13. Modern Friedmann cosmology 14. Standard cosmology 15. New cosmological models 16. The observational evidence explained in terms of the quasi-steady state model 17. The intrinsic redshift problem 18. Creation centers and black holes 19. Modern observations of faint galaxies and related objects 20. Large scale distribution of matter 21. A brief account of the radiation fields in the universe: the observations and their interpretation 22. Summary 23. Some unsolved problems.

Numerical Study on the Two-Dimensional Heat Flow in High-Power Density Welding Process

This work presents a two-dimensional quasi-steady state model to study the fluid flow and heat transfer in high-power density welding process of thin AISI-304 stainless steel plates. The enthalpy method and the finite volume method were used for a numerical analysis of the mushy region phase change as well as the heat flow at the weld pool and the heat-affected zone. The results show that the mushy region distributed around the weld pool becomes wider downstream and the surface heat losses by convection and radiation can be significant factors in welding process especially when a welding speed is relatively low.

Optimal design and operation of a multi-product batch distillation column using dynamic model

Although the operation of a batch distillation column involves dynamic behavior from the beginning to the end, the quasi-steady state model or the short-cut method has been widely implemented in the design of the column owing to simple computation in spite of the expected discrepancy with real process operation. In this study, a dynamic process model is utilized in the optimal design of the batch distillation process and the successive quadratic programming is employed as an optimization procedure. A ternary system is examined to see that the dynamic model design gives a significant improvement, especially for the operation having a dynamic manipulation of reflux ratio. The outcome of the optimization for the example system indicates that more amount of product with less operation time than that of the quasi-steady model is available. In addition, the optimization of net profit tells that the optimum number of trays is 23 for the sample system. The optimum operation schedule of the system is also obtained from the optimization of operational profit. Finally, the effect of side product recycle is investigated.

Modeling of high-temperature catalytic combustors: Comparison between theory and experimental data

The objective of this work was to model experimental results using the simplest possible mathematical model. Here we report on preliminary results obtained with a one-dimensional model used for parameter-fitting of experimental combustion data with an inlet temperature ramp. It was possible to fit our one-dimensional model with simple power law kinetics to an experimental curve. It was also possible to use a quasi-steady state model with a computing time about a hundred times shorter than for a corresponding transient model.

Thermal Field Simulation of LEC Process by Finite Volume Method

Thermal field is obtained for the Liquid Encapsulated Czochralski process by Quasi-Steady State Model. Our model includes the effects of convective heat transfer in the melt and radiational heat transfer of the equipment surfaces. To calculate the radiational heat flux, the view factor calculation is performed. Encapsulant layer is assumed to be totally opaque or transparent to the radiation. The thermal field formation and the temperature of the heater depend on the thermal transparency of the encapsulant layer. The effects of melt flow and thermal transparency of the encapsulant layer are analysed. The proposed model can be extended to the semi-transparent model and used as thermal field prediction model for optimization of LEC process.

Simulation of an Atmospheric Residue Desulfurization Unit by Quasi-Steady State Modeling

The current trend in petroleum refining is to maximize the conversion of the bottom of the barrel to improve the profitability of the refinery. Atmospheric residue desulfurization (ARDS) plays a key role in this, especially, when processing crudes with moderate to high sulfur contents. A deterministic quasi-steady state model has been developed to simulate the long term behavior of the reaction section of an atmospheric residue desulfurization (ARDS) unit, consisting of four co-current catalytic trickle bed reactors in series. The model uses the properties of the feedstock and the catalyst and is capable of simulating profiles of sulfur, coke, and metal depositions and the temperature along the reactors, taking into account also catalyst deactivation. Hydrogen quenching has also been simulated and simulation results predict all the essentials of the long term behavior of both experimental and industrial scale ARDS reactors satisfactorily. Comparing the simulation results with actual commercial data, the model predicted perfectly the middle part of the run. The model is unable to simulate the End-of-Run conditions due to pore mouth plugging phenomenon.

Simulation of an Atmospheric Residue Desulfurization Unit by Quasi-Steady State Modeling

The current trend in petroleum refining is to maximize the conversion of the bottom of the barrel to improve the profitability of the refinery. Atmospheric residue desulfurization (ARDS) plays a key role in this, especially, when processing crudes with moderate to high sulfur contents. A deterministic quasi-steady state model has been developed to simulate the long term behavior of the reaction section of an atmospheric residue desulfurization (ARDS) unit, consisting of four co-current catalytic trickle bed reactors in series. The model uses the properties of the feedstock and the catalyst and is capable of simulating profiles of sulfur, coke, and metal depositions and the temperature along the reactors, taking into account also catalyst deactivation. Hydrogen quenching has also been simulated and simulation results predict all the essentials of the long term behavior of both experimental and industrial scale ARDS reactors satisfactorily. Comparing the simulation results with actual commercial data, the model predicted perfectly the middle part of the run. The model is unable to simulate the End-of-Run conditions due to pore mouth plugging phenomenon.