ANALYSIS OF EXPERIMENTAL AND NUMERICAL RESULTS OF A TURBULENT SWIRLING FLOW IN A TUBE

In many applications swirling flow is used to enhance heat and mass transfer. One of the problems of modelling a turbulent swirling flow is the choice of the turbulent closure model which is acceptable for engineering purposes. To evaluate which model performs best, numerical results are compared with experimental data. Local velocity measurements are carried out on a swirling flow in a circular tube. The measurement method is hot-wire anemometry combined with visualization techniques. The numerical analysis is carried out using the k-ε model and the Algebraic Stress Model. In the experiment a symmetrical swirl was observed, Comparing the experimental data with the numerical results shows that the Algebraic Stress Model represents the experimental data quite well, whereas the k-ε model fails.     

CAD与CAPP集成研究回转体类零件特征识别

本文研究了回转体轴类,轴套类零件的特征识别。对这类零件常用的特征单元进行了定义,描述了这类零件的特征模型:介绍了它的识别方法和特征参数定义方法。     

Simulation of nitrogen dynamics and biomass production in winter wheat using the Danish simulation model DAISY

A dynamic simulation model for the soil plant system is described. The model includes a number of main modules, viz., a hydrological model including a submodel for soil water dynamics, a soil temperature model, a soil nitrogen model including a submodel for soil organic matter dynamics, and a crop model including a submodel for nitrogen uptake. The soil part of the model has a one-dimensional vertical structure. The soil profile is divided into layers on the basis of physical and chemical soil characteristics. The simulation model was used to simulate soil nitrogen dynamics and biomass production in winter wheat grown at two locations at various levels of nitrogen fertilization. The simulated results were compared to experimental data including concentration of inorganic nitrogen in soil, crop yield, and nitrogen accumulated in the aboveground part of the crop. Based on this validation it is concluded that the overall performance of the model is satisfactory although some minor adjustments of the model may prove to be necessary.     

ON THE UNIMODALITY OF THE EXACT LIKELIHOOD FUNCTION FOR NORMAL AR(2) SERIES

Abstract. For stationary second-order autoregressive normal processes, the conjecture of uniqueness of the solution of the exact likelihood equations is examined. A sufficient condition for uniqueness is given; this condition is satisfied with very high probability if the number of observations is not extremely small. Moreover, it is shown that not more than two maxima may exist. Examples of data which actually produce a likelihood function with two local maxima are given.     

Pervaporation performance analysis and prediction—using a hybrid solution-diffusion and pore-flow model

A hybrid mathematic model for pervaporation is proposed which incorporates the concepts of solution-diffusion model and pore model. The model allows performance prediction as well as the establishment of the internal concentration and pressure profiles within the membrane. The model parameters specific to the particular membrane and mixture system are determined using liquid sorption and pervaporation experimental data. The model is experimentally examined using ethanol–water mixtures and poly(dimethyl siloxane)–poly(vinyldiene fluoride) (PDMS–PVDF) composite membranes. The characteristics of flux and separation factor predicted using the model are in fair agreement with the experimental data under various feed concentrations and downstream pressures for different membrane arrangements, including single-layer, reverse single-layer and double-layer PDMS–PVDF composite membranes. Internal profiles of pressure, concentration and component mole fraction can be established using the model. Concentration polarization phenomena for ethanol and water are located at membrane interfaces and vapor–liquid interfaces, respectively. Performances of several different membrane designs are compared using the model.     

Packed-microtubes model for flowthrough chromatography of protein

A mathematical model for flowthrough (perfusion) chromatography, namely packed-microtubes (PMT) model, has been proposed for a column packed with biporous (BiP) anion exchanger in which the mesopores and flowthrough pores are created with liquid and solid porogens, respectively. The model is established based on the assumption that the BiP particle is made up of packed microtubes. Bovine serum albumin (BSA) is used as a model protein and three kinds of anion exchangers (i.e., mesoporous, macroporous and BiP resins) are used as adsorbents to determine the model parameters and to evaluate the model. Adsorption equilibrium and finite bath experiments are performed to determine the adsorption isotherms and kinetics parameters. Both the bound amounts of the protein on the surface of the mesopores and macropores are experimentally determined and taken into account in the mathematical model. With all the model parameters determined by independent experiments or calculated from available correlations, model simulations are performed and compared with the experimentally determined breakthrough profiles of the BiP column. It is found that the model predictions agree reasonably well with the experimental data obtained under various conditions and the PMT model fit experimental data better than the modified double linear driving force (LLDF) model proposed by Leitão and Rodriogues (1999. Biochemical Engineering Journal 3, 131) in which the adsorbent particle is considered to be made up of packed microparticles. The results indicate that the PMT model is more reasonable for this kind of BiP adsorbent.     

Dynamics of fluid circulation in coupled free and heterogeneous porous domains

Fluid flow in coupled free and porous domain, particularly when the porous medium is heterogeneous, is encountered in many hydro-environmental conditions, e.g., leakage from underground pipe, combined groundwater lake-subsurface interactions. One of the most difficult problems in the study of coupled flow behaviour has been the development of a universally applicable modelling scheme for combining the flow regimes. This is because the free/porous interfacial properties (e.g., shear-stress; velocity slip) that govern the coupled flow behaviour are difficult to determine experimentally under hydro-environmental conditions. On the other hand, the implications of various forms of heterogeneity in the porous media properties can be very different on the fluid-flow behaviour. Difficulties may also arise in direct coupling of the model equations that govern the fluid flow in the individual regions (e.g., Navier-Stokes for free-flow region and the Darcy's equation for the porous flow region). Consequently, models of coupled free and porous flow for hydro-environmental conditions are not very well developed at the moment. While there are some indications that fluids in coupled free and porous domains may circulate (i.e., development of flow cells), there is a lack of appropriate 3D analysis on how heterogeneities in porous media may affect such flow patterns. In this paper, we aim to analyse how porous media heterogeneity affects the dynamics of flow circulation in the porous side of a coupled free and porous domain. For this purpose, we analyse flow patterns in several model domains made up of two porous layers with differing permeabilities. The governing model equations are discretised and solved using the standard finite volume method on a staggered cell-centred mesh. The temporal discretisation is done using the explicit method. An in-house graphical user interface (GUI) has been created specifically to aid in the visualisation of otherwise complex flow patterns. The GUI contains many post-processing options and provides a comprehensive tool for the analysis of hydrodynamics and contaminant motion (not discussed in this paper) in coupled free and porous flow domains. This GUI is described in this paper briefly. The effects of altering the aspect ratio (i.e., multi-scale) of the domain on the coupled flow pattern have also been discussed.     

The prediction of transport parameters in filamentous fermentation broths based on results obtained in pseudoplastic polymer solutions

Transport phenomena studies on single phase “model” fluids are of limited value in biochemical engineering if they cannot be translated to the heterogeneous systems encountered in real fermentation processes. In this paper we discuss the utility of polymer solutions as models of filamentous fermentation broths for evaluation of: pipeline friction factors and impeller power numbers (turbine and helical ribbon). To a first approximation, polymer solutions can serve as suitable models for the prediction of laminar flow pressure drop in pipelines and turbulent power consumption in stirred tanks. However, results obtained on polymer solutions do not directly apply to filamentous fermentation broths for predictions of laminar flow impeller power consumption and the transition point for turbulent flow in stirred tanks. These discrepancies are believed to result from the existence of a time dependent yield stress in filamentous fermentation broths.     

Thermodynamic assessment of MCl–YCl3 (M=Na,K, Rb,Cs) systems

Thermodynamic properties and phase diagrams of the MCl–YCl₃ (M=Na, K, Rb, Cs) systems were reassessed by using the CALPHAD method with the latest phase diagram data. A two-sublattice ionic solution model (M⁺)_P(Cl⁻, ${\mathrm{YCL}}_6^{3-}$, YCl₃)_Q reflecting the ionic behavior of the components was adopted to describe the liquid phase in the systems. A new set of optimized model parameters was found, and the calculated phase diagrams and enthalpies of mixing have good agreement with experimental data. The calculated liquidus near to YCl₃ side agrees much better with experimental data compared with previous work. In consideration of high and low temperature modifications as well as stability of intermediate compounds, Gibbs energies of formation of these compounds evaluated in the present work are more reasonable.     

Critical transistors nexus based circuit-level aging assessment and prediction

Accurate age modeling, and fast, yet robust reliability sign-off emerged as mandatory constraints in Integrated Circuits (ICs) design for advanced process technology nodes. In this paper we introduce a novel method to assess and predict the circuit reliability at design time as well as at run-time. The main goal of our proposal is to allow for: (i) design time reliability optimization; (ii) fine tuning of the run-time reliability assessment infrastructure, and (iii) run-time aging assessment. To this end, we propose to select a minimum-size kernel of critical transistors and based on them to assess and predict an IC End-Of-Life (EOL) via two methods: (i) as the sum of the critical transistors end-of-life values, weighted by fixed topology-dependent coefficients, and (ii) by a Markovian framework applied to the critical transistors, which takes into account the joint effects of process, environmental, and temporal variations. The former model exploits the aging dependence on the circuit topology to enable fast run-time reliability assessment with minimum aging sensors requirements. By allowing the performance boundary to vary in time such that both remnant and nonremnant variations are encompassed, and imposing a Markovian evolution, the probabilistic model can be better fitted to various real conditions, thus enabling at design-time appropriate guardbands selection and effective aging mitigation/compensation techniques. The proposed framework has been validated for different stress conditions, under process variations and aging effects, for the ISCAS-85 c499 circuit, in PTM 45 nm technology. From the total of 1526 transistors, we obtained a kernel of 15 critical transistors, for which the set of topology dependent weights were derived. Our simulation results for 15 critical transistors kernel indicate a small approximation error (i.e., mean smaller than 15% and standard deviation smaller than 6%) for the considered circuit estimated end-of-life (EOL), when comparing to the end-of-life values obtained from Cadence simulation, which quantitatively confirm the accuracy of the IC lifetime evaluation. Moreover, as the number of critical transistors determines the area overhead, we also investigated the implications of reducing their number on the reliability assessment accuracy. When only 5 transistors are included into the critical set instead of 15, which results in a 66% area overhead reduction, the EOL estimation accuracy diminished with 18%. This indicates that area vs. accuracy trade-offs are possible, while maintaining the aging prediction accuracy within reasonable bounds.