Population balance models for the thermal degradation of PMMA

A widely accepted view of the thermal degradation of polymers such as PMMA is that an initiation reaction produces radical fragments that undergo rapid depropagation and are also converted back to molecules by a termination reaction. This mechanism is applied to a population of linear molecules and radicals and the evolution of the population is modelled by appropriate discrete sets of ordinary differential equations. In particular, end-chain and random initiation reactions with first-order termination are analysed and compared with experimental data. We find on comparison with TG data for PMMA that the initiation reaction is important in dictating the qualitative behaviour of the overall rate of thermal degradation. Furthermore, the behaviour of degradation rate with initial degree of polymerisation is also investigated and interpreted within the framework of the model.     

Solving population balance equations for two-component aggregation by a finite volume scheme

A conservative finite volume approach, originally proposed by Filbet and Laurençot [2004a. Numerical simulation of the Smoluchowski coagulation equation. SIAM Journal on Scientific Computing 25(6), 2004-2048] for the one-dimensional aggregation, is extended to simulate two-component aggregation. In order to apply the finite volume scheme, we reformulate the original integro-ordinary differential population balance equation for two-component aggregation problems into a partial differential equation of hyperbolic-type. Instead of using a fully discrete finite volume scheme and equidistant discretization of internal properties variables, we propose a semidiscrete upwind formulation and a geometric grid discretization of the internal variables. The resultant ordinary differential equations (ODEs) are then solved by using a standard adaptive ODEs-solver. Several numerical test cases for the one and two-components aggregation process are considered here. The numerical results are validated against available analytical solutions.     

Coupled population balance–CFD simulation of droplet breakup in a high pressure homogenizer

A framework for a one-way coupling between population balance equation (PBE) and computational fluid dynamics (CFD) for emulsions undergoing breakup in a turbulent flow-regime is implemented in the open-source CFD package OpenFOAM. The PBE is discretized using a volume conservative scheme. This framework was applied to emulsification of food-grade vegetable oil-in-water emulsions in a Niro Soavi high pressure homogenizer (HPH) with different pressure drops and using oils of varying viscosities. Different breakage rate models were implemented, as well as the model of Becker et al. (2014) which is an extension of the Luo and Svendsen (1996) model to account for the dispersed phase viscosity. The Becker et al. (2014) model was found to give better predictions after three consecutive passes, without the need for additional empirically determined parameters. The multi-scale PBE–CFD modelling approach allowed a detailed analysis of the breakup process in the gap and jet of the HPH valve.     

Integral approximation—an approach to reduced models for particulate processes

In this contribution, a model reduction technique for population balance systems describing particulate processes is presented. This technique is based on integral approximation and allows the derivation of highly accurate moment models. In contrast to other model reduction methods which can be found in literature, this integral approximation technique can be applied for arbitrarily complex phenomena specifications. The applicability of the presented method will be demonstrated for different example processes by comparing the dynamic behavior of the original population balance models with those of the derived reduced models of moments.     

Population balance modeling of bubble size distributions in a direct-contact evaporator using a sparger model

The study of bubble size distributions in direct-contact evaporators was addressed both theoretically and experimentally. Recently developed models for calculating bubble coalescence and breakage frequencies in isothermal bubble columns were adapted to the population balance equation using the bubble mass as the internal coordinate which was discretized using an expansion of the number density function by impulse functions. A sparger model was developed based on experimental data for a non-coalescing system and using bubble formation models for isothermal and non-isothermal conditions. Bubble size distributions in a direct-contact evaporator operating in the quasi-steady-state regime for four different gas superficial velocities, including the homogeneous and heterogeneous regimes, together with the sparger model, were used for estimating the three empirical parameters from the population balance model, which were observed to be functions of the gas superficial velocity. In all cases considered, the population balance model fitted the experimental data rather well and the regressed parameters exhibit the physically expected behavior with changes in the gas superficial velocity.     

Approximate ODE models for population balance systems

We propose an approximate polynomial method of moments for a class of first-order linear PDEs (partial differential equations) of hyperbolic type, involving a filtering term with applications to population balance systems with fines removal terms. The resulting closed system of ODEs (ordinary differential equations) represents an extension to a recently published method of moments which utilizes least-square approximations of factors of the PDE over orthogonal polynomial bases. An extensive numerical analysis has been carried out for proof-of-concept purposes. The proposed modeling scheme is generally of interest for control and optimization of processes with distributed parameters.     

Modeling and simulation of mixing in water-in-oil emulsion flow through a valve-like element using a population balance model

Emulsion flows are very common in natural processes as well as in several engineering areas, such as in the process of desalting crude oil that occurs in refineries. This kind of flow is described as a polydispersed multiphase flow. In this work, we evaluated the behavior of water-in-oil emulsion flowing through a duct with an element used to mimic the effect of a globe valve. An Eulerian multi-fluid approach was employed by solving the population balance equation coupled with computational fluid dynamics. Coalescence and breakage models recently developed were extended to this inhomogeneous model. A bivariate population balance problem was also solved to demonstrate the mixing caused by the valve-like element. The simulated results showed good agreement with the available experimental data for the Sauter and DeBroukere mean diameters.     

MPEG-4道路监控视频压缩卡

文中结合目前监控技术,提出基于PCI总线的MPEG-4视频压缩卡设计方案.该方案可通过软件设置监控参数,以满足多种监控要求,应用范围广,有较好得社会效益.     

基于Web的实有人口信息综合服务平台

在如今人口流动如此平凡的状况下,以往以“户籍制度”管理人口的方式已经完全不能够满足对流动人口信息的掌握,因此现在提出以“以房管人”的理念管理实际居住人口,这种管理模式是符合目前流动人口管理的一种有效方式。通过结合．NET平台、数据库和当前流行的Ajax技术等相关计算机技术,以B／s结构模式开发浦兴社区实有人口信息综合服务平台,来达到对实有人口信息的管理和为各个业务部门提供完整的数据共享模式,为整个社区的电子政务提供服务。     

Different perspectives: A comparison of newspaper articles to medical examiner data in the reporting of violent deaths

This study compared violent death information reported in state-wide newspaper articles to the medical examiner reports collected for a state public health surveillance system—the National Violent Death Reporting System (NVDRS). While suicides accounted for 83% of deaths in the NVDRS database, more than three-quarters (79%) of violent deaths reported in newspaper articles were homicides. The majority of the suicide incidents were reported in 1-2 newspaper articles whereas the majority of homicide incidents were reported in 11-34 articles. For suicide incidents, the NVDRS reported more circumstances related to mental health problems while newspaper articles reported recent crisis more often. Results show that there is a mismatch in both frequency and type of information reported between a public health surveillance system (NVDRS) and newspaper reporting of violent deaths. As a result of these findings, scientists and other public health professionals may want to engage in media advocacy to provide newspaper reporters with timely and important health information related to the prevention and intervention of violent deaths in their community.