旋转刮膜式分子蒸馏器

分子蒸馏器是分子蒸馏装置的主体设备。本文就分子蒸馏技术的原理与特点、旋转刮膜式分子蒸馏器的结构设计技术、工艺操作要点及其工业化应用等领域进行了探讨。     

Online ice crystal size measurements during sorbet freezing by means of the focused beam reflectance measurement (FBRM) technology. Influence of operating conditions

In ice cream and sorbet manufacturing small ice crystals are desired to deliver a product with a smooth texture and good palatability. This research studied the influence of the operating conditions on the ice crystal size and the draw temperature of the sorbet during the freezing process. The evolution of ice crystal size was tracked with the focused beam reflectance measurement (FBRM) technique, which uses an in situ sensor that makes it possible to monitor online the chord length distribution (CLD) of ice crystals in sorbets containing up to 40% of ice. The refrigerant fluid temperature had the most significant influence on the mean ice crystal chord length, followed by the dasher speed, whereas the mix flow rate had no significant influence. A decrease in the refrigerant fluid temperature led to a reduction in ice crystal size, due to the growth of more small ice crystals left behind on the scraped wall from previous scrapings. Increasing the dasher speed slightly reduced the mean ice crystal chord length, due to the production of new small ice nuclei by secondary nucleation. For a given refrigerant fluid temperature and dasher speed, low mix flow rates resulted in lower draw temperatures, due to the fact that the product remains in contact with the freezer wall longer. High dasher speeds warmed the product slightly, due to the dissipation of frictional energy in the product, the effect of which was in part moderated by the improvement in the heat transfer coefficient between the product and the freezer wall.     

SK手刮聚脲技术在泵站出水流道加固中的应用

聚脲弹性体材料因其材料特性,在水利工程上适用于处理混凝土伸缩缝、裂缝及有抗冲耐磨要求的混凝土表面。博湖西泵站更新改造中,出水流道加固采用SK手刮聚脲施工技术,较好地解决了出水流道漏气漏水问题,对该技术的应用做了详细介绍和总结。     

Residence time distribution measurements and simulation of the flow pattern in a scraped surface heat exchanger during crystallisation of ice cream

Scraped surface heat exchangers are used in the food industry to process highly viscous fluids, and ice-cream in particular, but most of the time, the influence of operating conditions on product quality is poorly understood. The objective of the study is to develop simple tools to help industrials understand, and then optimise their fabrication process. Residence Time Distribution (RTD) has been characterised in an industrial pilot system during real ice cream production, after the method had been validated in an experimental set-up with a simple mixture of water and sucrose. It has been shown that in its dimensionless form, RTD depend slightly on flow rate and scraper rotational speed. A simple model of flow pattern applicable to SSHE during crystallisation was developed to reproduce the observed RTD. It distinguishes two zones: the volume of fluid near the cooling wall where ice is generated and which is swept by the blades and the volume of fluid near to the rotor. Therefore, the model considers two parallel plug flow reactors with axial dispersion, and which exchange fluid by radial mixing. After adjustment of the model parameters, a good agreement was obtained with experimental results. The flow rate is lower in the zone near the cooling wall; this can be due to a higher ice concentration leading to higher viscosity. This approach can contribute to better understand, optimise and control SSHE used for ice cream production.     

Pricing and ordering decisions in a supply chain with imperfect quality items and inspection under buyback of defective items

In this article, the economic production and inventory model in a three-layer supply chain including one distributor, one manufacturer and one retailer for a single-product and general demand functions under three scenarios is developed. We assume that during the production process, both healthy and defective items are generated. As the first scenario, we develop the first model, in which the defective items are not reworked and all considered as scrape, while in the second model, we assume that the defective items are reworked and are sold as perfect item. In the second scenario, we assume that defective item can be sold with lower price than the selling price. Moreover, raw materials with imperfect quality are sent back from a distributor to outside supplier under a lower price. Determining the order quantity of the distributor and the selling prices of the distributor and the manufacturer as well as the retailer was the goal of this article such that the total profit of each member is maximised. In order to solve the models, the Stackelberg approach is employed between the members, and the concavity of the profit functions is proved using several theorems. Then, closed form solutions are derived for the decision variables and a solution algorithm is proposed to determine the optimal solutions. Finally, a numerical example is presented to illustrate the applicability of the model.     

Rheological characterisation of sorbet using pipe rheometry during the freezing process

Sorbet produced without aeration is a dispersion of ice crystals distributed randomly in a freeze-concentrated liquid phase. The rheological properties of this suspension will be affected by the viscosity of the continuous liquid phase and the volume fraction of ice crystals. The knowledge of the viscosity of sorbet is essential for the improvement of product quality, the selection of process equipment, and for the optimal design of piping systems. This work aimed firstly, at studying the influence of the ice volume fraction (determined by the product temperature) on the apparent viscosity of a commercial sorbet, and secondly, to propose a rheological model that describes the evolution of the viscosity of the product as a function of the ice volume fraction. The rheology of sorbet was measured in situ by means of a pipe rheometer connected at the outlet of a continuous scraped surface heat exchanger (SSHE). The pipe rheometer was composed of a series of pipes in PVC of different diameters, making it possible to apply a range of apparent shear rate from 4 to 430 s⁻¹. The flow behaviour index of sorbet decreased as the temperature of the product decreased, the effect of which indicates that the product becomes more shear thinning as the freezing of sorbet occurs. The consistency coefficient and therefore the magnitude of the apparent viscosity of sorbet increased with the decrease in product temperature and with the increase of the ice volume fraction. Results also showed that the rheological model described the experimental data within a 20% error.     

Determination of heterogeneities in a scraped surface heat exchanger using electrochemical sensors

An experimental investigation of a scaled-down model of an industrial exchanger, using an electrochemical technique, was undertaken in order to show the presence of hydrodynamic heterogeneities at low axial Reynolds number. Heterogeneities were revealed in the bowls with respect to the generalised Taylor number as the result of the perturbations added to the flow by blade rotation at both ends of the exchanger. Shear heterogeneities associated to flow visualisations were correlated to temperature heterogeneities observed in the bowls. Shear fluctuations were revealed in the scraped part describing two distinctive zones at low rotation speed caused by varying viscosity in the flow field. A complex spiral flow was observed by flow visualisation characterising a mass transfer evolution comprised between these two distinctive zones at low Taylor number.     

Dynamic Crystallization of Dark Chocolate as Affected by Temperature and Lipid Additives

The dynamic crystallization was studied in a lab-scale Scraped Surface Heat Exchanger by following variations with time of torque applied during different isotherms between 24.9°C and 31.0°C. Crystallization was in two steps for T 26.2°C but it was in one step at T<26.2°C. The first step corresponded to crystallization of about 1% solid fat and was related to that of saturated triacylglycerols (SSS) which segregated from other cocoa butter triacylglycerols (TAGs) because of their low solubility in TAGs. The second step, an abrupt increase of apparent viscosity, leading to complete crystallization was attributed mainly to the monounsaturated TAGs in the β form. Different amounts of tristearin increased the apparent viscosity and reduced the latent time preceding the first step, but did not influence the main crystallization. Stearic acid and distearin additions also influenced chocolate crystallization.     

基于IFIX刮板输送机实时监测系统研究

运用工业组态软件IFIX作为监控实验平台,结合PLC技术,通过对井下机械化采煤设备关键技术研究实验平台中的刮板输送机工作状态参数的数据采集、信号处理、传输、通讯和实时显示,设计了针对上述实验平台的刮板输送机实时监测系统。并通过IFIX过程数据库中的数据块将采集到的数据存入关系数据库SQL Server2005,可以进行数据查询、分析,且为以后故障诊断提供技术支持。同时通过ASP与ADO技术可将现场数据发送到网络,实现监测参数远程显示。