批式循环粮食干燥机板式换热器优化设计

基于前人研究得出的高效小型批式粮食干燥工艺,将批式循环粮食干燥机用列管式换热器设计为板式换热器,以更易得到的100℃高温蒸汽代替800℃烟气,将板式换热器采用更为高效的材料,最后在保证换热效率不变的情况下利用matlab优化工具箱优化换热器的尺寸。研究表明:改善之后的换热器具有更高的换热效率,减少了换热器占地面积以及材料的浪费。     

计算流体力学在食品传热传质过程中的应用

对计算流体力学(CFD)技术进行了简单介绍，并对采用CFD技术模拟食品加工过程中的传热传质过程的研究现状进行了综述，探讨了采用CFD对这些传热传质过程进行数值模拟的优势。CFD模拟的结果详细、直观，模拟得到的流体流动和各种热力学参数的分布信息，可以为装置的设计、传热过程的优化提供参考。     

计算流体动力学在食品热处理中的应用

简要介绍了计算流体动力学(CFD)在食品热处理中的求解过程、软件结构及常用软件,并对CFD模拟食品焙烤与热杀菌过程的相关研究进行了综述,同时总结了CFD的优点与不足,并展望了其在食品热处理中的发展与应用前景。      

波纹翅片管心偏移条件下空气侧传热流动性能数值研究

建立了波纹翅片管换热器空气侧流动传热的数学与物理模型,并用CFD软件Fluent进行了数值模拟,计算模型的可靠性通过实验进行了考核.研究了单排波纹片在不同管心偏移量下的压降和换热量的变化规律,分析了在7种管心偏移量和5个迎风面流速下的空气侧流动与换热特性,发现管心向下游偏移2.0 mm可以获得最大的换热量.     

3D milk-fouling model of plate heat exchangers using computational fluid dynamics

A 3D fouling model for milk pasteurization using PHEs (plate heat exchangers) was developed using CFD (computational fluid dynamics). Based on the hydrodynamic and thermodynamic performances of PHEs in a 3D environment, the chemical reaction equations employed for protein denaturation and absorption onto the stainless steel surface were coupled using the fluent software. The 10-channel PHE system with both counter-current and cocurrent flows was applied to validate the model by visualizing and quantifying the milk deposit formulated in the fluid channels. The predicted mass deposit values were in good agreement with the experimental data with the prediction error of 0.01 g or 1%. The simulation results based on new PHE system, designed for the uniformity of flow distribution, showed the deposited mass could be reduced to 1/10, compared to the current system under identical energy condition. Although the computational efforts required were quite intensive, the 3D fouling model was validated as an effective tool for design of new plate shape and corrugation profile optimized for minimizing milk fouling.     

Circulation cleaning of a plate heat exchanger fouled by tomato juice

A diluted tomato paste, applied as evenly as possible to one side of plate heat exchanger plates, has been used to study the effect of three temperatures (20, 70 and 90°C) when using water as a circulation cleaning fluid. From the experimental results it would appear that 70°C is the optimum temperature for this duty. Increasing the temperature to 90°C caused protein denaturation of the deposited tomato soil and cleaning efficiency was reduced. The soiling technique used in this work was found to be simple and consistent in studying the cleaning-in-place of the plate heat exchanger, and the direct weighing method of measuring soil removal was found to be reproducible.     

Circulation cleaning of a plate heat exchanger fouled by tomato juice

The effect of a change in flow rate of a 2% w/w caustic soda solution on the circulation cleaning of a plate heat exchanger fouled with diluted tomato paste has been investigated at a temperature of 90°C and fixed circulation cleaning times of 5 and 10 min.
For both circulation cleaning times a transition point was noted in the range 2.75–2.86 1/min (Reynolds number range 6600–6300, shear stress range 0.77–0.82 N/m²). Below the transition point the effect of flow rate on cleaning efficiency was minimal, but at flow rates above the transition point there was a marked increase in cleaning efficiency as the flow rate (and hence shear stress at the surface) increased.     

新型底锥型螺旋板式热交换器特点简介

节能清淤是每一个方便面生产厂家最关注的问题。入世以后，特别是２００１年下半年以来，方便面制造业无论产量、品质都有了明显的提高和发展。据统计２００１年方便面生产产值达到２６０亿，是历年来最高峰。如此大的行业其能源消耗和油炸介质（棕榈油）的洁净问题成为大家最关注的敏感点，新型底锥型螺旋板热交换器就是为同时改善上述两个问题的工作状况而专门设计的。特点一采用整板卷制、无中心隔板焊缝工艺，解决了传统工艺换热器容易泄漏的问题。其结构决定了换热介质与物料全逆流的交换途径，大大提高了换热效率。特点二传统螺旋板式…     

Analysis of heat transfer during ohmic processing of a solid food

To produce a safe cooked food product it is necessary to ensure a uniform heating process. The aim of this study was to develop a mathematical model of a solid food material undergoing heating in a cylindrical batch ohmic heating cell. Temperature profiles and temperature distribution of the ohmic heating process were simulated and analysed via experimental and mathematical modelling which incorporated appropriate electromagnetic and thermal phenomena. Temperature profiles were measured at nine different symmetrically arranged locations inside the cell. The material was ohmically heated imposing a voltage of 100 V, while electrical field and thermal equations were solved for experimental and theoretical models by the use of FEMLAB, a finite element software. Reconstituted potato was chosen to represent a uniform solid food material and physical and electrical properties were determined prior to the experiment as a function of temperature. The simulation provided a good correlation between the experimental and the mathematical model. No cold spots within the product were detected but both experimental and model data analysis showed slightly cold regions and heat losses to the electrode and cell surfaces. The designed model could be used to optimize the cell shape and electrode configurations and to validate and ensure safe pasteurisation processes for other solid food materials.     

Numerical simulation of solid–liquid food mixture in a high pressure processing unit using computational fluid dynamics

Temperature distribution, velocity and pressure profiles during high pressure compression (500 MPa) of liquid food (water) and solid–liquid food mixture (beef fat and water), within a three dimensional cylinder basket is simulated. The computations domain in both cases was performed for a cylinder with a diameter of 38 mm and height of 290 mm, which are the same dimensions of the high pressure unit “FOOD-LAB model S-FL-850-9-W” available at the University of Auckland, New Zealand. The governing equations for continuity, momentum and energy conservation are solved using a commercial computational fluid dynamics (CFD) package (PHOENICS), version 3.5, which is based on a finite volume method of solution. The simulation for liquid food only shows the effect of forced and free convection flow on the temperature distribution in the liquid at the early stages of compression. This is due to the difference between the velocity of the pumping fluid as it enters the cylinder inlet hole (10⁻²–10⁻³) m s⁻¹ and the velocity in the treatment chamber (10⁻⁸–10⁻⁹) m s⁻¹. The simulation for the solid–liquid mixture shows as well, the temperature distribution in the solid and liquid at different stages of compression. It shows that the solid pieces are more heated than the liquid, which is due to the difference in their compression heating coefficient. Validation of the computed temperature in both cases is found to be in an agreement with those measured experimentally and reported in the literature.     

基于计算流体力学对啤酒发酵罐的模拟

利用计算流体力学模拟技术对不同高径比的350 m3锥形啤酒发酵罐进行数值模拟。模拟结果表明,在啤酒发酵冷却降温过程中,不同高径比的锥形发酵罐在相同条件下罐内温度分布情况明显不同,高径比为3∶1～4∶1时降温效果更好。不同发酵罐内的速度分布也存在明显差异,除了高径比为2:1的发酵罐存在一个整体的循环对流外,其他发酵罐内发酵液均以局部小涡流的状态存在。通过对不同高径比的发酵罐内的温度场和速度场的分析,可以为啤酒发酵罐的选型提供一定的理论依据。     

Modeling the fluid dynamics in a human stomach to gain insight of food digestion

Abstract: During gastric digestion, food is disintegrated by a complex interaction of chemical and mechanical effects. Although the mechanisms of chemical digestion are usually characterized by using in vitro analysis, the difficulty in reproducing the stomach geometry and motility has prevented a good understanding of the local fluid dynamics of gastric contents. The goal of this study was to use computational fluid dynamics (CFD) to develop a 3-D model of the shape and motility pattern of the stomach wall during digestion, and use it to characterize the fluid dynamics of gastric contents of different viscosities. A geometrical model of an averaged-sized human stomach was created, and its motility was characterized by a series of antral-contraction waves of up to 80% relative occlusion. The flow field within the model (predicted using the software Fluent™) strongly depended on the viscosity of gastric contents. By increasing the viscosity, the formation of the 2 flow patterns commonly regarded as the main mechanisms driving digestion (i.e., the retropulsive jet-like motion and eddy structures) was significantly diminished, while a significant increase of the pressure field was predicted. These results were in good agreement with experimental data previously reported in the literature, and suggest that, contrary to the traditional idea of a rapid and complete homogenization of the meal, gastric contents associated with high viscous meals are poorly mixed. This study illustrates the capability of CFD to provide a unique insight into the fluid dynamics of the gastric contents, and points out its potential to develop a fundamental understanding and modeling of the mechanisms involved in the digestion process. Practical Application: This study illustrates the capability of computational fluid dynamic techniques to provide a unique insight into the dynamics of the gastric contents, pointing out its potential to develop a fundamental understanding and modeling of the human digestion process.     

Nano-fluid thermal processing of watermelon juice in a shell and tube heat exchanger and evaluating its qualitative properties

Due to specific thermophysical properties of nanofluids, compared with conventional thermal fluids (steam and hot water), their application in diverse industries, to improve heat transfer and to save energy, has increased. One important aspect of applying nanofluid thermal processing is shortening the process time which could have high potentials in the food industry since nutritional and bioactive components would be maintained much higher than common thermal processes. In this project, possibility of replacing water with alumina-water nanofluids (2 and 4% concentrations) during high temperature short time processing (75, 80 and 85 °C for 15, 30 and 45 s) of watermelon juice in a shell and tube exchanger regarding its qualitative properties (lycopene, vitamin C, color, pH and TSS) was investigated. Reduction in process time when applying 2 and 4% nanofluids, up to 24.88 and 51.63%, had considerable effects on maintaining qualitative properties for watermelon juices. For instance, thermal processing by 0, 2 and 4% nanofluids at 75 °C for 15 s could keep 81.15, 84.81 and 91.28% of lycopene and 61.11, 63.70 and 67.04% of vitamin C, respectively. pH and TSS indices of processed watermelon juices were in the range of 5.58–5.82 and 9.0–9.4, respectively, showing no considerable correlation with the heating media used in thermal processing. Our results revealed that nutritional and physicochemical properties of watermelon juice processed with alumina nanofluids were better than common thermal processing by water with 9.89, 6.18 and 50.38% higher lycopene, vitamin C and color retention in the final product, respectively.Industrial RelevanceEven so thermal processes are effective in preventing microbial spoilage of fruit juices, high volume of energy transfer in long durations into food products with heat sensible ingredients or properties results in biochemical and nutritional losses, development of unpleasant reactions, changes in overall quality of food products, and high energy consumption. Nowadays, consumers demand for food products with long shelf lives, high quality and proper prices are increasing. So, to meet these demands, food industries are looking for alternative thermal technologies to reduce losses in food characteristics and process costs, and introduce a fresh, nutritious, healthy and affordable food produce.Thermal conductivity of conventional fluids is much lower than metals and oxidized metals. For example, thermal conductivities of copper and alumina are 700 and 60 times higher than the thermal conductivity of water, respectively. Accordingly, fluids with suspended particles of metals or oxidized metals benefit from better heat transfer properties. The term of Nanofluid refers to each stable two-phase compound that includes both base fluids and nanoparticles (lower than 100 nm, at least in one dimension).There is no research dealing with effects of adding nanoparticles to conventional thermal fluids for fruit juices processing. So, the goal of this research was to introduce nanofluid technology for thermal processing of food products for the first time, increasing heat transfer efficiency in shell and tube exchangers by nanofluids and frugality in energy consumption for pasteurization, reducing thermal processing duration and better quality retention of food products.     

Investigation and modelling of natural convection and conduction heat exchange: study on food systems with modified starch by means of computational fluid dynamics

This study is focused on the effects of starch gelatinisation on heat exchange in food systems containing four modified starch concentrations (0, 2, 6 and 10%). Viscosity profiles of samples were experimentally measured: the effect of gelatinisation was evident, particularly at 6% and 10%, where the viscosity increased from 0.010 to 70 Pa s and to 1507 Pa s, respectively. The heat exchange rate showed a decrease with the increasing of starch concentration, and the effects were observed until 6%. Four Computational Fluid Dynamics (CFD) models were also developed, experimentally validated (RMSE < 1.5 °C) and used to study the heat exchange. Velocity profiles showed that the convective flows slowed down from 2.5 to 0 mms^?1 after the gelatinisation. Finally, the effects on the slowest heating/cooling zone (SHZ/SCZ) location in the CFD models were studied: at 0% and 2%, the SHZ settled 15 and 80 mm from the bottom of jars in heating and cooling phase, respectively. At 6% and 10%, before the starch gelatinisation phase, the SHZ was located in a similar position of the 0% and 2% while when the gelatinisation occurred the SHZ slightly moved towards the geometric centre (50 mm) as for an only‐conductive product.     

Analysis by Raman spectroscopy of the conformational structure of whey proteins constituting fouling deposits during the processing in a heat exchanger

Whey protein fouling deposits generated on the hot wall downstream a plate heat exchanger were analyzed by micro Raman spectroscopy (MRS) carried out in the 800-1800 cm⁻¹ range. Deposits were formed using a model beta-lactoglobulin (BLG) fouling solution which was made using a whey protein isolate powder (89 wt.% in BLG) and a known amount of calcium. Thermal denaturation of the fouling solution was also analyzed by MRS as well as isolated BLG aggregates obtained by microfiltration of heated solutions. Specific Raman signatures of aggregates were identified, which were not detected in the Raman spectra of denatured (i.e. unfolded BLG molecule) solutions. MRS analyses at different depths of the deposit reveal a loss of α-helix structures, as observed in denatured BLG solutions, without the detection of aggregate signatures. For the range of calcium content investigated (from 97 to 160 mg l⁻¹), no effect of calcium ions on the molecular conformation of BLG within the deposit was shown. Of great significance, results suggest that, for our set of operating conditions used, the mass distribution of the fouling deposit in a plate heat exchanger is primarily controlled by the distribution of the unfolded protein generated by the denaturation process.     

高校餐厅食品加工违规行为视频分析算法与系统设计

目的 开发视频分析子系统分析食品加工违规行为, 提高高校餐厅的食品安全风险预防能力。方法 介绍了该视频分析子系统的组成和违规行为分析过程的主要工作流程; 详细阐述了检测员工不着工作服、用素食案板加工生肉2种典型违规行为的视频分析算法的基本原理、主要公式和算法流程; 并对2种典型违规行为进行了大量测试。结果 本视频分析系统对员工未着工作服行为的检测准确率达到了99%, 对员工在素食案板上加工生肉行为的检测准确率达到了98%。结论 本研究所开发的视频分析子系统可提高预防食品安全风险的能力。     

Modelling aluminium leaching into food from different foodware materials with multi-level factorial design of experiments

To estimate the contribution of aluminium (Al) leaching from different materials used for food preparation and serving to the dietary Al intake, Al release from foodware typically used in everyday life was investigated using multilevel factorial design (MFD) of experiments. For Al characterisation, sample preparation and an analytical method using inductively coupled plasma atomic emission spectroscopy was developed and validated. Parameter influence (temperature: x (1), contact time: x (2), pH: x (3), salt concentration: x (4), viscosity: x (5)), was evaluated with analysis of variance suggesting that the influence of viscosity is not significant compared to the other four studied parameters. Therefore, predictive, exponential quadratic regression models were established with x (1)-x (4). Cross-validation and a set of independent experiments in real food products were used to test the prediction force of the different models. They both suggest that the quality of the models established for Al foil, Al plate and ceramic ware is satisfactory, but less good for glassware and stainless steel. Indeed, in the studied conditions, leaching from these latter food wares was often close to or even below the limit of quantification suggesting that the principal sources of Al intake from food contact materials during food processing are utensils made of Al and ceramic ware.