Characterization of Tomato Pulp Stickiness during Spray Drying using a Contact Probe Method

A contact probe test was developed to characterize the surface stickiness of a tomato pulp droplet at various moisture contents and temperatures. To provide tomato pulp samples with different moisture contents, tomato powder produced by a laboratory spray dryer was wetted to seven different moisture levels. The instantaneous tensile force curve was recorded during the probe withdrawal from which the maximum tensile force and other useful information were obtained and cross-examined against images of bonding, debonding, and failure of the material. Generally, at higher moisture contents tomato pulp exhibited cohesive failure followed by semi-adhesive failure, but when moisture content decreased to a certain level, a peak tensile pressure was observed and the failure was adhesive. In addition, higher temperatures shifted the points of adhesive failure toward lower moisture content.     

糯玉米淀粉提取及理化性质的研究

以糯玉米为原料，采用湿法提取淀粉工艺，制得淀粉得率高，质量优质的纯净糯玉米淀粉，通过正交实验设计筛选出最佳的提取方案：浸泡温度，浸泡溶液亚硫酸浓度，浸泡时间分别为50℃，0．3％，60h，影响淀粉得率的主要因素是：时间，浓度，温度，糯玉米淀粉较普通玉米淀粉相比具有糊化温度低，黏度高，透明度高等特点。     

基于Linear Cohesion模型的含水堆积体滑坡过程数值模拟

水通常是堆积体滑坡发生的触发因素,采用数值方法模拟堆积体滑坡时加入水的液桥力有助于提高计算结果的合理性。为了研究含水堆积体滑坡过程的各项运动特性,提出采用Linear Cohesion接触模型模拟含水湿润状态下松散堆积体滑坡的运动过程,利用离散元程序EDEM 2017建立了含水堆积体滑坡水槽数值模型,计算堆积体从失稳-滑动-堆积整个运动过程。结果表明:能量密度k是Linear Cohesion模型模拟含水堆积体滑坡的关键参数;当k<5000 J/m^3时,随着能量密度值逐渐增大,堆积体滑动过程的流动性越来越小,最大平均速度值和最大动能越大,当k≥5000 J/m^3时,含水堆积体的各项滑动特征变化不明显;较小能量密度的湿颗粒堆积体在滑动过程中结构体易发生破坏,形成的颗粒群流动性更强,滑动距离更远,扩大了滑坡灾害的影响范围。相关研究成果对今后类似的含水堆积体滑坡灾害的预测和评估有一定参考价值。     

Shear decohesion of clamped abraded steel interfaces reinforced with epoxy adhesive

This paper presents an experimental assessment of quasi-static shear strength of the combined mechanically clamped and epoxy adhesive reinforced steel interfaces. The effect of the surface roughness and clamping load on the combined interfacial decohesion and slipping is investigated. The maximum shear strength of the adhesive reinforced specimens with fine ground, coarse ground and grit blasted contact surface finishes is reported with comparison to the results of the identical non-reinforced specimens. Results have been assessed both in terms of calculated fracture energy and interface decohesion. The bonded interfaces with grit blasted finish showed considerably higher maximum shear stresses as compared to the identical ground cases. The shear strength contributions of strong clamping and reinforcing conformed well to the principle of superposition for all experimented interface types.     

NEW MEASUREMENTS OF THE STICKY BEHAVIOR OF SKIM MILK POWDER

The drying of sugar-rich foodstuffs is often complicated by depositions on the walls of spray dryers, due to the stickiness of the products. This material property has been found to depend on both product temperature and moisture content and undergoes a rapid change from non-sticky behaviour to sticky behaviour with only a small change in these parameters. In this investigation, this so-called sticky point is measured for skim milk powder by measuring the cohesive force between stirred particles in a heated flask. The line separating the sticky and the non-sticky regions is given as a function of bulk temperature and moisture content. For the temperature range from 25 to 95°C investigated here, the line shows good agreement with the predicted glass transition temperature for lactose, shifted up by 23.3 K. This information can then be used in CFD simulations carried out to model the build-up of wall depositions inside spray drying chambers. As a first order approximation to estimate the behaviour of a particle impacting on a wall, sticky particles can be assumed to adhere to the wall, whereas non-sticky particles can be considered to bounce off it.     

An Advanced Centrifugal Technique to Characterize the Sticking Properties of Tomato Pulp during Drying

An advanced centrifugal technique was developed to characterize the stickiness of tomato pulp at various moisture contents and temperatures. To provide tomato pulp samples with different moisture contents, tomato powder produced by a laboratory spray dryer was wetted to six different moisture levels. By noting the rotational speed for a tomato pulp droplet detachment and weighing the mass of the droplet remaining on the surface it is possible to gauge the approximate attachment forces holding the droplet to the substrate. The effects of droplet mass and centrifugation time after reaching the desired rotor speed on the detachment rate were also studied. The detachment force was found to increase at the beginning and then started decreasing as the moisture content decreased presenting a maximum at moisture content of about 34%. In addition, the higher the droplet temperature, the higher the attachment force.     

Friction and compression characteristics of chickpea flour and components

Chemical composition and selected physical properties of chickpea flour, the starch fraction and the protein fraction were determined. Coefficient of internal friction, coefficient of external friction (on steel, concrete, Teflon and polypropylene), cohesion and adhesion of samples were measured. Chickpea flour and starch fraction had the highest coefficient of internal friction and cohesion, respectively. The coefficient of external friction of chickpea flour and components on concrete was markedly higher than other surfaces. The starch fraction had the highest compressibility and asymptotic modulus at most of the preset loads. The compressibility and asymptotic modulus increased with porosity. Chickpea flour with the lowest porosity had the lowest asymptotic modulus. All samples underwent particle rearrangement during compression.     

影响粉末流化的本征作用力及其调节

本文归纳了人们对粒间力的分析和计算，指出了影响颗粒间作用进而影响其流化质量的各种因素，并从改善微细物料流化质量的角度，综述了近年来国内外流化微细物料的诸多措施，将其归结为两大类型：外力场方法与本征途径，以作为进一步探求微细物料流态化的研究基础．     

Physical and frictional properties of non-treated and steam exploded barley, canola, oat and wheat straw grinds

During storage and handling, accurate knowledge of the physical and frictional behaviors of biomass grinds is essential for the efficient design of equipment. Therefore, experiments were performed on non-treated and steam exploded barley, canola, oat and wheat straw grinds to determine their coefficient of internal friction and cohesion at three hammer mill screen sizes of 6.4, 3.2 and 1.6 mm, three normal stress values of 9.8, 19.6 and 39.2 kPa at 10% moisture content (wb). At any specific hammer mill screen size, the geometric mean particle size and bulk density of non-treated straw was significantly larger than steam exploded straw. The bulk density of ground straw significantly increased with a decrease in hammer mill screen sizes. The steam exploded straw grinds resulted in higher coefficient of internal friction compared to non-treated straw grinds primarily because of lower bulk densities. The coefficient of friction for non-treated barley, canola, oat and wheat straw were in the range of 0.505 to 0.584, 0.661 to 0.665, 0.498 to 0.590, and 0.532 to 0.591, respectively. Similarly, the coefficient of friction for steam exploded barley, canola, oat and wheat straw were in the range of 0.562 to 0.738, 0.708 to 0.841, 0.660 to 0.860, and 0.616 to 1.036, respectively, which were higher than non-treated straw of the kind. Power, logarithmic or exponential equations were developed to predict the coefficient of internal friction and cohesion with respect to average geometric mean particle sizes for non-treated and steam explode barley, canola, oat and wheat straw grinds.