冷冻结晶法纯化制备高纯度磷脂酰乙醇胺

为解决工厂低磷脂酰胆碱(PC)含量大豆粉末磷脂的积压问题,以及获得高纯度的磷脂酰乙醇胺(PE),以用碱性乙醇从低PC含量大豆粉末磷脂中提取的粗PE产品为原料,通过冷冻结晶法纯化制备高纯度PE。在单因素实验的基础上,以PE含量为指标,通过响应面实验对冷冻结晶纯化条件进行了优化。结果表明,PE的最佳冷冻结晶纯化条件为：料液比1∶40,冷冻时间21.5 h,冷冻温度-25℃,乙醇体积分数94%,乙醇碱浓度为94%乙醇与25%氨水体积比100∶8。在最佳条件下,产品PE含量为76.56%,PE回收率为81.25%。因此,冷冻结晶法纯化工艺可用于制备高纯度PE。     

软黏土三维水-热-力耦合冻融模型及应用

人工地层冻结法是沿海地区软黏土进行地层加固的一种常见绿色工法,地下空间开挖的大型及复杂化使目前冻结法面临更加复杂的渗流环境.为此,通过分凝冻胀理论刚性冰模型的三维化推广,建立能考虑水分迁移的热-水-力耦合作用冻胀融沉模型,以模拟复杂渗流环境下的人工冻结工程.基于模型使用COMSOL有限元进行模拟,与同尺寸室内模型试验数...     

微冻和冷藏对牙鲆贮藏品质的影响

以感官、理化和微生物为指标,研究了微冻（-2℃）和冷藏（4℃）对牙鲆品质变化及货架期的影响。结果表明,随着贮藏时间的延长,牙鲆鱼的感官品质显著下降（p<0.01）,菌落总数、挥发性盐基氮（TVB-N）含量、硫代巴比妥酸（TBA）值和K值均呈显著上升趋势（p<0.01）,且微冻贮藏时各指标的变化速率都低于冷藏;质构特性中的硬度、弹性、咀嚼度和粘聚性随贮藏时间的延长而显著下降（p<0.05）,p H与贮藏时间及其他理化指标（TBA除外）相关性不显著。综合感官评分、TVB-N值及菌落总数等指标得出牙鲆在4℃和-2℃贮藏条件下的货架期分别为9 d和12 d。与冷藏相比,微冻能更有效地抑制微生物的生长,延长其货架期。      

液氮冻结食品冻结时间的计算方法及实验验证

冻结时间是评价冻结食品质量的重要指标,正确计算冻结时间是食品冻结装置优化设计及运行的关键。本文通过建立液氮速冻实验平台,测试了食品的冻结时间,介绍了现有的理论模型,选择了几种典型的计算方法应用于食品冻结,并将各模型的理论结果与实验值进行比较,分析各偏差原因,获得计算食品冻结时间最准确的方法。以有限长圆柱状食品为例,通过研究发现在整个氮气温度场中国际制冷学会模型计算结果与实验值最相近,平均偏差为8.86%,分段计算法次之,平均偏差小于15%。     

负温对土动剪切模量阻尼比的影响规律

 以我国引进的首台低温共振柱仪为依托,研究不同负温下冻结土的初始剪切模量、剪切模量比和阻尼比非线性曲线的变化规律和模式。对低温共振柱仪试验技术进行研究,结果显示,采用常温试验方法进行低温共振柱试验,会导致结果离散过大,通过试验确定围压介质、冻结时间等试验条件和参数。同时,采用更符合客观实际的围压、固结和冻结方式,以粉土为样本,在室温和不同负温下进行对比试验。结果表明：负温对土的初始模量和剪切模量比影响显著,0 ℃～－4.0 ℃为敏感段,－4.0 ℃后为平稳段;敏感段内,随负温增加,初始剪切模量呈Boltzmann函数形式急速增加,参考剪应变则呈Boltzmann函数形式迅速下降,平稳段上,二者随负温增加分别平稳上升和下降;负温下阻尼比曲线在剪应变小于一定值时高于常温曲线,而在大于该应变时常温试验曲线则超过负温曲线;负温对最大阻尼比有较大影响,随负温增大,最大阻尼比呈指数形式降低。该试验采用专门的低温共振柱仪完成,围压、固结和冻结条件更接近客观实际,得到的负温对土动剪切模量阻尼比的影响模式更真实可靠,可为季冻土区抗震规范中设计谱修正以及季冻土区重大工程抗震设计中获得合理地震动输入提供依据。     

The Interface Position and Centre Concentration during Freezing of Carrot Juice in Cylindrical Containers

Finite difference modelling, incorporating a variable space network approximation, was used to study the freezing of carrot juice in cylindrical containers. Ambient temperatures ranged from −6·5 to −14·2°C. The problem was formulated as a moving boundary to find the position of the hypothetical solid–liquid interface and the concentration at the centre. Experimental results obtained for the freezing of carrot juice were satisfactorily represented by the variable space network approximation technique, except for failure at the central positions. This failure was believed to be due to some simplifying assumptions such as constant thermophysical properties and a sharp interface, as well as possible experimental errors.     

Impact of frozen storage on polyacetylene content, texture and colour in carrots disks

This study investigated the effect of freezing method (slow or blast freezing) with or without blanching during storage at −20 °C on the levels of three polyacetylenes, falcarinol (FaOH), falcarindiol (FaDOH), falcarindiol-3-acetate (FaDOAc) in carrot disks. The quality of the carrot disks was also assessed using instrumental texture and colour measurements. Blast frozen carrot disks retained higher amounts of polyacetylenes compared to their slow frozen counterparts. Whilst the levels of retention of total polyacetylenes was higher in unblanched than blanched disks prior to freezing there was a sharp decrease in the levels of polyacetylenes in unblanched frozen carrots during the storage period for 60 days at −20 °C. FaDOH was observed to be the most susceptible to degradation during frozen storage of unblanched carrot disks, followed by FaOH and FaDOAc. The changes in the level of polyacetylenes during storage were adequately described by using Weibull model. The texture and colour were also found to decrease during frozen storage compared to fresh carrots.     

厚表土层湿土结冰温度与冻结壁厚度确定的研究

用研制的冰点仪，对含水土的结冰温度与赋存深度、含盐量和含水率的关系进行了实验研究．获得了含水土结冰温度与诸参数的关系，给出了求算结冰温度和判定冻结壁实际厚度的方法和计算公式．     

新型高效冷冻脱水器的设计研究

传统冷冻脱水器通常为折流板换热器,由于要满足结冰要求,换热管管径一般比较大,传热效果差,不能有效脱水。冷冻脱水器的热阻主要在管程气体侧,新型高效冷冻脱水器使用变截面强化传热管代替光滑圆管,换热管扭曲段可以使流体沿螺旋线流动,形成强烈扰流,破坏边界层,提高传热效率;管内气体中的凝结水由于密度大,在气流离心力作用下,会迅速甩向管壁,凝固成冰,提高冷冻脱水效果。壳程省去折流板结构,流体流动由错流变为纵流,降低系统功耗,且节省材料,降低成本。