The lyophilization of dispersed systems: influence of freezing process, freezing time, freezing temperature and RBCs concentration on RBCs hemolysis

In this work, we studied the influence of different parameters controlling cooling stage on biological dispersed system injury. The human red blood cell (RBCs) was chosen as work model. The study examined the influence of two freezing processes on RBCs hemolysis, one process producing big crystals, the other producing small crystals. Using both processes, we examined the effect of freezing temperature, freezing time, and RBCs concentration on injuries to RBCs. Freezing damage was assessed by the hematocrite measure before freezing and after thawing. The process producing a small number of big ice crystals (Pa) seems—in relation to the one producing a large number of small ice crystals (Pb)—to be less traumatic for the RBC, although the two are not statistically different. Freezing temperature and freezing time influence the preservation of RBCs. At 0 and -20°C there were high preservation and total hemolysis, respectively. At -5°C and -10°C, the RBC hemolysis depends on freezing temperature and freezing time. The RBCs hemolysis rates increases when freezing time increases and when freezing temperature decreases. The rates of RBCs preserved decreases with RBCs concentration some with either the freezing process used (Pa or Pb). More, an accentuation of the difference between the two used freezing processes on RBCs hemolysis was retrieved. The analysis of the conductivity evolution within the RBCs suspension frozen showed that the destruction of the RBCs is had essentially to the solution effects. When the crystallization eutectic takes place, the RBCs are already completely destroyed.     

水产品超声辅助浸渍冷冻技术研究进展

目的 为延长水产品销售周期,最大程度保持其营养品质,促进水产品冷冻保藏及加工技术的发展和产业化。方法 归纳总结超声辅助浸渍冷冻的作用机理,并探究其对冰晶形成和生长以及水产品保鲜加工的影响。结果 超声辅助浸渍冷冻能有效提高冷冻效率,减小冰晶晶核规格,缩短冷冻时间,减缓水产品蛋白质变性与脂质氧化速率,改善水产品质构、保持其营养价值,是水产品冷冻处理的有效途径。结论 超声辅助浸渍冷冻技术能在一定程度上解决水产品冷冻过程中存在的问题,为水产品冷冻技术产业化提供支持。超声辅助浸渍冷冻技术在作用机制、适用范围和特定环境下的作用衰减等方面存在着一定缺陷,还需深入阐述其作用机理,为冷冻智能装备开发提供保障。     

Freezing processes in high-pressure domains

Experimental freezing of water in high-pressure domain is studied considering temperature reduction (TRF) as well as high-pressure-assisted freezing (HPAF). The most important advantage of HPAF is that the whole volume of the sample is subcooled when an expansion is made, so a rapid and uniform nucleation and growth of ice crystals are produced. In this work through mathematical modelling the amount of ice appearing instantaneously in the latter freezing, is predicted.     

平板过冷却器内结冰行为的实验研究

本文设计并搭建了一套过冷水动态制冰系统,开发了一种可视化平板过冷却器,通过实验研究流动和换热对过冷却器内结冰行为的影响,并基于经典成核理论与边界层理论对其作用机理进行解释。实验结果表明：平板过冷却器内存在两种典型结冰行为,结冰行为一表现为过冷却器内不结冰,系统可连续制取冰浆;结冰行为二表现为过冷却器内发生结冰,系统不能制取冰浆。载冷剂进口温度过低、制冰溶液流量过大或过小均会促进结冰行为二的出现,不利于系统制冰稳定性。发生结冰行为二时,相对距离d为0.15的壁面优先发生结冰,且该处壁面的温度总低于其余区域,因此优先发生结冰的局部条件是具有更低的壁面温度。     

液氮冻制冰套法对水三相点温度的影响

介绍了液氮作为冷却剂在水三相点容器内冻制冰套的方法。利用该方法同时在两个不同真空度的水三相点容器内分别冻制冰套。通过实验，研究了此方法对所复现的水三相点温度的影响。实验结果表明：冻制过程中产生的应力以及开始生成的小冰晶引起水三相点温度偏低；并且，其对水三相点温度的影响随着水三相点容器内真空度的降低而增大。随着应力慢慢消除，小冰晶逐渐长大为大冰晶，所复现的水三相点值逐渐回升并趋于稳定。因此，为了高精度复现和准确测量水三相点，采用该冻制方法时，必须将冰套老化至少5天以后，才可以消除其对水三相点温度的影响。     

Investigating the ice crystal morphology in frozen cooked rice based on size,fractal dimension and ANN modeling

Cooked rice was frozen in an air blast freezer at freezing temperatures of −5, −10, −15, −30 and −45 °C and stored at −5, −10, −15, −30 and −45 °C for up to 90 days. Cross-sectional images were captured using a fluorescence staining method, and then the equivalent diameters and perimeters of ice crystals were determined. The size and fractal dimensions were affected by the relationship between the freezing and storage temperatures. Artificial neural network analysis revealed that the behavior of response surface curves of both sizes and fractal dimensions were similar. The models demonstrated that the storage temperature of −25 °C for 90 days was required for maintaining the size and morphology of ice crystal immediately after freezing at −25 °C. These models would be effective tools for identifying the optimum operating conditions of frozen cooked rice based on the relationship between the ice crystal size and morphology.     

静电场对红细胞与冰晶间相互机械性作用的影响

以红细胞悬液为研究模型,通过在对其进行慢速冻结的过程中引入静电场,具体研究了静电场对降温过程中冰晶形成与生长的影响,以及由此而引起的冰晶与细胞间相互机械作用的变化.实验结果表明:静电场在一定程度上改变了冰晶的形成与生长特性,在较强的静电场的影响下,冰晶明显变粗,成为块状,细胞完全融入粗大的冰晶之中,在冻结的末期,细胞不再受到冰晶挤压,从而减少了其所受的机械性损伤.     

家用制冰机结冰过程的理论与实验研究

根据家用制冰机的工作原理和结构利用焓法对其制冰过程建立数学物理模型，采用全隐式格式开展有限差分数值模拟研究。在一台家用制冰样机上进行实验测试，通过改变环境温度观测冰层厚度与制冰时间的关系，并将实验结果与数值解进行对比。结果表明，数值解与实测值之间相对误差的绝对值小于3％。升高环境温度，在同样的时间内成品冰厚度减小，质量下降。     

接触角和质量分数对液滴冻结过程的影响

本文通过FLUENT软件的凝固/熔化模型,模拟了接触角及质量分数对纯水和氯化钠溶液在冷表面冻结过程的影响,选择铜片为亲水表面,纳米膜表面为疏水表面,对液滴在不同表面特性条件下的冻结过程进行实验研究。结果表明：液滴在冷表面的冻结特性与接触角、质量分数有关。当溶液质量分数一定时,接触角越小,液滴冻结速度越快,完全冻结时间越短;在冻结过程的初始时刻,接触角越小,液滴底部温度越低;当冻结时刻相同、液滴高度一致时,液滴表面的温度和液相分数均比液滴内部低;接触角相同时,溶液质量分数与液滴的开始冻结温度成反比,与完全冻结时间成正比。对比实验结果与模拟可知,不同质量分数的氯化钠液滴在接触角为60°和100°时,冻结时间的变化趋势一致,但实验值大于模拟值。     

Freezing degree-days in New York state

Freezing degree-days (FDD) are examined for the period 1950–1980 at 62 locations. FDD are defined as departures in the mean daily temperature from 0°C with means below 0°C given a positive sign and means above 0°C given a negative sign. Accumulation of FDD begins 1 October. A negative accumulation is set to zero. The maximum FDD accumulation is reached during late January or February in southeastern New York, during early to middle March across central sections, and during late March or early April in the Adirondack Mountains. Temperatures above freezing after those dates lead to a decrease in FDD accumulations and indicate the melting period. The average maximum accumulation of FDD ranges from 100 on Long Island to 1000 in the Adirondack Mountains. Regression equations estimate the average annual maximum accumulation of FDD and the date of the maximum using site elevation and latitude.     

超声辅助冷冻技术在食品浸渍式冷冻中的研究进展

目的 概述超声辅助冷冻技术在食品浸渍式冷冻中的研究进展,为今后新型技术辅助浸渍式冷冻提供研究方向.方法 研究超声辅助冷冻的成核机理和对冰晶生长的影响,以及超声对溶液性质的影响,并对超声辅助冷冻技术在食品浸渍式冷冻中的应用进行综述.结论 超声辅助浸渍式冷冻技术可以广泛应用在各类食品加工中,有很大的研究和发展空间.超声辅助冷冻技术能够进一步加快食品浸渍式冷冻的冻结速率,减小食品内部冰晶尺寸,较好地改善了冷冻食品的品质和风味,在食品加工中具有广阔的应用前景,可以高效应用于食品工业.     

预处理及解冻方法对马铃薯冻融品质的影响

目的 提高马铃薯冻融后的品质,为PEF预处理在蔬菜冷冻领域的应用提供理论依据。方法 探讨预处理方法(脉冲电场、热处理)和解冻方法(常温解冻、水里解冻、冰箱解冻)对马铃薯冷冻–解冻过程及品质的影响,分析冰晶成核温度、融化温度、汁液损失比、色泽、硬度等理化指标,并通过低场核磁共振仪分析冻融后样品不同状态下水分间的迁移情况。结果 热烫和高压脉冲电场(Pulsed Electric Field,简称 PEF)预处理均可显著降低冷冻时间、提高冰晶成核温度。PEF预处理样品在最大冰晶体形成带的滞留时间相较于对照组样品降低了26.3%。在不同解冻方式下,PEF预处理和热烫预处理均可降低马铃薯冻融后的汁液损失。在常温下解冻,对照组、热烫组、PEF预处理组的汁液损失率分别为24.12%、17.39%、15.53%。PEF预处理和热烫预处理可减缓食品在冻融过程中的颜色和硬度的变化进程。结论 PEF预处理可以改善冻融后马铃薯的品质,可为PEF在果蔬冷冻领域的应用提供理论参考。     

冻结间冷却设备的选配与布置

冻结间是冷冻（冷藏）企业生产环节中的重要组成部分,性能如何,不仅关系产品质量,也对能耗产生直接影响。合理选配、布置冻结间冷却设备,是提高冻结间性能的重要手段。本文就冻结间冷却设备选配和布置的基本方式进行论述。     

Investigation of the Ice–Water Vapor Equilibrium Along the Sublimation Line

An accurate knowledge of the thermodynamic properties of water at low temperature plays an important role in atmospheric processes, chemical physics, and metrological applications. Preliminary investigations of the water vapor?Cice equilibrium along the sublimation line have been carried out at Istituto Nazionale di Ricerca Metrologica (INRIM). The measurements covered the temperature range from ?50?°C to 0?°C, corresponding to a saturation vapor pressure from about 4?Pa to 611?Pa. The measurements were performed using a small gold-plated cell kept in a liquid bath at a constant temperature with millikelvin stability. The sample cell was connected to a manifold where the pressure was measured using two capacitive diaphragm pressure gauges. The paper reports the water sample preparation, measuring method, and measurement corrections. Measurement results are discussed and uncertainty sources estimated. The resulting expanded relative uncertainty (k = 2) varies from 0.038 % at 0?°C to 0.70 % at ?50?°C.     

The freezing and supercooling of garlic (Allium sativum L.)

This work shows that peeled garlic cloves demonstrate significant supercooling during freezing under standard conditions and can be stored at temperatures well below their freezing point (?2.7 °C) without freezing. The nucleation point or ‘metastable limit temperature’ (the point at which ice crystal nucleation is initiated) of peeled garlic cloves was found to be between ?7.7 and ?14.6 °C. Peeled garlic cloves were stored under static air conditions at temperatures between ?6 and ?9 °C for up to 69 h without freezing, and unpeeled whole garlic bulbs and cloves were stored for 1 week at ?6 °C without freezing.     

Mechanical Properties of Solid‐Sintered Porous Silicon Carbide Ceramics

The freeze‐drying combining solid sintering is a good method to fabricate porous SiC ceramics with good high temperature mechanical properties. Though SiC ceramics are sintered at a high temperature of 2150 °C, there are still large quantity of macropores generated by sublimating large ice crystals and micropores in the ceramic wall caused by small ice crystals sublimating, SiC particles stacking, and burning out of polyvinyl alcohol (PVA). The content of PVA affects the microstructure and strength. As increasing the content of PVA, the size of pores caused by sublimating the ice crystals decreases while both open porosity and room temperature strength increase. After being treated at a temperature of 1200 and 1500 °C, the ceramics exhibit good thermal shock damage resistance.     

有限长圆柱状食品冻结时间的计算方法及实验验证

食品冻结时间的准确计算关系到食品冻结装置的优化设计及运行。本文提出了一种新的食品冻结时间计算方法，将冻结时间划分为三个阶段：冷却阶段、冻结和再降温阶段，并对各个阶段建立了动态计算模型。通过对有限长圆柱状食品的实验研究，将普朗克计算式与通过该模型计算得到的结果和实验数据进行比较，结果证明建立的计算模型是可靠的。     

Vacuum freezing type ice slurry production using ethanol solution 1st report: Measurement of vapor–liquid equilibrium data of ethanol solution at 20 °C and at the freezing temperature

In this study, an original method for the production of ice slurry from ethanol solution without using a refrigerator is proposed. This system has advantages compared with similar existing systems using materials other than ethanol solution. In this paper, the vapor–liquid equilibrium data of ethanol solution at 20 °C and at the freezing temperature are measured, which is necessary to calculate the COP of this ice slurry producing system. In the experiments, two experimental methods are proposed to measure the saturated pressure and the vapor composition of ethanol solution. Each method has an advantage in their operating temperature range. As a result, the vapor–liquid equilibrium diagrams of ethanol solution at 20 °C and at the freezing temperature, and approximations of saturated pressure of various concentrations of ethanol solution for varying liquid temperature, are obtained.     

Freezing due to direct contact heat transfer including sublimation

From the energy saving viewpoint, the utilization of LNG cold is very important in the refrigeration industry concerning the low temperature region. In this paper, as a basic study of the freezing due to direct contact, including evaporation, solid–liquid direct contact heat transfer associated with sublimation has been investigated using the dry ice in water experimentally and theoretically. Based on a two-layers-model composed of CO₂ vapor and the bulk water around the dry ice, the velocity and temperature fields in two layers was calculated numerically and the calculated results for the freezing condition of the bulk water were compared with the experimental results.     

The modelling of the freezing process in fine-grained porous media: Application to the frost heave estimation

The solution of the moving-boundary problem, related to heat- and mass-transfer processes in freezing, fine-grained, porous media under phase-transition conditions is presented. It is assumed that a freezing zone, characterized by a wide temperature range of phase transitions, is formed. Therefore a three-zone model is developed. The preservation of the term ∂L/∂t(L is the ice content) in the system of equations has made it possible to determine the ice distribution within the frozen and the freezing zones. For loamy soils the dependence of the freezing process on the characteristic parameters, the Stefan and Lewis numbers, was analyzed. It was found that increasing the enthalpy of phase transition, i.e., decreasing the Stefan number Ste, resulted in diminution of the frozen zone but, at the same time, the ice content within this zone increased. Intensification of the migration process, i.e., increasing the Lewis number Le, also led to diminution of the frozen zone, in which the ice content and, consequently, the total moisture (including ice) were increased. For large Lewis numbers the freezing zone was observed to decrease. When the water migration process is absent (Le = 0), the calculations, which were based on the described model show that in the course of freezing the redistribution takes place only between moisture and ice contents. The total moisture remains constant and equal to the initial water content. The theoretical conceptions and results derived from the analytical solution are in agreement with experimental findings. The presented model predicts the freezing process in porous media and satisfactorily reflects observed phenomena. The utilization of the considered problem solution to the prediction of the frost heave phenomenon in soils freezing processes shown that the calculated frost heave curve matches the experimental results very closely indicating that the model can well reproduce the frost heaving process associated with the freezing. Propagation of the freezing front in the test is predicted the experimental results with reasonable accuracy.