The mechanism of repeated-segregation for the formation of thick layered ground ice

In this article, a mechanism of repeated-segregation for the formation of thick layered ground ice has been suggested. The mechanism consists of the following processes: (1) Moisture migration to the freezing front and ice lensing there as a result of upward freezing from permafrost. (2) Unequal law of migration of unfrozen water (the combined effect of the following processes: the upward migration of unfrozen water in a frozen active layer in the cold season; water migration and ice lensing in the frozen ground behind the freezing front during upward freezing; water migration and ice lensing in the still frozen ground beneath the thawing plane in the warm season). (3) Self-purification of ice. (4) Syngenetic growth of ground ice due to the addition of material onto the ground surface. (5) Annual repetition of the processes mentioned above. Thus, a new type of ground ice — repeated-segregation ice — is distinguished.     

螺旋藻细胞冷冻过程微尺度传热传质特性

为了探索保持螺旋藻活性的最佳冷冻条件,研究了冷冻过程凝固界面和螺旋藻细胞之间相互作用的物理现象,在考虑细胞和冰界面之间的耦合传热传质、膜的传输特性和凝固界面的移动过程的情况下,建立了螺旋藻细胞冷冻过程冰界面与细胞之间相互作用的数学模型,检查了螺旋藻细胞被冰界面包围过程的温度场和浓度场,研究了螺旋藻细胞被冰界面包围过程中细胞体积的收缩情况及影响因素.计算结果表明,膜的渗透性和冷却速率是影响细胞体积收缩的主要因素.该模型可优化减小螺旋藻细胞损伤的最佳冷冻条件.     

Dynamic Low-Frequency Electrical Impedance of Biological Materials Subject to Freezing and Its Implementation in Cryosurgical Monitoring

A precise monitoring of the extent of freezing during a cryosurgical process has been an important problem in health-care clinics. Among various existing techniques, the dynamic electrical impedance utilizing the impedance jump to detect the ice moving front, is a suitable way because the impedance of frozen tissue is much higher (3 to 4 orders of magnitude or even larger) than that of unfrozen tissue. Based on two experimental setups, the dynamic low-frequency impedance (DLFI) and impedance changing rate (ICR) for selected biological materials (fresh pork and rabbit tissues) subject to freezing were systematically measured. Their transient behaviors were investigated, and implementations in a practical cryosurgery to detect ice front propagation were analyzed. Furthermore, in vitro experiments were performed on distilled water and phantom gel. The experimental results, obtained with a two-electrode measuring technique, are as follows: (1) The impedance of all samples has a rapid response to the external freezing. (2) The impedance will not jump into an insulation region when the cooling temperature is not low enough. (3) As an alternative to DLFI, ICR imaging can also give important information for the phase-change process, which may lead to an efficient method to detect the ice-ball growth. (4) There is an evident variation in DLFI for different biological tissues when subjected to the same cooling temperatures; this value also differs for the same tissue under different cooling conditions.     

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。     

天然浮石混凝土孔溶液结冰规律的研究

以内蒙古天然浮石作为粗骨料,通过冻融核磁共振技术模拟冻融循环温度变化过程,并测得天然浮石混凝土在冷冻和融化过程中孔溶液信号量、结冰速率、T2谱和孔径分布的变化规律,结果表明:用冷冻过程中的含冰量来评价孔溶液结冰引起的静水压比较符合实际情况;天然浮石混凝土发生冻害的温度主要是-15℃以上。探讨了天然浮石混凝土孔溶液的结冰规律。     

Modeling of ice formation in porous solids with regard to the description of frost damage

The freezing and thawing of liquid in porous media in connection with the question concerning the frost durability of solid materials is an important subject for discussion in civil engineering. Each construction or body which is in contact with liquid and frozen water is criticized by its resistance to the environment. The durability concerning frost attacks of a building material is affected by its porosity and the pore size distribution. The ice formation is a phenomenon of coupled heat and mass transport in freezing porous media, and is primarily caused by the expansion of ice in connection with hydraulic pressure. The volume increases due to the freezing front inside the porous solid. Taking into account the aforementioned effects in porous materials, a simplified macroscopic model within the framework of the Theory of Porous Media (TPM) for the numerical simulation of initial and boundary value problems of freezing and thawing processes of super saturated porous solids will be presented. The phase change between the ice and the liquid phase is modeled by different real densities of the phases.     

Macroscopic behavior of freezing saturated silty soils

The macroscopic behavior of freezing saturated silty soils was studied through a series of nine laboratory experiments. Under the range of test conditions, the heaving rate remained near-constant throughout a given experimental run as long as the overburden load was unchanged; water flow varied throughout the early period of experiments and then also stabilized at a near-constant rate; and ice lenses were found to grow predominantly at the freezing front but also occasionally on its cold side.Because the amount of water frozen in the soil per unit time is shown to be largely independent of the growth of visible ice lenses, segregation ice probably forms pervasively throughout the soil samples, frequently on a scale too small to be visibly detected. An experimentally demonstrated consequence of this pervasive segregation ice is the low strength of apparently unlensed, newly thawed soils, relative to the same soil at the same water content which has never been frozen.     

Numerical analysis of coupled water,heat and stress in saturated freezing soil

Clapeyron equation can be applied in freezing soil to describe the relationship among temperature, water pressure and ice pressure when ice and water coexist in phase equilibrium. The mathematical deduction shows that the driving force that makes the unfrozen water in soil moves from high temperature area to low temperature area is determined by gravity, temperature and pore pressure. Upon proposing the concept of separating void ratio as a judge criterion for the formation of ice lenses, adjusting the hydraulic conductivity to describe the unfrozen water gathering at the front of ice lenses and the growth of ice lens, a mathematical model of coupled water, heat and stress is established. A typical process of coupled water, heat and stress that happens in a saturated freezing soil column is simulated by COMSOL Multiphysics simulation software. The amount of frost heave is calculated, and the result of simulation gives the distribution bar graph of ice lenses and distribution curves of temperature, equivalent water content and pore pressure, and shows how they change.     

Self-assembly of cerium oxide nanostructures in ice molds

The formation of nanorods, driven by the physicochemical phenomena during the freezing and after the aging of frozen ceria nanoparticle suspensions, is reported. During freezing of a dilute aqueous solution of CeO2 nanocrystals, some nuclei remain in solution while others are trapped inside micro- and nanometer voids formed within the growing ice front. Over time (2-3 weeks) the particles trapped within the nanometer-wide voids in the ice combine by an oriented attachment process to form ceria nanorods. The experimental observations are consistent with molecular dynamics simulations of particle aggregation in constrained environments. These observations suggest a possible strategy for the templated formation of nanostructures through self-assembly by exploiting natural phenomena, such as voids formed during freezing of water. This research suggests a very simple, green chemical route to guide the formation of one- and three-dimensional self-assembled nanostructures.     

The adsorption force theory of frost heaving

Presented in this paper are the theorization of a traditional concept of the mechanics of frost heaving, as well as a critical review of the recent developments in this field. The key to the theorization is the following: (1) the film water adsorbed on soil particles can build up an internal solid-like stress, and (2) the flow of film water is different from the conventionally accepted flow of pore water. It is expected that modern continuum mechanics will, in the future, improve the theory of film water which, in this paper, has been formulated by use of the classical method.The freezing film water, trying to retrieve the loss of its thickness to the frozen ice, generates a suction force that draws water to the freezing front where the frost-heaving pressure pushes up the overburden. The temperature of the freezing film water that has generated the solid-like stress, is lower than the temperature of the freezing pore water. This distribution of freezing temperatures in the region of film and pore waters explains the observation that the freezing front causing frost heaving is not a planar surface but a three-dimensional zone diffused in the direction of heat transfer. Frost-heaving pressure can be derived as part of the solution of the boundary-value problem of the frost-heaving differential equations.     

Use of neutron activation analysis for evaluating the efficiency of water treatment to remove heavy metal ions by zone freezing

The efficiency of zone freezing for potable water treatment to remove inorganic impurities was examined. The content of impurities in model solutions before and after zone freezing was evaluated by neutron activation analysis with the formation of ⁵⁶Mn, ^116m In, and ¹⁹⁸Au radionuclides. The zone freezing procedure is the most efficient at low ice front velocities (no greater than 0.15 cm h⁻¹).     

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.     

Influence of cyclic freeze-thaw on the mobilization of LNAPL and soluble oil in a porous media

Subsurface behavior of spilled fuel in freezing and frozen porous media including fractured bedrock is not well understood. To simulate a bedrock fracture, a freezing cell consisting of two parallel glass plates filled with glass beads was constructed to study the impact of cyclic freeze-thaw on LNAPL movement. The test procedure involved introduction of LNAPL atop the cell that contained water mixed with fluorescein dye. Freezing progressed from the top down, with observation and measurement of the LNAPL migration using a high-resolution digital camera and time-lapse photography. Both diesel and soluble oil were used for the experiments. Tests with soluble oil involved thorough mixing at 12.5% volume ratio with the fluorescein-water mixture in the freezing cell. The results showed upward mobility of the LNAPL under cyclic freezing and downward progressive expulsion of the soluble oil ahead of the advancing freezing front. The results corroborated literature findings on organic solute expulsion ahead of freezing front, and provided insight into the behavior of trapped LNAPL below the water table when subjected to freeze-thaw conditions. Additionally, micro fissures were observed in the formed ice inside the freezing cell under prolonged freezing. Such micro fissures may provide potential migration pathways for fresh spilled fuel in permafrost environments.     

The effect of supercooling on ice structure in tuna meat observed by using X-ray computed tomography

Several studies have reported that freezing a homogeneous food such as soy bean curd with deep supercooling (supercooled freezing) results in the formation of many particle ice and homogenous ice structure. However, ice crystal morphology may be affected by the cellular structure of the food. In this study, the ice crystal structure in tuna meat, a cellular food, frozen by the supercooled freezing method was investigated by X-ray computed tomography and compared with ice structures in tuna meat frozen by conventional freezing methods. The results showed that rod-like ice crystals grew parallel with the myofibers, and inhomogeneous ice structures formed in tuna meat frozen by the supercooled freezing method regardless of the degree of supercooling, in contrast to the ice structure in frozen soy bean curds. These ice crystals linked with each other to form rod-like ice structures due to mobility limitations imposed by the cellular structure.     

Numerical modelling of an innovative microwave assisted freezing process

This study aimed to model an innovative process of pulsed microwave assisted freezing (MAF), which was expected to improve frozen product quality. The phase change model was based on spherical ice crystal growth and an original enthalpy formulation. The objective was to understand better the thermal interactions between microwaves and a product being frozen in a TE10 waveguide in which nitrogen gas and microwaves reach the product on the top surface. The 2D model was validated against the literature data and used to perform numerical simulations. The freezing front location and the reflection at air-product interfaces have a large impact on microwave behaviour in the product, especially on hot-spot displacement. As in some experimental works, temperature oscillations were observed. It is shown that their amplitude is related to the pulse duration. These results will help in designing experimental procedures to study the interest of using low energy pulsed microwaves during freezing.     

充冷过程中冷板内特性研究

针对机械冷板冷藏车冷板充冷时间长的问题,根据热量守恒原理建立了冷板内共晶冰冻结过程的数学模型,并对影响冷板充冷过程的关键因素进行了讨论,用准静态方法对蒸发盘管外共晶冰的形成过程进行了数值计算.计算结果表明,随着盘管周围共晶冰厚度的增加,共晶冰冻结缓慢;降低蒸发温度,减少冷板外热负荷,可以明显减少共晶冰的冻结时间;冻结过程中,冷板内的逐时蓄冷量基本不变.     

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.     

The front-tracking scheme for the one-dimensional freezing problem

The one-dimensional freezing problem can be solved numerically for the temperature distribution accompanied by explicit reference to the position of the freezing front at each time interval. A new front-tracking scheme provides accurate determination of the phase front, which is an essential requirement for the temperature distribution in the different phases of such problems. The front is made to coincide with a grid-node throughout the analysis. The scheme uses a combination of the finite difference and the finite element methods for obtaining the solution of the freezing problems.     

小鼠睾丸组织玻璃化保存的初步实验研究

对于无法取精的不育患者或患有癌症需放化疗的青春期前男孩,睾丸组织冷冻是潜在的有效保存生育力的方法.本文对小鼠块状睾丸组织的玻璃化保存方法进行了研究,运用差示扫描量热仪,对在不同体积分数保护剂中浸泡了不同时间后的小鼠块状睾丸组织进行热分析,随后对其进行玻璃化冻存,并将睾丸组织慢速冷冻保存与玻璃化冻存进行了对比.结果表明:...     

Effect of cooling rate on freezing of a saturated soil

Assuming that overburden pressure does not constitute a limiting factor for frost heaving and that all pore spaces among particles have the same size, we have discussed the freezing of such idealized soil saturated with water under conditions where the temperature of the ground surface falls at a given rate. From the law of conservation of mass and heat alone, we obtained a necessary condition for three kinds of frozen soil: (1) a frozen soil with an ice layer due to segregational freezing; (2) homogeneously frozen soil containing no visible ice layers resulting from in situ freezing of pore water; and (3) a frozen soil with rhythmic ice banding.