超声辅助冷冻对湿面筋蛋白中冰晶粒度分布及总水含量的影响

超声辅助食品冷冻过程是一种新的技术。本文通过对湿面筋蛋白中冰晶粒度分布及总水含量的检测,探讨超声改善冷冻食品品质的微观作用机制,为超声冷冻新技术在食品化工中的应用奠定化学工程学基础。测定了有无超声环境下冷冻的湿面筋蛋白经过不同冷冻贮藏时间后总水含量, 结果显示：随着冷冻贮藏时间的延长,超声环境下冷冻的湿面筋蛋白中总水含量比传统环境下高。用扫描电镜和压汞仪间接观察和分析了冷冻的湿面筋蛋白中冰晶的形状和粒度分布。研究表明,适宜的功率超声辅助下,冷冻过程能在湿面筋蛋白内部形成细小且分布均匀的冰晶体,减少面筋蛋白网络结构的破坏,从而改善冷冻食品的品质。     

A Method for Single Particle Mass Spectrometry of Ice Nuclei

High altitude cirrus clouds play an important role in the terrestrial radiation budget. Cirrus clouds are composed of ice particles that generally form on only a small subset, from 1 in 10 to 1 in 10 5 , of the background aerosol. Ice particles may form due to the homogeneous freezing of aqueous aerosols or by the action of heterogeneous ice nuclei (IN). IN possess the ability to form ice at a higher temperature for a given vapor pressure of water than is required for homogeneous freezing. Apart from a few studies of refractory components, the chemical composition of these climatically important particles remains largely unknown. Almost nothing has been reported about the semivolatile and volatile components of IN. One of the principal reasons is that collection of cirrus precursors ideally should take place immediately after ice formation, before significant alteration of the crystals due to particle and gas-phase scavenging. Here we describe a method to measure the concentration and activation conditions of aerosols by exposure to temperatures and relative humidities (RH) similar to those that initiate cirrus cloud formation in the atmosphere. Laser mass spectrometry was subsequently used to investigate only those particles that nucleated ice. With this technique we were able to differentiate particles known to act as IN from those that entered the ice phase homogeneously. Deployment to study aerosol effects on ice formation in cirrus clouds is presented, although this method is applicable to the entire tropospheric mixed-phase and ice-phase regimes.     

Influence of Ultrasound-Assisted Osmotic Dehydration and Freezing on the Water State,Cell Structure,and Quality of Radish (Raphanus sativus L.) Cylinders

Ultrasound-assisted osmodehydrofreezing technique is a partial dehydration technique prior to freezing to diminish the tissue damage and preserve the quality by quickly removing part of the water from vegetable tissues. In this study, radish cylinders with three different water contents (85%, 80% and 75%, w/w) were dehydrated by osmotic dehydration (OD) and ultrasound-assisted osmotic dehydration (UOD). The effects of OD and UOD pretreatment on the characteristics (e.g., latent heat of fusion of ice, freezable water and microstructure) of dehydrated products and quality attributes (e.g., freezing time, firmness, drip loss and ascorbic acid content) of osmodehydrofrozen products were investigated. Ultrasound application significantly shortened the time of dehydration and subsequent freezing. Compared to OD products with equal water content, UOD products exhibited less freezable water content and better preservation on firmness and microstructure. After freezing/thawing, frozen products of UOD also displayed less drip and ascorbic acid losses and better firmness than that of OD.     

Development of a eutectic freezing process for brine disposal

At the eutectic point, both ice and salt crystallize out of salt water and brine volume is minimized. Thus, continuous eutectic freezing has major potentials for brine disposal and concentration of industrial wastes. This paper presents a laboratory study of the principal unit operations: crystallization, separation, and washing. The results prove technical feasibility and underlie a conceptual design of a two-stage eutectic freezing process. Process economics are also discussed.     

Three-Dimensional Measurement of Ice Crystals in Frozen Materials by Near-Infrared Imaging Spectroscopy

A novel technique was developed to recognize ice crystals in biological materials and to analyze their three-dimensional morphology using a Cryogenic Micro-Slicer Spectral Imaging System with a micro-slicer unit and a near-infrared spectral imaging unit. Consecutive cross-sections of a frozen sample were exposed by the multi-slicing operations with a minimum thickness of 1 µm, and their images were taken by the imaging unit. Spectroscopic analysis using a near-infrared spectrum meter showed an absorption peak at 1460 nm for pure water. Based on the observations of the absorption band of ice crystals in the wavelength range of 1450–1570 nm and its peak at 1495 nm, a commodity-type bandpass filter with a central wavelength of 1500 nm was adopted to identify ice crystals in near-infrared images. The absorption peak of water exhibited a tendency to move toward longer wavelengths with decreasing sample temperature from 25 °C to ?15 °C. The filtered images of ice crystals in frozen samples were darker than the other components at the peak wavelength of ice crystals. The three-dimensional reconstructed morphology of ice crystals revealed that they were formed along the direction of heat transfer while freezing. The proposed method provides a novel tool to investigate the effects of freezing conditions on the size, morphology and distribution of ice crystals.     

Ice-mould freeze casting of porous ceramic components

Porous, hollow ceramic components were produced by freeze casting technique. For this purpose aqueous slurries with high solid contents were prepared which were stable against freezing down to at least −5 °C. Ice cores were made by coating steel components with freezing water which were subsequently dip-coated with the ceramic suspensions. After freeze drying which removes both, the ice core and the frozen suspension liquid, and sintering, ceramic components with a high amount of open porosity including steel parts could be achieved. As an example hydroxyapatite was used for showing the opportunities of the freeze casting technology among others for applications in the field of bone replacement. The influence of the solid content of the hydroxyapatite slurries on the ice crystal growth has been investigated by means of compact hydroxyapatite bodies which were prepared by freeze casting using ice moulds with cylindrical cavities.     

海水雾化冷冻脱盐技术研究

首先利用雾化冷冻方法来处理渤海湾海水,使得海水部分冷冻为海冰,更多的盐分被包含在未发生冷冻的海水中而脱离冰体.在海冰形成过程中,由于冰晶形成速度要大于海水脱离冰晶的速度,所以最初形成的冰晶、冰针和冰片会发生合并,合并过程中包裹海水形成了"盐胞",因此海冰具有一定的含盐量.然后依次利用重力法和离心法对雾化冷冻得到的海冰进行深层脱盐.依次通过上述3种方法,能够将海水的盐度从25.5‰降低到2.9‰,脱盐率为88.63%.     

Mathematical modeling of the freezing process of concrete and aggregates

A two dimensional finite element computer model for predicting frost penetration in saturated porous materials is presented. Based on available second order parabolic differential equations for predicting temperature and moisture content, and equations relating freezing temperature and water potential, the finite element model predicts temperature, water and ice content, frost penetration, and generated pore water pressures as a function of freezing time and given boundary conditions, Comparison of models results with available experimental data for mature cement pastes rendered reasonable agreement between the model and data.     

Development and characterization of a “store and create” microfluidic device to determine the heterogeneous freezing properties of ice nucleating particles

Abstract

Understanding heterogeneous ice nucleation induced by ice nucleating particles (INPs) is hindered by analytical challenges in accurately determining the freezing temperature spectrum, abundance, and physicochemical properties of INPs. Here we evaluate the performance of a microfluidic device that employs a “store and create” approach to measure the ice nucleation properties of approximately 600 uniformly sized nanoliter water droplets. These droplets are immersed in surfactant-free environmentally sustainable squalene oil and do not contact the polymer walls of the microfluidic device. The device interfaced with a cold plate temperature controller has a greatly reduced background freezing temperature spectrum for filtered water droplets compared to conventional microliter droplet-on-substrate freezing methods. Droplets containing particles of interest are readily generated on-chip from a suspension of particles in water. Background freezing for 6 nL water droplets exhibits a median freezing temperature of ?33.7?±?0.4?°C, close to the theoretical freezing temperature of ?34.5?°C. The immersion freezing temperature spectra obtained from Snomax bacterial and illite mineral particles compares well with literature data, and the freezing contribution from either type of particle can be separated from a mixed suspension. Our approach generates a highly uniform droplet size distribution, causes no clogging of the microfluidic device, and is capable of reproducible droplet refreezes. The high-resolution freezing spectra obtained from large droplet number arrays enables the use of the derivative INP temperature spectrum analysis to quantitatively distinguish between different classes of INPs. The lower and consistent filtered water background freezing temperature enables measurements of almost the entire immersion freezing temperature regime from ?33 to 0?°C, and quantification of weaker but often abundant INPs such as those found in biomass-burning smoke aerosol.

Copyright © 2019 American Association for Aerosol Research     

真空冷冻——汽相冷凝海水淡化新技术研究

真空冷冻－－汽相冷凝海水淡化新技术的依据海水的三相点理论，使海水同时蒸发与结冰的一种低能耗、轻腐蚀结垢的海水海化方法。文章研究了各步骤的工艺条件，并完成了实验室小型装置，重点讨论了压力和温度对海水蒸发与结冰的影响、冰盐水的分离方法和冰晶洗涤以及蒸汽冷凝。结果表明产品淡化水可达到国家饮用水标准，蒸汽冷凝解决了蒸汽去除难的问题。     

Experiments and insights of desalination by a freezing/thawing method at low subcooling

Desalination by freezing/thawing method was a very important method to obtain fresh water from sea water. In this work, desalination by freezing/thawing method was conducted with initial sodium chloride of 3.5 wt% in consideration of stirring speed, freezing time and subcooling. The subcooling ranged from 1.2 K to 4 K. The optimum conditions for desalination in this work were stirring speed of 200 r·min^-1, freezing time of 120 min, and subcooling of 3 K. The results also showed that sodium chloride cannot be effectively removed by once freezing/thawing process. The maximum removal efficiency of sodium chloride was 64.3%. Two major reasons resulting in the impurity of obtained melted water by freezing/thawing method were proposed. The first reason was the inevitable adhesion of salt solution to the surface of ice, which could be removed easily by distilled water flushing. The second reason was that salt solution was heterogeneously wrapped in the accumulated ice, which was difficult to be removed by distilled water flushing. The liquid flushing method was proposed to verify the conjecture, and the results were in accordance with the two reasons mentioned above. Additional method, such as multiple flushing liquid method, was suggested to be used during the freezing/thawing process for effectively removing sodium chloride, and obtaining fresh water.     

Experiments and insights of desalination by a freezing/thawing method at low subcooling

Desalination by freezing/thawing method was a very important method to obtain fresh water from sea water. In this work, desalination by freezing/thawing method was conducted with initial sodium chloride of 3.5 wt% in consideration of stirring speed, freezing time and subcooling. The subcooling ranged from 1.2 K to 4 K. The optimum conditions for desalination in this work were stirring speed of 200 r·min⁻¹, freezing time of 120 min, and subcooling of 3 K. The results also showed that sodium chloride cannot be effectively removed by once freezing/thawing process. The maximum removal efficiency of sodium chloride was 64.3%. Two major reasons resulting in the impurity of obtained melted water by freezing/thawing method were proposed. The first reason was the inevitable adhesion of salt solution to the surface of ice, which could be removed easily by distilled water flushing. The second reason was that salt solution was heterogeneously wrapped in the accumulated ice, which was difficult to be removed by distilled water flushing. The liquid flushing method was proposed to verify the conjecture, and the results were in accordance with the two reasons mentioned above. Additional method, such as multiple flushing liquid method, was suggested to be used during the freezing/thawing process for effectively removing sodium chloride, and obtaining fresh water.     

Part I - Regional Activities : Section I - Desalination in the Americas

A dynamic model of a continuous crystallizer has been attempted as an extension of our work on the continuous freezing of ice from saline solutions and subsequent melting of the ice to give a potable water. In pilot plant equipment three distinct zones are designated as freezing, purification and melting, and our ultimate aim is to achieve a unified model applicable to the total system. The scope of this paper covers the freezing section in which basic equations for heat and mass transfer were applied covering the different components.     

Macroscopic ice lens growth in hardened concrete

Spalling of concrete has been observed in water retaining concrete structures exposed to long periods of freezing weather. A hypothesis is that poor quality concrete, inadequate compaction or aging make hardened concrete susceptible to macroscopic ice lens growth, i.e. ice segregation. To simulate winter conditions, the top surface of concrete specimens was subjected to freezing, whereas the bottom surface was submerged in heated water. Given constant thermal conditions, ice segregation occurred in sound concrete with w/c-ratio 0.9 and higher. In concrete with internal frost damage, ice segregation occurred within a few days regardless of the w/c-ratio. Ice segregation also occurred in specimens with paper sheets cast into the concrete to form cavities. However, the period of freezing required to facilitate ice segregation increased with decreasing w/c-ratio. The risk of macroscopic ice lens growth in actual structures cannot be overlooked since unfavourable temperature and moisture conditions may exist in winter.     

Freeze Decontamination Process: Modeling in a Simplified Case of Completely Mixed Aqueous Phase and Observations with Ultrasonic Agitation in the Liquid during Freezing

Abstract

Correlations among variables of the freeze decontamination process have not been developed to precisely predict experimental observations of purified solid ice out of a given aqueous solution on a macroscale. A lack of such information has been one of the main reasons for the very small practical application of the process so far. A simplified model has been presented in an effort to take into account the inhomogeneity of the solid phase. Pure ice spikes scattered on a cold surface have been supposed to grow opposite to the direction of heat dissipation, leaving unfrozen liquid channels among them along their length. The ice phase has thus been supposed to consist of pure ice spikes and a quantity of liquid entrapped among them. The liquid at the freezing front and in bulk is supposed to be completely mixed. Volume changes on freezing have also been taken into account. The model has been compared with experimental observations on a specially fabricated apparatus. Temperatures of a cold freezing surface have been continuously lowered while following a ?0.0017 K/s gradient during experiments. An ultrasonic mixing technique has been applied to the liquid during freezing to eliminate impurity (cesium nitrate) concentration gradients in the liquid. A comparison of the model with experimental observations has been made with the help of a decontamination factor (DF) [concentration of impurity in the initial liquid/ concentration of impurity in the frozen mass (after it has been melted)] versus V/V ₀ (volume of unfrozen liquid left at any point during freezing/volume of initial liquid taken) plots. Although a scatter in the experimental results has been observed, there was broad agreement with the model trend. The average value of DF has been as high as 46. The investigation has highlighted the importance of the factors that determine the fraction of pure ice spikes in the growing solid at any point during freezing.     

Undercooling,Freezing Point Depression,and Ice Nucleation of Soil Water

Certain aspects of the phenomena of undercooling and ice nucleation in soils are discussed with respect to recently established properties of phase boundary water in soils. Nucleation temperature as a function of water content is given for representative clays. In view of the fact that silicate surfaces seem always to be separated from ice by an interfacial layer of unfrozen, liquid like water a new concept of heterogeneous nucleation is outlined. It is proposed that ice nucleation occurs in the undercooled interfacial water layer at some distance removed from the particle surfaces. This concept, in effect, suggests that heterogeneous nucleation (nucleation of ice due to the influence of a substrate) in all its essential aspects may be only a special case of homogeneous nucleation (no substrate present) of water.     

The University of Toronto Continuous Flow Diffusion Chamber (UT-CFDC): A Simple Design for Ice Nucleation Studies

A new instrument, the University of Toronto Continuous Flow Diffusion Chamber (UT-CFDC), has been designed to study ice nucleation at low temperatures. Based on previous continuous flow instruments, it is a parallel plate model that minimizes convective instabilities by operating horizontally with the warmer plate on top. A variable position sample injector can account for effects arising from gravitational settling of ice particles that form. The residence time in the chamber can vary between 2.6 to 25 s and ice particle formation is monitored with a two-channel optical particle counter. Observation of homogeneous freezing of 100 nm sulfuric acid aerosols was used to verify the accuracy of the calculated relative humidities (RHs) in the chamber to be ±4%, where we report onset RHs for 0.1% of the particles freezing in the temperature range of 218 to 243 K. We also show that the chamber accurately establishes conditions of water saturation by conducting water uptake studies onto sulfuric acid aerosol at 243 K. The two channel OPC allows for ice and water droplet formation to be distinguished under such conditions. The chamber is a simple, cheap, and small design that can be readily assembled for laboratory studies.     

Mixtures of Organic and Inorganic Salts to Prevent Coal Freezing

Methods are proposed for the production of effective new reagents: binary salt systems that form low-temperature eutectics with water and readily melt ice, thereby preventing the freezing of coal in autumn and winter. Considerations of availability, cost, and physicochemical properties are of most importance in the selection of mixtures of organic and inorganic salts that are able to prevent the freezing of coal at temperatures down to–40°C. Research shows that the freezing point of solutions of organic-salt mixtures are lower than those of the individual mixture components. This may be explained by a synergetic effect. The consumption of the proposed salt mixtures for the prevention of coal freezing is considerably less than that of comparable systems containing only a single salt.     

Desalination by the improved vacuum freezing high pressure ice melting process

The VFPIM process has the following advantages: It does not require a compressor nor an absorbing solution for low pressure water vapor, nor a refrigeration loop (heat pump) to reuse the heat released in the condensation or desublimation of the low pressure water vapor in supplying the latent heat of melting ice. The process uses commercially available components and can thus be operated reliably.Some of the key unit operations are similar to those in existing vacuum freezing processes, but those unique to this process are: desublimation of low pressure vapor, pumping of an ice water slush containing a high ice content, melting of ice inside a heat conductive conduit and exchange ice formation operations. An extended surface freezer was found to have several advantages over the conventional spray freezer.     

Frozen slurry-based laminated object manufacturing to fabricate porous ceramic with oriented lamellar structure

The freeze drying-based additive manufacturing can be used to process porous ceramics. However, the lack of freezing direction leads to the disorderly porous structure. This paper proposes a frozen slurry-based laminated object manufacturing (FS-LOM) for processing porous ceramics. Slurry was composed of water, alumina powder, and organic binder. The water in the fresh slurry layer crystallized to obtain a good support strength. The outline of 2D pattern was cut with laser to gasify ice crystal and binder. After stacking, the ice crystal freeze dried to obtain a porous structure. The lamellar ice crystals were induced to growth vertically by layer-by-layer freezing. The uniformity and orientation of the pore structure were improved, and the compression strength of the parts were improved. Due to the support of frozen slurry, the deformation of the green part was avoided.