A Review of Thermo- and Diffusio-Phoresis in the Atmospheric Aerosol Scavenging Process. Part 2: Ice Crystal and Snow Scavenging

The role of phoretic forces in the identification of particles acting as ice nuclei in mixed phase cloud is discussed. A method used to identify the effective ice nucleating particles is to sample ice crystals, which are afterwards sublimated, and to examine the particles remaining after evaporation. The procedure takes into account only crystal with a maximum diameter of 20 μm, by assuming that small crystals do not scavenge aerosol during growth, and therefore that crystals contain only the effective nucleating particles. This assumption is questionable, however, as experiments have shown that even small ice crystals can scavenge aerosol. Another approach has been to compare the number and elemental composition of residual particles in small ice crystals and of aerosol near the cloud. By considering as example soot and black carbon aerosol, contradictory conclusions on their importance in the processes of ice nucleation have been reported in the literature. We suggest that, in addition to physico-chemical properties of soot/carbon aerosol particles, even the microphysical and environmental parameters involved in the transition of aerosol from gas phase to ice crystals in cloud should be considered. The contribution of phoretic forces should also be considered. After initial growth ice crystals can continue to grow by water vapour diffusion. Laboratory experiments confirm the contribution of diffusiophoresis with Stefan flow in the scavenging by snow crystals up to 3 mm in diameter. The particle scavenging efficiency of snow crystals is related to crystalline shape and depends on air relative humidity and temperature.

Factors affecting ice crystal purity during freeze concentration process for urine treatment

Freeze concentration has great potential in treating wastewaters containing soluble pollutions. It is important for freeze concentration process to produce ice crystals with large size and high purity. In this work raw urines of 4660 -7914 mg/L in COD, 512. 71 -872. 41 mg/L in NH3 -N and 22600 -28800 μs/cm in electric conductivity were studied. Urines were frozen by a digital refrigerated circulator bath. Ice crystals were purified by ice-water steep and vacuum filtration. The COD, NH3 - N, and electric conductivity levels of the melted ices were measured to reflect ice crystal purity. Effects of coolant temperature, ice crystal shape, initial solution temperature, solution concentration, ice seeding, re-crystallization process and crystallization time on ice crystal purity were analyzed. The results show that an appropriate coolant temperature, suspended ice crystals, an initial solution temperature of about 6 ℃, introduction of seed ice, addition of re-crystallization process, and crystallization time of less than 30 min axe in favor of producing ice crystals with high purity. Under such conditions, more than 99 percent of inorganic salts, COD and NH3 - N sources in raw urine could he removed.

Observation on the modifying activity of the protein from Elytrzgia repens rhizome for ice crystal

In winter, spring and summer, the rhizome of wild Elytrzgia repens of Heilongjiang Province was selected to extract the soluble which whole protein and the apoplastic protein, and analyzed by SDS-PAGE. The result indicated that there were two specific polypeptides in two types protein from winter; their relative molecular weight were identified as 52 ku and 26 ku by analyzing software; the apoplastic protein from winter had the ability of modifing the growth of ice crystal which appeared hexagonal in shape observed with the phase-contrast photomicroscope. So the apoplastic protein from winter has the antifreeze characters and the 52 ku protein is more likely the antifreeze protein

Influence of Mass and Radius of Ice Crystals on Hydrometeors,Internal Energy,and Kinetic Energy:A Numeric Model Study

Two cloud-scale experiments with two different ice-phase schemes were carried out for a precipitation event that occurred in eastern China in 2005.The results were analyzed to examine the influences of the change of ice-particle mass and radius on hydrometeors,internal energy,and kinetic energy,as well as the primary factors responsible.It was found that the ice content increases notably and the snow content decreases due to the change.This is the consequence of the modulation of cloud microphysical processes.In particular,the Bergeron process and the accretion of snow and cloud ice are markedly influenced.The differences of internal energy and kinetic energy between the two experiments are caused by adjustments to pressure-flux divergence,the coupling of temperature and divergence,and gravitational work,and the reason is that these three factors result in differences of local changes of internal and kinetic energy.

A MODELING STUDY OF PARAMETERIZATION SCHEMES FOR DEPOSITIONAL GROWTH OF ICE CRYSTAL:FOUR RAINFALL CASES OVER TROPICS AND MIDLATITUDES

Depositional growth of ice crystal is one of the major processes for development of precipitation systems and can be represented by depositional growth of cloud ice from cloud water(P_(IDW)) and depositional growth of snow from cloud ice(P_(SFI)) in cloud-resolving model. Four parameterization schemes are analyzed in the cloud-resolving model simulations of four rainfall cases over the tropics and midlatitudes. The comparison of time and model domain mean data shows that Shen's scheme produces the closest rainfall simulation to the observation. Compared to Zeng's scheme,Shen's scheme improves the mean rain-rate simulation significantly through the dramatic decrease in depositional growth of cloud ice from cloud water. Compared to other schemes, Shen's scheme produces the better rainfall simulation via the reduction in the mean rain rate associated with the enhanced gain of cloud water and ice.

Calculation of Ice Crystal Diffraction

The diffraction angular distributions are calculated for different ice crystals (e.g,solid and hollow hexagonal columns,solid plates and single hexagonal bullet) randomly oriented in space,based on the theory of Cai and Liou.Results of solid column and plate are compared with those from formulas of Wendling et al and Liou.The resull comparison shows that all three procedures discussed in this paper have good agreement.After considering the coin putation time and comparison results,it is suggested that the formula of Wendling et al.can be used to calculate the solid column diffraction,and the formula of Liou can be used to calculate the plate diffraction.The comparison also shows that the diffraction results of solid columu,hollow column and single bullet ice particles randomly oriented in space are very close.

Numerical Simulation of the Scavenging Rates of Ice Crystals of Various Microphysical Characteristics

Numerical models of trajectories of small aerosol spheres relative to oblate spheroids were used to determine ice crystal scavenging efficiencies. The models included the effects of aerodynamic flow about the ice particle, gravity, aerosol particle inertia and drag and electrostatic effects. Two electric configurations of the ice particle were investigated in detail. The first applied a net charge to the ice particle, of magnitude equal to the mean thunderstorm charge distribution, while the second applied a charge distribution, with no net charge, to the ice particle to model the electric multipole charge distribution. The results show that growing ice crystals with electric multipoles are better scavengers than single ice crystals with net thunderstorm charges, especially in the Greenfield gap (0.1 to 1.0 um), and that larger single crystals are better scavengers than smaller single crystals. The results also show that the low density ice crystals are more effective scavengers with net charges than they are with charge distribution.

Distributions of crystals and gas bubbles in reservoir ice during growth period

In order to understand the dominant factors of the physical properties of ice in ice thermodynamics and mechanics, in-situ observations of ice growth and decay processes were carried out. Two samplings were conducted in the fast and steady ice growth stages. Ice pieces were used to observe ice crystals and gas bubbles in ice, and to measure the ice density. Vertical profiles of the type and size of ice crystals, shape and size of gas bubbles, and gas bubble content, as well as the ice density, were obtained. The results show that the upper layer of the ice pieces is granular ice and the lower layer is columnar ice; the average crystal size increases with the ice depth and remains steady in the fast and steady ice growth stages; the shape of gas bubbles in the upper layer of ice pieces is spherical with higher total content, and the shape in the middle and lower layers is cylinder with lower total content; the gas bubble size and content vary with the ice growth stage; and the ice density decreases with the increase of the gas bubble content.

SCATTERING PHASE MATRICES OF ICE CRYSTALS WITH HEXAGONAL PRISM AND TRIANGULAR PYRAMID FORM—A VECTOR RAY TRACING METHOD

The work presented previously by the authors(Cai and Liou,1982)has been extended in this paper. By making use of our improved model the calculations on scattering phase matrices of hexagonal prism ice crystals(HPIC)have been conducted for monodisperse and polydisperse systems.Compared with the model of Cai and Liou,the required computational quantity is decreased by about two orders of magni- tude and the errors of results are less for the new model.Meanwhile,the scattering phase matrices of triangular pyramid ice crystals(TPIC)are also computed in the paper,and the comparison between the scatterings of the two forms of ice crystals is performed.

Ice Crystal Growth Mechanism and Structure-activity Relationships of Graphene Oxide/Poly(vinyl alcohol)Aerogels

Aerogels are special porous materials with low thermal conductivity,light weight,high energy absorption rate and large surface area,which have been applied in many fields.However,controlling the aerogel microstructure remains an academic challenge.Herein,by employing graphene oxide(GO)as the aerogel skeleton and utilizing poly(vinyl alcohol)(PVA)to regulate the ice crystal growth,we elucidate the relationships between the physicochemical properties of GO/PVA aerogel precursors and the nucleation and growth of ice crystals by using an ice-templating method.We demonstrate that due to the hydrogen bond formed between PVA and water molecules,resulting in the initial crystallization temperature being reduced from-12.60℃(GO/PVA-0.01)to-16.21℃(GO/PVA-0.1).Meanwhile,the strong hydrogen bond between PVA and GO limits the diffusion of water molecules,thereby inhibiting the growth of ice crystals,decreasing the pore size of the GO/PVA aerogel from 9.96 nm(GO/PVA-0.01)to 7.19 nm(GO/PVA-0.3),and thus the compressive strength of the aerogel increases from 0.045 MPa to 0.13MPa.Overall,the finding of this study can be extended to other aerogel precursors,and exhibit important scientific value and practical significance for the preparation of aerogel materials with highly controllable structures and performances.

MEASUREMENTS OF ICE-FORMING RATES PRODUCED BY SUPERSONIC FLOW AND INVESTIGATION OF MECHANISMS OF ICE CRYSTAL GENERATION

The ice forming rates p_i produced by supersonic flow have been measured in supercooled fog suspended in a cold chamber at temperatures of 0 to-12℃.It has been shown that the ice-forming rates are 10^(11)to 10^(12)crystals per gram of air at Mach numbers of 1.1 to 1.84 and total pressures below 6 atm,and that the ice-forming rates slowly increase with increasing Mach numbers and total pressures and with decreasing ambient temperatures.These results are theoretically consistent with the rules for expansion in supersonic flow. In review of mechanisms of ice crystal generation,authors propose that the homogeneous nucleation-freezing (condensation-freezing)of water vapor in supersonic flow be the dominant mechanism.In our opinion,supersonic flow, for artificial precipitation,could be expected to provide an economical,non-polluting and convenient technology,and suitable for the long-distance operation.The data obtained from our experiments indicate that it is feasible to develop a new technique for weather modification.

Ice Slurry Formation in a Cocurrent Liquid-Liquid Flow

A new technique for ice slurry production was explored. Multiple small water-drops were formed in another immiscible chilled liquid by a single-nozzled atomizer and frozen in the fluidized bed by direct contact heat transfer. Experiments were conducted to investigate the dynamic behaviors of the ice crystal making system. The results demonstrate that the ice crystals could be produced continuously and stably in the vertical bed with the circulating coolant of initial temperature below -5℃. The size distribution of the ice crystals appears non-uniform, but is more similar and more uniform at lower oil flow rate. The mean ice crystal size rests seriously with the jet velocity and the oil flow rate. It decreases with decreasing the oil flow rate, and reaches the maximum at an intermediate jet velocity at about 16.5 m.s y. The ice crystal size is also closely related to the phenomenon of drop-coalescing, which can be alleviated considerably by reducing the flow rate or lowering the temperature of the carrier oil. However, optimization of liquid-liquid atomization is a more effective approach to produce fine ice crystals of desired size.

Torrential Rainfall Responses to Ice Microphysical Processes during Pre-Summer Heavy Rainfall over Southern China

In this study, the effects of key ice microphysical processes on the pre-summer heavy rainfall over southern China during 3-8 June 2008 were investigated. A series of two-dimensional sensitivity cloud-resolving model simulations were forced with zonally uniform vertical velocity, zonal wind, horizontal temperature, and water vapor advection data from the National Centers for Environmental Prediction （NCEP）/Global Data Assimilation System （GDAS）. The effects of key ice microphysical processes on the responses of rainfall to large-scale forcing were analyzed by comparing two sensitivity experiments with a control experiment. In one sensitivity experiment, ice crystal radius, associated with depositional growth of snow from cloud ice, was reduced from 100 #m in the control experiment to 50 #m, and in the other sensitivity experiment the efficiency of the growth of graupel from the accretion of snow was reduced to 50~ from 100% in the control experiment. The results show that the domain-mean rainfall responses to these ice microphysical processes are stronger during the decay phase than during the onset and mature phases. During the decay phase, the increased mean rain rate resulting from the decrease in ice crystal radius is associated with the enhanced mean local atmospheric drying, the increased mean local hydrometeor loss, and the suppressed mean water vapor divergence. The increased mean rain rate caused by the reduction in accretion efficiency is related to the reduced mean water vapor divergence and the enhanced mean local hydrometeor loss.

Upper limits for chlorophyll a changes with brine volume in sea ice during the austral spring in the Weddell Sea,Antarctica

During the winter and spring of 2006, we investigated the sea ice physics and marine biology in the northwest Weddell Sea, Antarctica aboard R/V Polarstern. We determined the texture of each ice core and 71 ice crystal thin sections from 27 ice cores. We analyzed 393 ice cores, their temperatures, 348 block density and salinity samples,and 311 chlorophyll a（Chl a） and phaeophytin samples along the cruise route during the investigation. Based on the vertical distributions of 302 groups of data for the ice porosity and Chl a content in the ice at the same position, we obtained new evidence that ice physical parameters influence the Chl a content in ice. We collected snow and ice thickness data, and established the effects of the snow and ice thickness on the Chl a blooms under the ice, as well as the relationships between the activity of ice algae cells and the brine volume in ice according to the principle of environmental control of the ecological balance. We determined the upper limits for Chl a in the brine volume of granular and columnar ice in the Antarctica, thereby demonstrating the effects of ice crystals on brine drainage, and the contributions of the physical properties of sea ice to Chl a blooms near the ice bottom and on the ice-water interface in the austral spring. Moreover, we found that the physical properties of sea ice affect ice algae and they are key control elements that modulate marine phytoplankton blooms in the ice-covered waters around Antarctica.

Modelling of heat transfer for progressive freeze concentration process by spiral finned crystallizer

This study presents a novel design for a spiral finned crystallizer which is the primary element of progressive freeze concentration(PFC) system, which simplifies the setup of the conventional system. After the crystallizer has been designed, the research experiments have been conducted and evaluated through a thorough analysis of its performance by developing a mathematical model that can be used to predict the productivity of ice crystal at a range of coolant temperature. The model is developed based on the basic heat transfer equation, and by considering the solution's and the coolant's convective heat transfer coefficient(h) under the forced flow condition.The model's accuracy is verified by making comparison between the ice crystal mass' experimental value and the values predicted by the model. Consequently, the study found that the model helps in enhancing the PFC system.

A Critical Review on Superchilling Preservation Technology in Aquatic Product

aquatic product, known as one of the good resources for white meat, has been widely accepted by the consumers due to its high protein, low fat, especially low cholesterol. With the fast development of living standards around the world, the consumer demands for high quality, nutrition, safety and freshness of ifshery food are increasing. Thus, high efifcient preservation technologies for aquatic products become particularly important. Superchilling is one of the controlled-temperature preservation technologies for seafood. Aquatic products can be kept in better quality under superchilling conditions. This review introduced the principle and development of superchilling process, mainly focusing on research progresses and technical dififculties of superchilling. The growth mechanism of ice crystals and the feasibility of application of computational lfuid dynamics in analyzing the temperatures variation and ice crystals during superchilling progress were also discussed, which will provide theoretical foundation for its improvement and application.

Optimization of ultrasonic-assisted freezing of Penaeus chinensis by response surface methodology

Objectives:Optimization of ultrasonic-assisted freezing of Penaeus chinensis by response surface methodology was studied in order to(1)obtain frozen Penaeus chinensis of high quality and(2)provide practical guidance for the application of ultrasonic-assisted freezing in Penaeus chinensis.Materials and Methods:Three independent and major variables were selected,including initial ultrasonic temperature(℃),ultrasonic power(W)and ultrasonic time(s on/2 s off).On the basis of one-factor experiments,17 groups of experiments were established by response surface methodology according to Box-Behnken design.Using multiple regression analysis the experimental data were fitted into a second-order polynomial equation,which was tested by proper statistical methods.Results:The optimal ultrasonic conditions were as follows:initial ultrasonic temperature 0℃,ultrasonic power 180 W,ultrasonic time 5 son/2 s off.Under the optimization conditions,the time of passing through maximum ice crystal generation zone was 105.500 s,which was very close to the predictive passage time of 101.541 s.Conclusions:Initial ultrasonic temperature,ultrasonic time and ultrasonic power played an important role in the process of ultrasonic-assisted freezing of Penaeus chinensis.Response surface methodology was used to optimize the three factors in ultrasonic-assisted freezing,which could greatly shorten the time of passing through the maximum ice crystal generation zone and maintain the tissue structure of Penaeus chinensis well.

Semi-Idealized Modeling of Lightning Initiation Related to Vertical Air Motion and Cloud Microphysics

A three-dimensional charge^lischarge numerical model is used, in a semi-idealized mode, to simulate a thunder- storm cell. Characteristics of the granpel microphysics and vertical air motion associated with the lightning initiation are revealed, which could be useful in retrieving charge strength during lightning when no charge^diseharge model is available, The results show that the vertical air motion at the lightning initiation sites （Wini） has a cubic polynomial correlation with the maximum updraft of the storm cell （WceH_m^x）, with the adjusted regression coefficient R2 of ap- proximately 0.97. Meanwhile, the graupel mixing ratio at the lightning initiation sites （qg-ini） has a linear correlation with the maximum graupel mixing ratio of the storm cell （qg-cell-max） and the initiation height （Zini）, with the coeffi- cients being 0.86 and 0.85, respectively. These linear correlations are more significant during the middle and late stages of lightning activity. A zero-charge zone, namely, the area with very low net charge density between the main positive and negative charge layers, appears above the area of qg-oewm and below the upper edge of the granpel re- gion, and is found to be an important area for lightning initiation. Inside the zero-charge zone, large electric intensity forms, and the ratio of qice （ice crystal mixing ratio） to qg （graupel mixing ratio） illustrates an exponential relation- ship to qg-ini. These relationships provide valuable clues to more accurately locating the high-risk area of lightning initiation in thunderstorms when only dual-polarization radar data or outputs from numerical models without char- ging/discharging schemes are available. The results can also help understand the environmental conditions at light- ning initiation sites.