Point source bubbler systems to suppress ice

An analysis of a point source bubbler system used to induce local melting of an ice cover is presented. The analysis uses empirical results of bubbler plume experiments and impingement heat transfer results to determine the rate of melting at the underside of an ice cover. Through a simple energy budget analysis of the ice cover, the melting of the ice cover and resulting extent of open water are determined as a function of air temperatures, depth and air discharge of the source, and water temperature. The analysis leads to a numerical simulation and an example simulation is presented.     

The influence of low-melting-point alloy on the rheological properties of a polystyrene melt

The rheological behavior of polystyrene melts filled with different loadings of Sn-Pb alloy has been studied. The filled polystyrene melts showed a pseudoplastic behavior, and the viscosity varied dramatically at the melting point of the alloy. The temperature dependence of the viscosity has been found to follow two separate Arrhenius equations for high and low temperatures, respectively. The presence of alloy filler was found to increase melt viscosity below the melting point of the alloy, but decreased it on reaching the alloy melting point. The melt elasticity was found to decrease with increase of alloy concentration, and increase abruptly at the alloy melting point. However, viscous flow was the dominant mechanism of deformation over the entire range of temperature studied.     

冰浆在蓄冰池中的贮存与融化研究进展

总结分析现有的蓄冰池中冰浆贮存及融化在机理、数学模型、实验方面的研究成果,在此基础上,实验研究了入口冰浆流量、冰浆固相含量、初始液面高度和进水管布置等参数对贮存和融化特性的影响。实验发现使用高浓度的二元溶液、高含量冰浆固相以及增大进口流量都可以使冰浆贮存更均匀;增大融冰溶液的流量、增加扰动以及均匀喷撒溶液是避免"沟道"效应从而实现快速、均匀融冰有效手段。     

难加工金属材料短流程高效制备加工技术研究进展

提出了难加工金属材料可以分为2大类的观点:一类是源于材料本征性能的难加工材料,具有高脆性,或高熔点、高变形抗力的特点;另一类是源于制备加工工艺复杂、成材率低的难加工材料。以作者课题组近年来的工作为基础,重点介绍了高硅电工钢、精密铜管、热交换用BFe10-1-1合金管材、高弹高导Cu-12%(质量分数)Al合金的短流程高效制备加工技术的研究开发进展情况。认为通过熔体和凝固过程的精确控制,可精确控制凝固组织和形状尺寸,是开发先进短流程制备加工技术的重要途径。     

Experimental study of melting ice cylinders in a warm air cross-flow

An experimental study is reported which investigates the melting of ice cylinders transverse to a warm humid flow, under controlled conditions in an air-conditioned wind tunnel. This work was initiated prior to a more general study of warm air defrosting of a complete heat pump evaporator. Tests were conducted with air at various temperatures, relative humidities and velocities. Similarly, the temperature of the core tube, on which the ice cylinders were mounted, was varied by alteration of the water-glycol mixture flowing through it. Two diameters of ice cylinder, 20 and 27 mm, were used. For core temperatures below the melting point of ice, the melting rate was shown to be a strong function of air humidity and temperature. With the core temperature above 0°C, the melting process was dominated by this factor so that air conditions were relatively unimportant.     

Investigation on concentration characteristics of ozone micro-bubbles fixed in ice and ozone gas released from ice

Ice formed from water in which ozone gas is dissolved is promising for the cold storage of foods because of the ozone's sterilization and deodorization capabilities. However, effective dissolution of ozone gas in water and taking ozone gas into ice are not easy. Furthermore, the decomposition rate of the ozone itself is usually very fast, regardless of its phase. Thus, to effectively take ozone gas into ice, the authors have developed ice containing ozone micro-bubbles. In this paper, ice containing ozone micro-bubbles formed by adding surfactant was kept for a desired time at a desired constant temperature without melting of the ice. The concentration of ozone micro-bubbles fixed in ice and the ozone gas concentration released from ice by melting were measured to investigate the ozone decomposition rate due to fixation in ice and the characteristics of the released concentration. Furthermore, the influences of surfactant on both concentrations were examined.     

Pulse electro-thermal de-icer (PETD)

De-icing is a process in which interfacial ice attached to a structure is either broken or melted and then the ice is removed by some sort of external force (e.g. gravity or wind-drag). Conventional thermal de-icing is effective but requires too much energy. Mechanical de-icing requires less energy but is less effective, often leaving significant amounts of ice behind, and may also damage structures and accelerate wear. We have invented, developed, and tested a pulse electro-thermal de-icer (PETD) that reduces the energy needed for de-icing by up to a factor of one hundred. PETD achieves this by melting only a thin layer of interfacial ice, leaving the temperature of the environment unchanged.In conventional de-icers, the heater is thermally connected to the ice, the structure, and the outside environment. This makes heat losses through conduction and convection inevitable to the point where the losses exceed by orders of magnitude the amount of “useful” heat needed to melt the interfacial ice. PETD cuts these losses by using a short heating pulse - approximately 1 ms to 5s long - to heat a minimal layer of interfacial ice. This short heating time limits the heat penetration depth into both the ice and the structure. A PETD pulse heats the ice-structure interface just above the melting point causing the ice to slide off on the resulting thin water film.PETD was successfully tested for a variety of applications including the de-icing of airplanes, car windshields, bridge over-structures, glass roofs, commercial and residential icemakers, and windmill rotors. The tests demonstrated almost instant action along with up to 99% savings of the electricity required by conventional thermal de-icers.This paper presents the PETD method, its theory, results of computer simulations, and extensive data from laboratory tests as well as several large-scale implementations of PETD on an airplane, a bridge, a building roof (> 10,000 m²), a car windshield, and a commercial ice maker.     

Plastic deformation of Al13Fe4 particles in Al–Al13Fe4 by high-speed compression

Spray-formed Al–Fe alloys having undergone high-speed deformation were examined under a high-voltage electron microscope. Two types of specimens were examined; one containing fine Al₁₃Fe₄ particles, and the other containing large particles. In the former specimen, deformation is found to proceed in three patterns, depending on specimen thickness and strain rate: (1) without deformation of the Al₁₃Fe₄; (2) breaking of the Al₁₃Fe₄; or (3) melting of the Al₁₃Fe₄. Local melting is found to alter some of the Al₁₃Fe₄ particles, to impart five-fold symmetry in diffraction or an amorphous structure. In the latter specimen, introduction of glide dislocations enabled us to determine a shear system in the mc102 monoclinic c2/m crystal of Al₁₃Fe₄. On the bases of these observations, the mechanism of high-speed deformation is discussed while taking into account the highly stressed and/or heated states of Al₁₃Fe₄ embedded in Al matrix.     

Modelling the time-dependent behaviour of ice

A four element non-linear viscoelastic model was recently introduced to depict the primary and secondary creep stages of ice, under relatively low stress levels, in agreement with available experimental data. This model, representing a hereditary constitutive law, was used in the analysis of viscoelastic columns.In order to simulate the behaviour of ice structures up to failure it is important that the material model include the ‘tertiary creep’ stage, which becomes particularly significant at high stress levels and/or at temperatures close to the melting point. The model should also take into account the limited tensile strain/stress capability of ice.This paper deals with an improved non-linear viscoelastic uniaxial model describing all three creep stages of ice, including the primary, secondary and tertiary stage. The model handles continuous variation in stress at a particular (constant) temperature. Tensile strain/stress cut-offs are built into the model to simulate the brittle behaviour of ice in tension.The model and the solution technique, which was developed and which is designed to allow ‘exact’ treatment of the non-linear constitutive relation for such viscoelastic materials, is applied to the time-deflection-behaviour of an imperfect ice column.     

Delaying Ice and Frost Formation Using Phase‐Switching Liquids

Preventing water droplets from transitioning to ice is advantageous for numerous applications. It is demonstrated that the use of certain phase‐change materials, which are in liquid state under ambient conditions and have melting point higher than the freezing point of water, referred herein as phase‐switching liquids (PSLs), can impede condensation–frosting lasting up to 300 and 15 times longer in bulk and surface infused state, respectively, compared to conventional surfaces under identical environmental conditions. The freezing delay is primarily a consequence of the release of trapped latent heat due to condensation, but is also affected by the solidified PSL surface morphology and its miscibility in water. Regardless of surface chemistry, PSL‐infused textured surfaces exhibit low droplet adhesion when operated below the corresponding melting point of the solidified PSLs, engendering ice and frost repellency even on hydrophilic substrates. Additionally, solidified PSL surfaces display varying degrees of optical transparency, can repel a variety of liquids, and self‐heal upon physical damage.     

穿甲靶板弹孔微观结构观察及侵彻过程分析

为研究穿甲侵彻机理,使用海37弹道炮,发射93W次口径穿甲弹,侵彻45靶板,采用扫描电镜和透射电镜研究弹孔周围微观结构特点.研究结果表明,绝大部分弹孔表面被溶化快凝物覆盖,其厚度约为10μm,其内未发现腐蚀组织.熔化物中含有钨的成分,说明在侵彻过程中产生的高压下,钨颗粒可以熔化.高速碰撞动能在侵彻瞬间可能使弹靶部分作用区域的温度超过钨的熔点.靶板材料在局部区域熔化和再结晶,破坏形式为延性扩孔破坏,观察弹孔周围未发现绝热剪切带.     

Superheating of ice slurry in melting heat exchangers

One of the main components of an ice slurry system is the melting heat exchanger, in which ice slurry absorbs heat resulting in the melting of ice crystals. Design calculations of melting heat exchangers are mainly based on heat transfer and pressure drop data, but recent experimental studies have shown that superheating of ice slurry should also be considered. This paper presents ice slurry melting experiments with a tube-in-tube heat transfer coil. The experimental results indicate that operating conditions such as ice slurry velocity, heat flux, solute concentration, ice fraction, and ice crystal size determine the degree of superheating. The various influences are explained by considering the melting process as a two-stage process consisting of the heat transfer between wall and liquid and the combined heat and mass transfer between liquid and crystals. Bigger ice crystals and higher solute concentrations decrease the rate of the second stage and therefore increase the degree of superheating.     

Investigation on adhesion force of TBAB hydrate to cooling copper surface

When ice slurry is employed for air conditioning, there is gap of 5–7 °C between the melting point of the ice and the cooling water temperature. However, TBAB hydrate slurry made from an aqueous TBAB solution can remove the gap because it has a more suitable melting point. Furthermore, the slurry is relatively a high latent heat of fusion and good fluidity. So, the slurry is the most promising material for air conditioning. However, it is expected that TBAB hydrate in the slurry strongly adheres to surface of a metal such as copper. However, to date, there have been no quantitative studies of the adhesion forces, so in the present work adhesion forces of TBAB hydrates to copper surface at 3 and 5 °C were measured varying TBAB solution concentrations. And the adhesion force and its surface temperature-dependency were investigated based on surface energies and observations of hydrates crystals.     

Influence of natural gas evolution while melting on the separation of the boundary layer

It is shown that under conditions of free convection the separation of air bubbles during the melting of ice and snow spheres displaces the point of separation of the boundary layer into the tail region. Relationships are derived for the separation angle as a function of the temperature difference and the porosity of the body.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 4, pp. 740–742, April, 1977.     

泡沫材料冰蓄冷板融化过程的研究

建立了填充泡沫材料冰蓄冷板内冰融化过程的数学物理模型,该模型考虑了融化液态水自然对流的影响。分别数值模拟了填充开孔聚氨酯泡沫、泡沫铜的冰蓄冷板的融化过程,研究了泡沫材料冰蓄冷板融化过程的速率、温度分布、相界面移动等规律。进行了实验对比,验证分析了泡沫材料的孔隙参数对融化速率的影响。结果表明,填充低导热系数泡沫材料可有效延长冰蓄冷板的释冷时间,该时间随泡沫孔密度的减小而增加、随孔隙率的增大而略减。填充高导热系数泡沫材料可有效改善冰蓄冷板温度分布,可加快冰融化速率,该速率随着泡沫孔隙率的减少而增加、随孔密度的减少而略增。     

黄河防凌爆炸破冰效果

根据黄河防凌破冰研究需要,利用数值仿真与试验验证的方法,研究了相同质量炸药在不同冰层位置条件下的爆炸破冰效果,结果表明:相对于冰下爆炸,炸药在冰面上爆炸时,对冰面破坏范围明显要小;同为冰下爆炸时,破冰范围先随着爆炸深度增加而增加,而后又随爆炸深度增加呈减小趋势,即存在一个最佳爆炸位置。     

The cohesive and adhesive strength of ice

The plane-strain fracture-energy test developed by Andrews and Stevenson has been applied to the study of ice adhering to substrates of stainless steel, titanium and anodised aluminium. In most cases the fracture is cohesive through the ice, and therefore yields a cohesive fracture energy (critical energy release rate). The value of this fracture energy, however, is dependent upon the nature of the substrate, stainless steel giving significantly lower values than titanium. The fracture energy is also affected by the rate of formation of the ice and by the rate of testing. Many of these effects can be traced to the influence of the substrate on the air-bubble content of the ice layer. At testing temperatures approaching the melting point of ice, a transition in fracture mode is observed from cohesive to adhesive, and the fracture energy diminishes. The addition of small amounts of sodium fluoride to the water from which the ice is formed, lowers the transition temperature to –5° C, and emphasizes the transition to the adhesive failure mode.     

Thermooptical properties of gold nanoparticles embedded in ice: characterization of heat generation and melting

We investigate the system of optically excited gold NPs in an ice matrix aiming to understand heat generation and melting processes at the nanoscale level. Along with the traditional fluorescence method, we introduce thermooptical spectroscopy based on phase transformation of a matrix. With this, we can not only measure optical response but also thermal response, that is, heat generation. After several recrystallization cycles, the nanoparticles are embedded into the ice film where the optical and thermal properties of the nanoparticles are probed. Spatial fluorescence mapping shows the locations of Au nanoparticles, whereas the time-resolved Raman signal of ice reveals the melting process. From the time-dependent Raman signals, we determine the critical light intensities at which the laser beam is able to melt ice around the nanoparticles. The melting intensity depends strongly on temperature and position. The position-dependence is especially strong and reflects a mesoscopic character of heat generation. We think that it comes from the fact that nanoparticles form small complexes of different geometry and each complex has a unique thermal response. Theoretical calculations and experimental data are combined to make a quantitative measure of the amount of heat generated by optically excited Au nanoparticles and agglomerates. The information obtained in this study can be used to design nanoscale heaters and actuators.     

Mechanical Properties, Damage and Fracture Mechanisms of Bulk Metallic Glass Materials

The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses （BMGs） and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.     

Electric resistance of water films on the surface of ice near the phase transition temperature

The electric resistance of the surface layer of a polycrystalline sample of freshwater ice has been measured on heating the sample up to the melting temperature. At the onset of ice melting, a monotonic decrease in the resistance of the ice surface changes to growth, and this again is followed by decrease in the course of melting. In the growth stage, the resistance exhibited a more than twofold increase. The observed behavior is related to breakage of a quasi-liquid surface layer possessing a higher conductivity, which is replaced by a layer of liquid water with a low conductivity.