真空法制备冰浆中冰晶粒径特性的实验研究

为获得真空法制得冰浆中冰晶的平均粒径及粒径分布规律,本文以乙二醇水溶液为制冰溶液,采用真空法制备得到冰浆,并通过显微装置观测冰浆中的冰晶形态。实验分别研究了搅拌速率、乙二醇初始浓度和含冰率(IPF)对冰晶平均粒径的影响,并将实验得到的粒径分布与正态分布、对数正态分布、伽马分布和威尔布分布进行对比。结果表明:不同实验条件下冰浆中冰晶粒径分布均可统一用伽马分布来描述;搅拌速率对冰晶平均粒径几乎无影响;冰晶平均粒径随溶液初始浓度的增大而减小,当乙二醇浓度从1%提高至7%时,冰晶平均粒径从74.8μm降至34.3μm;含冰率达到一定大小时,才会对冰晶平均粒径产生较显著的影响,表现为含冰率越高,平均粒径越大。     

有关因素对冰浆制取过程中过冷度影响的实验研究

实验研究了搅拌速度、液浴温度、添加醇类物质和成核剂等因素对冰浆形成过程中过冷度及结冰特征的影响。结果表明,在制冰浆过程中,对水溶液进行搅拌有利于提高水过冷现象的稳定性。在搅拌速度0~100r/min时,不容易出现过冷现象而直接结冰;过冷度随搅拌速度增大而增大,在搅拌速度为200r/min时达到最大值4.35℃,之后过冷度急剧下降。在液浴温度降低情况下水过冷度先明显变大,随后变化不明显。添加乙二醇后,有效的改善了冰晶的细腻程度,在低浓度区(乙二醇浓度6%),过冷度呈小幅上升趋势;在中高浓度区(乙二醇浓度6%),过冷度随着乙二醇浓度的增加急剧的减小。添加成核剂后过冷度明显下降,过冷解除时间提前,与硫酸铁和二氧化硅相比,硼砂成核性较差,但是形成的冰晶具有较好的特性。     

超声场对过冷水溶液结晶的影响

过冷水法动态冰浆制取技术是一种有望实现大规模应用的动态制冰方法,工业上常用施加超声场的方式解除过冷水的过冷态并生成冰浆。本文实验研究了不同超声场对质量分数为3%的氯化钠溶液结晶过冷特性、生成冰晶尺寸及粒径分布的影响。结果表明：一定功率和频率的超声场的引入可快速解除过冷,使溶液在接近超声辐照温度下成核,且高功率、低频率的超声场更有利于成核发生。当功率、频率、辐照温度分别在10.0~40.0 W、28~40 kHz及0~4.0 ℃范围内,最佳超声场设置方案为超声功率40.0 W、频率28 kHz、辐照温度2.0 ℃;超声场的施加可显著减小冰晶尺寸;随着成核后超声辐照时间的延长,冰晶粒径先增大后趋于平缓,超声功率及频率的变化对冰晶粒径尺寸的影响无显著作用。     

超声波作用下动态闪蒸制备冰浆

本文基于闪蒸理论,设计了一套超声波作用下动态闪蒸制备冰浆的实验装置。研究同一真空度下不同超声波功率、喷射体积流量及不同质量浓度的乙醇添加对冰浆真空动态闪蒸特性的影响。结果表明:与无超声波作用相比,超声波对增大水的闪蒸强度作用明显;体积流量一定时,降温降压速率随超声波功率的增大而增大,较高的超声功率有助于增强水的闪蒸强度,有利于动态制冰;而同一超声功率下随着体积流量的增大最终平衡压力也越高。较大体积流量不利于闪蒸的持续进行;乙醇添加剂能促进溶液降温,质量浓度越高,温度降得越低;质量浓度为5%时,可消除溶液过冷度,更利于产生冰晶。     

水平直管内冰浆流动过程冰晶粒径演化研究

本文采用实验研究与数值模拟相结合的方法,研究了冰浆在水平直管内流动过程中冰晶粒径的分布及其演化规律。通过CFD-PBM耦合模型模拟研究冰浆在不同过冷度、流速、含冰率下冰晶粒径分布及其演化规律,并通过实验对数值模拟结果进行验证。结果表明:在含冰率为15%的冰浆管道入口处,冰晶粒径数量密度分布均近似高斯分布;随着冰浆流速和含冰率的增加,沿流动方向中心轴的冰晶平均粒径增大,截面冰晶粒径分布越不均匀;流速越小、含冰率越大,冰晶粒径的长度数量密度分布曲线的峰值升高,峰值所对应冰晶粒径的平均值减小。     

基于模块化过冷解除的冰浆制取系统实验研究

过冷水法动态冰浆制取技术具有传热效率高、系统简单等优点,但过冷却器易发生冰堵是影响其稳定性的突出问题。本文提出一种基于模块化过冷解除装置的动态制冰系统,利用设置在过冷却器内的可灵活拆装式螺旋叶片对制冰溶液进行过冷解除,同时刮削换热壁面上粘附的冰晶。测试了不同工况下该制冰系统的性能,结果表明该制冰系统可稳定产出冰浆并有效改善冰堵问题,最高含冰率达9.1%,最大持续制冰时间可达521 s。冰浆含冰率与持续制冰时间成正比。NaCl添加剂质量分数为6%时对冰浆含冰率和持续制冰时间的改善效果显著。实验获得制冰系统最佳运行参数:制冰溶液体积流量为0.50 m^3/h、二次冷媒起始温度为-15℃、螺旋叶片转速为175~225 r/min。     

冷却速率对洋葱内表皮细胞结构的影响

本文通过控制冷却速率观测了洋葱内表皮细胞结构的动态变化,根据透光强度定量分析了胞内冰晶对细胞结构的影响,对内压与体积的变化关系进行讨论,并研究了冷却速率对过冷度、结晶时间及细胞形变的影响。结果表明:冷却速率越慢,细胞内产生的冰晶数量越少,体积越大,对细胞造成的机械损伤越大。冷却速率从2℃/min升至90℃/min时,细胞的平均灰度值下降了37.2%;体积随内压的增大而减小,内压变化越大,细胞结构的变化越显著,在2℃/min时,冷却-复温后,内压增大了0.388×10~(-2) Pa,体积减小了2.264×10~(-13) m~3。冷却速率对细胞的过冷度、结晶时间及变形量影响显著,在90℃/min时,冷却-复温后相对体积变化为1.24%。     

多壁碳纳米管作用下乙醇溶液静态闪蒸特性实验研究

为研究用于工业真空制备二元冰的最佳工况,本文基于静态闪蒸理论,设计并搭建了一套固体吸附条件下乙醇溶液真空闪蒸制冰实验系统。在同一初始压力下(100 Pa),研究了不同乙醇浓度、环境温度和多壁碳纳米管尺寸对静态闪蒸制冰特性的影响。结果表明:乙醇的添加在防止重结晶的同时可以降低蒸馏水真空闪蒸制冰的过冷度,较高浓度的乙醇溶液不利于闪蒸制冰,5%质量浓度的乙醇溶液闪蒸特性稳定,可将蒸馏水过冷度降低60. 62%,较适合静态闪蒸制冰;随着环境温度升高,闪蒸室内溶液闪蒸量增大,随着环境温度从10℃升至20℃,闪蒸率从25. 45%增至44. 04%。较低的环境温度有利于真空闪蒸制冰;随着添加多壁碳纳米管粒径的减小,乙醇溶液过冷度减小,当多壁碳纳米管外径为5～18 nm时,真空闪蒸的含冰率相对于5%质量浓度的乙醇溶液提高51. 45%,相对于蒸馏水提高38. 22%。过冷度相对于5%质量浓度的乙醇溶液降低24. 36%,相对于蒸馏水降低70. 21%,对于减小蒸馏水过冷度和提高含冰率效果显著。     

过冷水动态冰晶制取的实验研究

本文提供了一种过冷水动态制取冰晶的实验装置,着重介绍了系统的设计过程以及各部分的技术要求.为保证系统稳定运行,本实验装置采取了一系列措施,包括冰晶消除、过冷解除以及防冻结策略等.实验采用自来水、纯水、6%的乙二醇溶液作为试样,在不同的冷却速率、速度以及壁面条件下进行了对比实验,并给出了定性分析.     

北京嘉里中心冰蓄冷系统的组成及施工技术

该系统属于冰晶式蓄冷系统 ,即是将低浓度载冷剂溶液 (通常为水与乙二醇溶液 ) ,经制冷机组冷却至冻结点温度以下 ,使载冷剂溶液产生直径约为 10 0 μm的冰晶 ,细微冰晶与载冷剂形成泥浆状的物质 (被称为冰浆 )经泵输送至蓄冰池而储存相变潜热 ,以提供高峰负荷的需要。文章介绍了该系统的组成、施工组织与施工过程。     

Ice adhesion of an aqueous solution including a surfactant with stirring on cooling wall: ethylene glycol—a silane coupling agent aqueous solution

Ice adhesion to the cooling wall directly hinders continuous ice formation or system performance due to the increase of flow and thermal resistance. In order to obtain the basic characteristics of two- or three-component aqueous solutions with EG, SCA and water on freezing, the influence of component ratio and supercooling degree on those solutions was investigated through a batch type freezing process of the solutions. Moreover, the strength of ice adhesion was shown to vary by stirring power. Ice adhesion was suppressed when (1) the solution including the additive SCA at comparatively high concentration; (2) the solution had high initial concentration of EG or SCA; (3) the brine temperature was higher; (4) the supercooling degree was comparatively small in the lower concentrations. No ice adhesion occurred at the stirring power below 30 W. Furthermore, particle size of the ice slurry was smaller in higher concentrations.     

改进型真空制冰系统的性能研究

为了降低真空制冰系统对真空度的要求,提出了在水中加入中介物质的方法,并建立了真空蒸发性能测试系统。采用浓度为26%的氨水为中介物质溶液,对真空下溶液的蒸发温度特性进行了实验研究,分析了对系统的影响。实验结果表明,在相同的初始温度和真空条件下,氨水的降温速率和降温范围明显高于蒸馏水,且在高于水的三相点压力时有冰晶形成;随着真空度的降低,氨水的降温幅度逐渐减小,但仍远大于蒸馏水,说明在相同的蒸发温度下,氨水对真空度的要求远低于蒸馏水。     

Study on ice slurry production by water spray

A theoretical and experimental study was performed to examine the water spray method of ice slurry production. First, the conditions for the formation of ice particles were investigated theoretically by the diffusion-controlled evaporation model. The prediction of the model was proved to agree relatively well with experiments in which we examined the conditions for a droplet of initial temperature 20°C and size 50 μm to change into an ice particle in a chamber of height 1.33 m. Second, the production of cold storage heat will increase almost proportionally to the number of spray nozzles because no substantial difference was found in the Sauter Mean Diameter (SMD) of sprays from single and twin nozzle. Third, an ice slurry was experimentally obtained by spraying droplets of 7% ethylene glycol aqueous solution in a vacuum chamber where pressure is maintained below the freezing point of the solution. Finally, based on the theoretical and experimental results, we propose an optimizing chart for providing the operating conditions to make ice slurry using the relations of the staying time of the droplet in the chamber, the injection pressure, the spray droplet size and the chamber pressure.     

Continuous ice slurry formation using a functional fluid for ice storage

A functional fluid composed of an oil–water mixture with an additive is transformed into an ice slurry by cooling while stirring. This paper describes a new continuous ice slurry formation method. Experiments were carried out by varying conditions such as the supply time of functional fluid, the stirrer torque, brine temperature and degree of supercooling. As a result, the characteristics of the ice formation and recovery processes were clarified. It was found that the ice particles gradually became uniform in size and spherical, and grew to 3.5 mm in diameter during about 10 h. The factors influencing the size of formed ice particles were discussed because the larger ice particles were expected to melt more rapidly. The ice particle size was found to increase with decreasing degree of supercooling and cooling rate, and with increasing stirrer wing diameter.     

真空法制取二元冰的理论分析

新的蓄冷介质越来越被人们重视,二元冰俗称冰浆是其中一个比较受到人们关注的一种蓄冷介质。制取冰浆的方法有很多种,其中真空法就是其中一种。因为它的制取步骤比较简单,不需要消耗太多的电力能源,同时制取二元冰的效率很高。通过对真空室内下落液滴的质量、速度、温度、下落距离建立微分方程,选定不同的初始条件和真空条件,模拟计算求解。通过对计算结果的比较、分析,明确指出在试验设计时应该选用喷射的液滴初始直径较小的喷头,同时保持真空室稳定在压力较小的环境下。     

An effective method for preventing ice-blockage in dynamic generation system with supercooling water

With the development of economy, environmental protection and energy saving has become a main topic generally cared about by people. The extensive application of ice slurry in various fields is an effective way to reduce energy consumption, especially in the air-conditioning system. As an environment-friendly medium, ice slurry can improve energy efficiency and reduce building energy consumption thanks to the latent heat of ice crystals and its good fluidity. Among those methods of ice-making, ice generating with supercooling water is a superior method because of its high efficiency and energy conservation. However, ice blockage in the supercooling heat exchanger is a prominent problem that reduces the efficiency of the ice generation system. In this study, in order to prevent or retard ice blockage, a fluorocarbon coating is used to make ice slurry continuously without any additive. The results show that the supercooling heat exchanger coated with fluorocarbon coating can be successfully applied to improve the efficiency of ice production, thus to reach the goal of energy saving.     

Continuous ice slurry formation by using W/O emulsion with higher water content

A W/O (water-in-oil) emulsion was made from a water–lamp oil mixture with higher water content and a small amount of an additive of amino group-modified silicone oil, and the emulsion could be changed into an ice slurry by cooling with stirring. By using a new continuous ice formation system proposed by one of the authors of this paper, the ice slurry could be formed continuously and stably in an ice formation vessel made of stainless steel. From the experimental results, the conditions were clarified for realizing continuous ice formation for 10 h without ice adhesion to the cooling wall. Moreover, in order to propagate supercooling dissolution of the emulsion effectively and to decrease viscosity in the ice slurry, voltages were applied to the emulsion and ice slurry formed, respectively, and it was clarified that the voltage impression was effective for both.     

冰浆生成器中抑制冰粘附的研究

冰浆中含有大量微小冰晶粒子,因此表现出有极好的流动、传热和储能特性。冰浆生成过程中,冰晶微粒易粘附在换热壁面,降低传热效率,增加流动阻力,甚至引起冰堵,影响冰浆的持续生成。分析了冰粘附特性,综述冰浆技术中冰移除技术的研究进展,建立冰浆生成实验台,采用综合控制制冰溶液和载冷剂流速的方法抑制冰堵的发生。