摘要
随着冷冻食品工业持续发展，冷冻食品需求日益增长，消费者对冷冻食品质量的要求也不断提高。冷冻食品的质量主要取决于冷冻过程中冰核产生和冰晶成长的情况，可通过冷冻技术来控制。已有研究发现超声波、磁场、电场等物理场对冷冻过程有影响。这些物理场可影响水和水溶液的过冷温度以及冰晶成长的速率，从而对冰晶形态有一定的影响。目前，静电场冷冻的研究较少，其影响也没有比较完整的结论，开展相关研究有助于为这一领域的基础研究提供实验数据及参考。本文将研究静电场对水和稀溶液冷冻过程的影响。
本文采用实验研究的方法，自行设计和搭建了静电场辅助冷冻实验台，选择去离子水、葡萄糖稀溶液、蔗糖稀溶液和氯化钠稀溶液作为研究对象。在样品冷冻过程中施加不同强度的静电场，并采集实验数据。实验涉及五个电场条件，分别对应外加电压为0、4、6、8、10 kV。本文主要研究静电场对样品冰核产生和冰晶成长的影响，以过冷温度和相变时间为参数进行比较。
实验结果表明，静电场对去离子水、葡萄糖稀溶液、蔗糖稀溶液和氯化钠稀溶液的影响效果均有不同。静电场对水分子的影响可分为分子转动可动性受限的不利影响和系统整体有序性增强的有利影响，导致仅当电场条件为外加电压8 kV时，去离子水过冷温度上升2.96℃，起晶时间缩短32.2%，静电场影响有利于冰核产生。对于葡萄糖稀溶液和蔗糖稀溶液，静电场影响与溶液浓度有关。随着溶液浓度增加，糖
分子水合层影响冰核产生的程度先增后减，则静电场影响程度先减后增。因此，对于5 g/L、50 g/L和150 g/L葡萄糖溶液，以及5 g/L和150 g/L蔗糖溶液，较高强度静电场有利于冰核产生。对于氯化钠稀溶液，随着溶液浓度增加，离子对冰核产生和冰晶生长的影响都呈现多极值变化。静电场对0.1 mol/kg ~0.5 mol/kg氯化钠溶液的影响以不利于冰核产生为主，而对0.6 mol/kg氯化钠溶液的影响以有利于冰核产生为主。关于冰晶成长，静电场对四种样品的都有抑制水分子扩散运动的不利影响。
本文通过分析实验数据，并结合分子动力学研究理论，得出静电场影响去离子水和稀溶液冷冻过程的一般规律，可为静电场应用于食品冷冻加工提供参考。
关键词：静电场；过冷；成核；结晶；溶液
ABSTRACT
As the industry of frozen food continuously developing and the demand for frozen food growing, consumers are demanding to improve the quality of frozen food. The quality of frozen food mainly depends on the ice nucleation and the growth of ice crystals, which can be controlled by freezing technology during the freezing process. It has been studied the freezing process under physical fields such as ultrasonic, magnetic field and electric field. The physical fields have influence on the supercooling temperature as well as the rate of ice crystal growth of water and aqueous solution. Th
ere have been relatively few studies on electrostatic field freezing so far, and as a ressult there is no complete conclusion on its influence and mechanism. Carrying on rearch on this aspect is helpful for providing experimental data and reference for basic rearch in this field. In this paper, the effect of electrostatic field on the freezing process of water and dilute solution is studied.
Experiment was the main rearch method in this paper, the experimental t-up was designed and built accordingly. Deionized water, dilute gluco solution, dilute sucro solution and dilute NaCl solution were lected as the rearch objects. During samples freezing, electrostatic field of different strength was applied, and the experimental data were collected. The experiment involved five electric field conditions, corresponding to the applied voltage was 0, 4, 6, 8, 10 kV respectively. This paper focus on the ice nucleation and the growth of ice crystals under electrostatic field, with the parameters of supercooling temperature and pha transformation time.
The experimental results show that the effects of electrostatic field on deionized water, dilute gluco solution, dilute sucro solution and normal saline are different. The influence of electrostatic field on water molecules can be divided into two aspects: the unfavourable effect of molecular rotation mobility limited and the favourable effect of the system overall order enhancement. As a ressult, for deionized water, an increa of 2.96℃of supercooling temperature and shortening of 32.2% of nucle
ation time were found only when electric field condition was applying 8 kV voltage, compared to that without electrostatic field. This indicates that the higher strength electrostatic field is conducive to the ice nucleation. For dilute solutions of gluco and sucro, the influence of electrostatic field relates to the solution concentration. With the increa of the solution concentration, the effect of the hydration layer of the sugar molecules on the ice nucleation first increas and then decreas, while the influence of static electric field decreas first and then increas. Conquently, for 5 g/L, 50 g/L and 150 g/L gluco solution, as well as the 5 g/L and 150 g/L sucro solution,
the higher strength electrostatic field is favorable to the ice nucleation. For dilute NaCl solution, with the increa of the solution concentration, the influence of ions on ice nucleation and growth of ice crystals prents a multi-extreme phenomenon. The influence of electrostatic field on ice nucleation is mainly unfavourable effect for 0.1 mol/kg-0.5 mol/kg NaCl solution, while that is mainly favourable effect for 0.6 mol/kg NaCl solution. With regard to the growth of ice crystals, the electrostatic field has an unfavourable effect on the diffusion of water molecules in the four samples.
工作表现鉴定In conclusion, some general rules of the static electric field effect on the freezing process were summarized through analysis of the experimental data combined with the result of molecular dynamics study, which could provide reference for the application of electrostatic field in frozen food
processing.
Keywords: electrostatic field; supercooling; nucleation; crystallization; solution
目录
摘要......................................................................................................................................... I ABSTRACT ............................................................................................................................. II 第一章绪论 (1)
1.1研究背景 (1)
一个纯粹的人1.2食品冷冻技术 (1)
马桶被大便堵了小妙招1.2.1食品冷冻理论 (1)
1.2.2新型冷冻技术的研究现状 (2)
1.3静电场在食品加工中的应用 (3)
1.4静电场冷冻的研究进展 (3)
1.4.1静电场冷冻研究的发展及现状 (3)
1.4.2静电场影响冷冻过程的能量分析 (4)
1.5研究意义及内容 (5)
第二章静电场冷冻实验系统和方法设计 (6)
2.1引言 (6)
2.2实验系统 (6)
2.3低温实验台 (6)
复读班
2.3.1制冷设备 (6)
姓名笔画排序2.3.2散热方式 (7)
2.3.3保温方式 (8)
2.4高压静电场发生装置 (9)
2.4.1可调高压直流电源 (9)
2.4.2静电场的产生 (9)
2.4.3电介质击穿与放电现象 (10)
2.4.4样品容器 (12)
2.5温度测量装置 (13)
个人现实表现
2.6实验方法 (13)
2.6.1实验步骤 (13)
2.6.2数据分析方法 (15)
2.7本章小结 (15)
第三章静电场对去离子水冷冻过程的影响 (16)
3.1引言 (16)
3.2材料和方法 (16)
3.2.1实验材料 (16)
3.2.2实验设备 (16)
3.2.3实验方法 (16)
3.3结果与讨论 (16)
3.3.1静电场对去离子水过冷温度的影响 (16)
3.3.2静电场影响去离子水冰核产生的机理 (20)
3.3.3静电场对去离子水相变时间的影响 (25)
3.3.4静电场影响去离子水冰晶成长的机理 (26)
3.4本章小结 (27)
第四章静电场对葡萄糖稀溶液冷冻过程的影响 (28)
4.1引言 (28)
4.2材料和方法 (29)
4.2.1实验材料 (29)
4.2.2实验设备 (29)
相交线的定义
祖国好4.2.3实验方法 (29)
4.3结果与讨论 (29)
4.3.1浓度对葡萄糖溶液过冷温度的影响 (29)
4.3.2浓度影响葡萄糖溶液冰核产生的机理 (30)
4.3.3浓度对葡萄糖溶液冰晶成长的影响 (32)
4.3.4静电场对葡萄糖溶液过冷温度的影响 (34)
4.3.5静电场影响葡萄糖溶液冰核产生的机理 (38)
4.3.6静电场对葡萄糖溶液冰晶成长的影响 (39)
4.4本章小结 (42)
第五章静电场对蔗糖稀溶液冷冻过程的影响 (43)
5.1引言 (43)
5.2材料和方法 (43)
5.2.1实验材料 (43)
