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本文设计了一套真空搅拌法流态冰制取装置,对冰浆的生成全过程进行了观测,通过实验研究了乙二醇添加剂、溶液体积、搅拌速度等因素对冰浆形成过程过冷状态的影响。结果表明:真空状态下冰浆的制取需经历溶液蒸发、沸腾、过冷及冰晶生成这四个阶段;冰晶生成瞬间系统的压力会发生突增,压力的升值即过冷结晶压差可用于表征过冷程度的高低;平均过冷结晶压差随乙二醇添加剂浓度的增大而减小,当乙二醇浓度从3%提高至6%时,过冷结晶压差从58.9 Pa降至49.4 Pa,降低了16.1%;溶液体积的增大会使平均过冷结晶压差减小,40 m L溶液的平均过冷结晶压差较20 m L溶液的平均过冷结晶压差下降了12.9%;搅拌速度对过冷程度几乎无影响。 相似文献
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选用液体石蜡为油相,油酸钠和十六烷基三甲基溴化铵(CTAB)作为乳化剂,利用高速搅拌和超声乳化的方法制备了一种新型液体石蜡乳液作为冰浆蓄冷介质。电导率测试表明:该乳液为O/W型,乳液的D50粒径为1.56μm。在乳液中添加乙醇和丁醇可有效抑制冰浆粘附聚甲基戊烯(PMP)、玻璃和不锈钢烧杯壁面。乳液在解除过冷后的初期,冰浆在不锈钢烧杯中形成速度最快,在PMP烧杯中形成速度最慢。在解除过冷相同时间内,添加乙醇的乳液体系蓄冰率(IPF)比添加丁醇的高,但随着结晶时间的增加,差值逐渐减小。解除过冷3 h后冰粒呈颗粒状,IPF在55%~65%之间,具有良好的流动分散性。 相似文献
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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。 相似文献
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过冷是材料液-固相变过程中为提供离子扩散、晶体生长及晶面扩大所需能量而产生的一种亚稳态。过冷是结晶过程的推动力,但大的过冷度导致相变材料结晶温度降低、结晶时间延迟,使得储存的潜热不能及时释放,储-放热温度不匹配,降低了热能利用效率。过冷度大已成为限制相变储热技术规模化应用的重要影响因素之一。大量实验结果表明:过冷现象与熔体晶核的生成与长大速率、环境温度、接触面的粗糙程度、熔体温度等因素有关,但其产生的内在机制尚不明确,影响规律和调控手段仍需借助实验探索。目前,主要采用外加添加剂或在胶囊化、流体化过程中加入添加剂的添加晶种法,以及通过搅拌、超声振荡和鼓泡等外部刺激的动力学成核法诱发过冷液体结晶。利用外加成核剂、纳米颗粒以及部分未熔化母相晶体作为晶核诱发非均匀成核是抑制过冷现象最常用、最有效的方法。为提高添加剂的分散性和抑制水合无机盐类相变材料的相分离现象,在添加成核剂的同时往往需要加入一定量的增稠剂,但成核剂和增稠剂的添加量需要优化。胶囊化可以改变相变材料的结晶特性,目前的研究一致认为在胶囊化前添加成核剂有利于改善相变材料的过冷度。动力学成核常采用的方法是超声振荡法,其通过空化作用使晶体持续破碎并与熔体混合而提高晶核的分散性和加速结晶过程。在超声的同时添加纳米颗粒也有利于抑制过冷度。本文简述了过冷现象和典型的过冷曲线,分析了影响过冷度的因素,并着重介绍了外加添加剂法、胶囊化法、功能流体法和超声振荡法等抑制过冷度的方法。 相似文献
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细胞溶液在慢速冷冻过程中会出现过冷现象,较大的过冷度会形成不可控的胞内冰。为减少过冷度,提高细胞存活率,本文提出一种用于L-02肝细胞植冰保存过程的超声波植冰系统,实验研究不同超声波强度、不同预冷温度和不同体积分数Me2SO对肝细胞存活率的影响。结果表明:当体积分数为0%~10%的Me2SO作为保护剂时,使用超声波植冰操作均能显著提高肝细胞冷冻存活率。当超声波强度为0.0329~0.431 6 W/cm2时,肝细胞存活率均在90%以上,组间无显著性差异(p<0.05),超声波强度大于0.431 6 W/cm2时,肝细胞存活率显著下降;使用体积分数为5%的Me2SO在﹣7 ℃进行超声波植冰,超声波强度为0.104 1 W/cm2时,肝细胞存活率最高,达到(97±2.6)%,与新鲜组无显著性差异;超声波植冰能够显著提高肝细胞存活率,降低保护液中Me2SO用量。 相似文献
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低共熔冰过冷问题的研究 总被引:2,自引:0,他引:2
本文通过分析低共熔冰过冷机理 ,得出结论 :过冷是为结晶过程提供推动力 ,在纯净、无杂质液态物质冻结所必须的 ;成核剂的存在 ,可以大大减小过冷度。经过过冷度测定实验和熔化潜热测定实验发现 :对于机械冷板冷藏车的冷冻板用共晶液 ( KCl溶液 ) ,Cu S是最合适的成核添加剂 ,在一般场合下也可以考虑使用 Si O2 作为成核剂 相似文献
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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. 相似文献
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To reduce the size of ice crystals in mushroom (Agaricus bisporus) contact ultrasound (300 W, 20 kHz) was applied during freezing and frozen storage. Stereomicroscopy was used to observe the ice crystal morphology, and DSC and NMR spectroscopy were performed to evaluate the water states in the samples. Results indicated that ultrasound irradiation initiated the nucleation of ice and reduced the mean size of ice crystals during freezing and frozen storage, and therefore improved the frozen product quality compared to the control samples. Most of the ice crystals in the ultrasound assisted frozen (UAF) samples were in the size range of 0–80 microns while that for the control samples were in the size range of 50–180 microns. SEM photos also proved that due to the application of ultrasound, the sizes of the ice crystals was reduced. This micro-scale information on the documentation of ice crystals will assist in understanding the ice crystal growth phenomena in an ultrasound assisted freezing process. 相似文献
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目的 概述超声辅助冷冻技术在食品浸渍式冷冻中的研究进展,为今后新型技术辅助浸渍式冷冻提供研究方向.方法 研究超声辅助冷冻的成核机理和对冰晶生长的影响,以及超声对溶液性质的影响,并对超声辅助冷冻技术在食品浸渍式冷冻中的应用进行综述.结论 超声辅助浸渍式冷冻技术可以广泛应用在各类食品加工中,有很大的研究和发展空间.超声辅助冷冻技术能够进一步加快食品浸渍式冷冻的冻结速率,减小食品内部冰晶尺寸,较好地改善了冷冻食品的品质和风味,在食品加工中具有广阔的应用前景,可以高效应用于食品工业. 相似文献
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The effect of supercooling on ice structure in tuna meat observed by using X-ray computed tomography
Several studies have reported that freezing a homogeneous food such as soy bean curd with deep supercooling (supercooled freezing) results in the formation of many particle ice and homogenous ice structure. However, ice crystal morphology may be affected by the cellular structure of the food. In this study, the ice crystal structure in tuna meat, a cellular food, frozen by the supercooled freezing method was investigated by X-ray computed tomography and compared with ice structures in tuna meat frozen by conventional freezing methods. The results showed that rod-like ice crystals grew parallel with the myofibers, and inhomogeneous ice structures formed in tuna meat frozen by the supercooled freezing method regardless of the degree of supercooling, in contrast to the ice structure in frozen soy bean curds. These ice crystals linked with each other to form rod-like ice structures due to mobility limitations imposed by the cellular structure. 相似文献
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目的 为延长水产品销售周期,最大程度保持其营养品质,促进水产品冷冻保藏及加工技术的发展和产业化。方法 归纳总结超声辅助浸渍冷冻的作用机理,并探究其对冰晶形成和生长以及水产品保鲜加工的影响。结果 超声辅助浸渍冷冻能有效提高冷冻效率,减小冰晶晶核规格,缩短冷冻时间,减缓水产品蛋白质变性与脂质氧化速率,改善水产品质构、保持其营养价值,是水产品冷冻处理的有效途径。结论 超声辅助浸渍冷冻技术能在一定程度上解决水产品冷冻过程中存在的问题,为水产品冷冻技术产业化提供支持。超声辅助浸渍冷冻技术在作用机制、适用范围和特定环境下的作用衰减等方面存在着一定缺陷,还需深入阐述其作用机理,为冷冻智能装备开发提供保障。 相似文献
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In this study, the effect of ultrasound irradiation temperature and ultrasound intensity on the freezing and nucleation in strawberry samples was studied. The application of ultrasound irradiation at different temperatures was able to induce nucleation at lower degree of supercooling compared to the control samples. The achieved degree of supercooling in the ultrasound irradiated strawberries was linearly correlated to the ultrasound irradiation temperature. At the ultrasound irradiation temperature of −1.6 °C, the characteristic freezing time (CFT) was significantly shorter than that in the control sample (p < 0.05). The application of ultrasound at higher intensities was found to effectively shorten the CFT. The degree of supercooling in ultrasound irradiated samples was not linearly correlated to ultrasound intensity. In conclusion, the combination of ultrasound irradiation temperature and intensity can be effective in controlling nucleation and freezing processes of perishable fruits such as strawberry. 相似文献
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Tsutomu Hozumi Akio Saito Seiji Okawa Kazuharu Watanabe 《International Journal of Refrigeration》2003,26(5):537-542
In order to clarify effects of electric charge on freezing of supercooled water, experiments were carried out with various kinds of electrodes in supercooled water. Water sample was kept in a test tube and cooled down at a constant cooling rate. When the water sample was maintained under a supercooling state, an electric charge was applied to the water sample with a small electric current. The degree of supercooling was measured continuously. Then the degree of supercooling at freezing was determined. Six kinds of materials were used for electrodes. Those materials were Aluminum, Copper, Argentum, Aurum, Platinum and Carbon. It was found that the effects of electric charge were distinct according to the material used for electrodes. The degree of supercooling at freezing was the lowest in the case of Aluminum. On the other hand, the highest value of the degree of supercooling at freezing was obtained in the case of carbon. The reason for the difference in the degree of supercooling at freezing by six materials was discussed. 相似文献