共查询到17条相似文献,搜索用时 218 毫秒
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影响水过冷度的因素很多, 同样实验条件下水的过冷度并非一个定值, 多孔球层的存在对水的过冷度产生一定影响。对蒸馏水和不同球径的多孔球层介质进行了32次过冷度测定实验, 并对蒸馏水和多孔球层介质的蓄冷特性进行了实验研究。过冷度实验结果采用统计方法进行分析, 并用CCD相机和热像仪对过冷现象进行观察。结果表明:大温差降温条件下水的平均过冷度要小于阶梯缓慢降温条件下水的过冷度;多孔球层球径越小, 平均和峰值过冷度越小, 但直径为11 mm出现特例, 其平均过冷度比8 mm直径多孔球层要小, 峰值也比8 mm的小;多孔球层固体基底的存在大大缩短了蓄冷相变时间。 相似文献
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无机盐溶液的过冷度极大地影响了相变材料的蓄冷特性。实验以NH4Cl溶液为例,研究了浓度与多孔介质对无机盐溶液的过冷度影响机理。通过改变无机盐溶液浓度与构建多孔介质小球的球径,探究无机盐溶液强化传热传质的方法。实验结果表明:浓度越高,无机盐溶液过冷度越低,离散程度越低,稳定性越高。当浓度达到15%时,溶液平均过冷度较5%浓度溶液可降低17.5%。构建多孔介质小球球径越小,无机盐溶液过冷度越低,离散程度越低,稳定性越高。当球径为5 mm时,溶液平均过冷度较无多孔介质情况下可降低21.7%。 相似文献
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无机盐溶液的过冷度极大地影响了相变材料的蓄冷特性。实验以NH4Cl溶液为例,研究了浓度与多孔介质对无机盐溶液的过冷度影响机理。通过改变无机盐溶液浓度与构建多孔介质小球的球径,探究无机盐溶液强化传热传质的方法。实验结果表明:浓度越高,无机盐溶液过冷度越低,离散程度越低,稳定性越高。当浓度达到15%时,溶液平均过冷度较5%浓度溶液可降低17.5%。构建多孔介质小球球径越小,无机盐溶液过冷度越低,离散程度越低,稳定性越高。当球径为5 mm时,溶液平均过冷度较无多孔介质情况下可降低21.7%。 相似文献
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在考虑晶粒成核、生长、聚并和破碎的情况下,采用分组法求解粒数衡算方程,通过耦合粒数衡算与多相流方程,建立了多尺度的结晶模型,模拟了表面刮削式制冰装置内水的动态结晶过程,获得不同温度、刮削速度、制冰时间等外界条件下晶粒数密度分布、云图等信息,分析了外界宏观条件对水的动态结晶过程的影响。结果表明:由于碰撞引起的晶粒聚并和破碎使得晶粒的尺寸分布更为集中和均匀;在过冷温差(流体局部温度与水的相变温度差值)不大于20℃,刮削速度不大于10 r·s-1范围内,降低壁面温度、增加刮削速度可以加速水的结晶与生长。 相似文献
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采用双流体模型对高压高过冷度下垂直圆管中水的过冷流动沸腾进行了数值模拟。通过对比不同气泡直径模型,揭示了气泡直径对于壁面传热方式的影响,确定了适合高压工况的气泡直径模型。考察了压力及壁面热通量对流动及传热特性的影响。计算结果表明,压力增加气泡脱离直径减小,单相对流传热所占比例增加,表面传热系数减小。高压高过冷度特征决定了气泡相分布极不均匀,随着热通量的增加,壁面附近容易形成气泡的密集,对过冷流动沸腾中的传热特性有重要影响。 相似文献
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模拟研究了泡沫铝、泡沫铜、网状聚氨酯泡沫的孔隙参数对多孔介质冰蓄冷板的融化过程的影响,得到了第三类边界条件下多孔介质冰蓄冷板融化过程的时间、温度分布、相界面移动等的规律。结果表明,多孔介质热导率越高,温度分布越均匀,相界面越模糊,冰蓄冷板融化时间越短;融化时间随多孔介质孔隙率的减小和孔密度的减少而缩短,孔隙率的影响程度大于孔密度;与纯冰相比,本研究中泡沫铜最多可将冰蓄冷板融化时间缩短15.2%。多孔介质热导率越低,冰蓄冷板的融化时间越长;融化时间随着孔密度的增加而缩短,随孔隙率的减小而略增;与纯冰相比,本研究中网状聚氨酯泡沫最多可将冰蓄冷板释冷时间延长11.8%。最后对填充泡沫铜和网状聚氨酯泡沫冰蓄冷板的融化时间进行了试验验证,试验结果与模拟结果较为一致。 相似文献
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Duwayne M. Anderson 《Israel journal of chemistry》1968,6(3):349-355
Certain aspects of the phenomena of undercooling and ice nucleation in soils are discussed with respect to recently established properties of phase boundary water in soils. Nucleation temperature as a function of water content is given for representative clays. In view of the fact that silicate surfaces seem always to be separated from ice by an interfacial layer of unfrozen, liquid like water a new concept of heterogeneous nucleation is outlined. It is proposed that ice nucleation occurs in the undercooled interfacial water layer at some distance removed from the particle surfaces. This concept, in effect, suggests that heterogeneous nucleation (nucleation of ice due to the influence of a substrate) in all its essential aspects may be only a special case of homogeneous nucleation (no substrate present) of water. 相似文献
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Stella Marusin 《Cement and Concrete Research》1981,11(1):115-124
Processes of freezing of water and melting of ice were studied using samples of hardened suspensions of plaster-of-paris with different mean pore sizes and constant porosities. Changes in the structure of the material were analyzed by measurement of the thermal and volume changes during cooling and heating cycles, and by the measurement of pore-size distribution and the changes of strength after the freezing cycles. It was shown that changes of volume within a temperature limit T=±20°C depend on the mean pore size and on the degree of water saturation. The disruption of the hardened plaster-of-paris structure was evaluated by determining the decrease in strength, if the nucleation of the ice crystals occurs during supercooling and the rate of their growth is greater than the rate of the amount of water forced out of the pores. The experimental observations support Power's theory concerning the frost resistance of porous material. 相似文献
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Ultrasound has been often used to assist nucleation process in liquid samples, while solid samples were barely taken into account. In this study, direct-contact ultrasound was used to realize the sonocrystallization for solid sample and the influence of ultrasound-assisted nucleation on freeze-drying process was investigated. First, a microscopic observation was performed to exam the effectiveness of direct-contact ultrasound on inducing nucleation for carrot slice at different supercooling degrees. Second, an ultrasonic vibrating plate was used to integrate the contact ultrasound into freeze-drying process and its influence on ice crystals size and sublimation rate was evaluated. The results showed that direct-contact ultrasound is applicable to stimulate nucleation in carrot slice at lower supercooling degree and obtain bigger ice crystals. Compared to the control sample, the sublimation time of the samples under sonocrystallization was significantly reduced, by 21.80%. Therefore, direct-contact ultrasound maybe a promising method to be applied in solid-sample freeze-drying process. 相似文献
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化学气相反应法合成SiC超细粉的成核和生长过程的研究 总被引:3,自引:0,他引:3
借助于TEM观察,讨论了化学气相反应法合成SiC超细粉的成长机理,分析结果显示,由于气体流速不同,合成的SiCF超细粉颗粒尺寸和颗粒形貌有较大变化,颗粒尺寸和颗粒形貌的变化成核和生长机理决定,一般涉及到均匀成术怜惜是相成核,团聚和熔融。 相似文献
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Hongyan Li Qi Li Hongli Liu Xurui Wang Kai Cao Jing Li Bo Zhang Wenjin Yuan 《Ceramics International》2021,47(16):22976-22984
A novel 3D microsphere fabricated with halloysite nanotubes was reported in our previous work. The hollow tubular structure in nano-scale of halloysite and the hollow structure in micro-scale of microsphere have attracted our attention. In this paper, phase change materials (methylmyristate and n-dodecane) were loaded in the spaces for the construction of anti-icing surface, and the related behavior and mechanism were investigation. The anti-icing performance of slippery liquid-infused porous surfaces (SLIPSs) were characterized by ice adhesion strength, freezing temperature and ice nucleation rate. The results showed that the phase change materials loaded in anti-icing coating eliminated the possibility of water vapor condensation in porous structure, greatly reduced the probability of nucleation on a concave surface, thus showed better anti-icing effect. Phase change materials play an important role in supercooling, effectively increasing the substrate temperature by 5.4 °C. Phase change anti-icing coating is a kind of functional material with great development potential. 相似文献
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在蒸馏水中加入多壁碳纳米管(MWCNT)纳米粒子,选用亲水性非离子型表面活性剂TNWDIS为分散剂。经过超声波震荡,配制分散均匀稳定的MWCNT-H2O纳米流体。利用静态真空闪蒸实验台,设定系统压力为100Pa,研究在吸附作用下多壁碳纳米管纳米粒子浓度、粒径、TNWDIS与MWCNT配比对闪蒸制取冰浆实验的影响。结果表明,多壁碳纳米管的加入可消除闪蒸制冰的相变蓄冷阶段、缩短液相降温时间使流体更早出现过冷现象;20~40nm粒径的MWCNT纳米粒子使用TNWDIS进行分散,质量分数范围在0.075%~0.15%时多壁碳纳米管纳米流体分散均匀稳定、达到最佳效果,其中质量分数为0.1%的纳米流体最大降低水的过冷度达62.2%;过冷度随着MWCNT纳米粒子粒径的增大而升高,闪蒸率基本维持在40%,但含冰率呈现非线性变化;20~40nm粒径的MWCNT纳米粒子使用TNWDIS配制成质量分数为0.1%的纳米流体,TNWDIS与MWCNT的分散配比建议采用0.5∶1,过冷度基本维持在2℃。 相似文献