不同凝核剂在不同表面凝固特性的实验研究

发布时间：2018-04-04 05:34

本文选题：冰浆　切入点：凝核剂　出处：《天津商业大学》2017年硕士论文

【摘要】：冰浆是利用显热与潜热共同蓄冷的蓄冷介质,其单位蓄冷量非常可观,在相同体积情况下,冰浆的蓄冷量要比其他的蓄冷介质多3~4倍,对电网峰谷的调节能力使冰浆在蓄冷空调方面有很好的应用前景。本文对制取冰浆所用的三种离子类添加剂溶液在不同表面的凝固特性进行了理论分析、实验研究及数值模拟。具体研究内容如下:(1)从理论上分析了冰晶成核机理,在同质成核的情况下,晶核可以继续生长的临界半径在10-11m的数量级上,临界成核能在10-22J的数量级上。研究了影响异质临界成核能与成核速率的影响因素,液滴在异质成核表面的接触角在0~20°与160~180°时对临界成核能的影响较大。讨论了溶液在平板表面的接触角、粗糙度、添加剂以及过冷度对冰晶成核的影响规律。(2)对纯水和不同浓度的氯化钠溶液在不同表面的模型进行简化,利用ANSYS Fluent对不同接触角的液滴凝固过程进行数值模拟,通过模拟得出:接触角较小的液滴的凝固速度大于接触角较大的液滴。在相同工况下,溶液开始凝固时间和凝固完成所用时间与氯化钠溶液的浓度呈正比,与接触角的大小成正比,这与理论分析相吻合。在凝固过程中首先从与壁面接触的底部开始凝固,并且液滴表面首先凝固然后内部再完全凝固,疏水表面上液滴的凝固时间大于亲水表面液滴的凝固时间,与实验观察结果一致。(3)搭建了冷表面液滴凝固性能测试装置,研究了纯水和三种不同浓度的离子类添加剂溶液在不同表面以及不同粗糙度条件下的凝固特性。对于亲水性表面,随着平板表面粗糙度的增大,溶液的临界成核能逐渐减小,而对于疏水性表面则相反,疏水表面对液滴凝固具有显著的延缓效果。溶液在不同表面的临界成核能随着过冷度的增大而逐渐降低。在相同的浓度及粗糙度下,氯化钠溶液的临界成核能比氯化钾溶液和碳酸氢钠溶液的临界成核能小,因此使用氯化钠溶液作为添加剂,可以促进冰晶的生成。
[Abstract]:Ice slurry is the use of sensible heat and latent heat storage medium common cold storage unit, the storage volume is very considerable, in the same volume, cold storage capacity of ice slurry storage medium other than the 3~4 times, the ability to regulate the peak valley of the ice slurry has good application prospect in the cold storage air conditioner. Three kinds of ionic additives used in the solution of making ice slurry is analyzed on the solidification characteristics of different surface, experimental study and numerical simulation. The main research contents are as follows: (1) from the theoretical analysis of the ice nucleation mechanism, in the case of homogeneous nucleation, crystal nucleus you can continue to grow the critical radius at the order of magnitude of 10-11m, the critical nucleation energy in the order of magnitude of 10-22J. Studied the factors which affect the nucleation rate of heterogeneous nuclear and critical droplet in a heterogeneous nucleation surface contact angle in 0~20 degrees and 160~180 degrees of critical nucleation energy. Loud. Discuss the solution on the plate surface contact angle, roughness, additives and undercooling on ice crystals into influence of nuclei. (2) of pure water and different concentrations of Sodium Chloride Solution is simplified in different surface model, numerical simulation of droplet solidification process of different contact angle using ANSYS Fluent, through the the simulation results show that the contact angle of smaller droplet solidification rate is greater than the contact angle of large droplets. In the same condition, the initial solution setting time and setting time for the completion of concentration and Sodium Chloride Solution is directly related to the large and small is proportional to the contact angle, which coincides with the theoretical analysis. In the process of solidification from the first contact with the wall of the bottom and the surface of droplet solidification, solidification and internal first completely solidified, the solidification time of droplet on hydrophilic and hydrophobic surface is greater than the solidification time of hydrophilic surface droplets, with the experimental observation. Results. (3) built a cold surface droplet solidification performance testing device of pure water, and three kinds of different concentration of ion additive solution in different surface roughness and different conditions. The solidification characteristics for the hydrophilic surface, with surface roughness increases, the critical nucleation energy solution decreases gradually. As for the hydrophobic surface on a hydrophobic surface, droplet solidification has significant effect on delaying. Solution in different surface critical nucleation energy with the increase of undercooling and gradually decreased. At the same concentration and roughness, Sodium Chloride Solution critical nucleation energy than potassium chloride solution and sodium bicarbonate solution into the critical nuclear small therefore, the use of Sodium Chloride Solution as additives, can promote the formation of ice crystals.

【学位授予单位】：天津商业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB64

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