冷表面结霜过程的实验研究

论文总字数：27286字

摘 要

本文设计了一个可视化实验装置，通过实验研究了水珠的生长和冻结过程、单个水滴的冻结过程以及霜的生长过程。并得出以下结论：

（1）在冷表面温度低于水蒸气的露点温度时，空气中的水蒸汽会凝结成水珠。冷表面的水珠的生长和冻结过程是冷表面结霜的前期过程，它主要由水蒸气冷凝成核、水珠生成、水珠聚合长大、水珠冻结几个阶段组成，当冷表面干净时，凝结的水滴呈球形。冻结时水滴的大小主要与冷表面温度和空气湿度有关，冷表面温度的增加和空气湿度的增加都会是冻结时水滴的直径增大。

（2）对于单个水珠的结冻过程，水滴在冷表面上接近球形，当水珠温度下降到0度时，呈过冷状态但并未发生相变，当水珠温度继续下降达到一定时间或者达到一定过冷度时，水珠才开始结冻。且水珠结冻先从底部开始，慢慢的往顶部蔓延，发生相变时由于放出相变潜热使得水珠温度升高。冻结后，由于液体凝结成固体时体积增大，水珠顶部会出现小的尖端凸起。霜从尖端开始长出。

（3）当冷表面的水珠发生冻结以后，霜晶开始从冻结水珠顶端开始长出。冷表面的霜生长过程由霜晶生长期，霜层生长期和霜层充分生长期三个阶段组成。霜枝不断变长，变多，不同霜柱之间开始交叉，霜层厚度快速增加。随后霜层出现折断和倒伏，霜层厚度增长较慢，霜晶顶部开始融化，霜层逐渐变得平坦，霜层内部密度增大。当空气湿度增大或者冷表面温度降低时，霜晶的增长速度增大。

关键词：冷表面；结霜；水珠冻结；霜层生长

An experimental study on frost formation on a cold surface

By Yang Yang

Supervised by Zhang Chengbin

Abstract：Frost formation is a very common phenomenon in nature and engineering etc. Frost will seriously affect the normal operation of the device, or even cause damage to the equipment.So the mechanisms of frost deposition,frost inhibition and defrost have been receiving more and more attention of scientists. Therefore, it has important scientific significance for the experimental research and observation of frost process on cold suiface.

A visualization system is designed in this paper. droplet growth, freezing process and frost growth process on the cold surface is discessed by the paper.A series of conclusions are obtained as follows:

(1)When air is exposed to the cold surface that is colder than dew point temperature, condenastion take place on the cold surface. The growth of the water droplets and the freezing process on the cold surface is early stages of cold frosting. It is mainly by nucleation of vapor condensation, droplets generation, droplets coalescence and droplets freezing. when the cold surface is clean, condensation of droplets is spherical. The size of droplets is mainly related to the cold surface temperature and air humidity, the increase of the temperature of the cold surface and the increase of the air humidity will be the increase of the diameter of water droplets.

(2) for a single droplet freezing process, water droplets on a cold surface is nearly spherical. when the temperature of droplets down to zero, droplets was supercooled state but not a phase transition, when the temperature continues to drop to reach for a certain time or reaches a certain degree of supercooling, droplets began to freeze. And the water droplets freeze start at the bottom and slowly spread to the top, since the release of latent heat so that the temperature drops during phase transformation. After freezing, due to increased volume of liquid condensed into a solid, water will appear small convex tip top. Frost begins to grow from the tip.

(3) when water of the cold surface freezing, frost crystal began to grow. The frost growth on the cold surface is composed of three stages: the frost crystal growth period , the frost layer growth period and the frost layer full growth period . When the air humidity increases or the temperature of the cold surface decreases, the growth rate of the frost crystal increases.

Keywords: cold surface; frost; water droplets freezing; frost layer growth

目录

1绪论……………………………………………………………………………1

1.1 研究背景和意义………………………………………………………………………………1

1.2 国内外研究现状………………………………………………………………………………1

1.2.1 结霜研究历程………………………………………………………………………………1

1.2.2 冷表面结霜因素研究………………………………………………………………………2

1.2.3 冷表面霜层物性研究………………………………………………………………………3

1.2.4除霜和抑霜…………………………………………………………………………………4

1.2.5结霜的物理和数学模型……………………………………………………………………5

1.3 本文主要研究内容……………………………………………………………………………6

1.4本章小结………………………………………………………………………………………6

2 实验装置以及实验过程………………………………………………………………………7

2.1实验装置………………………………………………………………………………………7

2.1.1制冷散热装置………………………………………………………………………………7

2.1.2可视化试验箱………………………………………………………………………………8

2.1.3图像采集系统………………………………………………………………………………8

2.1.4数据采集系统………………………………………………………………………………8

2.2实验方法………………………………………………………………………………………9

2.2.1表面接触角的测量…………………………………………………………………………9

2.2.2冷表面温度的调节………………………………………………………………………10

2.2.3拍摄方式…………………………………………………………………………………10

2.2.4水珠冻结时间和半径的测量方法………………………………………………………10

2.2.5霜层高度的测量…………………………………………………………………………11

2.3本章小结……………………………………………………………………………………11

3实验结果………………………………………………………………………………………12

3.1 水珠生长和冷冻过程的实验结果…………………………………………………………12

3.2单个水珠冻结过程的实验结果……………………………………………………………14

3.3 霜层生长过程的实验结果…………………………………………………………………15

3.4 理论解释……………………………………………………………………………………19

3.5本章小结……………………………………………………………………………………20

4结论……………………………………………………………………………………………21

1. 致谢…………………………………………………………………………………………22
2. 参考文献……………………………………………………………………………………23

冷表面结霜过程的实验研究

1. 绪论

1.1 研究背景和意义

结霜是自然界和工业中的一个重要现象，当物体表面温度低于空气中水蒸气的露点温度时，水蒸汽就会发生相变在该表面凝结，随着温度进一步降低，凝结的液体就会发生冻结。随后，在冻结的液体表面上会出现霜晶，进而形成霜层。如果冷表面温度足够低，空气中的湿蒸汽会在壁面凝华直接形成霜晶。

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