기포를 동반한 유동장에서의 해수 동결거동에 관한 연구

Abstract

One of the most essential things to maintain our lives is water. Water consumption is rapidly increasing due to the exclusive overpopulation, industrial development and improvement of people's living standards. However, only 1% of water source is available for human being, so the ever-increasing scarcity of water is getting serious as time goes by.

Korea also will be no exception of this tendency and many researches have often proven how urgent Korea is water deficiency problem. In order to reduce this problem, we try to make the most water through building multi-functional dams, rainmaking and developing desalination system. Among those, desalination system is expected to be the most effective method because of its availability of seawater. It'll enable us to get water steady and readily. When we select particular kind of desalination system devices, that decision is mostly influenced by fresh water produce cost. In order words, its efficiency depends on whether we can achieve possible energy source easily or not.

As environmentally friendly means, many people are encouraged to use LNG (Liquefied Natural Gas) in Korea and many countries of the world. Amount of LNG consumption is currently heading higher. In general, LNG which is stored below -162℃ in super-liquid tank requires certain energy to gasify because it changed into the gaseous state with high pressure wasted cold energy when it is sent to each part in need. LNG loses lots of cold energy (850kJ/kg) during this process of absorbing heat.

To take advantage of this wasted cold energy, we are developing the systems such as producing the frozen food processing, dry ice, liquefied hydrogen, liquefied nitrogen and seawater freezing desalination. Therefore we'll mainly focus on the development of a seawater freezing desalination system and design technique using wasted cold energy necessary to freezing behavior of seawater. This study is intended to achieve qualitative and quantitative fundamental data with respect to it.

The device mainly consists of test section(transparent acryl rectangular duct), a brine loop

visualizing the flow in freezing part, etc.

After considering mean concentration of seawater measuring water and refined salt with digital balance and salinity meter, the operating fluid can function as 3.5wt% NaCl aqueous solution.

We operate brine loop using ethylene glycol 40% aqueous solution within the temperature of -21.12℃(eutectic point of seawater). Visualizing section using nylon12 tracer measures PIV with Argon-ion laser. After injecting -0.5℃ air into the test-section accompanied by flow field, investigated the flow appearance in around cooled parts by using the PIV system.

The experiments were carried out for a variety of parameter, such as sea water velocity, air-bubble flow rate, and cooled part temperature. The shape of freezing layer, freezing rate and salinity of frozen layer were observed and measured. And the flow patterns around cooled parts were visualized using the PIV to analyze the relationship between the flow structure and the freezing characteristics. It was found that the experimental parameters gave a great influence on the freezing rate and the salinity of the frozen layer

maintaining the temperature of cooled parts, PIV(Particle Image Velocimetry) system