기계공학과

1. Phase-Change Heat Transfer

Boiling Heat Transfer Enhancement: Microporous Coating

Improvements in boiling heat transfer performance create thermal management solutions for data center or supercomputer cooling. Microporous coatings are one way to improve boiling heat transfer performance. The boiling enhancement method forms micro-scale cavities to promote boiling heat transfer, lower the superheat of the wall, and improve the boiling heat transfer coefficient. Typical fabrication methods, including sintering, electrodeposition, and micro fin shapes, are studied in the advanced thermal management laboratory at Ajou University.

Boiling Heat Transfer Enhancement: Micro Metallic Foam

In pool boiling studies using metallic foams, foam thickness is an essential design factor, and the effect of thickness is more dominant at higher pore densities. Nevertheless, studies on the boiling performance of metal foams with a micro-thick are still lacking. This study confirmed the effect of improving boiling heat transfer performance through micro-thick copper metallic foams in the saturated water pool.

Boiling Heat Transfer Enhancement: Sandblasting

Sandblasting is a type of surface modification method in which abrasive released under strong pressure collides with the surface to make the surface rough. In Pool boiling, rough surfaces typically produce boiling at a relatively low superheated surface temperature compared to smooth surfaces, indicating higher CHF points. We use various abrasive materials to determine the release pressure of the abrasive to meet the target surface roughness and conduct research to confirm the improvement of boiling performance due to surface roughness.

2. Thermal Management

Battery Thermal Management (Electric Vehicles and Energy Storage Systems (ESS))

Lithium-ion batteries have been used as energy sources for various electronic devices owing to their high energy density, low self-discharge rate, and no memory effect. The cell temperature of a lithium-ion battery should be maintained at the optimum range from 15 to 35 oC to secure the cell's stable and efficient electrochemical performance. A thermal runaway can be initiated when the cell temperature rises above approximately 80 oC, where the breakdown of the SEI (Solid electrolyte interphase) layer starts. Besides, the temperature difference within a cell must be less than 5 oC to prevent cell malfunction, owing to the localized deterioration. Therefore, the battery thermal management system (BTMS) is essential to maintain the cell temperature within a suitable range and minimize the temperature difference over the entire cell.

3. TGP (Boiling-Driven Heat Spreader)

Boiling-Driven Heat Spreader (BDHS)

Boiling-driven heat spreader (BDHS) is a heat spreader that uses a boiling mechanism and has a simple structure without a wick to maintain the circulation of the working fluid. Since the bubble pumping effect circulates the working fluid, it operates up to a high heat flux of 200 W/cm2, and there is no heat transfer performance deviation depending on the orientation. In addition, BDHS has the advantage of being easily embedded into existing thermal management devices due to its simple structure.

4. Thermosyphon

TPCT (Two-Phase Closed Thermosyphon)

TPCT (Two-Phase Closed Thermosyphon) is a device that is used for many heat transfer applications. It is a type of heat pipe that uses a two-phase flow to transfer heat. The two-phase flow is created by boiling a working fluid in an evaporator section and condensing it in a condenser section. The working fluid is then returned to the evaporator section by gravity force. By using phase-change phenomena, TPCT has highly effective thermal conductance. TPCTs are used in many applications, such as electronics cooling, solar thermal systems, and space applications. They are also used in many other industries, such as chemical processing and waste heat recovery.

Confinement Effect

Recently, interest in compact TPCT has been increasing due to thermal confinement and miniaturization of heat transfer devices. Compact TPCT has different internal two-phase flow characteristics compared to TPCT of general size, which also shows a difference in thermal performance. This is called the confinement effect of TPCT. However, the operating mechanism of Compact TPCT has not yet been clarified. Therefore, we investigate the internal two-phase flow and heat transfer characteristics of compact TPCT using TPCTs of various dimensions.

Geyser Boiling

Geyser boiling is a kind of water-hammering phenomenon that occurs in the Two-Phase Closed Thermosyphon(TPCT). It is known that this can physically damage the TPCT and should be avoided. Until now, several geyser boiling studies in the TPCT have been conducted, but most of them have been limited to only visualization or thermal performance. Therefore, our research group aims to provide quantitatively the fatigue failure of TPCTs and the force generated by geyser boiling, which has not been studied yet. Ultimately, we want to contribute to the design of TPCT by proposing lifetime and design parameters related to geyser boiling.

Thermosyphon Heat Exchanger (Heat Pipe Heat Exchanger)

Recently, global warming has been a pressing danger to our society. To cope with global warming, an effective device to recover waste heat becomes more important than ever. A heat pipe heat exchanger is a device that transfers heat between two or more fluids. It uses bundles of heat pipes to transfer thermal energy effectively. A heat pipe with high heat transfer capability using latent heat makes a highly effective heat exchanger compared to traditional heat exchangers. Also, the isothermal operation of heat pipe leads to strong tolerance towards thermal deformation. These advantages make heat pipe heat exchangers more attractive, and the market share of heat pipe heat exchangers is increasing continuously. As a result, we are developing heat exchangers more effectively and researching ways to its fabrication easier.