Sung-Seek Park

Multi-walled carbon nano tubes effects for methane hydrate formation

Methane hydrate is considered an excellent way of transporting and storing natural gas in large quantities. However, when methane hydrate is formed artificially, the amount of consumed gas is relatively low due to a slow reaction rate between water and methane gas. Therefore, for the practical purpose in the application, the present investigation focuses on the rapid hydrate formation and the amount of consumed gas by adding MWCNT to pure water. The results show that when the multiwall carbon nano tubes of 0.004 wt% was added to pure water, the amount of consumed gas was about 300% higher than that in pure water and the hydrate formation time decreased at the low subcooling temperature

A Study on Regenerative OTEC System using the Condenser Effluent of Uljin Nuclear Power Plant

For the past few years, the concern for clean energy has been greatly increased. Ocean thermal Energy Conversion(OTEC) power plants are studied as a viable option for the supply of clean energy. In this study, we examined the thermodynamic performance of the OTEC power system for the production of electric power. Computer simulation programs were developed under the same condition and various working fluids for closed Rankine cycle, regenerative cycle, Kalina cycle, open cycle, and hybrid cycle. The results show that the regenerative cycle showed the best system efficiency. And then we examined the thermodynamic performance of regenerative cycle OTEC power system using the condenser effluent from Uljin nuclear power plant instead of the surface water. The highest system efficiency of the condition was 4.55% and the highest net power was 181 MW.

A Comparative Study on the Characteristics of the MWCNTs and PVP Added Nanofluids

In this study, the characteristics of multi-walled carbon nanotubes added nanofluid were investigated. Sodium Dodecyl Sulfate, SDS, and Polyvinylpyrrolidone, PVP, were employed as the dispersant. SDS or PVP was added in pure water. And then, 0.0005, 0.001, 0.002, 0.003. 0.004, 0.005,0.01, and 0.02 vol% of CM-95 and CM-100 were dispersed respectively. The thermal conductivity and the viscosity were measured with a transient hot-wire instrument built for this study and the DV II+ Pro viscometer. The results showed that PVP had good thermal conductivity at 300 wt% and the thermal conductivity of CM-100 was better than that of CM-95. However, the viscosity of CM 100 was higher than that of CM 95.

A Study on the Influence of Boiling Heat Transfer of Nanofluid with Particle Length and Mixing Ratio of Carbon Nanotube

A boiling heat transfer system is used in a variety of industrial processes and applications, such as refrigeration, power generation, heat exchangers, cooling of high-power electronics components, and cooling of nuclear reactors. The critical heat flux (CHF) is the thermal limit during a boiling heat transfer phase change; at the CHF point, the heat transfer is maximized, followed by a drastic degradation beyond the CHF point. Therefore, Enhancement of CHF is essential for economy and safety of heat transfer system. In this study, the CHF and heat transfer coefficient under the pool-boiling state were tested using multi-wall carbon nanotubes (MWCNTs) CM-95 and CM-100. These two types of multi-wall carbon nanotubes have different sizes but the same thermal conductivity. The results showed that the highest CHF increased for both MWCNTs CM-95 and CM-100 at the volume fraction of 0.001%, and that the CHF-increase ratio for MWCNT CM-100 nanofluid with long particles was higher than that for MWCNT CM-95 nanofluid with short particles. Also, at the volume fraction of 0.001%, the MWCNT CM-100 nanofluid indicated a 5.5% higher CHF-increase ratio as well as an approximately 23.87% higher heat-transfer coefficient increase ratio compared with the MWCNT CM-95 nanofluid.

A Comparative Study on the Effect of THF and Oxidized Carbon Nanotubes for Methane Hydrate Formation

ABSTRACT:Methane hydrate is formed by physical binding between water molecules and methane gas, which is captured in the cavities of water molecules under the specific temperature and pressure. 1 m 3 hydrate of pure methane can be decomposed to the methane gas of 172 m 3 and water of 0.8 m 3 at standard condition. Therefore, there are a lot of practical applications such as separation processes, natural gas storage transportation and carbon dioxide sequestration. For the industrial utilization of hydrate, it is very important to rapidly manufacture hydrate. So in this study, hydrate formation was experimented by adding THF and oxidized carbon nanotubes in distilled water, respectively. The results show that when the oxidized carbon nanofluids of 0.03 wt% was, the amount of gas consumed during the formation of methane hydrate was higher than that in the THF aqueous solution. Also, the oxidized carbon nanofluids decreased the hydrate formation time to a greater extent than the THF aqueous solution at the same subcooling tempera-ture.Keywords:Methane hydrate(메탄 하이드레이트), Tetrahydrofuran(THF), Oxidized carbon nanofluids(산화탄소나노유체), Formation(생성), Subcooling(과냉도)

A Study on the Methane Hydrate Formation Using Natural Zeolite

Gas hydrate is formed by physical binding between water molecule and gas such as methane, ethane, propane, or carbon dioxide, etc., which is captured in the cavities of water molecule under the specific temperature and pressure. hydrate of pure methane can be decomposed to the methane gas of and water of at standard condition. If this characteristic of hydrate is reversely utilized, natural gas is fixed into water in the form of hydrate solid. Therefore, the hydrate is considered to be a great way to transport and store of natural gas in large quantity. Especially the transportation cost is known to be 18~25% less than the liquefied transportation. However, when methane gas hydrate is artificially formed, its reaction time may be too long and the gas consumption in water becomes relatively low, because the reaction rate between water and gas is low. Therefore, for the practical purpose in the application, the present investigation focuses on the rapid production of hydrates and the increment of the amount of captured gas by adding zeolite into pure water. The results show that when the zeolite of 0.01 wt% was added to distilled water, the amount of captured gas during the formation of methane hydrate was about 4.5 times higher than that in distilled water, and the methane hydrate formation time decreased at the same subcooling temperature.

A Comparative Study on the Characteristics of Carbon Nanofluids for Efficiency Enhancement of Low Temperature Heat Exchanger

Abstract ―In this study, for efficiency enhancement of low temperature heat exchanger, the thermal conductivity and the viscosity of carbon nanofluids and oxidized carbon nanofluids were measured at 10℃ and 25℃, respectively. Carbon nanofluids were made by ultrasonic-dispersing ones in distilled water after Multi-Walled Carbon Nanotubes (MWCNTs) mixed Sodium Dodecyl Sulfate (SDS, 100 wt%), Polyvinyl pyrrolidone (PVP, 300 wt%) each. Oxidized carbon nanofluids were made by ultrasonic-dispersing Oxidized Carbon Nanotubes (OMWCNTs) in distilled water. The thermal conductivity of carbon nanofluids was measured by using a transient hot-wire method. The viscosity was measured by using a digital viscometer. As a result, the thermal conductivity of oxidized carbon nanofluids was the highest of those compared and the other carbon nanofluids at the same mixture ratio and temperature, and the viscosity was measured the lowest of those compared and the other carbon nanofluids. Key words : Low temperature heat exchanger, Carbon nanotubes, Nanofluid, Thermal conductivity, Viscosity

A Study on Influence of Flow Boiling Heat Transfer on Fouling Phenomenon in Nanofluids

Abstract A boiling heat transfer is used in various industry such as power generation systems, heat exchangers, air-conditioningand refrigerations. In the boiling heat transfer system, the critical heat flux (CHF) is the important factor, and it indicatedsafety of the system. It has kept up studies on the CHF enhancement. Recently, it is reported the CHF enhancement, whenworking fluid used the nanofluid with high thermal properties. But it could be occurred nanoflouling phenomenon fromnanoparticle deposition, when nanofluid applied the heat transfer system. And, it is reported that the safety and thermal efficiency of heat transfer system could decrease. Therefore, it is compared and analyzed to the CHF and the boiling heat transfer coefficient on effect of artificial nanofouling (coating) in oxidized multi-wall carbon nanotube nanofluids. As theresult, the CHF of oxidized multi-wall carbon nanofluids and the CHF of artificial nanofouling in the nanofluids increased to maximum 99.2%, 120.88%, respectively. A boiling heat transfer coefficient in nanofluid increased to maximum 24.29%higher than purewater, but artificial nanofouling decreased to maximum -7.96%.