• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1226-1231
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• 2009

This paper presents operating characteristics of internal heat exchanger(IHX) for $CO_2$ geothermal heat pump in the heating mode. Mass flow rate of $CO_2$, inlet temperatures of $CO_2$ at high and low pressure side were selected as main effect factors by using fractional factorial DOE(Design of Experiments). And RSM(Response Surface Method) was used in optimization phase. The results show that heat transfer rate of IHX increases when either inlet temperature of low pressure side decreases or inlet temperature of high pressure side increases. Effectiveness of IHX increases with increasing of inlet temperature of either high pressure side or low pressure side. Finally, performance contour map was provided over the operation ranges of the main design factors.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권1호
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• pp.17-24
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• 2007

An experimental investigation was carried out for 4 different types of the aluminum foam heat sinks which were inserted into the annulus. The purpose of this study is to examine the feasibility of a heat sink with high performance forced convective water cooling in the annulus. The local wall temperature distribution, inlet and outlet pressures and temperatures, and heat transfer coefficients were measured for heat flux of 13.6, 18.9, 25.1, 31.4 $kW/m^2$ and Reynolds number ranged from 120 to 9,000. Experimental results show that the departure from the Darcy's law is evident from the pressure loss and the friction factor is much higher while the significant enhancement in Nusselt number is obtained, and average Nusselt number of aluminum foam with high pore density is much higher than that of aluminum foam with low pore density. Correlations for the friction factor is proposed and used for design of thermal applications.

• 한국자동차공학회논문집
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• 제23권1호
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• pp.18-24
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• 2015

In this study, a $CO_2$ air-conditioning system was investigated with different types of electrically driven compressors, parallel flow type gas cooler, four-pass type evaporator, internal heat exchanger integrated with accumulator, and electric expansion valve. The experimental study was conducted under various operating conditions (ie., different rotational compressor speeds, air inlet temperatures and air velocity coming into heat exchangers). The experimental results showed the cooling capacity was 3.5kW at $35^{\circ}C$ ambient temperature when the vehicle was idle (ie., the worst condition for cooling off the gas cooler). In terms of performance effect of the compressor, the e-RP model had a slightly better cooling capacity and coefficient of performance than the e-GR model under the same test conditions. An experimental equation for optimum cooling-performance control was also suggested based on the results. A high-pressure control algorithm for the super critical cycle was determined to achieve both maximum cooling performance and efficient energy consumption. The results from the experimental equation coincided with those of previous experimental studies.

• 한국유체기계학회 논문집
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• 제11권5호
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• pp.50-56
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• 2008

Metal cutting operations involve generation of heat due to friction between the tool and the pieces. This heat needs to be carried away otherwise it creates white spots. To reduce this abnormal heat cutting fluid is used. Cutting fluid also has an important role in the lubrication of the cutting edges of machine tools and the pieces they are shaping, and in sluicing away the resulting swarf. As a cutting fluid, water is a great conductor of heat but is not stable at high temperatures, so to improve stability an emulsion type mixed fluid with water and oil is often used. It is pumped over the cutting site of cutting machines as a state of atomized water droplet coated with oil by using jet. In this paper, to develop cutting fluid supplying nozzle to obtain ultra thin oil film for coating water droplet, a numerical analysis of three dimensional mixed fluid Jet through multi-stage nozzle was carried out by using a finite volume method. Jet flow characteristics such as nozzle exit velocity, development of mixing region, re-entrance and jet intensity were analyzed. Detailed mixing process of fluids such as air, water and oil in the nozzle were also investigated. It is easy to understand complex flow pattern in multi-stage nozzle. Important flow Information for advance design of cutting fluid supplying nozzle was drawn.

• 한국대기환경학회지
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• 제4권2호
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• pp.38-46
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• 1988

NOx is an important air pollution material which is generated when fossil fuels are burning, NOx removal in flue gas by selective catalytic reduction was studied over various catalysts in a fixed bed continuous flow reactor. The ranges of experimental conditions were at the temperatures between $200^\circ$C and $350^\circ$C, the $NH_3/NOx$ mole ratios between 0.8 and 1.4, oxygen concentrations between 1.5% and 3% and the space velocities between 5, 000 $hr^-1$ and 12, 500 $hr^-1$. The efficiency of NOx removal in the ranges of experimental conditions was highest at the temp. of 300$^\circ$C, oxygen concentration of 2.5-2.6% and $NH_3/NOx$ mole ratios of 1.0-1.2. The catalyst with high activity for NOx removal in flue gas was found to be $MoO_3-V_2O_5/TiO_2$.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.774-778
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• 2004

The atomization process of a circular $SF_{6}$ liquid jet issued into an otherwise quiescent, high-pressure $N_2$ gas was observed to explore the breakup mechanism of liquid ligaments involved in turbulent atomization. Both liquid and gas temperatures were fixed at a room temperature but the gas pressure was elevated to more than twice the critical pressure of $SF_{6}$. Therefore, the liquid surface was in a thermodynamic state close to a critical mixing condition with suppressed vaporization. Since the surface tension and the surface gas density approach zero and the surface liquid density, respectively, phenomena equivalent to those which would appear when a very high speed laminar flow of water were injected into the atmospheric-pressure air can be observed by issuing $SF_{6}$ liquid at low speeds in micro-gravity environment which avoid disturbances due to gravity forces. The instability ob near-critical mixing surface jet was quantitatively characterized using a newly developed device, which could issue a very small amount of $SF_{6}$ liquid at small constant velocity into a very high-pressure $N_2$ gas.

• 한국가시화정보학회지
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• 제19권2호
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• pp.56-62
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• 2021

Solid oxide fuel cells (SOFCs) is the high efficiency fuel cell operating at high temperatures ranging from 700-1000℃. Design of the flow paths of the fuel and air in SOFCs is important to improve cell performance and prevent cell degradation. However, the uneven distribution of current density in the traditional type having one inlet and outlet causes cell degradation. In this regard, the parallel flow path with two inlet and outlets was designed and compared to the traditional type based on computational fluid dynamics (CFD) simulation. To check the cell performance, hydrogen distribution, velocity distribution and current density distribution were monitored. The results validated that the parallel designs with two inlets and outlets have a higher cell performance compared to the traditional design with one inlet and outlet due to a larger reaction area. In case of uniform-type paths, more uniform current density distribution was observed with less cross-sectional variation in flow paths. In case of contracted and expanded inflow paths, significant improvement of performance and uniform current density was not observed compared to uniform parallel path. Considering SOFC cell with uniform current density can prevent cell degradation, more suitable design of SOFC cell with less cross-sectional variation in the flow path should be developed. This work can be helpful to understand the role of flow distribution in the SOFC performance.

• 청정기술
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• 제29권4호
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• pp.297-304
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• 2023

첨단 전자 제품 산업의 비약적인 발전은 환경적 측면에서 고농도 암모니아 폐수의 증가를 초래했다. 고농도 암모니아 폐수를 안정적으로 처리하기 위해 다양한 방법의 기술이 시도되고 있으나, 지금까지 성공적인 기술이 개발되어 적용되지는 못하고 있다. 본 연구에서는 첨단 전자산업에서 발생하는 고농도 암모니아 함유 폐수에 대하여 밀폐(closed) 순환형 대향류 충전탑 형식의 실증설비를 이용하여 온도, 공기부하율 그리고 폐수부하율 변화에 따른 암모니아성 질소의 제거효율과 제거 특성을 평가하였다. 폐수량 20.8 m³ h^-1, 공기량 18,000 Nm³ h^-1의 운전 조건에서 온도를 45, 50, 55 그리고 60℃로 변경하여 운전한 결과, 암모니아성 질소(NH₃-N)의 제거율은 각각 87.5, 93.4, 96.8 및 98.7%로 온도가 제거율에 미치는 가장 큰 영향 인자임을 알 수 있었다. 공기부하율을 증가시키면 제거율도 증가하나, 흡수탑의 액적(droplet)이 탈기탑으로 유입되어 제거율 증가는 크지 않았다. 폐수 부하율이 변경되어도 제거율은 크게 변하지 않았는데, 이는 제거율에 영향이 없는 것이 아니라, 상대적으로 높은 공기부하율에 기인한 것으로 판단된다. 실증연구를 통해 암모니아 탈기법은 첨단 전자산업에서 발생하는 고농도 암모니아 폐수를 안정적으로 처리할 수 있는 적정한 공법임을 확인할 수 있었다.

• 한국산학기술학회논문지
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• 제20권1호
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• pp.21-27
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• 2019

그간 소형 제빙기에는 R-404A가 사용되어 왔으나 지구 온난화와 관련하여 대체 냉매 적용이 시급한 실정이다. 본 연구에서는 제빙기에 적용되어 온 R-404A를 대체할 R-448A와 R-449A에 대하여 drop-in test를 수행하였다. 시험은 외기 온도와 증발판에 공급되는 물 온도를 변화시키며 수행되었다. 실험 결과 R-404A의 일 평균 제빙량은 R-448A보다는 5.3%, R-449A보다는 4.2% 크게 나타났다. 이는 R-404A의 기체 밀도가 커서 냉매 순환량이 증가하기 때문으로 판단된다. 한편 R-448A와 R-449A의 제빙량을 비교하면 외기온도나 믈 온도가 낮아 제빙량이 많으면 R-448A가, 외기 온도나 물 온도가 높으면 R-449A가 우수한 성능을 보인다. 일 평균 소비 전력량은 R-448A나 R-449A보다 R-404A에서 대략 10% 크게 나타났다. 한편 성적계수의 경우 R-448A와 R-449A는 거의 동일하고 R-404A의 값보다는 3.0% 크게 나타났다. 현재 R-448A, R-449A의 증발, 응축 열전달에 대한 데이터가 부족한 실정으로 향후 이 부분에 대한 기초 연구가 필요할 것으로 판단된다.

• 대한기계학회논문집B
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• 제28권11호
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• pp.1440-1448
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• 2004

Multiple solutions in natural convection of air (Pr=0.7) between two horizontal walls with mean temperature difference and the same periodic nob-uniformities are investigated. An analytical solution is found for small Rayleigh number, and the general solution is investigated by using a numerical method. In the conduction-dominated regime, two upright cells are formed between two walls over one wave length. When the wave number is small, the flow becomes unstable with increase of the Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The multicellular flows at high Rayleigh numbers consist of approximately square-shape cells. And several kinds of multiple flows classified by the number of cells are found.