• Journal of Advanced Marine Engineering and Technology
• /
• 제28권5호
• /
• pp.754-761
• /
• 2004

In this paper, evaporating heat transfer characteristics in the refrigeration and air-conditioning facilities were studied using the environmentally friendly refrigerants R-1270 (Propylene). R-290 (Propane). R-600a (Iso-butane) and HCFC refrigerant R-22 The test tube was surrounded by an annulus with water flowing counter to the refrigerant. The tube is copper. with an outside diameter of 12.7mm and the wall thickness of 1.315mm. The test results showed that the local evaporating heat transfer coefficients of hydrocarbon refrigerants were superior to that of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-1270. The average evaporating heat transfer coefficient increased with the increase of the mass velocity and it showed the higher values in hydrocarbon refrigerants than R-22 Comparing the heat transfer coefficient of experimental results with that of other correlations. the presented results had agood agreement with the Kandlikar's correlation. This results form the investigation can be used in the design of heat transfer exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.

• 대한기계학회논문집
• /
• 제19권10호
• /
• pp.2586-2594
• /
• 1995

Two phase flow phenomena are observed in many industrial facilities and make much importance of optimum design for nuclear power plant and various heat exchangers. This experimental study has been investigated the classification of the flow pattern, the local void distribution and convective heat transfer in swirl and non-swirl two phase flow under the isothermal and nonisothermal conditions. The convective heat transfer coefficients in the single phase water flow were measured and compared with the calculated results from the Sieder-Tate correlation. These coefficients were used for comparisons with the two-phase heat transfer coefficients in the flow orientations. The experimental results indicate, that the void probe signal and probability density function of void distribution can used into classify the flow patterns, no significant difference in voidage distribution was observed between isothermal and non-isothermal condition in non-swirl flow, the values of two phase heat transfer coefficients increase when superficial air velocities increase, and the enhancement of the values is observed to be most pronounced at the highest superficial water velocity in non-swirl flow. Also two phase heat transfer coefficients in swirl flow are increased when the twist ratios are decreased.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2011년도 추계학술대회 초록집
• /
• pp.143.2-143.2
• /
• 2011

Energy foundations and other thermo-active ground structure, energy wells, energy slab, and pavement heating and cooling represent an innovative technology that contributes to environmental protection and provides substantial long-term cost savings and minimized maintenance. This paper focuses on earth-contact concrete elements that are already required for structural reasons, but which simultaneously work as heat exchangers. Pipes, energy slabs, filled with a heat carrier fluid are installed under conventional structural elements, forming the primary circuit of a geothermal energy system. The natural ground temperature is used as a heat source in winter and heat sink in summer season. The system represented very high heating and cooling performance due to the stability of EWT from energy slab. Maximum heat pump unit COP and system COP were 4.9 and 4.3.

• 한국태양에너지학회 논문집
• /
• 제26권1호
• /
• pp.21-28
• /
• 2006

Changes in building construction methods and repairing of older buildings have reduced infiltration rate. Synthetic materials, release airborne particles and uneven healthy odor are increased. For preventing pollutants introduce fresh outdoor air into the building, simply letting fresh outdoor air into building, however, Is not a cost-effective way to ventilation. When additional ventilation is added to an existing HVAC system, the heating and cooling equipment, often cannot handle the increased load. A HRV provides a way to minimize in energy costs while introducing fresh air to a building. In this study, the economical research of HRV, made of three types of materials, are conducted. Heat recovering characteristics are studied at seasonal outdoor air conditions based on the outdoor air property condition at, Seoul in 2002. As a results, the average sensible effectiveness is 0.75 in the sensible heat exchanger and average total effectiveness is 0.65 in the total heat exchanger. The pay back period of the sensible heat exchangers are $3.2{\sim}3.5$ year and it of total heat exchanger is 2.2 years.

• 설비공학논문집
• /
• 제8권1호
• /
• pp.120-139
• /
• 1996

Experiment was performed to study the heat transfer characteristics in 27 kinds of 15 : 1 scale models of multi-louverred fin heat exchangers with a wide range of variables(R $e_{Lp}$ =100~1, 800, $L_p$/F$p$=0.3~0.9, $\theta$=20$^{\circ}$~40$^{\circ}$). Thermofoil heaters were used to heat the louver fins and the local average Nusselt number for each louver in the louver array was obtained at constant wall temperature conditions. Correlations are developed to predict the heat transfer characteristics and drag coefficients. Generally, the heat transfer characteristics in the multi-louvered fins is shown to be similar to those of the laminar heat transfer on a flat plate. As the Reynolds number, the louver pitch to fin pitch ratio$L_p$/F$p$and the louver angle($\theta$) increase respectively, the average Nusselt number increases, but the variation of average Nusselt number as a function of the louver angle is smaller than that as a function of the louver pitch to fin pitch ratio. In case of$L_p$/F$p$ <0.5, the average Nusselt number of the 3rd louver is especially lower than the others, it is expected that it is due to the flow structure such as a recirculation flow and a flow separation.

• 수산해양교육연구
• /
• 제5권2호
• /
• pp.119-127
• /
• 1993

This work studies for heat transfer and pressure drop performance of integral inner and outer fin tubes, designed to enhance the heat transfer performance of smooth tubes for in recipro and turbo refrigerator or high performance compact heat exchangers. Eight different inner spiral fin copper tubes with integral fin at outside surfaces were employed to improve boiling heat transfer coeffcient. For comparison, tests were made using a plain tube having the inside diameter and an outside diameter equal to that at the root of the fins for the finned tubes. Pool boiling heat transfer is investigated experimentally and theoretically on single tube arrangement. The refrigerant evaporates at a saturation state of 1 bar on the outside tube surface heated by hot water. The refrigerant R11 ($CFCl_3$) was used at a pressure of $P_s=1bar$ as a convenient test fluid with a boiling temperature of $T_s=23.6^{\circ}C$. The observed heat transfer enhancement of boiling for finned tubes significantly exceeded that to be expected on grounds of increased area. The maximum Vapor - side enhancement(i.e., vapor - side heat transfer coefficient of finned tube/vapor - side coefficient for plain tube) was found to be around 4 at 1299fpm - 30grooves tube.

• Nuclear Engineering and Technology
• /
• 제53권8호
• /
• pp.2488-2498
• /
• 2021

The wall film-wise condensation plays an important role in the heat transfer processes of heat exchangers, refrigerators, and air conditioner. In the field of nuclear engineering, steam condensation is often utilized in safety systems to remove the core decay heat under both transient and accident conditions. In particular, passive containment cooling system (PCCS), are designed to ensure containment safety under severe accident conditions. A computational fluid dynamics (CFD) scale analysis has been conducted to calculate the heat transfer rate of the PCCS. However, despite the increase in computing power, there are challenges in the long-term transient simulation of containment using CFD scale codes. In this study, a heat structure coupling between the CFD and system analysis codes was performed to efficiently analyze PCCS. In addition, the component unstructured program for interfacial dynamics (CUPID) was improved to analyze the condensation behavior of ternary gas mixtures. Thereafter, the condensation heat transfer on the primary side was calculated using the improved CUPID and CFD code, whereas that on the secondary side was simulated using MARS. Both the coupled codes were validated against the CONAN facility database. Finally, conjugate heat transfer simulations with wall condensation in the presence of non-condensable gases were appropriately performed.

• 청정기술
• /
• 제23권3호
• /
• pp.223-236
• /
• 2017

기후변화 대응을 위한 청정 화력발전 기술의 일환으로 폐기물과 바이오매스를 중심으로 한 신재생연료의 이용이 크게 증가함에 따라 특히 고온 고압 스팀 생산이 필요한 발전용 보일러 열교환기의 고온부식(High temperature corrosion) 문제가 심각한 현안으로 대두되고 있다. 이러한 문제점은 저급연료에 포함된 염화알칼리 성분이 보일러 내 열교환기 중 표면온도가 가장 높은 과열기(Superheater) 또는 재열기(Reheater)에 점착된 후 염소에 의해 부식이 가속화되어 일어난다. 이를 해결하기 위해 설계 변경, 재료 개선, 연료 전처리 등의 고온부식 회피 방법과 함께 첨가제를 이용한 고온부식 방지 기술이 활용되고 있다. 본 연구에서는 보일러에서 고온부식 방지를 위한 다양한 접근 중 특히 첨가제를 이용한 연구개발 현황을 소개한다.

• 대한기계학회논문집B
• /
• 제35권10호
• /
• pp.1033-1040
• /
• 2011

예혼합 버너는 높은 효율과 낮은 배기 때문에 가정용 보일러 버너 시스템에 매우 강력한 버너이다. 일반적으로 가정용 보일러 버너는 내부에 농후한 예혼합 불꽃으로 구성하고 연료는 2차공기의 공급에 의하여 완전연소 되는 분젠 버너를 이용한다. 이것은 상대적으로 긴 불꽃 길이와 높은 과잉공기비에서 작동하기 때문에 높은 효율을 갖는 소형 보일러에 적용하기 어렵다. 이 논문에서 메탈 화이버, 세라믹, SUS 핀과 같은 매질을 사용하는 예혼합 연소 버너의 특징을 실험하였다. 특히, 표면 매질의 비반응 유동 특성은 버너 표면 전체의 유동 속도를 측정하고 조정하였다. 연소 실험은 화염 사진과 화염 온도 측정에 의하여 수행되었다. CO와 NO는 다양한 과잉 공기비와 열량값에 대하여 버너 표면 매질, 연소실, 열교환기의 특성을 측정하고 평가하였다.

• 대한기계학회논문집B
• /
• 제35권8호
• /
• pp.805-814
• /
• 2011

알루미늄 플레이트-핀 열교환기는 석유 및 가스 처리공정에서 널리 사용되고 있다. 알루미늄 플레이트-핀 열교환기의 성능은 각 유체의 헤더 및 분배기에서의 분배 성능에 의하여 크게 영향을 받는다. 본 연구에서는 CFD(Computational fluid dynamics)를 이용하여 알루미늄 플레이트-핀 열교환기의 측면 입구 형태의 분배기를 모델링하고, 입구 조건과 형상비의 변화에 따른 상대 및 절대 불균등 분배도를 고찰하여 최적 분배기 형상비를 제시하였다.