• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1528-1535
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• 2009

Characteristics of R-22 and R-134a two-phase vaporization in horizontal small tubes were investigated experimentally. In order to obtain the local heat transfer coefficients, the test was ran under heat flux range of 10 to $40\;kW/m^2$, mass flux range of 200 to $600\;kg/m^2s$, saturation temperature range of 5 to $10^{\circ}C$, and quality up to 1.0. The test section, which was made of stainless steel tube and heated uniformly by applying an electric current to the tube directly, have inner tube diameters of 0.5, 1.5 and 3.0 mm, and lengths of 0.33 and 2.0 m. The effects on heat transfer coefficient of mass flux, heat flux and inner tube diameter were presented. The experimental heat transfer coefficients were compared with the predictions using existing heat transfer coefficient correlations. A new boiling heat transfer coefficient correlation based on the superposition model, with considering the laminar flow, was developed.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권2호
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• pp.85-93
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• 2001

The present study experimentally investigated the effect of refrigeration oil on the condensation heat transfer for R-22 and R-407C in a microfin tube with a U-bend. Mineral oil and POE oil were used for R-22 and R-407C respectively. Experimental parameters were an oil concentration from 0 to 5%, a mass flux from 100 to 400 $kg/m^2s$ and an inlet quality from 0.5 to 0.9. The enhancement factors for both R-22 and R-407C refrigerants at the first straight section decreased continuously as the oil concentration increased. The decreased rapidly as the mass flux decreased and the inlet quality increased. The heat transfer coefficients in the U-bend showed the maximum at the 90$^{\circ}$position. the heat transfer coefficients at the second straight section within the dimensionless length of 48 were larger by a maximum of 33% than the average heat transfer coefficient at the first straight section.

• 설비공학논문집
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• 제12권6호
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• pp.541-549
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• 2000

The present study experimentally investigated the effect of refrigeration oil on the condensation heat transfer for R-407C and R-22 in a microfin tube with a U-bend. POE oil ($74.1\;\textrm{mm}^2/s,\;40^{\circ}C$,) and mineral oil $62.5\;\textrm{mm}^2/s,\;40^{\circ}C$,) were used for R-407C and R-22 respectively Experimental parameters were an oil concentration from 0 to 5%, a mass flux from 100 to $400kg/m^{2}s sand an inlet quality from 0.5 to 0.9. The enhancement factors for both R-22 and R-407C refrigerants at the first straight section decreased continuously as the oil concentration increased. They decreased rapidly as the mass flux decreased and the inlet quality increased. The heat transfer coefficients in the U-bend showed the maximum at the $90^{\circ}$/TEX> position. The heat transfer coefficients at the second straight section within the dimensionless length of 48 were larger by a maximum of 33% than the average heat transfer coefficient at the first straight section.

• 대한기계학회논문집B
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• 제25권3호
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• pp.405-413
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• 2001

The present study investigates convective heat/mass transfer and flow characteristics inside a rotating two-pass rectangular duct. A naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The objective of this study is to determine the effects of turning geometry with rotation for 0.0$\leq$Ro$\leq$0.24. The results reveal that the sharp-turn corner has the larger pressure drop and lower heat transfer in the post-turn region than those of the round-turn corner. The strong secondary flow enhances heat transfer for the round-turn corner. Coriolis force induced by the rotation pushes the high momentum core flow toward the trailing wall in the first passage with radially outward flow and toward the leading wall in the second passage with radially inward flow. Consequently, the high heat transfer rates are generated on the trailing surface and the leading surface in the first and second passage, respectively. However, the strong secondary flow due to the turning dominates the flow pattern in the second passage, thus the heat transfer differences between the leading and trailing surfaces are small with the rotation.

• Korean Chemical Engineering Research
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• 제54권5호
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• pp.648-652
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• 2016

본 연구에서는 구아니딘계 초염기인 1,1,3,3-테트라메틸 구아니딘(TMG)과 에틸렌 글라이콜로 구성된 비수계 흡수제를 충진탑에 적용하여 이산화탄소 흡수특성을 고찰하였다. 흡수탑은 내경이 1 in이고 높이는 0.6 m이며 탑 내부는 $0.16in{\times}0.16in$의 규격을 갖는 다공 충진물로 채웠다. 흡수탑에서의 이산화탄소 제거 효율에 대한 흡수제 농도, 조업온도 등의 영향 뿐 아니라 이들이 물질전달 저항에 미치는 영향을 고찰하였다. 이산화탄소에 대한 TMG의 로딩값은 약 ${\alpha}=1.0mol_{CO2}/mol_{TMG}$에 달하였으며 이산화탄소가 적게 로딩된 흡수제에서는 총괄 물질전달 계수가 TMG의 농도에 비례하였으나 ${\alpha}=0.5$ 이상의 로딩값에서는 총괄 물질전달계수가 오히려 감소하였다. 이는 흡수제의 이산화탄소에 대한 로딩값에 따른 흡수제 점도 증가로 인한 액체상에서의 물질전달 저항 증가로 해석할 수 있다.

• 설비공학논문집
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• 제17권6호
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• pp.569-580
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• 2005

The present study investigates the convective heat/mass transfer characteristics in wavy ducts of a primary surface heat exchanger. The effects of duct aspect ratio and flow velocity on the heat/mass transfer are investigated. Local heat/mass transfer coefficients on the corrugated duct sidewall are determined using a naphthalene sublimation technique. The aspect ratios of the wavy duct are 7.3, 4.7 and 1.8 with the corrugation angle of $145\Omega$. The Reynolds numbers, based on the duct hydraulic diameter, vary from 300 to 3,000. The results show that at the low Re(Re $\leq$ 1000) the secondary vortices called Taylor-Gortler vortices perpendicular to the main flow direction are generated due to effect of duct curvature. By these secondary vortices, non-uniform heat/mass transfer coefficients distributions appear. As the aspect ratio decreases, the number of cells formed by secondary vortices are reduced and secondary vortices and comer vortices mix due to decreased aspect ratio at Re$\leq$1000. At Re >1000, the effects of corner vortices become stronger. The average Sh for the aspect ratio of 7.3 and 4.7 are almost same. But at the small aspect ratio of 1.8, the average Sh decreases due to decreased aspect ratio. More pumping power (pressure loss) is required for the larger aspect ratio due to the higher flow instability.

• 한국추진공학회지
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• 제2권2호
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• pp.56-63
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• 1998

본 논문에서는 주유동의 난류강도 변화에 따른 복합각도로 분사되는 단일 막냉각홀 주위에서의 국소 열/물질전달계수 특성을 살펴보기 위하여 실험을 수행하였다. 단일 막냉각홀 시편은 평면에 대하여 $30^{\cire}$의 경사각을 가지고 있으며, 횡방향으로는 주유동에 대해 $45^{\cire}$의 각도로 분사하여 복합각도 분사시 주유동의 난류강도 변화에 따른 효과를 살펴보았다. 또한 막냉각제트의 분사율을 0.5에서 2.0까지 변화시켜가며, 주유동의 높은 난류강도조건에서 분사율 변화시 막냉각홀 주위의 열/물질전달특성에 미치는 효과를 살펴보았다. 주유동의 난류강도를 변화시키기 위하여 막냉각홀 상류에 난류발생격자를 설치하였다. 격자를 설치하지 않은 경우, 주유동의 난류강도는 0.5%이며, 난류발생격자의 종류 및 설치위치를 달리하여 난류강도를 3%에서 10%까지 변화시켜가며 실험하였다. 막냉각홀 주위에서 국소적인 열/물질전달계수 값을 얻기 위하여 물질전달 실험방법인 나프탈렌 승화법을 사용하였다. 주유동의 난류강도가 낮은 경우 분사홀 주변에서 막냉각제트 혹은 주유동에 의한 열/물질전달 촉진영역이 뚜렷한 경계를 갖지만, 난류강도가 증가하면서 전 영역에 걸쳐 열/물질전달이 촉진되었으며 주유동과 막냉각제트의 활발한 혼합작용으로 인해 영역의 구분이 점차 소멸되었다. 또한 주유동의 높은 난류강도 효과는 막냉각제트의 분사율이 높은 경우 뚜렷이 나타났다.

• 설비공학논문집
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• 제21권12호
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• pp.663-670
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• 2009

Two-phase flow boiling heat transfer of R-410A in horizontal small tubes was reported in the present experimental study. The local heat transfer coefficients were obtained over a heat flux range of 5 to 40 kW/$m^2$ a mass flux range of 170 to 600 kg/$m^2s$, a saturation temperature range of 3 to $10^{\circ}C$, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5 and 3.0 mm, and lengths of 330 and 3000 mm, respectively. The test section was heated uniformly by applying a direct electric current to the tubes. The effects on heat transfer of mass flux, heat flux, inner tube diameter, and saturation temperature were presented. The experimental heat transfer coefficients are compared with six existing heat transfer coefficient correlations. A new boiling heat transfer coefficients correlation based on the superposition model for R-410A in small tubes was developed with mean deviation of 10.13%.

• 에너지공학
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• 제19권4호
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• pp.234-239
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• 2010

원형 파이프를 유동하는 6.5% EG 수용액으로부터 만들어진 아이스슬러리의 열전달 특성을 분석하기 위한 실험을 수행하였다. 실험 장치의 시험부는 13.84 mm 내경과 1,500 mm의 길이를 가진 동관으로 제작되었다. 아이스슬러리는 시험부 주변에 이중관 형태로 만들어진 원형관 내부를 유동하는 온수에 의해 가열되었다. 본 연구의 실험에 적용된 IPF와 질량 유속은 각각 0 ~ 25% 그리고 1000 ~ 3,000 kg/$m^2s$의 범위이었고, 온수의 온도와 유량은 일정하게 유지하였다. 측정된 열전달량은 질량 유량과 IPF가 증가함에 따라 증가하였으나, IPF의 영향은 높은 질량 유량에서는 작은 것으로 나타났다. 낮은 질량유량에서는 열전달 계수의 급격한 상승이 15 ~ 20%의 IPF에서 나타났다. 마지막으로 측정된 열전달계수는 기존의 열전달상관식들에 의해 계산된 열전달계수와 비교하여 제시하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1104-1109
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• 2004

The present study has been conducted to investigate convective heat/mass transfer inside the cooling passage with bleed holes. The rotating square channel has 40.0 mm hydraulic diameter and the bleed holes on the leading surface of the channel. The hole diameter of bleed hole is 4.5 mm and its spacing (P/d=4.9) is about five times of hole diameter. Mass flow rate through bleed holes is 10% of the main flow rate and rotation number is changed form 0.0 to 0.4. A naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The cooling performance is influenced by mass flow rate through bleed holes and Coriolis force of rotating channel for fixed reynolds number. The heat transfer is enhanced around holes on the leading surface because of trapping flow by bleeding. However heat transfer on the leading surface is decreased due to Coriolis force.