• Asian-Australasian Journal of Animal Sciences
• /
• 제11권3호
• /
• pp.293-299
• /
• 1998

This study was undertaken to measure the concentrations of estradiol-$17{\beta}$, progesterone and testosterone, and to study their relationship with each other and with follicular size in individual buffalo ovarian follicles categorized as small (4 to 5 mm diameter), medium (6 to 9 mm diameter) and large (${\geq}10mm$ diameter). Steroid hormone concentrations varied markedly within follicles of each size category. Estradiol-$17{\beta}$ concentrations (pmol/ml) were positively related to follicular diameter (R = 0.34, n = 308, p < 0.001) and were significantly higher (p < 0.001) in large (1$118.46{\pm}30.25$), compared to those in medium follicles ($50.32{\pm}8.29$) which, in turn were significantly higher (p < 0.001) than those in small follicles ($19.70{\pm}$5.57). Progesterone and testosterone concentrations (pmol/ml) were not related to follicular diameter and were not different among small ($330.99{\pm}27.32$ and $17.68{\pm}2.44$ respectively), medium ($384.84{\pm}26.20$ and $36.47{\pm}4.55$, respectively) and large follicles ($253.25{\pm}32.23$ and $22.57{\pm}4.48$, respectively). Estradiol-$17{\beta}$ and progesterone concentrations were positively related (R = 0.39, n = 47, p < 0.01) in small, unrelated in medium and negatively related in large follicles (R = -0.59, n = 23, p < 0.01). There was no relationship between estradiol-$17{\beta}$ and testosterone concentrations in follicles of all the three size categories. Progesterone and testosterone concentrations were positively related in large follicles (R = 0.57, n = 18, p < 0.02). There was no relationship between the two hormones in small and medium sized follicles. When the follicles with estradiol-$17{\beta}$/progesterone molar ratios of > 1.00 were considered non-atretic, and the rest at different stages of atresia, 197/208(95%) follicles were found to be atretic.

• 설비공학논문집
• /
• 제17권7호
• /
• pp.649-658
• /
• 2005

Flow condensation heat transfer coefficients (HTCs) of R22, R410, Propane (R290) were measured inside a horizontal 9 hole aluminum multi-channel flat tube. The main test section in the refrigerant loop was made of a 0.53m long multi-channel flat tube of hydraulic diameter of 1.4 mm. Refrigerant was cooled by passing cold water through an annulus surrounding the test section. Data were obtained in qualities of $0.1\~0.9$ at mass flux of $200\~400kg/m^2s$ and heat flux of $7.3\~7.7kW/m^2$ at the saturation temperature of $40^{\circ}C$. All popular heat transfer correlations in single-phase subcooled liquid flow and flow condensation originally developed for large single tubes predicted the present data of the multi channel flat tube within $25\%$ deviation when effective heat transfer area was used in determining experimental data. This suggests that there is little change in flow characteristics and patterns when the tube diameter is reduced down to 1.4 mm diameter range. Hence, a modified correlation based on the present data was proposed which could be applied to small diameter tubes with effective heat transfer area. The correlation showed a mean deviation of less than $20\%$ for all data.

• 대한기계학회논문집B
• /
• 제27권2호
• /
• pp.163-172
• /
• 2003

Boiling heat transfer coefficients and pressure drops for R-22 and R-407C were measured in horizontal micro-channels. The test section is stainless steel tube, inner tube diameters are 1.8mm and 2.8mm, and the respective lengths are 1500mm and 3000mm. The range of mass flux is 300-600kg/$m^2$s and heat flux is 5-15kW/$m^2$. In this results, pressure drop increased linearly for both R-22 and R-407C with increased mass flux, but the increase of heat flux did not affect the pressure. In addition, the pressure drop was fairly increased in the high quality region rather than low quality region. In the range of low quality, the mass flux had a small affect on the heat transfer coefficients, however, in high quality region, the heat transfer coefficients increased even more with increasing mass flux. Under the low quality region and low mass flux, the heat transfer coefficients increased with increasing heat flux densities. The effects of inner tube diameter were clearly observed. Namely, the measured pressure drop inside inner tube diameter 1.8 mm is higher than 2.8 mm with increasing the mass flux and heat flux. Also, the measured local heat transfer coefficient inside inner tube diameter 1.8 mm is higher than 2.8 mm in the range of high qualities. The experimental data for R-407C compared with proposed correlation using pure refrigerant. The experimental data for R-407C was more decreased than the proposed correlation for pure refrigerant up to 50% or more.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2005년도 동계학술발표대회 논문집
• /
• pp.249-255
• /
• 2005

Flow condensation heat transfer coefficients(HTCs) of R22, R4IO, Propane(R290) were measured inside a horizontal 9 hole aluminum multi-channel flat tube. The main test section in the refrigerant loop was made of a 0.53 m long multi-channel flat tube of hydraulic diameter of 1.4 mm. Refrigerant was cooled by passing cold water through an annulus surrounding the test section. Data were obtained in qualities of 0.1 ${\sim}$ 0.9 at mass flux of $200{\sim}400$ $kg/m^2s$ and heat flux of $7.3{\sim}7.7$ $kW/m^2$ at the saturation temperature of $4^{\circ}C$. All popular heat transfer correlations in single-phase subcooled liquid flow and flow condensation originally developed for large single tubes predicted the present data of the multi channel flat tube within 25% deviation when effective heat transfer area was used in determining experimental data. This suggests that there is little change in flow characteristics and patterns when the tube diameter is reduced down to 1.4 mm diameter range. Hence, a modified correlation based on the present data was proposed which could be applied to small diameter tubes with effective heat transfer area. The correlation showed a mean deviation of less than 20% for all data.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.1270-1275
• /
• 2004

Flow condensation heat transfer coefficients(HTCs) of R22 and R134a were measured on horizontal aluminum multi-channel tube. The experimental apparatus was composed of three main parts ; a refrigerant loop, a water loop and a water-ethylene glycol loop. The test section in the refrigerant loop was made of aluminum multi-channel tube of 1.4 mm hydraulic diameter and 0.53 m length. The refrigerant was cooled by passing cold water through an annulus surrounding the test section. The data scan vapor qualities $(0.1{\sim}0.9)$, mass flux ($200{\sim}400$ $kg/m^{2}s$) and heat flux ($7.3{\sim}7.7$ $kW/m^{2}$) at $40{\times}0.2^{\circ}C$ saturation temperature in small hydraulic diameter tube. It was found that some well-known previous correlations were not suitable for multichannel tube. So, It must develop new correlations for multi-channel tubes.

• 청정기술
• /
• 제13권2호
• /
• pp.151-158
• /
• 2007

프레온계 냉매의 지구온난화와 오존층파괴 문제로 인해 대체냉매로서 R-410A가 주목을 받고 있다. 이러한 대체냉매를 세관에 적용시킬 경우 효율을 향상시킬 뿐만 아니라 지구환경에 미치는 영향을 감소시키고, 대기를 청정하게 만드는 기술 및 방안으로 각광 받고 있다. 따라서 본 연구에서는 R-22의 대체냉매로 각광받고 있는 R-410A의 세관응축기 내에서의 응축열전달 특성에 대해 실험적으로 고찰하고자 하였다. 실험장치는 유동양식, 열전달, 압력강하 특성을 파악할 수 있도록 제작되었고, 주요 구성품은 냉매펌프, 증발기, 응축기(시험부), 사이트 글라스(가시화부), 압력탭, 측정장치 등이다. 시험부의 내관은 내경 3.36 mm와 5.35 mm인 수평평활 동관이다. 실험변수들의 범위로서 질량유속 $200{\sim}500\;kg/m^2s$이고, 열유속은 $1.0{\sim}2.4\;kW$이다. R-410A의 응축열전달 계수가 R-22에 비해 최대 5% 정도 높은 것을 알 수 있었다. 세관 내 R-410A와 R-22의 유동양식은 환상류 영역이 지배적으로 나타남을 관찰하였고, 건도가 0.2 이하인 영역에서는 성층류가 나타남을 확인할 수 있었다. 내경 3.36 mm의 압력강하가 내경 5.35 mm에 비해 $30{\sim}50%$정도 높았다. 종래의 응축 열전달 상관식과 실험데이터를 비교한 결과, Fujii의 상관식과 최대 40%이내에서 일치하였다.

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

• 설비공학논문집
• /
• 제16권8호
• /
• pp.748-755
• /
• 2004

Flow boiling heat transfer in small-diameter round tubes has been experimentally studied. The experimental apparatus consisted mainly of refrigerant pump, condenser, receiver, test section of a 1.67 mm inner-diameter round tube and pre-heater for control of refrigerant quality at the inlet of test section. To investigate the effect of bubble nucleation site characteristics of different tube materials, three different tubes of copper, aluminum and brass were used. The ranges of the major experimental parameters were 5∼30 ㎾/$m^2$ of the wall heat flux, 0.0∼0.9 of the inlet vapor quality and the refrigerant mass flux was fixed at 600 kg/$m^2$s. The experimental results showed that the flow boiling heat transfer coefficients in small tubes were affected only by heat flux, but independent of mass flux and vapor quality. The effect of tube material on flow boiling heat transfer was observed small.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2004년도 동계학술대회 논문집
• /
• pp.120-120
• /
• 2004

• 청정기술
• /
• 제14권1호
• /
• pp.53-60
• /
• 2008

본 연구에서는 내경이 각각 5.80 mm와 10.07 mm인 두 개의 수평 이중관열교환기 내에서의 탄화수소계 냉매의 응축열전달과 압력강하에 대한 실험을 $35.5{\sim}210.4\;kg/m^2\;s$의 질량유속과 응축온도인 $40^{\circ}C$에서 수행하였다. 탄화수소계 냉매 R-290과 R-600a의 응축열전달계수가 프레온계 냉매인 R-22보다 높았다. 응축압력강하는 R-600a > R-290 > R-22 순으로 나타났고, 내경이 5.8 mm인 관 내 보다 10.07 mm인 관 내의 압력강하가 R-600a에서는 $6{\sim}15%$ 정도 높았으며, R-290과 R-22에서는 각각 $9.8{\sim}12.5%$와 $2.1{\sim}4.6%$ 정도 높게 나타났다. 실험으로 구한 응축열전달계수와 종래의 상관관계식을 비교해 본 결과, 모든 관경에 대해 Haraguchi 등의 상관관계식과 가장 좋은 일치를 보였다.