• Journal of Advanced Marine Engineering and Technology
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• 제33권7호
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• pp.994-1002
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• 2009

In this paper, effect of air gap thickness between absorber plate and glass cover on top heat loss of a closed loop oscillating heat pipe (CLOHP) solar collector was investigated. The CLOHP, which is made of copper with outer diameter of 3.2mm and inner diameter of 2.0mm, comprises 8 turns with heating, adiabatic and cooling section. The heating section of the heat pipe was attached to absorber plate which heated by solar simulator simulated by halogen lamps. The cooling section of the heat pipe was inserted into collector's cooling section that made of transparent acrylic. Temperatures of absorber plate, glass cover, and ambient air measured by K-type thermocouple and were recorded by MV2000-Yokogawa recorder. Top heat loss coefficients and top heat loss of the collector corresponding to some cases of air gap thickness were determined. The result of experiment shows the optimal air gap thickness for minimum top heat loss of this solar collector.

• Journal of Mechanical Science and Technology
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• 제15권11호
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• pp.1541-1547
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• 2001

The non-dimensional fin length for optimum heat loss from a thermally asymmetric rectangular fin is represented as a function of the ratio of the bottom surface Biot number to the top surface Biot number, fin tip surface Biot number and the non-dimensional fin width. Optimum heat loss is taken as 98% of the maximum heat loss. For this analysis, three dimensional separation of variables method is used. Also, the relation between the ratio of the bottom surface Biot number to the top surface Biot number and the ratio of the right surface Biot number to the left surface Biot number is presented.

• International Journal of Air-Conditioning and Refrigeration
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• 제13권3호
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• pp.145-151
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• 2005

A thermally asymmetric straight rectangular fin is analysed and optimized using the two-dimensional separation of variables method. The optimum heat loss is presented as a function of bottom to top Biot number ratio, fin base length and top Biot number. Decreasing rate of the optimum fin length with the increase of the fin base length is listed. The optimum fin tip length is shown as a function of bottom to top Biot number ratio, fin base length and tip to top Biot number ratio. One of the results shows that the optimum heat loss and the actual optimum fin length decrease while the optimum fin tip length increases as the fin base length increases.

• 태양에너지
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• 제18권3호
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• pp.15-24
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• 1998

태양열 집열기의 열손실은 크게 3가지 즉 상부 열손실, 하부 열손실, 측부 열손실로 대별되나 단열이 양호한 집열기에서는 일반적으로 측면으로의 열손실은 무시한다. 측부 열손실을 제외한 두 열손실 중에서도 상부 열손실은 집열기의 대부분의 열손실을 차지하는 지배적인 요소이다. 따라서 태양열 집열기의 집열 성능을 정확하게 파악하기 위해서는 상부 열손실 계수를 정확하게 계산할 필요가 있다. 본 연구에서 사용한 평판형 태양열 집열기(재생기)는 하계에는 제습 및 냉방을 행하고 동계에는 난방을 행하는 전천후 집열판으로 제작되었다. 따라서 장치의 전환없이 겨울에 난방용으로 사용하였을 경우의 집열 성능을 파악하기 위하여 옥외에서 실험을 하였다. 동계 기간 실험을 통하여 본 집열기의 상부 열손실 계수는 약 $3{\sim}4.5W/m^2^{\circ}C$임을 알 수 있었다. 그리고 집열표면에 선택흡수막을 입혀서 난방용으로 사용하면 주위와의 복사 열손실을 크게 줄일 수 있기 때문에 본 집열기의 집열 성능을 향상시킬 수 있을 것으로 사료된다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제6권2호
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• pp.109-120
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• 2002

The dimensionless heat loss from a modified asymmetric rectangular fin is investigated as a function of the fin top and tip Biot numbers using the two-dimensional separation of variables method. A rectangular fin is modified by attaching the wing on the top side of the fin. Fin effectiveness and efficiency with the variation of the location of the wing and the width of the wing are presented. The relationship between top surface Biot number and bottom surface Biot number as well as the relationship between the dimensionless wing height and the location of the wing for equal amount of heat loss is also discussed.

• 한국유체기계학회 논문집
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• 제5권1호
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• pp.49-54
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• 2002

HANARO, 30 MW of research reactor, was installed at the depth of 13m in an open pool. The $90\%$ of primary coolant was designed to pass through the core and to remove the reaction heat of the cote. The rest, $10\%$, of the primary coolant was designed to bypass the core. And the reactor coolant through and bypass the core was inhaled at the top of chimney by the coolant pump to prevent the radiated gas from being lifted to the top of reactor pool. But, the part of core bypass coolant was not inhaled by the reactor coolant pump and reached at the top of reactor pool by natural convection, and increased the radiation lovel on the top of reactor pool. To reduce the radiation level by protecting the natural convection of the core bypass flow, the hot water layer (HWL, hereinafter) was installed with the depth of 1.2 m from the top of reactor pool. As the HWL was normally operated, the radiation level was reduced to five percent ($5\%$) in comparing with that before the installation of the HWL. When HANARO was operated at a higher temperature than the normal temperature of the HWL by operating the standby heater, it was found that the radiation level was more reduced than that before operation. To verify the reason, the heat loss of the HWL was calculated by Visual Basic Program. It was confirmed through the results that the larger the temperature difference between the HWL and reactor hall was, the more the evaporation loss increased. And it was verified that the radiation level above was reduced mote safely by increasing the capacity of heater.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.221-226
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• 2001

HANARO, 30MW of research reactor, was installed at the depth of 13m of open pool, The $90\%$ of primary coolant was designed to pass through the core and to remove the reaction heat of the core. The rest $10\%$, of the primary coolant was designed to bypass the core. And the reactor coolant through and bypass the core was inhaled at the top of chimney by the coolant pump to protect that the radiated gas was lifted to the top of reactor pool. But, the part of core bypass coolant was not inhaled by the reactor coolant pump and reached at the top of reactor pool by natural convection and increased the radiation level on the top of reactor pool. To reduce the radiation level by protecting the natural convection of the core bypass flow, the hot water layer (HWL, hereinafter) was installed with the depth of 1.2m from the top of reactor pool. As the HWL was normally operated, the radiation level was reduced to five percent ($5\%$) in comparing with that before the installation of the HWL. When HANARO was operated with higher temperature than the normal temperature of the HWL by operating the standby heater, it was found that the radiation level was more reduced than that before operation. To verify the reason, the heat loss of the HWL was calculated. It was confirmed through the results that the larger the temperature difference between the HWL and reactor hall was, the more the evaporation loss was increased. And it was verified that the radiation level above was reduced more safely by increasing the capacity of heater.

• International Journal of Air-Conditioning and Refrigeration
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• 제10권4호
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• pp.192-200
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• 2002

A modified asymmetric rectangular fin is analysed using the two-dimensional separation of variables method. This modified rectangular fin is made by attaching the wing on the top side of a rectangular fin. Heat loss from each side of this modified rectangular fin is calculated. The relative increasing ratio of heat loss between a modified rectangular fin and a rectangular fin is presented as a function of dimensionless fin volume, wing height and the location of the wing. Especially, to show the remarkable effect of the wing on the heat loss, the relative increasing ratios of heat loss between two different volume increasing methods are listed.

• 설비공학논문집
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• 제11권2호
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• pp.215-223
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• 1999

Evaporation heat transfer coefficient and pressure loss were measured for three different micro-fin tubes and a smooth tube. The experiments were carried out with R-22 over a wide range of vapor Quality, mass velocity and heat flux. Heat transfer coefficient of the tube with slightly modified fin shape was found to be higher than that of the commercial reference tube by 60%. The improvement of heat transfer has been achieved without noticeable increase of pressure loss. Heat transfer coefficient was increased with increasing quality, refrigerant mass flux, and heat flux. However, the effect of refrigerant mass flux and heat flux was not great. Heat transfer coefficient at bottom was lower than that at top of the tube in low quality region, which suggested the existence of stratification in the micro-fin tube. Pressure drop was linearly increased with increasing refrigerant quality and was proportional to about square of mass flux.

• 설비공학논문집
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• 제12권4호
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• pp.388-397
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• 2000

Comparison of the heat conduction into a trapezoidal fin and the heat loss from the fin by convection is made in this study Also, the ratio of heat loss from each surface to the total heat loss and the temperature distribution are analyzed using a 3-D analytical method. A trapezoidal fin whose tip height is half the root height is chosen as the model. The results show that the heat transfer rates from the tip and from both sides are comparable with each other as the non-dimensional width and length vary while the heat transfer rate from the bottom and top is dominant.