• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1969-1973
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• 2007

The purpose of this study is to investigate the performance of a sea water heat source cascade heat pump system. R717(Ammonia) is used for a low-stage working fluid while R134a is for a high-stage. In order to gain a high temperature supply water in winter season, the system is designed to perform a cascade cycle. In this study, two experiments were carried out. One is a system starting test from the low load temperature of $10^{\circ}C$. The other is a system performance investigation over the R717 compressor capacity changes. Experimental results show that when it starts from the low load temperature, the suction temperature of the low-stage compressor is higher than that of a high-stage. The system performance increases when a water source temperature or a low-stage compressor rotational frequency goes higher.

• 대한기계학회논문집B
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• 제22권11호
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• pp.1509-1520
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• 1998

An experiment was carried out for the fully developed turbulent flow of water in tube coils on the condition of uniform heat flux. The present work was conducted for various ranges for Dean number(1794~1321), Prandtl number (2.5~4.5), curvature ratio parameters (22~60). Heat transfer to steady viscous flow in coiled tubes of circular cross section was studied for fully developed velocity and temperature fields under the thermal boundary condition of uniform heat flux. The peripherally local Nusselt number correlated as a function of Dean and Prandtl numbers. We studied the flow in heat coiled tubes under the influence of both centrifugal and buoyancy forces in order to gain insight into the flow pattern. In the present study, we obtained three emperical formulas, $Nu_v=0.0231Re^{0.84}Pr^{0.4}(a/R)^{0.13}$ (vertical) $Nu_c=0.0241Re^{0.86}Pr^{0.4}(a/R)^{0.08}$ (corrugated) $Nu_h=0.0227Re^{0.84}Pr^{0.4}(a/R)^{0.09}$ (horizontal).

• 한국기계가공학회지
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• 제18권5호
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• pp.90-95
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• 2019

This study aims to gain the design data through the process design of the organic Rankine cycle, which can produce 250kW of electric power through waste heat recovery. In this study, a simulation was conducted using APSEN HYSYS to make the model for the process design of the 250kW-class waste heat recovery system. For the thermodynamic model, the test was conducted with hot water as the heat source, the water steam as the cooling water for the cooler, and the refrigerant R245FA in the cycle. In the final design, it was expected and found from the simulation that the cycle efficiency was 12.62% and that 250kW of power was produced considering the margin of 80%.

• Transactions on Electrical and Electronic Materials
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• 제8권6호
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• pp.246-249
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• 2007

A triple-band antenna was developed and fabricated by LDS(Laser Direct Structuring) process. The effects of the plating rate and heat treatment condition were investigated and the gains of fabricated antennas were measured at various frequencies. The laser irradiated surface shows clearly that there are prominence and depression. It shows anchoring effect between a plating material and ablation surface. The plating rate was decreased when the plating material is exhausted in the solution. This solution needs to refreshed by the new aid solution. The copper plating thickness is decreased with the increase of heat treatment temperature in the same time but it does not change other condition. The gain of LDS antenna showed higher than the generally processed antenna. This result was related with practical use of the dimension and effective dielectric constant.

• 한국광학회지
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• 제3권4호
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• pp.222-226
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• 1992

$Ar^{+}$레이저로 펌핑되는 Nd:glass레이저를 제작하여 그 특성을 조사하였다. 레이저 공진기는 오목거울 두 개와 98% 고반사 평면경, 그리고 Brewster 각도로 놓인 Nd:glass 의 이득 매질로 구성되었으며, 효율적인 펌핑을 위해서 $Ar^{+}$레이저 광선을 공진기 길이 방향으로 입사하여 공진모우드의 beam waist에서 초점이 맺히도록 하였다. Nd:glass의 열존도도가 작아서 흡수된 펌핑빔에 의해 생성된 잔열로 인한 매질의 손상이 우려되기 때문에 mechanical chopper 로 펌핑빔을 100Hz로 끊어서 입사하여 잔열의 생성을 줄였다. 1.5W로 펌핑될 때 Nd:glass 레이저의 출력은 70mW이었고 발진이 되는 문턱에서의 펌핑파워는 520mW이었으며 slope efficiency는 7.4%이었다.

• 설비공학논문집
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• 제26권11호
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• pp.512-521
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• 2014

Recently, multiple glazing units, frames, complex fenestration systems, and windows with shading devices have been developed to save cooling energy in buildings. However, very little work has been conducted on developing a direct experimental test method of the solar heat gain coefficient(SHGC) for new fenestration techniques. This study aims to develop and evaluate a test apparatus to measure the SHGC, according to the KS L 9107 test method. The performance of the solar simulator was class A, B, and A, for spectral match, non-uniformity, and instability irradiance, respectively. The differences between the measured and calculated SHGC values were found to range between 0.001 and 0.011, and for all test specimens they agreed within 4%. These results establish the validity of the test apparatus. This system is thus expected to be useful in assessing the energy performance for various types of fenestration.

• 설비공학논문집
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• 제23권11호
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• pp.711-717
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• 2011

In this study, 5 types of PVS(Passive ventilation system) units are made and experimented its ventilation performance, thermal performance according to open rate and hole diameter of perforated aluminum plane. Results are as follows. 1) The ventilation performance increases approximately 50~70% according by the open rate of PVS increasing. Also, the ventilation performance increases about 2%~12% according by the hole diameter of PVS increasing. 2) In winter temperature/pressure condition(in : $20^{\circ}C$, out : $-2^{\circ}C/{\Delta}P$ : 0.2~5.0Pa) the temperature of inflow air decreases according by the open rate of PVS increasing. Heat gain performance decreases 10.1%, 25.6% when open rate increases 3) In the same condition, Heat gain performance decreases 18.3%, 18.8% according by the hole diameter of PVS increasing.

• 한국환경과학회지
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• 제18권1호
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• pp.33-39
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• 2009

Based on the monthly weather report of Korea Meteorological Administration (KMA) and daily sea surface temperature (SST) data from National Fisheries Research and Development Institute (NFRDI) in 2006, heat budget was estimated at Gampo in the eastern coast of Korea, the region occuring the cold water known as upwelling in summer. Net heat flux was transported from the air to the sea surface during February to November, and it amounts to $345Wm^{-2}$ in monthly mean value. During December to January, the transfer of net heat flux was conversed from the sea surface to the air with $-56Wm^{-2}$ in minimum of monthly mean value in January. Long wave radiation was ranged from $6Wm^{-2}\;to\;106Wm^{-2}$. Sensible heat was varied from $-36Wm^{-2}$(June) to $61Wm^{-2}$(February) and showed negative values from April to August. Latent heat showed $20Wm^{-2}$(July) with its minimum in July and $49Wm^{-2}$ with its maximum in March in monthly mean value. The annual mean of net heat flux is $129Wm^{-2}$, giving an annual heat surplus of $22Wm^{-2}$. Thus, during summer, the upwelled cold water at Gampo, appears to compensate the heat gain. However the ways in which these compensations are accomplished remains to be clarified.

• Journal of the Korean Wood Science and Technology
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• 제42권1호
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• pp.13-19
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• 2014

국내의 주 생산 수종인 잣나무 $90{\times}90mm$ 각재의 적정한 열처리 조건을 찾기 위해 3가지 열처리 스케줄을 적용하여 재색과 물성에 미치는 영향을 연구하였다. 1차 열처리시 온도는 $170^{\circ}C$와 $190^{\circ}C$, 시간은 예비가열시간 1시간을 포함하여 9시간과 13시간을 적용하였다. 2차와 3차 열처리는 모든 공시 각재에 동일하게 $190^{\circ}C$-9시간을 적용하였다. 열처리 횟수가 증가할수록 백색도 $L^*$는 직선적으로 감소하였으며 표준편차도 감소하였다. 열처리 횟수가 증가할수록 색차 ${\Delta}E^*$는 직선적으로 증가하였으며, 표준편차가 커지는 경향이 있었다. 알려진 바와 달리 열처리 시편의 평균 종압축강도가 무처리 시편보다 9% 높았다. 항팽윤율과 중량증가율을 측정하여 열처리 시편의 치수안정성이 무처리보다 크게 증가하였음을 보였다.

• Advances in Energy Research
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• 제4권4호
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• pp.299-323
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• 2016

Cylindrical parabolic solar concentrators of small concentration ratio are attractive options for working temperatures around $120^{\circ}C$. The heat gained can be utilized in many applications such as air conditioning, space heating, heating water and many others. These collectors can be easily manufactured and do not need to track the sun continuously. Using a heat pipe as a solar absorber makes the system more compact and easy to install. This study is devoted to modeling a system of cylindrical parabolic solar concentrators of small concentration ratio (around 5) fitted with a heat pipe absorber with a porous wick. The heat pipe is surrounded by evacuated glass tube to reduce thermal losses from the heat pipe. The liquid and vapor flow equations, energy equation, the internal and external boundary conditions were taken into consideration. The system of equations was solved and the numerical results were validated against available experimental and numerical results. The validated heat pipe model was inserted in an evacuated transparent glass tube as the absorber of the cylindrical parabolic collector. A calculation procedure was developed for the system, a computer program was developed and tested and numerical simulations were realized for the whole system. An experimental solar collector of small concentration, fitted with evacuated tube heat pipe absorber was constructed and instrumented. Experiments were realized with the concentrator axis along the E-W direction. Results of the instantaneous efficiency and heat gain were compared with numerical simulations realized under the same conditions and reasonably good agreement was found.