• 대한기계학회논문집B
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• 제25권2호
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• pp.225-234
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• 2001

This paper represents the vector fields, three dimensional mean velocities, the turbulent intensities, the turbulent kinetic energy, and the Reynolds shear stresses in the X-Y plane of gas swirl burner with a cone type baffle plate measured by using X-probe from hot-wire anemometer system. This experiment is carried out at flow rates 350 and 450ℓ/min respectively, which are equivalent to the combustion air flow rate necessary for heat release 15,000 kcal/hr in gas furnace, in the test section of subsonic wind tunnel. The vector plot shows that the maximum axial mean velocity component exists in the narrow slits situated radially on the edge of gas swirl burner, for that reason, there is some entrainment phenomena of ambient air in the outer region of burner. Moreover, mean velocities in the initial region are largely distributed near the outer region of burner at Y/R≒0.97, but they diffuse and develop into the center flow region of burner according to the increase of axial distance. The turbulent intensities and the turbulent kinetic energy due to large inclination of mean velocity and swirl effect show that the maximum value in the initial region of burner is formed in the narrow slits situated radially on the edge of gas swirl burner and large values are mainly formed in the entire region of burner after X/R=2.4358, hence, the combustion reaction is anticipated to occur actively near this region. And the Reynolds shear stresses are also largely distributed from slite to vanes of gas swirl burner in the intial region, but their values largely disappear after X/R=3.2052.

• 대한기계학회논문집B
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• 제20권12호
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• pp.4013-4026
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• 1996

A numerical simulation has been carried out for the jet impinging on a flat plate and a semi-circular concave surface. In this computation finite volume method was employed to solve the full Navier-Stokes equation based on a non-orthogonal coordinate with non staggered variable arrangement. The standard k-.epsilon. turbulent model and low Reynolds number k-.epsilon. model(Launder-Sharmar model) with Yap's correction were adapted. The accuracy of the numerical calculations were compared with various experimental data reported in the literature and showed good predictions of centerline velocity decay, wall pressure distribution and skin friction. For the jet impingement on a semi-circular concave surface, potential core length was calculated for two different nozzle(round edged nozzle and rectangular edged nozzle) to consider effects of the nozzle shape. The result showed that round edged nozzle had longer potential core length than rectangular edged nozzle for the same condition. Heat transfer rate along the concave surface with constant heat flux was calculated for various nozzle exit to surface distance(H/B) in the condition of same jet velocity. The maximum local Nusselt number at the stagnation point occurred at H/B = 8 where the centerline turbulent intensity had maximum value. The predicted Nusselt number showed good agreement with the experimental data at the stagnation point. However heat transfer predictions along the downstream were underestimated. This results suggest that the improved turbulence modeling is required.

• 한국지하수토양환경학회지:지하수토양환경
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• 제22권5호
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• pp.23-29
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• 2017

This study was conducted to evaluate performance of geothermal heat exchanger (GHE) in the combined well and open-closed loops geothermal (CWG) systems. The CWG systems were designed to combine open loop geothermal heat pumps and closed loop geothermal heat pumps for high energy efficiency. GHE of the CWG systems could be installed at pumping wells for agricultural usage. To get optimal heat exchange capacity of GHE of the CWG systems, 4 GHEs with various materials and apertures were tested at laboratory scale. Polyethylene (PE) and stainless steel (STS) were selected as GHE materials. The maximum heat exchange capacity of GHEs were estimated to be in the range of 33.0~104 kcal/min. The heat exchange capacity of STS GHEs was 2.4~3.2 times higher than that of PE GHE. The optimal cross section area of GHE and flow rate of circulating water of GHE were estimated to be $2,500mm^2$ and 113 L/min, respectively. For more complicated GHE of the CWG systems, it is necessary to evaluate GHEs at various scales.

• 설비공학논문집
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• 제16권5호
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• pp.438-443
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• 2004

The objective of this paper is to study the effects of the input gas flow rate and the ambient temperature variation on the absorption cycle performance. An air-cooled NH$_3$-$H_2O$ absorption chiller is tested in the present study. The nominal cooling capacity of the single effect maching is 17.6 ㎾ (5.0 USRT). The cooling capacity, coefficient of performance, burner efficiency, and each state point are measured with the variations of the heat input and the ambient temperature. It is found that the COP and cooling capacity increase with increasing the generator exit temperature up to a certain temperature and then decrease. It is also found that the COP and the cooling capacity decrease with increasing the ambient temperature. The maximum COP of 0.51 is obtained from the present experiment.

• 설비공학논문집
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• 제10권4호
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• pp.475-482
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• 1998

In this paper, an experimental study was conducted to investigate the performance of the spherical ice particle production system which uses the technology of water spray in a vacuum chamber for increasing the heat transfer area. As a result, following conclusions were obtained. The diffusion-controlled evaporation model agreed relatively well with experiments. The spray flow rate influences the performance of the system rather than any other factors, for example, the spray nozzle position, the nozzle number. As the spray rate increases, the system efficiency increases. It is due to the entrainment of small droplets among the spray with the exhausted vapor. Thus the system should be designed and operated to prevent the entrainment. Assuming the compressor efficiency to be 70%, the COP of the system reaches highly up to 6 at a maximum spray rate. Under the conditions, however, the rigid ice layer is obtained because ice particles bond together with increase of the spray rate. Therefore, the spray rate should be controlled properly to make the spherical ice particles.

• 한국태양에너지학회 논문집
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• 제22권1호
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• pp.23-30
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• 2002

본 연구는 축방향 내부 핀을 가진 열사이폰의 작동유체의 체적변화에 대한 응축 및 비등열전달 성능에 관한 연구이다. 열사이폰 내부의 작동유체는 증류수를 사용하였다. 열사이폰의 총체적에 대한 작동유체의 양을 변화시키면서 실험데이터를 산출하였다. 열사이폰의 응축부에 대한 열유속과 응축열전달계수를 구하였으며, 실험결과를 이론모델과 비교분석하였다. 실험결과로부터 열사이폰의 열전달 성능은 작동유체의 체적변화에 크게 의존하였다. 축방향내부 핀을 가진 열사이폰의 열전달 성능은 평튜브로 제작한 열 사이폰보다 크게 향상되었다. 이와 같은 열사이폰을 태양열 분야의 열교환기에 응용할 경우, 고성능화와 소형화할 수 있다. 그리고 산업현장에서 실제적으로 적용하기 위해 총열전달계수를 산출하였다.

• 한국주조공학회지
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• 제43권6호
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• pp.271-278
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• 2023

본 연구에서는 임펠러 회전속도와 불활성 가스 유량을 바꾸어가며 A356 용탕 탈가스 실험을 수행하여 탈가스 시간에 따른 용탕 온도, 성분 및 밀도 변화를 측정하였다. 용탕 온도의 경우 탈가스 처리가 진행됨에 따라 서서히 감소하였으나 임펠러 회전속도 혹은 불활성 가스 유량과 용탕 열손실 간의 뚜렷한 상관관계는 확인할 수 없었다. 임펠러 회전속도와 불활성 가수 유량에 상관없이, A356 용탕 내 Mg 및 Ti 함량은 600초 이상 탈가스 처리 후에도 그 함량이 거의 변하지 않았으며, Sr의 경우 최대 70 ppm정도 그 함량이 낮아지는 것을 확인하였다. 측정된 용탕 밀도로부터 도출한 용탕 내 수소 농도와 탈가스 모델 식을 활용하여 실험 조건 별 탈가스 속도를 정량적으로 비교 분석해본 결과, 본 연구에서 다룬 탈가스 조업 환경에서는 임펠러 회전속도 보다는 불활성 가스 유량이 탈가스 속도에 영향을 미치는 것을 확인할 수 있었다.

• 한국화재소방학회논문지
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• 제26권2호
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• pp.75-83
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• 2012

반밀폐된 구획에서 발열량 변화에 따른 환기부족화재의 비정상 열 및 화학적특성에 관한 실험적 연구가 수행되었다. 이를 위해 실규모 ISO 9705 표준화재실의 출입구 폭이 0.1 m로 축소되었으며, 구획 중앙에 설치된 분사노즐을 통해 헵탄 연료의 유량은 선형적으로 증가되었다. 구획 내부의 온도, 열유속, 화학종농도 그리고 발열량의 연속적 측정이 이루어졌으며, 비정상 열 및 화학적특성을 표현하기 위하여 총괄 당량비의 개념이 적용되었다. 주요 결과로서, 총괄 연소효율과 구획 내부의 국부 연소효율은 시간에 따라 매우 다른 결과를 보이며, 이론과 측정된 발열량을 통한 총괄 당량비 역시 큰 차이를 보이게 된다. 온도, 열유속 및 화학종 농도의 시간에 따른 변화는 총괄 당량비 개념를 통해 표현될 수 있었다. 구획 내부에서 CO의 농도는 총괄 당량비 2.0~3.0의 범위에서 최대값을 보이며, 보다 과농한 조건에서 점차적으로 감소되는 현상이 발견되었다. 추가로 본 실험을 통해 얻어진 반밀폐된 구획화재의 비정상 열 및 화학적 거동은 향후 현실적인 화재 모델링을 위한 검증 데이터로 활용될 수 있을 것으로 기대된다.

• 대한기계학회논문집
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• 제16권11호
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• pp.2196-2202
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• 1992

본 연구에서는 초전도 양자 간섭장치(SQUID, superconductiong quantum inte- rference device)를 냉각시킬 수 있는 정도의 소용량(3.995K에서 0.1W)의 GM/J-T 냉동 기에 대하여 요구되는 냉각용량을 만족시키면서 최대의 성능을 나타낼 수 있는 열교환 기의 면적배분 조건을 구하였다. 즉 냉동 성능을 알고 있는 상용 2단 GM 냉동기와 소형 극저온 냉동기에 널리 사용되는 열교환기로 이루어진 복합적인 GM/J-T 냉동기에 대하여 열교환기 총면적이 주어졌을 때, J-T 회로내의 냉매(헬륨)의 유량과 각 열교환 기 전열 면적의 비를 변수로 최적설계를 행하였다.

• 설비공학논문집
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• 제12권1호
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• pp.59-66
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• 2000

In a previous paper, we have examined the effects of nozzle configuration and jet to jet spacing on the heat transfer of 1 row of circular water jets. In this paper, experiments have been conducted to obtain the effects of nozzle to target plate distances on the heat transfer of 1 row of 3 jets and 1 row of 5 jets. The nozzle configurations are Cone type, Reverse cone type and Vertical circular type. Nozzle to target plate distance H was varied from 16 mm(H/D=2) to 80mm(H/D=10). For fixed value of mass flow rate and nozzle to target plate distance, larger values of average Nusselt number were obtained for the smaller jet to jet spacing. For the array of water jets, the average heat transfer was decreased slightly with increasing nozzle to target plate distance at low jet velocity of $\textrm{V}_{o}$=3 m/s. However, except for $\textrm{V}_{o}$=8 m/s of 1 row of 5 jets, it was increased with increasing nozzle to target plate distance at high jet velocity of $\textrm{V}_{o}$$\geq$6m/s. We proposed to apply the nozzle configuration of maximum average heat transfer to each nozzle to target plate distance for 1 row of 3 jets, and, it was Reverse cone type nozzle for 1 row of 5 jets(Reynolds number$\geq$36000).