• 대기
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• 제23권1호
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• pp.39-45
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• 2013

A parameterization for the scattering of longwave radiation by ice clouds has been developed based on spectral scattering property calculations with shapes and sizes of ice crystals. For this parameterization, the size distribution data by Fu (1996) and by Michell and Arnott (1994) are used. The shapes of ice crystal considered in this study are plate, solid column, hollow column, bullet-rosette, droxtal, aggregate, and spheroid. The properties of longwave scattering by ice crystals are presented as a function of the extinction coefficient, single-scattering albedo, and asymmetry factor. The heating rate and flux by the radiative parameterization model are calculated for wide range of ice crystal sizes, shapes, and optical thickness. The results are compared with the calculated results using a six-stream discrete ordinate scattering algorithm and Chou's method. The new method (with various habits and size distributions) provides a good simulation of the scattering properties and cooling rate in optically thin clouds (optical thickness < 5). Depending on the inclusion of scattering by ice clouds, the errors in the calculation of the cooling rates are significantly different.

• Nuclear Engineering and Technology
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• 제53권12호
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• pp.3918-3929
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• 2021

In this study, we experimentally investigate of a two-phase natural circulation loop that functions as a passive containment cooling system (PCCS). The experimental apparatus comprises two loops: a hot loop, for simulating containment under severe accidents, and a natural circulation loop, for simulating the PCCS. The experiment is conducted by controlling the pressure and inlet temperature of the hot loop in the range of 0.59-0.69 MPa (abs) and 119.6-158.8 ℃, respectively. The heat balance of the hot loop is established and compared with a natural circulation loop to assess the thermal reliability of the experimental apparatus, and an additional system is installed to measure the vapor mass flow rate. Furthermore, the thermal-hydraulic characteristics are considered in terms of a temperature, mass flow rate, heat transfer coefficient (HTC), etc. The flow rate of the natural circulation loop is induced primarily by flashing, and a distortion is observed in the local HTC because of the fully develop as well as subcooled boiling. As a result, we present the amount of heat capacity that the PCCS can passively remove according to the experimental conditions and compared the heat transfer performance using Chen's and Dittus-Boelter correlation.

• 연구논문집
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• 통권29호
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• pp.5-15
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• 1999

Present study deals with performance analysis of an inert gas generator (IGG) which is to be used as an effective mean to suppress the fire. The IGG uses a turbo jet cycle gas turbine engine to generate inert gas for fire extinguishing. It is generally known that a lesser degree of oxygen content in the product of combustion will increase the effectiveness of fire suppressing. An inert gas generator system with water injection will bring advantages of suffocating and cooling effects which are considered as vital factors for fire extinguishing. As the inert gas is injected to the burning site, it lowers the oxygen content of the air surrounding the flame as well as reduces the temperature around the fire as the vapour in the inert gas evaporates during the time of spreading. Some important aspects of influencing parameters, such as, air excess coefficient. $\alpha$, compressor pressure ratio, $ pi_c$, air temperature before combustion chamber, $T_2$, gas temperature after combustion chamber, $T_3$, mass flow rate of water injection, $M_w$, etc., on the performance of IGG system are investigated. Calculations of total amount of water needed to reduce the turbine exit temperature to pre-set nozzle exit temperature employing a heat exchanger were made to compare the economics of the system. A heat exchanger with two step cooling by water and steam is considered to be better than water cooling only. Computer programs were developed to perform the cycle analysis of the IGG system and heat exchanger considered in the present study.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.1974-1979
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• 2007

In this study, Ice slurry generator heat transfer characteristics are experimentally investigated for the ice slurry generating system with scraper which is pneumatically operated. The ice slurry generator has the same shape as the vertical double tube type heat exchanger. Refrigerant is flowing in the outside tube and ethylene glycol solution in the inside tube. Refrigerant and solution water are parallel flow type which entering bottom of generator and leaving top of generator. The experimentations are conducted under the various test conditions such as compressor speed and cooling water temperature. For the above experimental conditions, heat transfer characteristics of the ice slurry generating system are evaluated in terms of the overall heat transfer coefficient and the heat transfer rate. And the experimental results show that the heat transfer rate of the system is increased as the compressor speed increases and the cooling water temperature decreases.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2006년도 전기학술대회논문집
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• pp.261-262
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• 2006

The effect of tube diameter on heat transfer characteristics of absorber in absorption chiller/heater using LiBr solution as a working fluid has been investigated by experimental study to develop a high performance and compact absorber. A system Includes a tube absorber, a generator, solution distribution system and cooling water system was set up. The diameter of the heat exchanger tube inside absorber was changed from 15.88mm to 12.7mm and 9.52mm. The experimental results show that the heat transfer coefficient, Nusselt number and heat flux increase as solution flow rate and cooling water flow rate increase. The heat transfer performance increases as tube diameter decreases. Among three different tube diameters, the smallest tube diameter 9.52mm has highest heat transfer performance. A comparison of the heat transfer coefficient obtained by the present study with those of previous experimental results showed good overall agreement.

• Journal of Advanced Marine Engineering and Technology
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• 제41권3호
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• pp.197-201
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• 2017

대부분의 어선에서는 포획된 어류를 관리하고 저장하기 위해 얼음 냉각 시스템을 사용한다. 그러나 얼음 냉각 시스템은 작동 시간의 제한뿐만 아니라 적절한 온도와 염분 농도를 유지하는 것이 어려운 단점이 있다. 본 연구의 목적은 어류 운반선의 어창에 적정한 해수온도 유지를 위한 해수 냉각 시스템용 만액식 증발 열전달 특성을 파악하는데 있다. 실험은 냉매의 해수 온도, 유량 및 포화 온도의 변화를 주며 열전달 특성을 파악하였다. 동일 열유속에서 Aluminium-Brass tube가 Copper-Nickel tube 보다 외측 열전달계수가 약 10% 큰 것으로 확인할 수 있었으며, 이를 통해 해수용 열교환기의 전열관으로 Aluminium-Brass를 적용하는 것이 열전달 측면에서 효과적일 것을 확인할 수 있었다. 만액식 단관 열전달계수와 18 kW급 만액식 해수냉각시스템의 총괄열전달계수의 비교를 통해 동일 조건에서는 25%정도 단관의 열전달계수가 큰 값을 나타내었으며, 이러한 결과는 만액식 관군 열교환기의 설계를 위한 중요한 자료가 되리라 판단된다.

• 한국농림기상학회지
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• 제3권4호
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• pp.206-214
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• 2001

본 연구는 경상남도 하동군 하동읍 화심리의 배 과수원에서 주변 지형 특성 및 해발고도별 서리 피해 상습지의 봄철 야간 냉각률, 특정일의 야간기상분포를 구명하고자 수행하였다. 냉각률은 평지에서 3, 4월이 가장 높아 0.7$^{\circ}C$/hr, 9월에 가장 낮아 0.3$^{\circ}C$/hr 정도로 0.4$^{\circ}C$/hr의 차이를 보였다. 일몰 후부터 일출 전까지의 야간기온 냉각률과 유효야간복사의 상관은 r=0.63$^{**}$ 였고, 풍속이 0.5 m/sec 이하에서 야간유효복사와 냉각률은 r=0.90$^{**}$ 으로 상관이 높았으며, 풍속이 강해지면서 냉각률과 상관관계는 낮아졌다. 맑았던 날의 냉각률은 평지(site 1,2,3), 경사면(site 4,5), 산 정상(site 6)에서 각각 시간당 약 1.4$^{\circ}C$, 1.2$^{\circ}C$, 0.6$^{\circ}C$ 하강하여 산 정상으로 갈수록 냉각률이 작아졌다. 맑고 평균풍속이 1.2~2 m/sec이며 산 정상이 경사면이나 평지보다 기온이 낮을 때, 2200~2300경에 경사면(site 4,5)에서의 기온은 떨어지는 것이 아니라 오히려 상승하였다.

• 오토저널
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• 제14권5호
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• pp.128-135
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• 1992

Using a commercial flow-analysis code VSAERO, a method to predict the drag of an automobile induced by the intake air of the cooling system has been devised. Given the pressure loss coefficient across the radiator, which varies with the radiator shape and the local Re, a simplified model of the internal flow is coupled with VSAERO to find the mass-flow rate through the car. The flow rate is obtained iteratively and that, in turn, gives the drag associated with this flow, which essentially is the momentum carried by the drained air. The results of a few sample cases are presented for two front-end shapes in combination with varying radiator frontal area.

• 설비공학논문집
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• 제6권4호
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• pp.453-462
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• 1994

An unsteady quasi one-dimensional model of momentum, heat and mass transfer in a falling film of a vertical plate absorber which is cooled by air was developed using the integral method. Energy conservation of the absorber wall is considered in the model. The model can predict absorption rate, film thickness and mean velocity as well as concentration and temperature profiles. Predictions of steady state temperature and concentration profiles for LiBr/water system for constant wall temperature condition are in good agreement with the two-dimensional finite difference method solutions. Effects of operating conditions, such as convective heat transfer coefficient between the cooling air and the absorber wall, cooling air temperature and film thickness at inlet, on absorption rate of water vapor into LiBr/water solution were shown.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 제5회 압연심포지엄 신 시장 개척을 위한 압연기술
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• pp.349-358
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• 2004

The strip temperature history of finishing mill process is one of the most important factors to stabilize the facilities and to achieve the better product quality including a better prediction of roll force etc. The ultimate goal of this study is to improve scientific understanding of the finishing mill process in the view of heat transfer science. Finishing mill cooling facilities of KwangYang $\#3$ hot rolling are introduced and heat transfer analyses from FET to FDT are particularly focused in this study Three major tasks are successfully achieved as follows: 1) The temperature Prediction Models are developed. 2) The average absolute error is found to be less then 10 Celsius degree (about $8.5^{\circ}C$). 3) Prediction rate (less then $\bar{+}20$) are $10.2\%$ improved $(80.1\;\rightarrow\;90.3\%)$.