• 대한기계학회논문집B
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• 제29권2호
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• pp.287-293
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• 2005

In the present study, to determine the flow rate of droplets supplied to heat transfer surface after (j-1)th rebound, $D_X[j{\ge}2]^{\ast}$, it was assumed that the rebound droplets are distributed according to the Gaussian distribution from 0 to L, in which the flight distance L is determined by maximum flight distance $L_{max}$. We also assumed that $L_{max}$ is dependent on the air flow velocity and mean size of droplets. The local heat flux of a dilute spray in high temperature region was predicted using the newly evaluated $D_X[j{\ge}2]^{\ast}$. In addition, the predicted results by the present model were compared with the existing experimental data.

• 대한기계학회논문집B
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• 제20권2호
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• pp.624-631
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• 1996

가솔린 화재의 소화과정을 규명하기 위하여 부력과 순수확산에 의해서만 연료와 산화제가 혼합되는 순수확산화염을 대항으로 수분무에 의한 소화실험을 체계적으로 수행하여 다음과 같은 결론을 얻었다. 1) 수분무는 특정 조건에서 수분무가 없을 때인 자연연소상태에 비하여 더 높은 값의 연소율을 가지게 되어, 오히려 화재의 연소를 촉진하게 된다. 2) 수분무시 연소율은 자연연소상태보다 더 높은 값으로 증가하다가 어느 순간 연료표면의 냉각조건이 충분히 이루어지면 소화기 일어나게 된다. 30 수분무에 의해 유입되는 공기는 분무 자체와 함쎄 화염을 반경방향으로 흐트러지게 함으로써 연료와 공기와의 접촉면적을 증대시켜 연소를 촉진하는 반면, 분무수가 연료 표면에 쉽게 도달할 수 있도록하여 연료표면을 보다 잘 냉각시키게 된다. 즉 주위공기의 유입은 연소율의 증가 및 감소에 영향을 미친다. 4) 본 실험조건에서는 분무수의 입경이 약 40.mu.m 이하인 액적들은 화염구역내에서 증발하거나 그 경로가 바뀌어 연료 표면에 도달되지 못함을 발견하였다. 5) 본 연구와 같이 주로 냉각작용에 의하여 화염이 소화되는 경우에는, 화염자체의 냉각효과 보다는 연료표면의 냉각에 의한 효과가 지배적임을 알 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제22권6호
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• pp.880-887
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• 1998

In order to study heat transfer characteristics of spray cooling for the purpose of uniform and soft cooling of high temperature surface a series of experiments for a hot horizontal copper flat plate was performed by downflow spray water using flat spray nozzle. Cooling curves were mea-sured under the various experimental conditions of flow rates and temperatures of cooling water Surface temperature surface heat fluxes and heat transfer coefficients of horizontal upward-facing flat surface were calculated with cooling curves measured at each radial positions near the cooling surface by TDMA method. Generally heat transfer characteristics for spray cooling is simi-lar to boiling phenomenon of pool boiling. The minimum heat flux(MHF) appear at the surface temperature of about ${\Delta}Tsat=250^{\circ}C$ and the critical heat flux(CHF) appear at about ${\Delta}Tsat=250^{\circ}C$.

• Journal of Advanced Marine Engineering and Technology
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• 제24권5호
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• pp.25-32
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• 2000

In this paper, experiments investigating the high-temperature region heat transfer coefficients for the spray cooling of hot flat plates were performed by down spray water using flat spray nozzles. The heat transfer surface is made of copper and is 100mm in length and 40mm in width and 15mm in thickness. The experimental condition of spray are as follows: temperatures of the water droplets are T=20~$80^{\circ}C$ and droplets volume fluxes are D=0.001565~0.010438$m^3/m^2s$. Next, correlating equations for the heat transfer characteristics of spray cooling in the high temperature region are developed from the effects of droplets volume flux and the surface temperature of heat transfer plate.

• 생물환경조절학회지
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• 제6권1호
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• pp.48-54
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• 1997

하절기 고온으로 인한 작물의 열악한 생육 환경개선을 위하여 미포그노즐을 이용하여 패트온실에서 증발 냉각 시험을 수행하였다. 본 연구에 사용된 미포그노즐의 분무특성을 말븐입자분석기로 분석한 결과 분무압 70kg/$\textrm{cm}^2$에서 분무입자의 크기는 평균 27$\mu\textrm{m}$로 나타났고, 이때의 분무량은 분당 100$m\ell$였다. 또한 평균 분무 입자의 크기가 27$\mu\textrm{m}$인 경우에 분무낙하량을 조사한 결과 낙하거리 150cm에서 총분무량의 88%가 공중에 부유하는 것으로 나타났다. 냉방시스템의 주요 구성 부분은 고압노즐, 양수펌프, 필터 및 미포그노즐 32개로 이루어졌고, 1분 분무-1분 환기로 이루어진 연속 분무 시험 결과 외기온 3$0^{\circ}C$의 조건에서 온실내 기온을 4$0^{\circ}C$에서 32$^{\circ}C$로 강하시킬 수 있었다 또한 분무시험시 측정한 온실내의 온습도 값을 psychrometric equation에 대입하여 온실내의 수분변화량을 분석할 수 있었으며, 이와 같은 분석을 통하여 온도강하정도와 온실내 공기의 절대습도비 변화량을 예측할 수 있는 실험식을 정립할 수 있었다. 이 실험식을 이용하여 우리 나라 표준형 온실 1-2W, 3-2G-3S에서 실내온도를 4$0^{\circ}C$에서 3$0^{\circ}C$로 강제 냉각시킬 때 필요한 분무수량을 분석한 결과 분무입자 27$\mu\textrm{m}$에서의 분무수량은 각각 80.7, 99.9$\ell$였으며, 포그시스템에 필요한 노즐의 수는 분당분무량 100$m\ell$의 경우 3분 분무기준으로 각각 270, 333개가 소요될 것으로 계산되었다. 앞으로 포그시스템을 활성화하기 위해서는 온실의 기상조건에 따른 증발율과 분무입자에 대한 심층적 연구가 요망된다.

• 대한기계학회논문집B
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• 제29권2호
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• pp.279-286
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• 2005

This study presents experimental results on the heat transfer coefficients in the film boiling region of spray cooling for actual metallurgical process. In this study, the heat flux distributions of a two dimensional dilute spray impinging on a hot plate were experimentally investigated. A stainless steel block was cooled down from intial temperature of about $800^{\circ}C$ by twin fluid (air-water) flat spray. It was found from the experimental results that the heat transfer area was classified into the stagnation region and wall-flow region. In the stagnation region, the experimental data of local heat transfer coefficient was closely correlated with the local droplet-flow-rate supplied from the spray nozzle directly. Thus, the local heat transfer coefficients are in good agreement with the predicted values from the correlations proposed by our previous study. In wall-flow region, however, remarkable differences are observed between experimental data and predicted values because the number of rebound droplets increase with increasing the distance from the stagnation point.

• 대한기계학회논문집B
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• 제30권12호
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• pp.1236-1242
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• 2006

The local heat flux of spray cooling in the film boiling region were experimentally investigated for the spray region of $D_{max}$ = $0.005{\sim}0.03m^3/(m^2s)$. A twin-fluid full cone spray nozzle was employed for the experiment and the distributions of droplet flow rates were obtained for air-water full cone sprays. A stainless steel block was cooled down from initial temperature of about $800^{\circ}C$ by full cone spray. In the region near the stagnation point, it was found that the experimental data are in good agreement with the results predicted from the correlations between the local heat transfer and the local droplet flow rate proposed in the previous report. However, it was found that the experimental data of $D_r$ > $0.01m^3/(m^2s)$ are a little smaller than the results predicted from the correlations.

• 한국생물환경조절학회:학술대회논문집
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• 한국생물환경조절학회 1999년도 학술발표논문집
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• pp.59-62
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• 1999

1. 미스트를 장시간 분사시킬 경우 분사기간동안 온도강하는 분사량에 무관하게 일정하나 분사종료 후 온도상승은 분사량이 많으면 온도상승이 현저히 지연된다. 반면 증가된 습도는 장시간 유지되기 때문에 적정 분사량이 존재한다. 2. 시설하우스내 고온장애와 습도장애를 극복하고 보다 유리한 실내환경을 유지하기 위해서는 적정 미스트 분무량을 유지시켜야 하며 동시에 분무시간과 휴지시간을 충분히 고려해야만 한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.175-180
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• 2001

In this study, the minimum heat flux conditions are experimentally investigated for the spray cooling of hot plate. The hot plates are cooled down from the initial temperature of about $900^{\circ}C$, and the local heat flux and surface temperatures are calculated from the measured temperature-time history. The results show that the minimum heat flux point temperatures increase linearly resulting from the propagation of wetting front with the increase of the distance from the stagnation point of spray flow. However, in the wall region, the minimum heat flux point temperature becomes independent of the distance. Also, the experimental results show that the velocity of wetting front increases with the increase of the droplet flow rate.

• Journal of Advanced Marine Engineering and Technology
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• 제26권3호
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• pp.320-327
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• 2002

An experimental study of heat transfer from hot flat surface to water sprays was conducted in high temperature region. Heat transfer measurements for hot flat surface were made by 4 sheathed C-A thermocouples. Droplets volume flux were also measured-independently at a position in spray field. The test conditions included variations in droplets volume flux, subcooling of cooling water of $1.565\times10^{-3} to 14.089\times10^{-3}m^3/m^2s and 80 to $20^{\circ}C$ respectively. The effects of inclination angle on heat transfer were investigated and changes in inclination angle of hot flat surface affected heat transfer coefficients of high temperature region.