• Title/Summary/Keyword: Pull hood

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Evaluation of Capture Efficiencies of Push-Pull Hood Systems by Trace Gas Method under the Presence of Some Cross-draft (방해기류 존재시 추적자 가스법을 이용한 푸쉬풀 후드 효율 평가)

  • Kim, Tae-Hyeung;Ha, Hyun-Chul;Kang, Ho-Gyung
    • Journal of Korean Society of Occupational and Environmental Hygiene
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    • v.16 no.3
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    • pp.290-301
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    • 2006
  • A push pull hood system is frequently applied to control contaminants evaporated from an open surface tank. Efficiency of push pull hood system is affected by various parameters, such as, cross draft, vessel shapes, tank surface area, liquid temperature. A previous work assisted by flow visualization technique qualitatively showed that a strong cross draft blown from the pull hood to push slot could destroy a stable wall-jet on the surface of tank, resulting in the abrupt escape of smoke from the surface. In this study, the tracer gas method was applied to determine the effect of cross-draft on the capture efficiency qualitatively. A new concept of capture efficiency was introduced, that is, linear efficiency. This can be determined by measuring the mass of tracer gas in the duct of pull hood while the linear tracer source is in between push slot and pull hood. By traversing the linear tracer source from the push slot to the pull hood, it can be found where the contaminant is escaped from the tank. Total capture efficiency can be determined by averaging the linear efficiencies. Under the condition of cross-draft velocities of 0, 0.4, 0.75, 1.05 and 1.47m/s, total capture efficiencies were measured as 97.6, 95.4, 94.6, 92.7 and 70.5% respectively. The abrupt reduction of efficiency with cross-draft velocity of 1.47m/s was due to the destruction of tank surface wall-jet by the counter-current cross-draft. The same phenomenon was observed in the previous flow visualization study. As an alternative to overcome this abrupt efficiency drop, the 20% increase of hood flow rates was tested, resulting in 20% efficiency increase.

Evaluation of Capture Efficiencies of Push-Pull Hood Systems by Cross Draft Directions and Velocities Using Smoke Visualization Technique (기류 가시화기법을 이용한 방해기류 방향과 속도에 따른 푸쉬풀 후드 효율 평가)

  • Song, Se-Wook;Kim, Tae-Hyeung;Ha, Hyun-Chul;Kang, Ho-Gyung
    • Journal of Korean Society of Occupational and Environmental Hygiene
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    • v.15 no.1
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    • pp.36-44
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    • 2005
  • A push pull hood system is frequently applied to control contaminants evaporated from an open surface tank in recent years. Efficiency of push pull hood system is affected by various parameters, such as cross draft, vessel shapes, size of tanks surface, liquid temperature, and so on. Among these, velocity of cross draft might be one of the most influencing factor for determining the ventilation efficiency. To take account of the effect of cross draft velocities over 0.38m/s, a flow adjustment of ${\pm}$20% should be considered into the push and +20% into the pull flow system Although there are many studies about the efficiency evaluation of push pull hood system based on CFDs(Computational Fluid Dynamics) and experiments, there have been no reports regarding the influence of velocities and direction of cross-draft on push-pull hood efficiency. This study was conducted to investigate the influence of cross draft direction and velocities on the capture efficiency of the push-pull ventilation system. Smoke visualization method was used along with mock-up of push-pull hood systems to verify the ventilation efficiency by experiments. When the cross-draft blew from the same origins of the push flows, the efficiency of the system was in it's high value, but it was decreased significantly when the cross-draft came from the opposite side of push flows Moreover, the efficiency of the system dramatically decreased when the cross-draft of open surface tank was faster than 0.4m/s.

A Study on the Hood Performance Improvement of Pickling Tank using CFD (전산유체역학을 이용한 산세조 후드 성능 개선에 관한 연구)

  • Jung, Yu-Jin;Park, Ki-Woo;Shon, Byung-Hyun;Jung, Jong-Hyeon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.15 no.1
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    • pp.593-601
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    • 2014
  • In this study, we investigated the methods of improving the capturing ability of acid fume by assessing the performance of slot-type external hood installed on both sides of an open surface tank for acid washing process. A field survey and the results of computational fluid dynamics revealed that capturing performance of existing hoods is very poor. To solve such problem, 'push-pull hood' that pushes from one side of an open surface tank and pulls on the other side was suggested. The initial prediction was that if a push-pull hood is used, the acid fume of an acid-washing tank surface could be moved towards the hood through the push flow. However, this study has confirmed that if the push flow velocity becomes too high, it could spread to other areas due to flooding from the hood. Therefore, if the push air supply is maintained at around 25 $m^3/min$(push 10 m/s), proper control flow is formed on the surface of a tank and acid fume that stayed at the upper part of the tank is smoothly captured toward the hood, significantly enhancing the capturing performance.

A Numerical Analysis on Improvement of Push-Pull Local Ventilation System (Push-Pull 국소환기시스템 개선에 관한 수치해석)

  • Yi, Chung-Seub;Jang, Sung-Cheol;Yoon, Kang-Ro
    • Proceedings of the SAREK Conference
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    • 2007.11a
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    • pp.594-599
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    • 2007
  • This study represents numerical analysis on the fluid flow and concentration characteristics by scattering fume at push-pull ventilation system. And the principal point is making optimum on improve an existing ventilation system. This phenomenon simulated about local ventilation system by using commercial CFD tool and base on these fact has find improvements. Advanced model shows most low different pressure and velocity which are suction capability at inlet surface of pull hood has most uniformity. When compared with existing model, Improved model has more good ventilation performance.

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Numerical Analysis on the Improvement of Fume Mixing Ratio in the Push-Pull Local Ventilation System (급기-흡기 국소환기시스템의 성능개선에 관한 수치해석)

  • Yi, Chung-Seob;Suh, Jeong-Se;Yoon, Ji-Hoon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.22 no.12
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    • pp.867-872
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    • 2010
  • Numerical analysis has been conducted to investigate the fluid flow and fume mixing ratio characteristics of scattering fume in a push-pull ventilation system and optimally improve the flow patterns of scattering fume in the existing ventilation system. This ventilation system has been simulated by using commercial CFD code. In the case of the existing system, although the air is sprayed from air-curtain to prevent the fume from being scattered in upper hood, the improved air supply hood can remove the fume from the wide area in the high pressure. It is verified that the deeper plating storage is more advantageous. Also, by installing the shied around the plating storage, the scattering of the fume to the atmosphere was prevented effectively by surrounding flux.

A Study of Local Ventilation Design on PC Programm (국소환기 설계의 전산화에 관한 연구)

  • Yoon, Myong Cho
    • Journal of Korean Society of Occupational and Environmental Hygiene
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    • v.3 no.2
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    • pp.213-226
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    • 1993
  • The purpose of this study is to computerize the design of single source for a duct work system which is essential for the improvement of working places. There are different types of hood, such as general hood, push pull hood and canopy hood. And out of these three types, general hood and canopy hood were used as subjects of this study. The software used here was Quattro Pro 123 programm, and the hardware was IBM PS/SX(type 5510-SK4 S/N 83-05164). And the results are tabulated in

    and
    . All of the hazardous factors of working places, except for physical factors, such as noise, vibration, illumination and etc, are control measurement related. In order words, workiong places that have problems with toxic gas, mist, fume, dust, odors, biological factors or wetness can be improved by means of the local ventilation design. However, the reqires very complicate processes, and in the case of canopy hood, particularly, one runs into difficulties due to frequent discrepancies generated from calculations through many processes. Recently, progress of the computer hardware technics has been dazzling, and also the software is development rapidly. As proven in the results of this study, it is good that designs for industrial ventilation systems are readily available for easy use. It is hopeful that young scholars will develop easier and quicker methods for local ventilation designs in the future.

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  • A Study on Worker Exposure to Hexavalent Chromium in Plating 0peration (중소기업 도금공정에서의 6가 크롬 폭로에 관한 연구)

    • Cheong, Hoe Kyeong;Paik, Nam Won
      • Journal of Korean Society of Occupational and Environmental Hygiene
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      • v.3 no.2
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      • pp.152-165
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      • 1993
    • This study was performed at eleven small-sized plating factories located in Seoul, Incheon, Ansan, and Taejeon from July 21 to October 6, 1992. The major objectives of this study were to evaluate worker exposure to hexavalent chromium and local exhaust ventilation (L.E.V.) systems at the chromium plating operations. The most suitable L.E.V. systems for chromium plating tanks were designed as examples for recommendation to the industry. The results are summarized as follows. The range of chromium plating operations investigated included decorative, hard, and black chromium plating on several kinds of parts. Most of plating tanks were not equipped with proper control methods against emission of hexavalent chromium mists and workers were not wearing appropriate personal protectives. The ariborne hexavalent chromium concentrations showed an approximate lognormal distribution. The geometric means of both personal and area samples were within the Korean and ACGIH standards, $50{\mu}g/m^3$. However, in comparison with the NIOSH criterion, $1{\mu}g/m^3$, the geometric means of personal samples at two factories and the geometric means of area samples at two factories exceeded it. The geometric means of personal and area samples of high exposure groups (above the NIOSH criterion) were 7 and 27 times higher than those of low exposure groups (below the NIOSH criterion), respectively. The L.E.V. systems of high exposure groups were improperly designed, and the factory with the highest exposure level had no L.E.V. systems at all on chemical etching process. Whereas at factories of low exposure groups, mist control methods such as mist suppressants, tank cover, and/or auxillary L.E.V. systems were added to L.E.V systems. The evaluation of L.E.V. systems showed that there was no chromium plating operation satisfying the ACGIH criteria for capture velocity, slot velocity, and exhaust rate simultaneously. To increase performance of L.E.V. systems, it must be designed to minimize the impact of boundary layer separation. Push-pull ventilation hood and downward plenum ventilation hood were suggested for the Korean industry.

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    Applicability of Computational Fluid Dynamics on Industrial Ventilation Engineering (산업환기공학에 대한 전산유체역학의 응용가능성)

    • Ha, Hyun-Chul;Kim, Tae-Hyeung;Shim, Kwang-Jin
      • Journal of Korean Society of Occupational and Environmental Hygiene
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      • v.8 no.2
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      • pp.163-177
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      • 1998
    • Computational Fluid Dynamics(CFD) was applied to predict air flow around the hoods : circular hoods, square hoods, and push-pull hoods. A commercially available CFD software, CFD-ACE(Ver. 4.0), was tested, which is based on the finite volume method using the ${\kappa}-{\varepsilon}$ turbulence model. Numerical results were compared with the experimental, analytical and numerical results from other studies. CFD solutions showed an excellent agreement with the previous experimental and numerical results. It is promising that CFD techniques could be applied on the variety of complex problems in the industrial ventilation engineering.

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