Annals of Occupational Hygiene Advance Access originally published online on December 9, 2004
Annals of Occupational Hygiene 2005 49(1):1-15; doi:10.1093/annhyg/meh065
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© 2004 British Occupational Hygiene Society Published by Oxford University Press;
Aerodynamic Characteristics and Design Guidelines of Push–Pull Ventilation Systems
1 Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei, Taiwan, PRC; 2 Department of Mechanical Engineering, Kuan Wu Institute of Technology, 151 Yide St., Beitou Chiu, Taipei, Taiwan 112, PRC; 3 Department of Occupational Safety and Health, Chang Jung Christian University, Kway Jen, Taiwan, PRC; 4 Institute of Occupational Safety and Health, Council of Labor Affairs, No. 99, Lane 407, Hengke Rd., Shijr City, Taipei, Taiwan, PRC; 5 Institute of Occupational Medicine and Industrial Hygiene, National Taiwan University, 1 Jen-Ai Rd., Sec. 1, Taipei, Taiwan, PRC
* Author to whom correspondence should be addressed. Tel: +886-2-2737-6488; fax: +886-2-2737-6460; e-mail: rfhuang{at}mail.ntust.edu.tw
Aerodynamic characteristics such as the flow patterns, velocity field, streamline evolutions, characteristic flow modes and characteristic flow regimes of the push–pull ventilation system are cross-examined by using the laser-light sheet smoked-flow visualization method and laser Doppler velocimetry. Four characteristic flow modes, which are denoted as dispersion, transition, encapsulation and strong suction, are identified in the domain of the push-jet and pull-flow velocities at various open-surface tank widths and rising gas velocities. It is argued phenomenologically, from the aerodynamic point of view, that operating the system in the strong suction regime would be a better strategy than operating it in other characteristic regimes for the consideration of capture efficiency. Design guidelines are developed and summarized based on the results obtained from this study. The regression formulas for calculating the critical values of the push-jet and the pull-flow velocities are provided for easy access. The sulfur hexafluoride tracer gas validation technique is performed to measure the capture efficiency. The results of tracer gas validations are consistent with those obtained from the aerodynamic visualization and measurements. The operation points obtained by employing the American Conference of Governmental Industrial Hygienists design criteria are compared with the results obtained in this study for both the aerodynamics and the capture efficiency. Methods for improving the capture efficiency and energy consumptions are suggested.
Keywords: aerodynamic characteristics • push–pull ventilation • tracer gas
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