Incomplete Mixing, Intermittency and Fluctuating Toxic Load Measurements in Indoor Plumes

October 19, 2007 - 12:00pm
Bldg. 90
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Why have people been able to get away with ignoring intermittency (periods of zero concentration or zero turbulent temperature difference) in heat and mass transfer for the past century? Why is intermittency crucially important in toxic load estimates for biological exposure? We will explore how a simple back-of-the-envelope model can be constructed for the respiration toxicology of concentration fluctuations at a fixed receptor (for example; your lungs). This simple model will show the origin of the toxic load exponent n=2.0 for concentration C in L=Cnt. An extensive set of laser-induced fluorescence measurements of turbulent dispersion from a point source plume in a water channel were made in shear flow boundary layers and grid turbulence. These experiments were used to develop general quantitative models for concentration mean, variance, intermittency, probability distribution and fluctuation time scale. The experimental results will show why the large observed levels of concentration fluctuation (with standard deviations 100% to 1,000% of the mean!) can be ignored in surface heat and mass transfer calculations at a wall, but must be included in calculations far from surfaces, such as the toxic load experienced by a person in a room. These results will provide further evidence for Wilson's Law1. 1 Wilson's Law states that “Mother Nature protects drunks, little children and ignorant engineers from harm.” For more information about this seminar, please contact: Rich Sextro(510) 486-6295

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