Direct capture efficiency of a local exhaust system is defined by introducing an imaginary control box surrounding the contaminant source and the exhaust opening. The imaginary box makes it possible to distinguish between contaminants directly captured and those that escape. Two methods for estimation of direct capture efficiency are given: (I) a numerical method based on the time-averaged Navier-Stokes equations for turbulent flows; and (2) a field method based on a representative background concentration.
This paper presents the results of full-scale experiments in a realistic building to evaluate natural convective heat and mass transfer through doorway-like apertures under small temperature differentials. The zone-to-zone temperature differences were nominally between re and 2.5°C. Heat transfer correlations, coefficient of discharge, and thermal stratification are reported for air (Pr = 0. 71), an enclosure aspect ratio of 0.26, aperture height relative to the enclosure height in the range of 0. 75 to l, and aperture width relative to the enclosure width in the range 0.29 to 0. 79.
Air flow conditions at the supply opening, which are used as boundary conditions in a numerical simulation, must be applied in order to proceed with the numerical solution of the air flow within a room. Among the conditions usually specified are the turbulence parameters, including the turbulence kinetic energy or the turbulence intensity and turbulent kinetic energy dissipation rate. Investigators have used a variety of expressions to estimate these quantities. A review of these expressions is presented in this paper.
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