Computed tomography and optical remote sensing: Development for the study of indoor air pollutant transport and dispersion.

摘要

This thesis investigates the mixing and dispersion of indoor air pollutants under a variety of conditions using standard experimental methods. It also extensively tests and improves a novel technique for measuring contaminant concentrations that has the potential for more rapid, non-intrusive measurements with higher spatial resolution than previously possible.; Experiments conducted in a sealed room support the hypothesis that the mixing time of an instantaneously released tracer gas is inversely proportional to the cube root of the mechanical power transferred to the room air. The constant of proportionality is determined and the relationship is used to predict mixing times for two indoor air flow scenarios: forced ventilation and strong natural convection. Predicted mixing times agree well with observation. The empirical relationship helps bridge the gap between the common but mostly untested assumption of instantaneous, perfect mixing and complex computational models for simulating pollutant transport and dispersion.; One table-top and several room-scale experiments are performed to test the concept of employing optical remote sensing (ORS) and computed tomography (CT) to measure steady-state gas concentrations in a horizontal plane. Various remote sensing instruments, scanning geometries and reconstruction algorithms are employed. Reconstructed concentration distributions based on existing iterative CT techniques contain a high degree of unrealistic spatial variability and do not agree well with simultaneously gathered point-sample data. A new reconstruction method, Smooth Basis Function Minimization (SBFM), is developed. SBFM treats concentration distributions as continuous and representable by a superposition of asymmetric smooth functions--bivariate Gaussians are used in this thesis. SBFM reconstructions of synthetic and experimental data show much better agreement with measured concentration profiles than reconstructions based on standard techniques.; The dispersion of tracer gas in a chamber is examined using a scanning open-path FTIR and SBFM computed tomography. Interpolation of successive path-integral concentration measurements for each ray yields input data for CT reconstructions at specific times during the experiment. This allows one to follow the evolution of the tracer gas concentration distribution in time. The results demonstrate significant potential for CT/ORS as a fast, accurate and relatively non-invasive technique to measure time-varying gas concentrations in a variety of applications.