Modeling And Characteristics Of Indoor Air Convection

Indoor air environment (IAE) is closely related to our health and work efficiency and hence has attracted considerable attention in the recent years. IAE is mainly a hybrid process of air flow and heat/mass transfer. Therefore, the knowledge of indoor air convective heat and mass transfer or indoor air convection, is fundamental to control our indoor air environment. The objective of the present dissertation is to investigate the modeling and characteristics of indoor air convection. The layout of the dissertation is as follows:The first chapter is to model and visualize the convective heat and mass transport. The traditional distributions of temperature and concentration just mark the final state that a convection system has reached but convey the information about how the heat and contaminant is transported across the system, and therefore we cannot get to know the natural characteristics of convection. The concept of convection transport is proposed to'see'the nature of the convective phenomena. The ability to see is very attractive, for the engineers and customers are much convinced by their seeing. Unified convection transport functions (streamfunction, heatfunction and massfunction) are derived from the governing equations to describe the fluid, heat and mass transport respectively.In chapter two, the visualization of convection transport provides a simple but effective way to evaluate the indoor air environment. The heat and contaminant transport structures indoors give us a bird-eye to see (a) if the heat and contaminant could be swept out as soon as possible, (b) if the harmful heat/pollutant sources do harm to our health, and (c) how to organize the heat and pollutant sources so as to achieve a high indoor air quality. A two-dimensional double diffusive laminar mixed convection, displacement ventilation, is fully investigated by the means of heat and contaminant transport structures to see the effects of the heat and pollutant sources and the external mechanical ventilation.Chapter three focuses attentions on the interaction between discrete heat sources (DHSs) indoors and their effects on IAE. In order to identify the discrete heat sources of different strength, type and size, a combined temperature scale is first developed. The advantage of the method is that the implicit interaction between DHSs is transformed to the explicit relations between their contribution ratios. The contribution ratio of the surface heat source is expressed by its boundary condition and that of the inner volumetric source expressed by the source term in the governing equation, and the total contribution ratios from all the discrete heat sources are unity. A related concept of thermal strength of DHS is then introduced to determine its role in the interaction between others.The effect of the position and strength of indoor heat and pollutant sources on indoor air environment is then numerical studied in chapter four. A two-dimensional double diffusive laminar natural convection in rectangular enclosure is detailed analyzed. The results show that when the thermal and solutal buoyancies aid each other, the airflow consists of one main cellular structure and is steady, regardless of the relative strength variation between the heat and pollutant sources. There are multiple flow structures, however, according to the relative strength when the buoyancies opposing each other.Natural modeling is suggested in chapter five to deal with the complicated indoor air convection. The complicated behavior and multiple states of indoor air convection are mainly related to the multiple physical processes, such as the thermal buoyancy, the solutal buoyancy and the mechanical ventilation. Therefore a natural modeling of indoor air convection is to analyze the interaction between all the possible physical processes. The basic characteristics of indoor air convection are then determined by the prevailing physical process.The SIMPLE algorithm for the numerical solution to convection problem is then investigated in the following chapter. The special features of pressure-correction equation and their effects on the performance of the SIMPLE algorithm have been thoroughly studied based on the principle of continuity conservation. The last chapter focuses on the experiment study. A small-scale water experiment is first set up by the particle image velocimetry and then validates the numerical simulation of the full-scale airflow indoors.