Study On Pollutant Control Principle And Performance Of Local Exhaust Hood

"Food is the paramount necessity of the people." The China’s catering industryspread all over the country and the restaurant industry occupies an important place inthe world. The design of kitchen ventilation is an important part of the design ofresidential buildings and public buildings. However, at present because of unreasonableventilation design, the thermal plumes and cooking oil fumes generated during Chinesecooking in the kitchen produced a series of environmental pollution problems. Chinesecooking characteristics, such as deep fried, fried, seditious, boiled and steamed wouldsend out harmful gases and particles that have great difference from the rest of theworld. Inhaling the lampblack can cause great harm to human health.This dissertation is focusing on theoretical derivation, field test, full scaleexperiment and numerical simulation, the thermal plume diffusion model of typicalChinese style of cooking mode. The factors that influenced the exhaust hood captureefficiency of commercial kitchens were also analyzed. And the dissertation furtherstudied the measures on improving the capture efficiency of exhaust hood. The mainresearch contents are shown as follows:Based on the comprising and analyzing the theory of buoyant plume and Gaussianapproximation and the virtual origin theory. Two thermal plume flow equations ofChinese and foreign design standards that commonly used in the application wereanalyzed and corrected. The empirical formula of the suitable coefficient of virtualorigin was proposed to calculate the kitchen thermal plume flow. This is a theoretical foundation for the calculation methods of minimum exhaust air flow rate of hood.An assessment of a current situation of Chinese commercial kitchen was carriedout to assess the impact of the typical ventilation systems of four commercial kitchenson their indoor thermal environment in China. To understand the effect of theventilation system, this study only focused on velocity field, temperature field, relativehumidity field, and concentration distribution varying with following whether cookingor not. The indoor thermal environment characteristics of commercial kitchen thatbefore and after cooking, different ventilation modes on pollutant dispersioncharacteristics and the influence of exhaust hood capture efficiency are discussed.Then, though full size experiments the pollutants spread characteristics duringcooking typical Chinese dishes (typical heat source model) is studied. Different cookingtechniques (frying, stir-frying, steaming and boiling), and the impact of use of theexhaust hood on thermal plume diffusion characteristics were analyzed.Finally, the numerical model was established to predict capture efficiency ofChinese style exhaust hood. Basic site tests and computational fluid dynamics (CFD)analysis were conducted. In this study, many types of hood shapes and side panels weredeveloped to improve the capture efficiency of traditional Chinese style cooking hoods.The arrangement of the exhaust ducts was also investigated.