Study On Control Characteristics Of Indoor Environment Influenced By High-temperature Buoyant Jets In Industrial Buildings

Survey data from the National Bureau of Statistics of the People’s Republic of China shows that the total completed area of industrial buildings has already reached up to 2.59 billion square meters from 2010 to 2014 in China. The huge areas of industrial buildings result in the serious air pollution inside the plants. Dust is one of the prevalent contaminants generated during some industrial production processes, which could do harm to working environment, outdoor atmospheric environment and workers’ health. Survey data from the Disease Prevention and Control Bureau of National Health and Family Planning Commission of the People’s Republic of China reveals that the total number of occupational disease cases has already reached up to 129060 from 2009 to 2013 in China. The number of pneumoconiosis cases accounts for more than 80% of the total number of occupational disease cases during the past five years. From the industry distribution, the main occupational disease cases are from coal, railway, nonferrous metals and metallurgy. The dust concentration reached up to 13 mg/Nm3 in an existing steel plant, which was far more than the dust concentration limits, i.e., 8 mg/Nm3 in occupied zones. A large amount of high-temperature smoke containing dust generaged during smelting in blast furnace workshops and most diameters of dust particle were less than 1.0 μm. So it is considered that dust particle movements are consistent with buoyant jets at high temperature and capturing buoyant jets means capturing dust particles in the local ventilation system. Therefore, the object of this research is chosen as high-temperature buoyant jet.The above data conveys that it is important to create a safe, healthy and productive work environment inside the industrial buildings. Therefore, the objective of this research is determined as control characteristics of indoor environment influenced by high-temperature buoyant jets in industrial buildings. The theoretical derivation analysis, the full-scale experiment, numerical simulation(Fluent) and the reduced-scale experiment are used to study the following aspects. Firstly, formulas for ellipse plumes are established and the flow-field characteristics of high-temperature buoyant jets are analysed influenced by different factors, such as the oultlet shape for buoyant jets, one-side confined condition and so on. Then, the flow-field characteristics of inclined ellipse buoyant jets influenced by exhaust hood are obtained and important empirical factors on pollutant capture efficiency in local ventilation system are given based on the analysis of different factors using the reduced-scale experiment. These factors include the effects of contaminant sources, different factors on pollutant capture efficiency in local ventilation system and the flow rate of general ventilation. Finally, characteristics of thermal stratification heights and contaminant distribution influenced by both local ventilation system and general ventilation system are analysed to evaluate indoor environment characteristics inside industrial buildings. At the same time, two new evaluation indexes for control effect of dynamic contaminants and for indoor environment in the existing industrial plants are proposed respectively. The primary conclusions inferred from the three aspects can be summarized as follows:(1)The formulas of axial velocity, cross-section flow rate and axial temperature for ellipse plumes and the formulas of axial excess temperature for circular and rectange plumes are derived. Then axial velocity and temperature of ellipse plumes are compared with axial velocity and temperature of circular and rectange plumes. In addition, the derived axial velocity and cross-section flow rate formulas for ellipse plumes are expressed accordingly based on the piecewise functions between air density and specific heat capacity and the temperature.(2)Reversed variations of the Archimedes number from a parallel-flow outlet(Ar0) showed that the dimensionless turbulence coefficient of the parallel-flow outlet was smaller than that of the circular aperture. In addition, when Ar0 ranged from 0.024 to 0.044, a semi-empirical equation was established to describe the trajectory of the hot jets from a parallel-flow outlet in a push-pull ventilation system.(3)Radial velocity developments of high-temperature annular buoyant jets with different annular jet widths revealed that the annular flow merged towards the axis of the annulus forming a velocity profile further downstream similar to that for a circular jet. When the ratio of outer diameter to inner diameter of the annulus was smaller than 5/2, the high-temperature annular buoyant jets could not be simplified as circular buoyant jets.(4)There is a risk of a sharp decline in capture efficiency after the critical amount of contaminant source. The concentration variations of dynamic contaminants seem like negative exponent function of e in the concentration decrease region. In addition, the concentration decrease of dynamic contaminants with reduced volume exhaust hood is much faster than that with enlarged volume at a certain flow rate.(5)Confined airflow boundaries, flow rate of the exhaust hood and aspect ratio of the hood are important empirical factors on pollutant capture efficiency in local ventilation system, based on the different function types between capture efficiency and Archimedes number.(6)Based on measurement data of thermal stratification heights in the reduced-scale experiment, the dimensionless thermal stratification height(yst*) range is summarized to be between 0.20 and 0.36 with the flow rate of the exhaust hood(qhood) varying from 25 m3/h to 120 m3/h. To ensure health of workers who need to operate in the upper space of the plant, safety operation heights should be lower than the corresponding thermal stratification heights in industrial plants.(7)The new evaluation index for control effect of dynamic contaminants is proposed to reflect the performance of the exhaust hood in this paper. Enlarging the volume of exhaust hood contributes more contaminants captured stably for paroxysmal contaminants generated from pouring process.In summary, optimized designs might be provided to improve the pollutant capture efficiency in local ventilation system, based on mastering the flow-field characteristics of high-temperature buoyant jets influenced by different factors, such as the oultlet shape for buoyant jets, one-side confined condition and airflow confluence from the exhaust hood. In addition, the development laws of thermal stratification heights may give a guide to workers’ safety operation heights in the upper space of industrial buildings. And these two new evaluation indexes could be used to evaluate control effects of dynamic contaminants and evaluate indoor environment in the existing industrial plants.