Study On Thermal Natural Ventilation Based On Different Combination Patterns Of Heat Sources And Thermal Stratification Height

In recent years,the energy consumption of industrial and civil buildings has increased greatly with the development of social economy.Industrial plants often emit large amounts of heat during the production process,and their thermal intensity can reach 50?300W/m³(their thermal intensity maybe larger in some industrial plants).The heat sources in the plant are complex and diverse(such as point,surface,and volume heat sources),and their locations and heights are also different.These factors make the precise design of thermal pressure natural very complicated.In the buildings with a large amount of heat dissipation,the indoor temperature distribution will change with the ventilation rate,and both the air temperature and ventilation rate need to be solved under coupling conditions.Moreover,in the building with high waste heat emission,the geometric and physical parameters of the heat sources will change under different combination patterns,which are directly related to the indoor temperature and ventilation capacity.Thus the analysis method of the natural ventilation in this kind of industrial building is different from the known room temperature problem.These involve how to simplify effectively the engineering problem of diversity and complexity,or how to complete the transition from pure theoretical model to application model.In this paper,the thermal pressure natural ventilation is taken as the implementation object to study the basic mode of thermal plume diffusion above the body heat source,multiple heat sources and elevated heat source under different height.Based the classic“emptying-filling box model”on indoor thermal stratification research,the formula of dimensionless stratified height under different heat sources conditions was established,and the calculation method of exaust air temperature and ventilation rate can be obtained.Then,the effects of building height,geometric parameters of heat source,height of heat source,effective opening areas and other factors on natural ventilation were analyzed.The thermal stratification height,exhaust temperature and ventilation rate calculation method under different combined heat source patterns in the industrial building were checked through theoretical analysis,laboratory test and CFD simulation.The main content is expressed as follows:Firstly,the basic model of the thermal plume diffusion above some kinds of heat sources(such as point,face,body heat source,etc.)and the interaction of the thermal plume in natural ventilation room were studied.According to the classification and judge foundation of different combination patterns of heat sources,the multiple heat sources could be divided into discrete sources or close sources and so on.Secondly,according to the calculation formulas of flow rate in different plume regions,the unified calculation formula of flow rate of thermal plume above the area heat source was established.Based on the classic“emptying-filling box model”,the theoretical model of thermal stratification height in a natural ventilation space within an area heat source was developed,which is validated by the numerical simulation.Then,the theoretical model of natural ventilation under the different forms of discrete heat source(for example,two discrete heat source with different diameters)was established,and the quantitative influence of room height,opening area and heat source diameter on the thermal pressure natural ventilation was analyzed.Thirdly,buoyancy-driven flows by two discrete point heat sources of equal strength at different levels in a naturally ventilated enclosure was studied.This paper presents the approximate theoretical models of the thermal stratification and exhaust air temperature in a naturally ventilated enclosure containing two point heat sources.The dimensionless thermal stratification height and exhaust air temperature were investigated theoretically,and numerical simulation were conducted to verify the theoretical models.In addition,buoyancy-driven flows by two close point heat sources(x₀?(7)h_s-h₀(8)?/0.35)of equal strength at the same level in a naturally ventilated enclosure was studied.The theoretical models of the thermal stratification is derived and validated by the numerical simulation.Based on the same principle,the theoretical model of the thermal stratification in a naturally ventilated enclosure with a point sources restricted by a side boundary was derived,and the quantitative influence of factors such as height of heat source on the thermal natural ventilation was analyzed.Finally,the condition of industrial buildings with many discrete point,area and body heat sources of different levels was summarized and analyzed.Based on different combination patterns of heat sources and thermal stratification height,the design principle of thermal natural ventilation in large industrial buildings has been proposed.And the calculation procedure of natural ventilation design was summarized to analyze the actual case of hydropower station in summer,which provides theoretical basis and technical reference for natural ventilation design of industrial buildings.