Experimental Study And Numerical Simulation Of Thermal Stratification Height In A Natural Displacement Ventilated System

Firstly,the study summed up the theoretical formulas recorded in classic papers about natural displacement ventilation,which were published in recent years at home and abroad, derived the key ones of them,sorted out the theoretical analysis of natural displacement ventilation process summarized by scholars in different countries,built up clear venation of the theoretical model,which could contribute to the relevant study in the future in a convenient and fast way.Moreover,according to the experimental conditions,built up relevant geometry model by numerical simulation software AIRPAK,and used it to investigate the temperature field and velocity field in the room.Obtained the temperature distributed characteristics and established following two study foundations for later stage:1) Demonstrated the similarity between the fine-bubble plume experiment model and the prototype of indoor natural displacement ventilation,coupled with the experiment data;2) According to the experiment data,analyzed the factors which had influences on indoor natural displacement ventilation.In addition,the study demonstrated the similarity between the fine-bubble plume experiment model and the prototype about the indoor natural displacement ventilation induced by a point source,and compared with the numerical simulation results,obtained the applicable range of the similarity,and conducted relevant analysis.Finally,two experimental plans were confirmed,one was fine-bubble plume model experiment,which was used to simulate and investigate the natural displacement ventilation process in practical building,then based upon the simplified experiment model,analyzed and compared the influencing relationship between the thermal stratification interface position and other factors,such as effective opening area,flow rate,buoyancy flux and so on;In order to check the accuracy and feasibility of the numerical method simulating the natural displacement ventilation process,another experiment is conducted by actually measuring temperature distribution in a practical natural displacement ventilated room,collected the experimental data and compared with the results of the numerical simulation.The experimental analysis showed that calculated data obtained by numerical simulating was in agreement with the experimental data,then sustained the numerical model and calculated method used in the study were applicable;The fine-bubble plume model could well simulate the natural displacement ventilation process in practical building;There were entrainment and de-entrainment phenomenon happened next to the thermal stratification interface,the entrainment occurs below the interface between the thermal stratification and the environmental air,and the de-entrainment occurs at the mixing part with the indoor air above the thermal stratification interface;When the buoyancy flux was steady,the thermal stratification height increased as the effect ventilated area become larger,while the ventilation flow rate increased as the thermal stratification height increased,when the intensity of the heat source kept constant, the ventilation flow rate increased with the enlargement of the effective ventilating area;When the buoyancy flux varied,the thermal stratification height decreased as the buoyancy flux increased,while the ventilation flow rate increased with the increasing of the buoyancy flux.The intensity of the heat source or ventilation flow rate could be controlled to keep a certain therimal stratification height.