Experimental Study Of Thermal Plume In Salt Water Model Based On Theory Of Attenuation Of Light

In recent years,people pay more and more attention to the technology of natural ventilation,which uses heat pressure or wind pressure to introduce fresh air into the room,improve the indoor air quality,and realize the passive energy saving of the building.In order to study the natural ventilation and determine the density distribution in the building space by salt water experiment,according to the attenuation principle of light passing through brine solution and the contrast between density of solution in the flow field and intensity of light,a method for determining the density distribution characteristics in the flow field by image gray level is proposed.The displacement flows and mixing flows generated by thermal pressure are simulated by this experimental method with the aid of the entrainment theory under the condition of single point source plume.In addition,considering the influence of virtual source location of plume,the dynamic behavior of stratified interface between fresh water and buoyant fluid in confined space is introduced.The entrainment coefficient of pure plume n is determined by salt water experiment,and verified by displacement flow experiment under the condition of internal heat source.The entrainment coefficient of pure jet is also tested.Through the experimental study,the following conclusions are obtained:(1)For displacement flow without heat source,for a given geometric size and initial buoyancy flux,the emptying time is determined by the effective area of the inlet and outlet A*,which is mainly determined by the smaller opening area.The experimental results show that for the displacement flow under a single thermal plume increases the thermal stratification increases,and the density in the thermal stratification region decreases with the effective area increases.(2)The mixed flowing experiment was performed under the condition of fixed thermal plume.It was determined that the flow correction coefficient ? is equal to 2.21,which is independent of the size of the opening and the density of the brine,and represents the ratio of the fixed buoyancy flux to the flow through the opening under the condition of variable buoyancy flux.The experimental results show that it is an effective method to determine the density distribution characteristics of the flow field by image gray.(3)Because the entertainment coefficient both affect the source parameter ? and the virtual source position z,the relationship trend between the source parameter ? and ? is obtained according to assuming the entertainment coefficient to combine with the experimental results.The interpolation method was used to determine the pure plume entrainment coefficient of 0.09262.The entrainment coefficient was verified by the displacement flow experiment under a point source.The standard deviation between the experimental point of the layered interface and the theoretical curve corresponding to the entrainment coefficient value of 0.09262 was 0.0174.(4)The entrainment coefficient of a turbulent jet was also calculated based on the stratified interface behavior in a confined space.The experimental results supported the speculation that the entrainment coefficient of the pure jet should be 0.057.In addition,the entrainment coefficient of plume and jet are also calculated by the relationship between the width-radius of the buoyant fluid and the distance from the source.The experimental data of the entrainment coefficient ? plotted against the parameter ? in available literature were compared with the values estimated using semi-empirical equations with two asymptotic values suggested in this paper.