Experimental Study On Thermal Effects Of Fine Particulate Deposition In Indoor

The sources of indoor fine particulate are complicated,fine particulate as a special source of pollution is profoundly changing our living environment.Fine particulate accompanied by respiratory system of the body enter into the human lung tissue,penetrate the alveoli and directly adsorbed on the surface of the strong carcinogenic,teratogenic,toxic and harmful substances through the body's blood circulation system to reach the body tissues and organs,thus affecting the heart,brain and other vital organs,may cause a series of disease,and even affect the incidence of lung cancer,so that have a great harm to human health;meanwhile it also brings negative influence to the art of cultural relics collection,precision instrument manufacturing,biomedicine and other aspects of sedimentation of fine particulate deposition.The behavior of fine particles in the interior to the surface of an object depends on the force conditions of the particles,which the effect of thermophoresis on fine particulate deposition is more greatly important.Therefore,the study on thermal effect of fine particulate deposition indoor is very important.In this paper,in view of the civil building interior is equipped with the radiator,or fitted the similar cases of high temperature heat source or low temperature cold source in industrial environment,there is a certain temperature gradient near the surface of the headed or cold,which will affect the motion characteristics of particles in the thermal boundary layer.Then the boundary layer thickness of externally sweeping across the horizontal wall with different wall temperature is analyzed.The thickness changing curves of the velocity boundary layer and thermal boundary layer under different wall temperature is obtained,along with x at different distance away from the front end of the surface.Large temperature gradient and velocity gradient are formed in the vicinity of the headed surface,the maximum thickness of the velocity boundary layer can reach 2.85 cm,and the maximum thickness of the thermal boundary layer can reach 3.14 cm,and the numerical simulation is carried out,So as to provide a theoretical basis for the test of the vertical hot wall in the thickness range of the thermal boundary layer and the size distribution of the particles;under the condition of different away from the surface at the front end of the distance x,different wall temperature and different particle diameter,the intensity of thermophoretic force,gravity,Saffman lift force and drag force are compared.In the range of particle size,the drag force occupies a dominant position,followed by the thermophoretic force and gravity,and the effect of Saffman lift force on the motion of fine particulate relatively small.This paper focuses on the experimental study on thermal effects of fine particulate deposition in indoor and distribution in temperature gradient field.The main work of the experimental study is as follows:First of all,in order to create a large certain temperature gradient near the wall,the size of 30cm×20cm horizontal hot wall is placed in indoor,which temperature can be adjusted within 0~350 ?,and a self-made thermoelectric refrigeration device provides a temperature of 1? around the same size level cold wall.The typical operating condition is selected,which the setting temperature of the hot wall is 100? and the cooling wall is 1?,the flow field in indoor under the influence of hot and cold wall is carried out testing for 13 minutes.It is concluded that the mean value of the flow velocity at the front end of the hot wall near 100? is 0.206 m/s.The existence of hot wall has a certain degree of disturbance to the flow field near the wall,and the higher the wall temperature,the more obvious thermals to lift near the wall.The large temperature and velocity gradient formed near the hot wall.Then,the nano silver particles with 20 to 500 nm as the labeled fine particulate are selected to research deposition regularity.Using aerosol generator to emit nano silver particles,and create a certain concentration of silver particles in the room,using field emission scanning electron microscope to observe the particle deposition in different temperature the level of heat and cold wall.At the same time(40 minutes)to select the same size of the field of view,the amount of dust under the field of view of the field of view and the size of the dust particle size.The obvious thermophoretic effect on fine particulate was observed,especially in the range of 50 to 400 nm,and the higher the temperature,the thermophoretic effect is more intense.In the end,the experimental study of the thermophoretic effect on the fine particulate near the vertical wall is carried out by emiting the sanitary cigarette particles.By using electric heating film as a stable heat source,the vertical wall and the heat source region formed by a certain temperature gradient at different temperatures are constructed.The particles near the region will escape from the hot surface movement,resulting in fine particles near the surface area of the vertical heat change number concentration is reduced and the particle size distribution.With the increase of temperature gradient in vertical,the particle size range of 20.77 to 213.10 nm incense burning cigarette smoke particulate number concentration the more obvious attenuation of the,and particle size range to 270.56 to 1093.64 nm particle number concentrations in the attenuation amount is relatively small.In the vertical plane,the number of sanitary cigarette smoke particulate matter was decreased,and the main contribution was from the decrease of particle number concentration in the range of particle size from 22.77 to 213.10 nm.This shows that the fine particulate in the range of 22.77 to 213.10 nm near the vertical wall are strongly affected by the action of the thermophoresis,which is more likely to drive the fine particulate in the particle size range away from the area near the heated surface.This paper draws the following conclusions: the heated wall has caused a certain extent influence on the particle motion and deposition within a certain area of the near wall.with the increase of wall temperature,the temperature gradient and the velocity gradient within the thermal boundary layer of the wall become larger,and then the thermophoretic effect has a decisive inpact on fine particulate deposition characteristics,thermophoresis deposition has become the major factor of nano and submicron particles near wall region,due to the increase of gravity,the larger particles are more likely deposition when compared to the nano and submicron fine particulate.