Transportation And Environmental Evaluation Of Gaseous Pollutants From Multiport Sources In Long And Narrow Industrial Buildings

With the rapid development of industrialization and urbanization in China,the building scale,the number as well as the construction speed of industrial buildings have been in the top position all over the world.The pollution sources in industrial buildings are generally characterized by high intensity and high toxicity.Thus,it is of vital important to control the pollutants emitted from the production process,so as to sustain the indoor environment quality and guarantee the worker health.As in the case of one production process,there are not only several pollution sources in a long and narrow industrial building,and each of them can emit various gaseous pollutants,but also the sources are not started synchronously.For these kinds of industrial plants,the air distribution and pollutant distribution still remain unclear by now.Therefore,in present research,based on the mechanism of fluid mechanics and thermodynamics,several issues were discussed in sequence by combination of theoretical analysis,experimental investigation and numerical simulation,including the flow field characteristics,pollutants distribution from multiport diffusers,transportation property of multi-component mixture solution and environment assessment of industrial plant.The research results can be applied to the ventilation technology of long and narrow industrial buildings with multiport sources.Firstly,the water-tank model experiment platform was established for the large-scale building based on principle of similarity in the fluid mechanics.Two flow patterns for single gaseous pollutant of industrial plant were revealed,namely,“Back-mixing”pattern and“One-way”pattern.And the difference between patterns activated by buoyancy force at both emission stage and attenuation stage were expounded from the mechanism level.Then,the dimensional analysis was conducted to determine the critical condition,Fr_l,to judge whether the“One-way”flow pattern reaches the top-level“Smooth”stage.Finally,based on mechanism analysis,it was proposed that in the long and narrow industrial buildings,the potential flow pattern is“One-way”to“Back-mixing”pattern.And the judging reference for“One-way”to“Back-mixing”pattern is b u_y’=037u_ymax’>H/2.Then,it was expounded from the mechanism perspective that when the pollutants were released asynchronously,there are differences among flow properties of gaseous pollutants in industrial plant with different flow patterns.In plant with“Back-mixing”flow pattern,the pollutants generated by former source could change the indoor environment flow field,which made the pollutants generated by later sources flowed into the indoor environment with density stratification.The highest level（z_m）that the pollutants from later source could reach depended on vertical density gradient d（ρ_ag）/dz and initial froude number Fr₀ of later source.When z_m<H,the pollutants from former source could inhibit that from the later source.After that,aimed at the transportation property of multi-component mixture solution from the same source,the deviationΔF_b caused by simplifying the multi-component mixture to binary mixture consisting of air and single gaseous pollutant under full-scale condition were obtained,including the according influencing factors.In addition,based on the mass transfer mechanism under thermodynamic conservation and its influencing factors,the simplifying condition of multi-component mixture solution during mass transportation was proposed and are as follows:（i）fluid parameters of Re～Ο（10³）and Ma<0.3;（ii）physical parameters of Kn<0.01 and T_b<T<0.3θ_v;（iii）before and after the simplification,R₁<0.01（the ratio ofΔF_b and inertia force less than 0.01）and R₂<0.01（the ratio ofΔF_b and buoyancy force less than0.01）.At last,by the method of confidence interval,the exact method to calculate the area of gaseous pollutant covered was put forward.The standardized concentration ratio（C_t）of target zone was proposed,which could evaluate the influence of gaseous pollutants on indoor environment in industrial plant.Some model experiments had been employed herer to proves the applicability and effectiveness of the index.And the results of the mumarical simulation cases shows that,before the G/L_P reached 1,increasing the ventilation quantity generated by“Back-mixing”pattern could decrease the covering area of gaseous pollutants greatly,so as to improve the indoor air quality.After the G/L_Preached 1,the abovementioned decreasing effect caused by ventilation quantity weakened quickly.