Research On Evaluation And Filtration Techniques For Size-resolved Cooking Fume Particles

Cooking fumes cause severe particulate matter(PM)pollution,which is increasingly threatening outdoor and indoor air quality and human health.An accurate and comprehensive evaluation of the source characteristics of cooking fume particles and high-efficient filtration technology are very important for the control of cooking pollutants,including the measurement and evaluation method of the deposited particles,and the coalescence filtration mechanism of liquid particles on the fiber medium,and the numerical and experimental development research of novel cylindrical microelectrostatic precipitator.Finally,according to the concept of filtration mechanism for size-resolved particles,a new multi-step cooking fume filtration system was developed.Main findings and innovation points were detailed below:(1)In this research,combining fluorescence tracer,passive sampling,microscopic vision,and droplet 3D reconstruction technologies,the fluorescence 3D microscopic passive measurement method(3D-FMP)was established.Through this method,accurate measurement of deposited particles(1-1000 μm)was achieved,which filled the research gap of the human body and kitchen surface contamination caused by splashing cooking oil droplets.The 3D-FMP method determined the emission characteristics and spatial decay pattern of deposited particles,as well as the effect of the exhaust hood airflow on deposited particles,the deposited particles on the countertop have a bimodal distribution and predominately in the 5-50 μm size range,mainly distributed in the range of 0.75 m around the cooking fume source and attenuated exponentially.The quantified size-resolved deposited particles provided a fundamental understanding of the deposition of cooking-emitted oil droplets to optimize the airflow organization at the front end of the cooking fume filtration system and improved the capture performance.(2)The fabric characteristic,filtration performance,quality factor,and postwashing reusability of three traditional nonwoven filter materials and a new threedimensional knitted filter material were studied.Based on the deposition mechanism of solid and liquid particles,the differences between filters of different grades and filter materials were also systematically compared and analyzed,and a rapid prediction model for resistance growth and lifetime was proposed.The mechanism of the effect of the drainage channels in parallel fiber structure on the coalescence filtration performance was revealed,as well as the higher quality factor,drainage rate,and postwashing reusability of the three-dimensional knitted filter material used in cooking fume filtration,and it was recommended as an ideal pre-filter.The new threedimensional knitted filter material solved the defect that the traditional non-woven filter materials were easy to block and non-renewable.(3)In this study,a new type of cylindrical micro-electrostatic precipitator was developed,which has high filtration efficiency of fine particles and low resistance.The dust collecting area and the dust holding capacity of the electrostatic precipitator were increased compared with traditional electrostatic precipitators,and the micro-channel section area was designed to increase with the direction of airflow,which improved the filtering efficiency of fine particles.Through the COMSOL multiphysics model numerical simulation,the Brinkman porous media model was proposed to simulate and predict the performance of the cylindrical micro-electrostatic precipitator.The singlechannel and overall structure parameters of the micro-electrostatic precipitator under the cylindrical structure and was verified by the prototype of the cylindrical microelectrostatic precipitator.(4)A new type of multi-stage cooking fume purification system was developed that combines the cylindrical micro-electrostatic precipitator and the three-dimensional filter material,which has the advantages of high efficiency of fine particles,low energy consumption,high space utilization,long service life,and can be cleaned and reused.Compared with the commercially available electrostatic precipitator,the filtration efficiency of particles with a particle size of 0.3-0.5 μm was increased by 30.4%.The three-dimensional woven filter material can be used as a pre-filter to prolong the service life of the cylindrical micro-electrostatic precipitator by 2.03 times.The cooking fume purification efficiency was as high as 98.4%,which was higher than the current national standard standards that the efficiency of the cooking fume purification system was greater than 95.0%.