Study On The Effect Of Various Return Air Modes On The Particle Concentration Distribution By The Orifice Plate Air Supply In The Clean Room

Clean room is a confined space where indoor air cleanliness,temperature,humidity,pressure,noise and other parameters are controlled as needed.As the quality and precision of pharmaceuticals,electronic products,etc.are directly affected by the ultra-fine particles in the clean production space,with the increasing requirements of product quality and precision,indoor particle concentration distribution control is particularly important.Based on the above background and drawing on a large number of domestic and international research results,numerical simulation and experimental research methods were adopted,and the high-precision constant temperature and humidity test bench was converted into a clean room test bench.The effect of the combination of the air supply from the orifice plate at the top of the clean room with the return air from the middle four sides of the wall,the return air from the floor and the return air from the two sides of the wall on the particle concentration distribution in the clean room was investigated.The particle concentration distribution characteristics of the clean room were analyzed under the coupling conditions of 16 times/h,20 times/h,30times/h and 40 times/h for different air return methods and air exchange times respectively.Also in the study,the number of return air openings of three return air methods,namely,four-side return air in the middle of the wall,floor return air and return air under both sides of the wall,were changed,and the effect of the number of return air openings on the indoor particle concentration distribution was compared and analyzed.The following conclusions were obtained:（1）The average value of indoor particle concentration was negatively correlated with the number of air changes when the return air method was the four side return air in the middle of the wall,the floor return air and return air under the wall on both sides.The average value of indoor particle concentration decreased gradually with the increase of air changes.Therefore,the maximum value of the average indoor particle concentration was obtained at the air change frequency of 16 times/h,and the minimum value of the average indoor particle concentration was obtained at the air change frequency of 40 times/h.（2）When keeping the ventilation times unchanged,the average value of the particle concentration in the return air under the walls on both sides was the largest,and the average value of the particle concentration in the return air on the four sides in the middle of the wall was the smallest.（3）The air exchange times and air supply velocity have great influence on the indoor particulate matter non-uniformity coefficient,and the K_cvariation range of the return air on the four sides in the middle of the wall was the largest,the K_cvariation range of the return air under both sides of the wall was the smallest.Under the same air exchange times,the indoor particle concentration non-uniformity coefficient of the return air on the four sides of the middle of the wall wall was the largest,the indoor particle concentration non-uniformity coefficient of the return air under both sides of the wall was the smallest.Under the same return air mode,the greater the number of air exchange,the greater the indoor particle concentration non-uniformity coefficient,and there was a positive correlation between them..（4）Keeping the number of air changes of the three air return methods constant at16 times/h,the average indoor particle concentration of different air outlets was negatively correlated with the number of air outlets.As the number of air outlets decreased,the average value of indoor particle concentration gradually increased.Therefore,the maximum value of the average indoor particle concentration was obtained when the number of air outlets was 1,and the minimum value of the average indoor particle concentration was obtained when the number of air outlets was 4.（5）Keeping the number of air changes of the three return air methods constant at16 times/h,the inhomogeneity coefficient K_c of indoor particle concentration was basically positively correlated with the number of air outlets.As the number of air outlets decreased,the particle concentration inhomogeneity coefficient K_c gradually decreased.When the inhomogeneity decreased,the indoor particle concentration distribution was more uniform.（6）For the clean room with orifice plate air supply method,in the scope of this research,the average value of particle concentration in the clean room was the lowest under the condition that the air return method was four sides of the middle of the wall,the number of air changes was 40 times/h and the number of air returns is 4;under the condition that the air return method was floor air return,the number of air changes was 16 times/h and the number of air returns was 1,the concentration of particles in the clean room had the lowest uneven coefficient and the best uniformity.