Research On Uniformity And Optimization Design Of Long Straight Pipe Air Supply System

In recent years,ventilation systems have been widely used in civil and industrial buildings.In civil buildings,the ventilation system is occupied to make the temperature,humidity,wind velocity,cleanliness and other indicators of the working area in the building to meet the comfort requirements of the occupants in the working area,so that the occupants could stay in a comfortable environment and thermal comfortability could be increased;While in industrial buildings,the ventilation system is mainly dedicated to reducing the concentration of pollutant gas and particulate matter and other polluting sources in the work area,ensuring that the staff can healthily stay in the work area for a long time and without being caused by pollution sources.As for other special occasions,such as hospital infectious disease areas,high precision laboratories,large computing stations,etc.,The indicators in the entire building are of importance to meet the requirements of personnel health and working process.For the special nature of the work,it is not only necessary to ensure that the local areas to meet the requirements,but to ensure that the entire area in the building meets the requirements,that puts forward certain challenges for the reasonable layout and uniformity of the ventilation system.In practical engineering applications,many ventilation systems will have uneven distribution problems when they work.This is particularly serious at the beginning and end of the ventilation system.The object of discussion in this paper is the long straight pipe air supply system.This paper uses the CFD calculation software ANSYS Fluent to simulate the air supply system,and analyzes the pressure and velocity distribution in the uniform cross-section air supply pipe,and studies the resistance characteristics of the ventilation duct.The uniformity of the flow field of the long straight duct air supply system is studied,and a reasonable static pressure distribution is determined according to the characteristics of the air supply resistance,so as to ensure that the air supply at the outlet is consistent.The characteristic parameters such as the number of outlets n and the distance between outlets △L that affect the uniformity of the uniform cross-section duct are analyzed;the deflection angle of each outlet of the variable cross-section duct and the uniformity of the air output volume are studied;in order to ensure that each outlet to reach the ideal flow requirement,the method of adding a short duct at the air outlet is adopted to obtain an ideal deflection angle distribution of the cross section at the air outlet and improve the uniformity of the long straight pipe air supply system.Research shows:(1)The number of outlets,the distance between outlets and other characteristic parameters have an impact on the uniformity of the uniform cross-section air duct.The number of outlets n has a greater influence on the uniformity of the air distribution.The larges the number of outlets is,the more uniform the overall air outlet is.(2)The variable cross-section air pipe can better adjust the pressure and velocity distribution in the pipe,so that the parameters at each air outlet tend to be consistent,and the uniformity is improved.(3)Adding a short duct can adjust the average deflection angle of the air outlet section,and change the length of the short tube,the length of the upper and lower openings,the inclination angle of the tube wall and other parameters,which can effectively improve the deflection angle.(4)Combining variable cross-section ducts with suitable short ducts can not only make the deflection angle of each outlet to meet the ideal requirements,but also meet the uniformity requirements of the airflow parameters of each outlet.Numerical simulation shows that the variable cross-section duct can better adjust the pressure in the duct and the air flow rate of each outlet.Within the scope of the study,when a uniform crosssection duct is combined with a short vertical duct with an extension of 15 cm,or a variable cross-section duct is combined with a short vertical duct with an extension of 20 cm,the overall deflection angle of the air duct increases greatly.The requirements of uniform vertical outflow can be meet.In the research scope of this article,when the inclined short pipe with an inclination angle of close to 45° is used,the overall outflow of the air duct can meet the requirements of uniformly inclined outflow and consistent inclination angle range.