Study On Numerical Simulation And Optimization Design Of Pipeline Mixer Based On Air And Oxygen Mixing

As a kind of important gas air mixing tool,the pipeline mixer has the advantages of strong mixing,reliable performance,rapid mass transfer and heat transfer,continuous process and so on.The content of this paper is based on a commissioned research project,which requires the design of the air-oxygen pipeline mixer within the design parameters so that the oxygen uniformity meets the requirements at the shortest mixing length.The trajectory of the gas jet and the variation of oxygen concentration in the jet axis were studied by theoretical analysis.On the basis of the design formula of the straight tube mixer by Fitzgerald,O,Leary and so on,taking into account the range of the parameters of gas mixing in this project,a new design formula of the straight pipe mixer,d/D=5.4(q/Q) is proposed in this paper.Based on the design formula,(1)The paper designs a single-hole straight pipe mixer is designed;(2)The paper designs a two-hole straight pipe mixer and a four-hole straight pipe mixer under the premise that the porous jet is linear superposition of multiple single hole jet;(3)Based on the analysis of the flow of the elbow,the paper puts forward the mixer with the elbow after the straight pipe,and designs the single-hole elbow mixer,the double-hole elbow mixer and the four-hole elbow mixer.In this paper,three types of straight pipe plumbers were numerically simulated,and the results indicated that,(1)While the range of x/D is between 2～10,the axis line of the oxygen jet is tangent to the axis of the main pipe,it means that the point with the largest concentration is on the axis line of the pipe and this conforms to the geometric center Jetting criterion,which verifies that the design formula of the pipeline mixer proposed in this paper is correct;(2)The RMS(root mean square)value of oxygen concentration in the cross section of the main pipe shows that the RMS value of the single-hole straight pipe mixer is the maximum,the double-hole straight pipe mixer is the second and the four-hole straight pipe mixer is the smallest.The results mean that the more the hole number is,the smaller the RMS value is.So the recommended choice is the four-hole straight pipe mixer,the structural parameters:aperture 2.5mm,evenly arranged along the circumference.Numerical simulation of air-oxygen mixing in four types of elbow pipe mixers was done in this paper.The RMS value of the oxygen concentration in the cross section of the main pipe shows that,the RMS value of the single-hole elbow pipe mixer is the maximum,the double-hole elbow pipe mixer is the second and the four-hole elbow pipe mixer is the smallest.Therefore,the recommended choice is the two-hole and the four-hole elbow pipe mixer.The structural parameters of the double-hole elbow mixer are that:aperture 5.0mm,respectively arranged on the inside and outside of the elbow.The structural parameters of the double-hole elbow pipe mixer are that:aperture 2.5mm,evenly arranged along the circumference.The mixing effect of the straight pipe mixer and the elbow mixer was compared.In the cross section when x/D is 10,the RMS values of oxygen concentration in the double-hole straight pipe mixer and the double-hole elbow pipe mixer are respectively1.21%and 0.48%.The RMS values of oxygen concentration in the four-hole straight pipe mixer and the four-hole elbow pipe mixer are respectively 0.34%and 0.32%.The results mean that the mixing effect of the elbow pipe mixer is bet ter than that of the straight pipe mixer.The numerical simulation of the mixing effect of four-hole straight pipe mixer and four-hole elbow mixer is carried out under the off-design condition when the oxygen flow rate of each hole is 0.7m~3/h and 1.1m~3/s.In the cross section when x/D is 10,the RMS values of oxygen concentration in the four-hole straight pipe miser increases respectively by 0.04%and 0.13%,the RMS values of oxygen concentration in the four-hole elbow pipe miser increases respectively by 0.01%and 0.03%.The result shows that the pipe mixer designed has strong adaptability to the variation of jet flow.