Design Of Magnetic Drive And Research On Flow Behavior Of Internal Cooling Medium

Rotational equipment for chemical applications in highly toxic and flammable conditions,such as the pump of hydrogen sulfide removal from natural gas,stirring tank reactor for hydrogenation of nitrobenzene,need to be equipped with safe and reliable sealing devices.In principle,the traditional mechanical seal cannot achieve zero leakage.The magnetic drive relies on the magnetic field between the inner and outer magnetic rings to transmit torque.There is a static isolation sleeve between the inner and outer magnetic rings.It is a device that converts dynamic seals into static seals without mechanical contact,having the advantage of zero leakage.But there are also problems such as eddy current heat leading to power loss and high temperature magnetic material demagnetization.In view of the above problems,this thesis firstly carried out the design and calculation of the magnetic drive seal,and then carried out the research on the cooling medium flow in the magnetic drive,in order to realize the optimization of the cooling medium flow for the enhancement of heat transfer.The main research contents of this work are as follows:(1)In order to meet the requirement of industrial tasks,it is usually using empirical formulas to design the inner and outer magnetic rings and sleeve sizes,to match the motor.Taking the design of the magnetic drive matching a 75 k W motor as an example,this thesis not only uses the Gaussian formula and empirical formula commonly used in the industry to successfully calculate the size of the magnetic sealing,matching the data of 75 k W motor,but also through the method of hierarchical serialization for the design optimization by using MATLAB combined with the empirical formula,which makes the size more refined and the driving efficiency higher.(2)Previous studies have shown that about 10 to 20% of the energy of the magnetic drive is converted into eddy current heat.For example,the magnetic drive matched with a 75 k W motor will have nearly 7.5 to 15 k W of power converted into heat.The magnetic drive is generally small in size,and how to strengthen the flow and heat transfer of the cooling medium is very important.Generally,the reactant flow is between the inner magnetic ring and the isolation sleeve,so the flow and heat transfer of the cooling medium mainly exist in the area enclosed by the outer magnetic ring,the isolation sleeve and the outer casing(this area is defined as "outer cavity").Based on the VOF multiphase flow model and the standard k-? turbulent flow model,the simulation of the cooling medium flow in the outer cavity of the magnetic drive was carried out by means of computational fluid dynamics(CFD).The results show that there is a "liquid ring" in the gap between the outer magnetic ring and the sleeve(that is,when the outer magnetic ring rotates,there is a steady-state non-ruptured liquid ring in the gap).In addition,with the increase of the rotational speed between the outer magnetic ring and the outer casing,the phenomenon that the cooling medium forms a vortex becomes more and more obvious.The above two phenomena are the source of the poor heat transfer that plagues the magnetic drive.(3)Based on the understanding of the above simulation results,the structure optimization of the magnetic drive is further carried out to realize the modulation of the cooling medium flow.The main methods are:(a)opening the outer magnetic ring component,the "liquid ring" phenomenon can weaken.For a good improvement,radial openings in the tangential direction are more effective than axial openings.Comparing different opening structures and the number of openings,in the magnetic drive matched with the75 k W motor,the best effect is to open ten radial holes of 12 mm in the 45°tangential direction;(b)between the outer magnetic ring and the casing,adding baffles in different positions to break the vortex.The research shows that the size of the vertical baffle was 390 mm × 15 mm × 20 mm,and the size of the bottom baffle was 60 mm × 50 mm × 20 mm,which can achieve better vortex breaking effect.