Numerical Simulation And Structural Optimization Of Heat Pipe Agitated Vessel

In the modern chemical industry production, most chemical reactions whichoccur in the agitated reactor with the heat exchange components are exothermicreaction. The majority of the reaction media are liquid phases, such as nitration,oxidation, esterification, diazotization, amidation. All of them are highly exothermicreaction. The amount of heat release can reach40kW·m-3, some can reach up to235kW·m-3, so the traditional heat exchange components aren’t able to satisfy the heatdissipation requirement of the contemporary highly exothermic reaction in theagitated vessel. This thesis innovatively adopts elliptical flat pipes to replace therectangle baffles in the agitated vessel, and set the elliptical flat pipes as heat pipes, soas to realize the high effective heat transmission via the high heat flux of the heatpipes.Based on the amide reaction in the production of the saccharin sodium,according to the national standards of the stirred tank design, the new structural heatpipe agitated vessel is designed. Firstly, the stirred tank model is simplified and thesimplified model is built in the pre-processing software Gambit of the CFD, then theUDF(User Defined Function) of the exothermic source of the stirred tank is wrote andimported into the Fluent to be complied and calculated. Through analyzing themixing uniformity time and temperature variation of the monitor, the result is got thatthe optimal grid number of the model is2million. Further, through comparing thesimulation results of the flow field, stirred power with the experimental results, thereliability of the numerical simulation is proved.With a reasonable change of the operating and structural parameters of theagitated vessel, the weightiness about the effect of the objective factors on the overallperformance of the agitated reaction vessel is got via numerical orthogonalexperiments. The results show that the rotor speed has a considerably greater impacton the performance parameters of the stirred tank than the other three structure parameters, in terms of the mixing energy per unit volume, the installing angle of thestirrer> the distance between the heat pipe center line and the reactor wall> thedistance between the lower blade and the reactor bottom; in terms of the optimaltemperature duration time, the installing angle of the stirrer> the distance betweenthe heat pipe center line and the reactor wall> the distance between the lower bladeand the reactor bottom; in terms of the mixing uniformity time, the distance betweenthe heat pipe center line and the reactor wall> the distance between the lower bladeand the reactor bottom> the installing angle of the stirrer.Given that the weightiness the three performance indexes hold in the overallperformance of stirred reaction vessel, simultaneously based on the weightiness aboutthe effect of the four objective factors on the overall performance, the optimal levelcombination of the four objective factors is got. The results show that the selectedrotor speed is300rpm, the selected distance between the heat pipe center line and thereactor wall is110mm, the selected distance between the lower blade and the reactorbottom is340mm, and the selected installing angle of the stirrer is0o.By detailedly analyzing the effect of the single factor on the overall performanceof the stirred reaction vessel, the results are got as follows. As the rotation speed ofthe agitator is240rpm or300rpm, the turbulence of the fluid around the heat pipes isintense, many swirls are formed, the die turbulence zone is small, the mixinguniformity time is short, and the optimal temperature duration time is long. As thedistance between the heat pipe center line and the reactor wall is85mm, many smallswirls are formed around the heat pipes, the range of the fluid’s turbulence is wide,the mixing of the fluid is intensified, but the effect of the change of the distancebetween the heat pipe center line and the reactor wall on the three monitors is little.As the distance between the lower blade and the reactor bottom is340mm, threecirculating eddies are respectively formed on both sides of the stirrer, the turbulenceof the fluid is violent, the heat transfer effect is apparent. As the distance between thelower blade and the reactor bottom is200mm or270mm, the final equilibriumconcentration of the monitor2is greater than it as the distance between the lowerblade and the reactor bottom is340mm or400mm. As the installing angle of the stirrer is0°, the mixing uniformity time is reduced, the optimal temperature durationtime is increased, and the temperature distribution of the fluid is uniform.