CFD Simulation Of Flow Boiling In The Shell Side Of Rod Baffle Multi-tubular Reactor

The multi-tubular fixed bed reactor possesses good heat removal capability.It is widely used in the chemical industry.The conventional reactor usually uses plate baffles to enhance turbulence,improve heat transfer process and support reaction tube bundle,but the plate baffles lead to high pressure drop and vibration of tube bundles.In light of these problems,rod baffle is adopted instead of plate baffle.However,there are flow dead zones accompanied by heat transfer deterioration in the central region of the reactor with rod baffles,because rod baffle lacks the radial forced baffled flow effect on fluid.This is the drawback of rod baffle.In the paper fluid flow and heat transfer process in the shell side of the reactor with rod baffle is researched by CFD method to explore the ways to improve the radial distribution.Pressurized boiling water is an effect heat transfer medium,which can improve the uniformity of radial temperature distribution.However,the flow boiling process in the shell side of the reactor is very complicated,and the flow and heat transfer regularities are still very unclear.In the paper the mathematic model of the flow boiling is built.Euler-Euler model,combining with interphase momentum,heat and mass transfer model and RPI wall boiling model is applied to simulating the process.The relative experimental data is used as benchmark to validate the reliability of the model.The comparison results of the unit model with no rod baffle,rod baffle indicate that rod baffle can force bubbles to move to the central region of flow channel and low the reaction tube temperature.By analyzing the flow field,reason why the rod baffle improves the distribution of void fraction is determined.The effect of rod baffle is listed as follows:(1)Rod baffle reduces the area of flow cross section and increases the axial flow velocity;(2)Rod baffle can promote the lateral flow;(3)In the back of rod baffle there is swirl flow that can generate an extra centrifugal force.The influence of rod baffle axial space on the distribution of void fraction,wall temperature of reaction tubes is investigated,and the optimized rod baffle axial space is 80~120mm.The 1/4 of the whole model of the reactor is used to investigate preliminarily the radial distribution of liquid temperature in the flow boiling process.It is found that radial temperature difference of liquid is about 7K which cannot meet the engineering need.In light of the issue,the effect of incident channel,length and the amount of incident channel on the radial distribution of liquid temperature is investigated in the paper.The optimal structure of the reactor is acquired,and the incident channel 3#,4# and 5# are set up.Finally,under different operating conditions the liquid temperature distribution in the reactor with optimal structure is studied.It is found that inlet velocity and wall heat flux affect the liquid temperature distribution.In the paper the flow boiling process in the shell side of the reactor with rod baffle is simulated by CFD method,and the temperature and flow field is acquired.The simulation results can provide guidance for designing multi-tubular reactor with rod baffle.