Research On Heat Flow Scale-resolving Simulation And Heat Transfer Enhancement Of Biomimetic Structure Of Plate-fin Heat Exchanger

To solve the heat transfer enhancement and drag reduction problems of heat exchangers most widely used in the industry,under the project support of “Multifunctional Coupling Design and Key Manufacture Technology of Biomimetic Superhydrophobic/Super-oleophobic Blade” from the Science and Technology Department of Jilin Province,this paper select the serrated plate-fin heat exchanger as the research object,which has the highest transfer efficiency and the smallest volume.Study the flow mechanism of heat transfer process and the method to improve the heat transfer performance.This paper uses Computational Fluid Dynamics(CFD)numerical simulation method,to analyze the complex heat flow field of heat transfer process in the exchanger.Then analyze the mechanism of heat transfer.Use bionics to improve heat exchanger fins,which provides a new solution to optimize the heat exchanger performance.The main work includes:1.Scale-Resolving Simulation methodThis paper select DDES,SBES,and DLES for comparative analysis.In order to reduce the workload,use classic post-step flow example to evaluate the scale analysis method,compare advantages and disadvantages of three models,such as calculation time,flow structure and so on.In the wall friction coefficient graph,SBES model fitting the test curve better.In the velocity and the particle trace graph,SBES model describe the reflow zone more complete.SBES and DLES models are more detailed to depict the turbulence kinetic energy.SBES model displays the vortex structure more clearly and orderly.The SBES model can describe the physical flow field more accurately with the shortest time.Therefore,this paper select SBES turbulence model to calculate the thermal flow field of the heat exchanger.2.Numerical simulation of serrated plate-fin heat exchangers with water vapor and air.Select the 1/8-13.95 type serrated plate-fin heat exchanger,which use water vapor and air as the work medium,to simulate the heat transfer process.In the Computational Fluid Dynamics(CFD),firstly use the same SST k-? model in the experiment,select the boundary conditions as PISO algorithm,second-order upwind spatial discrete format,incompressible fluid and non-slip wall.And draw the high-quality hexahedral structure grid in computational domain.Compare the heat transfer performance parameters from the simulation with the test data,found that the deviation of heat transfer factor j is 5.10% and the deviation of friction factor f is 7.34%,Proved that it is reliable to use numerical simulation method to predict heat exchanger performance.Secondly choose SBES turbulence model,use the same grid and physical conditions to scale analyze the heat exchangers.Compare the CFD results with the test data,found that the heat transfer factor j deviation is 6.2979%,the friction factor f deviation is 1.3196% while the Reynolds number Re=800.From the fluid flow structure cloud graph of heat transfer process,SBES model can describe the flow field more detailed.It shows that the scale resolving SBES model is better to calculate heat transmit.3.Numerical simulation of serrated plate-fin heat exchanger with oil-water mediumTo broaden the application range,change working medium with No.8 hydraulic transmission oil at 125° C.and water at 60° C.Select SBES turbulence model for calculation.Use the same 4.36 million hexahedral meshes,boundary conditions to simulate and analyze the internal flow field of heat exchanger.When Reynolds number Re = 1000,the average velocity of z = 0.015 m slice is 3.8149 m/s,the average turbulent kinetic energy is 0.2952 m2/s2,and the average temperature at the outlet of the hot channel is 114.15°C.4.Study on heat transfer of serrated plate-fin heat exchanger based on shark-like bionic structureUsing bionics ideas,change the geometry of model with shark splitting structure,to improve the performance of serrated plate-fin heat exchanger.Calculate with the bionic model and compare the optimized result with original data at different Reynolds number,ie,the different inlet velocity.After calculating the opening size of 1.06 mm and the opening angle of 25°,the average velocity is 3.8521m/s,that increases 9.75% at Re=1000,z=0.015 m slice.The average turbulent energy is 0.3411 m2/s2,which increases 15.55%.The average temperature of hot channer outlet is 113.53°C,which decreases 0.62°C.It is proved that the open structure of optimized model can enhance turbulence degree and improve heat transfer performance of heat exchanger.