Study On Flow And Heat Transfer Performance Of Nanofluid In Heat Exchanger

Energy plays an important role in the progress of society,and providing more efficient energy-saving management methods is particularly important for the development of energy.The application of nanofluids in heat exchangers has certain engineering significance for solving the heat transfer problem of high heat flux.In this paper,the convective heat transfer of nanofluids in heat exchangers is taken as the object,and the influence of nanofluid parameters and corrugated fin structure on the flow and heat transfer performance of heat exchangers is studied.and finally the fluid flow experiment of corrugated fin channel is carried out.The main research contents and conclusions are as follows:（1）Establishing an accurate numerical calculation model is very important for studying the thermal-hydraulic properties of nanofluids.First,single homogeneous model was used to numerically calculate the flow and heat transfer characteristics of nanofluids in heat exchanger with quatrefoil perforated plate.The study found that the single homogeneous model ignored the flow of nanoparticles in the fluid.The two-phase Mixture model takes into account the slip speed between the base fluid and the nanoparticles.In order to analyze the flow characteristics of the nanoparticles in the fluid and explore the mechanism of enhanced heat transfer by the nanofluids,On the basis of the Mixture model,the Brownian motion and thermophoretic diffusion of the nanoparticles are used as the slip velocity mechanism between the two phases to optimize the Mixture model.Compared with the experiment in the literature,it is found that the error of the entrance section is larger,and the other results are better.Coincide.Studies have found that Brownian force and thermophoretic force can enhance the convective heat transfer between nanoparticles and base fluid.（2）Use the B-Mixture model to numerically calculate the flow and heat transfer characteristics of the nanofluid in the corrugated fin channel,analyze Re（100-600）,volume fraction（0-2%）,particle diameter（20-80nm）,The impact of particle types on the heat transfer performance of the channel.When the particle diameter is 50nm,the heat transfer coefficient and pressure drop will increase with the increase of Re and volume fraction.The comprehensive performance is the best when the volume fraction of Re=600 is 2%.When Re and volume fraction remain unchanged,PEC increases with the decrease of particle diameter,and the comprehensive performance is best when the particle diameter is 20nm and the volume fraction is 2%.Among the three types of nanofluids,compared with Zn O and Cu O,Al₂O₃-water nanofluid has the highest heat transfer coefficient and the smallest pressure drop,and Al₂O₃-water nanofluid has the best comprehensive performance.（3）The distribution of nanoparticles is affected by the volume fraction,particle size,and type of nanofluid.Smaller particle sizes are more affected by the Brownian force,which will make the nanoparticles diffuse more uniformly.When the particle size is the same,it is greatly affected by the thermophoretic force,and the thermophoretic force is affected by the volume fraction and temperature gradient.The distribution of nanofluids varies greatly on the wall,and the decrease in concentration will result in a decrease in viscosity,and the decrease in barriers at the wall will increase the flow rate,thereby enhancing the heat transfer capacity at the wall.（4）The influence of the fin structure on the flow and heat transfer of the corrugated channel.In the case of constant volume fraction and Re,The comprehensive performance increases with the increase of wavelength s,wave amplitude a,and fin height b,and increases with the decrease of fin width w and phase shiftθ.When the volume fraction is 2% and Re=600,the wavelength s=15mm increases 3.4%and 10.1%compared with the comprehensive performance of 12mm and 9mm.The amplitude of a=2mm is 45%and 10.4%higher than the comprehensive performance of the amplitude of 0.75mm and 1.5mm.The comprehensive performance of corrugated fin b=8mm is 27.5%and 16.6%higher than the height of 6mm and 4mm.The fin width w=2mm is 4.9%and 18.4%higher than the comprehensive performance of 3mm and 4mm.The phase shiftθ=0°is3.86%and 22.7%higher than the comprehensive performance ofθ=30°andθ=60°.Although the change of angleθwill increase the heat transfer capacity of the fin channel,the pressure loss is greater than the enhancement of heat transfer.（5）The laser Doppler velocity measurement system was used to measure the velocity at different positions in the corrugated fin channel.The comparative analysis found that the numerical simulation results are in good agreement with the experimental measurement data,which is within the allowable error range of the project,which proves The accuracy of the numerical calculation model.