Research On The Effect Of Acoustic Waves On The Flow Field And Convective Heat Transfer In The Heat Exchanger Tube Array In The Furnace

In recent years,"carbon peaking and carbon neutral" has been consistently advocated,the dual carbon policy leading to essentially zero carbon emissions.To help achieve the dual carbon goal,acoustic wave technology is used as a physical method in a wide range of industries,at the same time,acoustic ash removal,acoustic temperature measurement and acoustic combustion have been applied to power station boilers.This paper focuses on the influence of acoustic wave characteristics on the convective heat transfer performance of heat transfer equipment to further improve the heat transfer characteristics of power station coal boilers,providing the necessary theoretical basis and technical support for power station boilers.In this paper,the coupling equation between acoustic wave and flow field is constructed.The interaction between acoustic waves and the flow field is analysed by numerical calculations and experiments,and the physical mechanism of the influence of acoustic waves on the flow field is elucidated,the effect of acoustic waves on local convective heat transfer at the wall is studied.The results of the study show that when the sound pressure level is below 125dB,the sound waves have essentially no effect on the fluid flow velocity.The direction of sound propagation is the same as the direction of flow velocity,and as the sound pressure level increases,the fluid pulsation velocity amplitude increases in a slow and then fast trend,gradual change of fluid flow regime from laminar to turbulent.When SPL=153 dB,the fluid pulsation velocity amplitude shows an explosive increase.The direction of sound propagation is reversed with the direction of flow velocity,when 125<SPL<145dB,the fluid pulsation velocity amplitude appears to increase rapidly and then grow slowly,delaying the transformation of the fluid flow state to turbulent flow.However,when SPL>145dB,it gradually becomes turbulent.For convective heat transfer at the wall of the channel,the acoustic frequency is below 500 Hz and the acoustic waves have essentially no effect on the heat transfer at the wall.When f>500Hz,the higher the sound pressure level the higher the sound energy and the higher the local Nusselt number at the same sound frequency.The effect of acoustic properties on the flow field and convection heat transfer mechanisms around the basic structural units of single-cylinder,double-cylinder and staggered triple-cylinder arrays is investigated.For a single cylinder,the relationship between the acoustic Reynolds number Rea and Sr clearly shows that the acoustic energy can induce the blocked fluid within the boundary layer of the cylindrical surface flow to gain more momentum,prompting the boundary layer to separate,the separation point is shifted along the cylindrical surface,the shape of the wake vortex gradually becomes irregular,the acoustic wave perturbs the free incoming flow velocity,which enhances the flow heat transfer on the windward side of the cylinder,and the acoustic wave accelerates the vortex to dislodge the body,resulting in the heat transfer on the windward side of the cylinder being enhanced.For the staggered arrangement of three cylindersrs,the effect of acoustic waves on the gap flow eliminates the gap flow blind zone and increases the average convective heat transfer coefficient of the tandem cylinders.and the experiments also verify that acoustic waves can enhance convective heat transfer on the surface of the cylinder.For the three cylinders in equilateral triangular arrangements,at small pitch ratios,and acoustic energy weakens the reattachment of the upstream cylindrical shear layer and the irregular deflection of the bias flow.At medium distance pitch ratios,the effect on the acoustic wave properties,Strouhal number,lift,and drag coefficients are analyzed.For convective heat transfer,based on the effect of the acoustic wave action on the flow field,the Nu0,Nu,and Nuavg of the three cylinders are increased when Rea and f increase.Experiments confirmed the ability of acoustic waves to enhance convective heat transfer on the surface of three cylinders in an equilateral triangle arrangement.At big pitch ratios,the sound wave acts on it in the same way as a single cylinder.Based on the basic structure of the coal economizer of a power station boiler,a computational physical model was established.The effect of acoustic wave characteristics on the surrounding flow field and convective heat transfer in a single tube row has been investigated by varying the angle of incidence of the acoustic wave.Studies have shown that the scattering of sound waves on the surface of a pipe row is a phenomenon that determines the appropriate frequency of sound waves based on the relationship between the wave number k and the pipe diameter a.The distribution of the pressure coefficient on the surface of the pipe row was analyzed for different incidence angles of sound waves,the relationship between the sound pressure level and the average resistance of the surface of the pipe row is investigated,the influence of acoustic properties on vortex intensity is analyzed,the effect of acoustic properties on the velocity distribution of the wake is discussed in detail.Numerical analysis of the variation of local convective heat transfer on the surface of a pipe row for different acoustic incidence angles.Experiments have verified that acoustic waves can improve convective heat transfer coefficients for different incidence angles of acoustic waves,with the highest convective heat transfer performance for acoustic waves incident vertically to the surface of the pipe row.The boiler economiser physical calculation model is developed.The effect of acoustic on the flow field and surface convection heat transfer in the two arrangements of the in-line and staggered tube arrays has been investigated.The propagation characteristics and sound pressure distribution of acoustic waves in two array structures are analyzed,the effect of acoustic frequency and sound pressure level on the flow of interstitial flow in a pipe discharge is described,the variation of the x-and y-directional components of the velocity and the variation of the dimensionless Reynolds stress are analyzed in the detail.Experiments have shown that the average convective heat transfer is higher in the in-line arrangement than the staggered arrays,and that acoustic waves enhance convective heat transfer on the surface of the tube array.The relative error of the experiments is less than 20%.This paper provides a basis for improving the convective heat transfer performance of boiler heat exchangers.