The Characteristics Of Heat Transfer Enhancement And Antifouling With Vortex Generators

Vortex generators have attracted more and more attention as a passive heat transfer enhancement technology.This paper will use the research of vortex generator in heat transfer enhancement,and focus on the geometric parameters and fluid operating parameters of the vortex generator on the heat exchange surface.The numerical simulation method was used to study the crystallization and particle fouling characteristics of the vortex generator on the heat transfer surface.Finally,the mechanism by which the vortex generator suppresses the deposition of fouling（crystallization and particles）on the heat transfer surface is revealed.In the range of Reynolds number 214-10703,the heat transfer and flow resistance characteristics in a rectangular channel of two rectangular wing vortex generators with and without a hole was studied by numerical simulation.Meanwhile,with the Colburn factor（j）,friction factor（f）,and the thermohydraulic performance factor（PEC）as the evaluation index,the structural parameters（hole diameter and position）of the rectangular wing vortex generator were studied in detail.By comparing the thermohydraulic performance factor indicators,the comprehensive performance of the rectangular wing vortex generator with a hole is better than that of the rectangular wing vortex generator without a hole.Furthermore,the Colburn factor and friction factor of the vortex generator with a hole decrease with the increase of hole diameter,and the decreasing amplitude of the friction factor is greater than that of the Colburn factor.The hole position of different rectangular wing vortex generators slightly influences the heat transfer enhancement,but the hole position has great influence on the flow resistance of VGs.The mathematical model of the formation process of CaSO₄ crystallization fouling was established without considering the fouling induction period.For particle fouling,first based on particle rebound deposition model,taking into account the effects of drag,gravity and buoyancy,Safman lift,Brown force,and thermophoretic force.Based on this,a mathematical model of particle fouling based on Lagrangian method is established.Then,some important depositional mechanisms are considered,such as Brownian diffusion,vortex diffusion,gravity deposition,thermophoresis,and turbulent-flow deposition.A mathematical model of particle fouling based on Euler method is established.Furthermore,the mathematical model of crystallization and particle fouling was compared with the experimental data to verify the accuracy of the model.The 3D ventilation duct is taken as an example.The Lagrangian and Eulerian method are used to compare the particle fouling under the same working conditions.The results show,regardless of the approach used,the non-dimensional deposition velocity on the first plate is significantly larger than that of the three plates behind it.The total fouling mass calculated using the Lagrangian and Eulerian approaches exhibits asymptotic properties,and both two approaches can be used to predict the total fouling mass.However,the total fouling mass curve calculated using the Eulerian approach is closer to the experimental curve.Furthermore,the Eulerian approach requires much less computational time than the Lagrangian approach,that is,the Eulerian approach has less computational cost.So the Eulerian approach is more appropriate for engineering involving long simulation periods.Using the above-described crystallization fouling model,the CaSO₄ fouling characteristics of the channels of the rectangular,half-circular,and triangular vortex generators were simulated.The effects of wor the inlet velocity,concentration,and wall temperature on the fouling characteristics of three vortex generators were investigated.The effects of the length,radius,and longitudinal spacing of the half-cylinder VGs on the fouling of the heat wall are studied in detail.In addition,based on the Euler particle fouling model,for the channel with rectangular wing vortex generator,the effects of different height,length,and longitudinal spacing on particle fouling characteristics were studied in detail.Then,the comparison of the rectangular wing vortex generator with or without a hole was carried out,and the hole diameter,lateral position,and longitudinal position of the rectangular wing vortex generator are studied.