Research On Vortex Enhanced Heat Transfer In Plate Heat Exchangers

Plate heat exchanger has become the most commercially valuable type of heat exchanger because of its compact structure,large logarithmic mean temperature difference,pressure reduction,superior mechanical strength and heat transfer performance compared with the traditional shell and tube heat exchanger.It is widely used in refrigeration and air conditioning,heating,food processing,chemical,Marine and energy power system and other industries.With the continuous development of industrial technology,the performance and efficiency of plate heat exchanger are more and more demanding,so the intensive heat transfer research of plate heat exchanger becomes more and more important.The root of enhanced heat transfer in plate heat exchangers lies in the change of plate shape which induces flow vortices,enhancing fluid turbulence and promoting heat transfer.However,the conditions under which vortices play a role in enhancing heat transfer,as well as the correlation between plate structure and vortex-enhanced heat transfer,require further in-depth investigation.To address this issue,this article primarily studies the heat transfer characteristics of two-dimensional laminar boundary layer separation vortices,two-dimensional planar vortex heat transfer under field synergy,and the role of vortices in enhancing heat transfer in plate heat exchangers.The research aims to provide a basis for optimizing the plate design of plate heat exchangers.The specific research content and main achievements are as follows:(1)To numerically simulate the flow and heat transfer in the plate boundary layer,various turbulence models are utilized.The reliability of these commonly used turbulence models is analyzed and compared with the T3 A experimental data.The numerical results show that the Transition SST model is in good agreement with the experimental and theoretical specifications of heat transfer in the boundary layer,as measured by the Nusselt number and friction coefficient.Furthermore,the appropriate wall function can significantly enhance the accuracy and speed of boundary layer flow calculations when the boundary layer mesh is not refined.This approach can help to reduce resource consumption and improve the computational efficiency of boundary layer flow simulations.(2)The reliability of the theoretical model of boundary layer separation under laminar flow conditions was verified by numerical simulation,and the heat transfer characteristics of the boundary layer separation vortex were also analyzed by numerical simulation.The results of the demonstrates that the Thwaites theory,when compared to the numerical solution of the N-S equation of flow heat transfer,is computationally more efficient and offers higher accuracy in predicting laminar boundary layer separation.The Thwaites theory can,therefore,be effectively applied to the design of plates in plate heat exchangers.However,it should be noted that heat transfer is substantially weakened by separation bubbles after boundary layer separation.(3)A parametric equation was established to describe the curvature of the plate,and the inverse pressure gradient within the boundary was adjusted by controlling the curve parameters,so as to achieve the flow field control and heat transfer enhancement.The results show that the curve boundary leads to the contraction of the flow passage and the acceleration of the flow rate.(4)Based on the field synergy theory,the synergy of velocity and temperature fields under different two-dimensional planar vortex structures is analyzed,and the heat transfer characteristics of vortices are studied.The results demonstrate that the presence of vortices within the flow field enhances the synergy degree of convective heat transfer,with the efficiency of convective heat transfer increasing in direct proportion to the scale of the vortices.This provides a basis for the research of enhanced heat transfer of plate heat exchanger.(5)The experimental study of inclined corrugated plate heat exchanger was carried out and the reliability of numerical simulation was verified.The vortex mode,flow structure and heat transfer performance,the effect of vortex on heat transfer enhancement of plate heat exchanger and the internal field coordination of plate heat exchanger were analyzed by numerical simulation.The results show that the bubble structure forms a vortex path that leads to enhancing heat transfer.Moreover,based on the comprehensive heat exchange performance evaluation index PEC,the bubblingplate heat exchanger with a height of 8mm has the best comprehensive performance.