| Plate heat exchanger is widely used in chemical,pharmaceutical,food and other industries for its excellent heat transfer performance.With the rise of the metallurgical industry,the wide-channel welded plate heat exchangers for liquid-solid phase gradually emerged.However,the complex interaction between the two phases in the narrow rectangular channel makes it difficult to obtain accurate analysis of the liquid phase and particle phase in the flow channel.Therefore,this project studied the flow state of liquid and solid phase in welded plate heat exchangers by experimental and simulation.Firstly,the resistance along the narrow channel is measured by experiments.Then the Euler-Euler two-fluid model is used to simulate the flow of liquid-solid phase in narrow channels.Finally,experiments are used to verify the correctness of the numerical model.Analysis of the liquid-solid two-phase flow in narrow channels.The results of vertical narrow channels showed that the two-phase flow enters a fully developed stage above 0.7 m in the vertical direction of the narrow channel.At the fully developed stage,the narrow channel cross-section,the particles receive the greatest pressure on the near-wall surface;The turbulent kinetic energy,,dissipative rate,particle velocity,and concentration in all directions in the narrow direction show a distribution trend of high in the central region and low in the region close to the sidewalls.With the increase of the inlet liquid velocity,the particle velocity and concentration in each section of the cross section increases.The concentration of particle which is located in the central region of the flow channel decreases whereas rises in the area close to the wall.As the initial solid volume fraction increases,the concentration of particle increases at each position in the cross section.While the velocity of particle decreases slightly in the central region of the flow channel and increases slightly in the vicinity of the wall.There are enrichment effects of particles at both ends of the narrow channel’s cross section near to the three sides.The non-dimensional proportion in the area where the gradient of particle velocity and concentration is large in the cross section of narrow channel increases with the increase of the inlet liquid speed yet it decreases when the initial solid volume fraction increases.As the size of particle increases,the non-uniformity of the particles in the flow channel increases.The results of the study showed that the two-phase flow enters the fully developed stage after 0.6 m in the horizontal direction of the narrow channel.At the fully developed stage,there are the maximum flow of particle pressure,turbulent kinetic energy and dissipation rate in the bottom of the track near to the wall.The solid volume distribution of the particles is lower in the lower part compared to the upper part.At the same level,the volume fraction of the solid phase near the wall is smaller than in the center of the flow channel.When the the initial solid volume fraction increases,or the inlet flow velocity increases,or the particle size decreases,the non-uniformity of the distribution of particles in the horizontal narrow channel decreases.In addition,the particles gather at the intersection of the vertical wall and the horizontal wall at the bottom of the narrow channel.While the aggregation of the particles will decrease withe increased of inlet velocity and reduced particle size.Relative to a horizontal circular channel with the same equivalent diameter,the uniformity of particle distribution in the narrow channel is better under the same operating conditions.The accumulation of particles at the corners of the bottom of the flow channel is significantly reduced after changing the corner of the narrow channel to chamfer.By analyzing the flow characteristics of the liquid-solid two-phase in the horizontal narrow channel and the vertical narrow channel,it can provide reference for the design and operation of the welded plate heat exchanger. |
PDF Full Text Request