Channel flows of Plate Heat Exchangers (PHEs) were assessed by experiments with three different chevron angle arrangements in turbulent regime. Two chevron angles were selected to assess low and high pressure drop cha...Channel flows of Plate Heat Exchangers (PHEs) were assessed by experiments with three different chevron angle arrangements in turbulent regime. Two chevron angles were selected to assess low and high pressure drop channels, besides a third mixed configuration as to achieve in-between results regarding hydraulic performance. Friction factor correlations were provided with the channel Reynolds number ranging from 1175 to 8325. Two-dimensional (2D) mean velocity field was obtained by Particle Tracking Velocimetry (PTV) with Reynolds number equal to 3450. To the best of our knowledge, this is the first experimental study that quantified the complete 2D velocity field of a typical PHE channel. This value allowed comparison with literature results of Plate and Shell Heat Exchanger (PSHE) channels with the same Reynolds number. PSHE mean velocity field is highly heterogeneous as compared to the one obtained for PHE channels. Peak velocity magnitude in the PSHE center is 50% higher than its bulk velocity, whereas this value is only 15% higher in the PHE center. Pressure drop in PHE mixed channels cannot be approximated by averaging chevron angles: furrow flow prevailed in the specified conditions. The axial velocity is asymmetric regarding the vertical plane. Smooth streamlines prevail in the channel inlet. Recirculation zones at the channel exit affect pipe flow in the manifold outlet with swirling flow structures. The necessary length to obtain fully developed pipe flow at the channel outlet was estimated. Significant velocity components occur in the distribution areas and can limit the heat exchanger performance. The results reported herein are essential to understand how the PHE channel geometry affects the velocity field and, therefore, local heat transfer and dissipation processes.展开更多
In this paper we study the effect of rolling friction on the dynamics in a single spout fluidized bed using Discrete Element Method （DEM） coupled to Computational Fluid Dynamics （CFD）. In a first step we neglect r...In this paper we study the effect of rolling friction on the dynamics in a single spout fluidized bed using Discrete Element Method （DEM） coupled to Computational Fluid Dynamics （CFD）. In a first step we neglect rolling friction and show that the results delivered by the open source CFD-DEM framework applied in this study agree with previous simulations documented in literature. In a second step we include a rolling friction sub-model in order to investigate the effect of particle non-sphericity. The influence of particle-particle as well as particle-wall rolling friction on the flow in single spout fluidized bed is studied separately. Adequate rolling friction model parameters are obtained using first principle DEM simulations and data from literature. Finally, we demonstrate the importance of correct modelling of rolling friction for coupled CFD-DEM simulations of spout fluidized beds. We show that simulation results can be improved significantly when applying a rolling friction model, and that experimental data from literature obtained with Positron Emission Particle Trackin~ fPEPT） technique can be satisfactorily reoroduced.展开更多
文摘Channel flows of Plate Heat Exchangers (PHEs) were assessed by experiments with three different chevron angle arrangements in turbulent regime. Two chevron angles were selected to assess low and high pressure drop channels, besides a third mixed configuration as to achieve in-between results regarding hydraulic performance. Friction factor correlations were provided with the channel Reynolds number ranging from 1175 to 8325. Two-dimensional (2D) mean velocity field was obtained by Particle Tracking Velocimetry (PTV) with Reynolds number equal to 3450. To the best of our knowledge, this is the first experimental study that quantified the complete 2D velocity field of a typical PHE channel. This value allowed comparison with literature results of Plate and Shell Heat Exchanger (PSHE) channels with the same Reynolds number. PSHE mean velocity field is highly heterogeneous as compared to the one obtained for PHE channels. Peak velocity magnitude in the PSHE center is 50% higher than its bulk velocity, whereas this value is only 15% higher in the PHE center. Pressure drop in PHE mixed channels cannot be approximated by averaging chevron angles: furrow flow prevailed in the specified conditions. The axial velocity is asymmetric regarding the vertical plane. Smooth streamlines prevail in the channel inlet. Recirculation zones at the channel exit affect pipe flow in the manifold outlet with swirling flow structures. The necessary length to obtain fully developed pipe flow at the channel outlet was estimated. Significant velocity components occur in the distribution areas and can limit the heat exchanger performance. The results reported herein are essential to understand how the PHE channel geometry affects the velocity field and, therefore, local heat transfer and dissipation processes.
基金the community of CFDEM project (2011) for giving important input and contributions to the development of this open source projectthe C.D. Research Association,the Federal Ministry of Economy,Family and Youth and the National Foundation for Research,Technology and Development
文摘In this paper we study the effect of rolling friction on the dynamics in a single spout fluidized bed using Discrete Element Method （DEM） coupled to Computational Fluid Dynamics （CFD）. In a first step we neglect rolling friction and show that the results delivered by the open source CFD-DEM framework applied in this study agree with previous simulations documented in literature. In a second step we include a rolling friction sub-model in order to investigate the effect of particle non-sphericity. The influence of particle-particle as well as particle-wall rolling friction on the flow in single spout fluidized bed is studied separately. Adequate rolling friction model parameters are obtained using first principle DEM simulations and data from literature. Finally, we demonstrate the importance of correct modelling of rolling friction for coupled CFD-DEM simulations of spout fluidized beds. We show that simulation results can be improved significantly when applying a rolling friction model, and that experimental data from literature obtained with Positron Emission Particle Trackin~ fPEPT） technique can be satisfactorily reoroduced.
