Unsteadiness and transition to turbulence in woven spacer filled channels for Membrane Distillation

34th UIT Heat Transfer Conference 2016

Ciofalo, M.^1 ; Ponzio, F.^1 ; Tamburini, A.^1 ; Cipollina, A.^1 ; Micale, G.^1

Dipartimento DICGIM, Università degli Studi di Palermo, Italy^1

关键词: High order harmonics;    K-Omega turbulence model;    Local oscillation;    Membrane distillation;    Spacer-filled channels;    Steady-state flows;    Thermochromic liquid crystals;    Transition to turbulence;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/796/1/012003/pdf
DOI  :  10.1088/1742-6596/796/1/012003

来源: IOP

【 摘 要 】

To characterize the performance of Membrane Distillation (MD) modules, channels filled with woven spacers were investigated by Computational Fluid Dynamics (including Direct Numerical Simulations and the use of the SST k-ω turbulence model) and by parallel experiments with Thermochromic Liquid Crystals. The cases considered here regard mutually orthogonal filaments with a spacer pitch to channel height ratio P/H=2, two spacer orientations θ with respect to the main flow (0° and 45°), and bulk Reynolds numbers Re from ∼200 to ∼2000, an interval of great interest in practical MD applications. For both values of θ, CFD predicted steady-state flow for Re up to ∼300, and chaotic flow for Re larger than ∼400. In the intermediate range Re≈300-400, periodic flow regimes were predicted for both orientations. These regimes were of particular interest and complexity, as they exhibited a slow global oscillation of the flow superimposed on high order harmonics corresponding to fast local oscillations. Experiments confirmed the appearance of unsteadiness for Re>∼300. Heat transfer and friction were little affected by unsteadiness and exhibited a smooth behaviour with Re. The agreement with the experimental results was good using DNS, and acceptable using RANS.