Fluid dynamic investigation of particle-laden suspensions on dimpled surfaces under fouling conditions
Résumé
The transfer of thermal energy is a core process in industrial processes. Improving the efficiency of heat exchangers could significantly reduce industrial energy consumption and costs. The thermo-hydraulic efficiency is widely used to evaluate heat exchanger efficiency. Dimples increase the thermo-hydraulic efficiency, but the performance of dimples under fouling conditions, and especially for particle-laden fluids, is inadequately investigated.
Experimental and numerical studies have shown that the application of dimples increases the turbulence near the wall, so that the heat transfer is increased, and deposited particles are detached from the wall. Here, the fluid-dynamic influence on particle transport is investigated by experimental determination of the three-dimensional velocity fields using stereoscopic micro particle image velocimetry (3D-µPIV) of a suspension in a flow channel. The influence of process parameters (flow velocity, particle concentration, dimple geometry) on turbulence, heat transfer and on particle deposition and removal is quantified.
The characteristic deposition pattern on dimpled surfaces is described by the adhesion and removal forces and is rated for different dimple geometries. With 3D-µPIV, the flow field inside the dimple is visualized and the formation of an oscillating vortex inside the dimple is proven experimentally. The existence of the vortex can explain the high heat transfer and the low fouling propensity of dimpled surfaces.