Investigation Of Flow Fields In A Dual WH Impeller Stirred Tank Using PIV Under Low Reynolds Number

Stirred tank is widely used in chemical engineering, food industry, pharmaceutical engineering and other fields. Most studies to date have concentrated on turbulent flow in mixing vessels, while there are many industrial applications involving highly viscous fluids or requiring very slow mixing rates. In this case, the flow is represented as transition flow or even laminar flow, while there are few corresponding researches. The flow characteristics in a dual WH impeller stirred tank with diameter of0.335m were measured by using PIV. The effects of the Reynolds number, spacing from bottom to bottom impeller(C1) and the spacing between two impellers (C2) on the flow characteristics were investigated.The flow induced by a dual WH impeller for three Re namely,900,1800and2400, is studied experimentally. It is found that the change of Re has little effect on flow characteristics under transition flow, with no significant change in flow pattern and velocity profile.The change of C1has a influence on both flow pattern and velocity profile near the tank bottom, but doesn’t have distinct effect on the flow above the bottom impeller. The increase of C1causes a decrease on average axial velocity near the bottom, as well as a generation of a weak loop in this zone, which is believed to be negative to overall circulation.The variation of C2has a significant influence on the flow characteristics under transition flow. There will be a single loop in the tank when C2is less than the critical value of0.45T, and a double loop when C2is more than that. Besides, the variation of C2has a obvious influence on the velocity profile in the whole tank, which leads to a sharply decrease on the velocity profile between impellers, at the same time, a increase on the velocity profile near the bottom.