Flow-accelerated corrosion

Page 1 : Flow-accelerated corrosion

Page 2 : Experimental loop and visualization of flow structure

Page 3 : Investigation of Influence of Inlet Flow Conditions on Flow Structure in a Dual Elbow

Experimental loop

We are using an experimental loop shown in the following figure. A multi-elbow is installed to the loop and the flow structure at the elbow is visualized by Particle Image Velocimetry (PIV). The test section is composed of two elbows with a straight pipe put between them. Flow structure is changed by inserting the straight pipe.

Experimental loop

Experimental results

It is confirmed that the flow structure in the dual elbow has specificity depending on the inlet flow condition to the elbow. As to a time-averaged flow in the flow direction in the case of the dual elbow at Reynolds number of 200000, a fast flow existed inside the elbow at a bending angle of 30 degree inside the 2nd elbow. The velocity of the fast flow was about 1.6 times larger than that of the inlet averaged flow to lead large shear velocity field. Additionally it was confirmed that the fast flow collided intermittently with the inside wall surface of the 2nd elbow. The purposes of this study are, therefore, to evaluate effect of changing the s-shaped dual elbow geometry on the flow structure relating to the FAC.
By changing the Reynolds number, the variations of the flow structure are evaluated. Total pressure loss coefficient is evaluated by changing the Reynolds number. It was confirmed that total pressure loss coefficient characteristic is same at Reynolds number of 50000-320000.
Furthermore, a flow structure in the vicinity of the wall is closely visualized to evaluate potential suppressing the FAC by putting the straight pipe between the two elbows. The wall shear stress and friction velocity are evaluated by velocity gradient in wall surface. The wall shear stress is suppressed to 90% by putting a 1D (=56mm) straight pipe between the two elbows, and the friction velocity is suppressed to 95% by putting a 1D straight pipe. There is a strong possibility that putting a straight pipe between the two elbows makes it suppression of FAC, and makes it ease the occurrence of the complex flow field.

Visualized flow structure