Experimental investigation of mass transfer in 90° pipe bends using a dissolvable wall technique

The mass transfer in 90° angle bends was measured using a dissolvable wall technique using test sections cast from gypsum. The method allows the surface morphology to evolve producing a roughened surface to mimic practical mass transfer situations. The experiments were performed for standard 90° pipe bends, with a diameter of 2.54 cm and radius of curvature r/D = 1.5 at a Schmidt number of 1280 and Reynolds number in the range Re = 40,000–130,000. A mass transfer enhancement relative to the upstream pipe was observed on the bend inner wall near the inlet, on the side walls throughout much of the bend and on the bend outer wall near the outlet. A maximum mass transfer enhancement of approximately 1.85 times was observed on the bend outer wall near the bend outlet, which was independent of Reynolds number. The Sherwood number at the high mass transfer locations is found to scale as Re0.92. The surface roughness in the upstream pipe and in the bend is found to decrease slightly with Reynolds number. The roughness scale e+ is estimated to be approximately 30–70 for the different Reynolds numbers.