2.1. Experimental setup.
The experiments were conducted in a 61 cm tall column of 8.2 cm square cross-section (Fig. 2). The base was sealed except for a 1.0 mm diameter hole through which an injection needle was inserted. The injection needle had an internal diameter of 0.6 mm. Air was injected through the needle by a Chemyx Fusion 200 syringe pump. The column was filled with a 25.4 cm layer of Carbopol capped with a 25.4 cm layer of water. To assist visualization the Carbopol was dyed pink, and the water blue. A Lumix GH4 camera, capable of operating at 96 frames per second with a resolution of 1920 × 1080 pixels, was placed in front of the column.
Carbopol EZ-2 (Lubrizol) solutions, mixed at different concentrations, were used for the lower layer. Due to their insignificant thixotropy these solutions exhibit ideal yield stress fluid behavior . It is also useful experimentally due to its transparency. The solutions were prepared using the method described in Zare and Frigaard . To achieve the desired concentration, a small amount of Carbopol EZ-2 was mixed with water and then neutralized by stirring in an appropriate amount of 0.1 g/l of sodium hydroxide (NaOH) for 24 h. The Carbopol/NaOH weight ratio was 3.5:1. The rheological properties of the fluid are set by the concentration and pH of the solution. To avoid thixotropic and evaporation effects, a new batch of Carbopol was made for each experiment, using identical preparation protocols.
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Date Published: Received 15 August 2021, Revised 15 November 2021, Accepted 16 November 2021, Available online 5 December 2021, Version of Record 17 December 2021.
- aDepartment of Civil Engineering, University of British Columbia, 6250 Applied Science Ln, Vancouver, BC, V6T 1Z4, Canada
- bDepartment of Mathematics, University of British Columbia, 2324 Main Mall, Vancouver, BC, V6T 1Z4, Canada
- cDepartment of Mathematics and Department of Mechanical Engineering, University of British Columbia, 2324 Main Mall, Vancouver, BC, V6T 1Z4, Canada