Abstract
Liquid coiling occurs as a viscous fluid flows into a stagnant reservoir causing a localized accumulation of settling material, which coils into a stack as it accumulates. These coiling flows are broadly characterized into three primary coiling regimes of viscous, gravitational, or inertial coiling, based on the velocity of the falling fluid, the height of the fall, the radius of the fluid rope, the stack height, and the fluid properties including viscosity. A computer-controlled flow delivery apparatus was developed here to produce precisely controlled flow conditions to study steady and transitional coiling regimes with independently varied parameters. Data were recorded using high-speed digital video cameras and a purpose-built digital image processing routine to extract rope and stack dimensions as well as time-resolved coiling frequency. The precision of the setup and data analysis methods allowed a detailed study of the transition between gravitational and inertial flow regimes. The results show a smooth transition between the regimes, with no evidence of the inertial-gravitational regime. Unsteady coiling was able to be momentarily produced by applying a perturbation to the system, but the unstable regime quickly decayed to either the base inertial or gravitational regime.
Highlights
Introduction and Liquid Coiling RegimesUnder appropriate conditions, a falling stream of viscous liquid may exhibit the phenomena of liquid coiling when encountering a quiescent reservoir of the same fluid
While Regions of interest (ROIs) are manually defined once, these windows change in size with respect to the changing size of the coil stack allowing for a measurement of transient liquid coiling tests
The liquid coil was examined under transient flow rate conditions to observe the changing coil properties of stack height, stack width, and frequency change while transitioning from the gravitational regime to the inertial regime and, from the inertial regime to the gravitational regime
Summary
A falling stream of viscous liquid may exhibit the phenomena of liquid coiling when encountering a quiescent reservoir of the same fluid. Deceleration of the falling liquid can cause the stream to spontaneously rotate about and accumulate into a cylindrical stack [1] This instability is analogous to buckling of solid columns under compressive loads [2]. Fluids 2018, 3, 107 viscosity, and drop height These factors affect the general shape of the coil stack and the range of the coil dimensions. Frequency does not guarantee explicit identification of the transitional inertial-gravitational regime This flow manifests in an unpredictable manner with rapid stack growth and collapse with variable coiling frequencies generally similar in magnitude to the gravitational and inertial regimes. An automated system was developed to produce these coiling flows with the ability to independently vary parameters of the flow with precise control This system is demonstrated under transient flow rate conditions with time-resolved measurements of coiling frequency, stack height, and stack diameter
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