In mist filtration, fiber-based coalescers are an established form of filtering droplets contained in mist. The filtration process can be divided into different process steps, describing the impact of the droplets on fibers, the formation of fluid structures and the liquid transport. In order to investigate mechanisms inside depth filters on a microscopic level, investigations are often reduced to single fibers. In this work, the coalescence and transport mechanisms of axially distributed water droplets on a vertical fiber, subjected to gravity, are reported. This is done with the latest high-speed camera technology commercially available. Automated tracking of droplets is used for a frame-by-frame investigation of droplet position, size, and oscillation. Coalescence mechanisms describe the process of fluid formation. The first observed coalescence mechanism is identified by the coalescence of droplets contained in mist with an adhering droplet at the fiber. The second coalescence mechanism describes the coalescence of two closely spaced sessile droplets on a fiber. As a result, the newly formed droplet oscillates and can begin to drain. Furthermore, the coalescence process of a draining and sessile droplet is reported. Both the draining droplet and the second droplet involved in the coalescence event can be subject to oscillation. The given temporal high-resolution information about the droplet position and deformation improves the understanding of droplet coalescence on fibers and by that also its influence on transport processes and therefore droplet drainage. Observed transport mechanisms which take part in the drainage process are gravitational draining, droplet bouncing, and droplet sweeping.
In mist filtration, fiber-based coalescers are an established form of filtering droplets contained in mist. The filtration process can be divided into different process steps, describing the impact of the droplets on fibers, the liquid transport, and the formation of fluid structures. According to the current state of knowledge, the transport of fluid along the fibre is caused by gravitational draining, pressure, shearing, and electrostatic forces. The formation of fluid structures includes the creation of larger droplets by coalescing and fluid sails between adjacent fibres [1–3]. In order to investigate mechanisms inside depth filters on a microscopic level, investigations are often reduced to single fibers [1, 4–6]. Zhang et al. [7] observed self-propelled detachment of coalesced droplets which were arranged side by side on identical axial position. In this work, the coalescence mechanisms of axial distributed water droplets on a vertical fiber, subjected to gravity, are investigated. This is done with the latest high-speed camera technology commercially available. Automated tracking of droplets is used for a frame-by-frame investigation of droplet position, size, and oscillation behaviour. Characteristic coalescence mechanisms are reported and describe the process of fluid formation. The first coalescence mechanism is identified by the coalescence of droplets contained in mist with an adhering droplet at the fiber. The second coalescence mechanism describes the coalescence of two closely spaced sessile droplets on a fiber. As a result, the newly formed droplet oscillates and can begin to drain. Furthermore, the coalescence mechanism of a draining and sessile droplet is investigated. Additional observed mechanisms describe the process of droplet transportation. These mechanisms are: gravitational draining, droplet bouncing, and droplet sweeping.
This study describes experimental results using carbon fiber-reinforced carbon (C/C) material for porous journal bearings under static conditions. Exerted radial forces of up to 90 N, a supply pressure of up to 6 bar and a maximum rotational speed of 8000 rpm were tested. The occurrence of pneumatic hammering was not observed under these operating points. Triangulation sensors were mounted vertically and horizontally as well as in front of and behind the tested bearing. These sensors measure eccentricity and misalignment. The orbit analysis demonstrated an improvement in concentricity with an increment in the supply pressure. The layered structure of the C/C material used for the porous liner is presented. A rotational speed below 8000 rpm negligibly influenced the load-carrying capacity and the flow rate. The vertical misalignment of the shaft was determined in relation to the force-applied test bearing to the shaft. In addition, two vertically positioned sensors on the support-bearing housing were used to discern the misalignment in the absolute system. On the other hand, reducing the speed to 1000 rpm increased the concentricity error. The shaft showed no significant signs of use after the experiments. The measurements confirm the suitability of the material for porous bearings.
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