Session: 11-15-01: Fluid Problems in Energy Systems

Paper Number: 166035

The Controlled Behavior of Free-Falling Liquid Jets for an Inertia Fusion Energy Application 

Energy runs the modern world. Ease of access and control of the resource is tied to national security and power. Leading methods of energy generation in today’s world rely on fossil fuels which are harmful to the environment and limited in supply. At nearly four million times more energy efficiency than fossil fuels, nuclear fusion offers a clean and renewable source of energy that can propel humanity into the future. Inertial Fusion Energy (IFE) is the leading method of achieving this process which involves the use of lasers to create a fusion reaction within a target capsule. In modern IFE reactor designs, the radiation must be captured for use in downstream power generation cycles, and the reactor walls must be protected from high energy neutrons. Designs using falling liquid jets of eutectic salts have been proposed to accomplish both requirements. However, these jets introduce challenging fluid dynamics optimization problems. Specifically, the jets must remain stable and produce minimal droplets, because the development of spray could both adversely impact the jet optical thickness, and the laser ignition process itself. This work examines optimal upstream flow conditioning elements and geometrical features to minimize jet surface fluctuations, break-up, and droplet production. Experiments are performed in a water jet facility issuing into a quiescent atmosphere. Dynamic similarity to the reactor application is maintained by matching the Reynolds number and Weber number regimes for turbulent atomization. This corresponds to a jet exit Reynolds number of approximately 175,000 and a Weber number of approximately 20,000. Jet stability is modified by changing flow conditioning elements upstream of the nozzle exit. The baseline configuration is a fully developed turbulent pipe flow. Modified configurations include conditioning elements to minimize turbulent fluctuations at the nozzle exit and reduce boundary layer thickness. This includes a diffuser with settling chamber, honeycomb to reduce secondary flow components, screens to damp turbulence, and a contraction to thin the boundary layers and further reduce turbulence. It is hypothesized that the flow conditioning sections will improve jet stability. Additionally, the apparatus is designed in a modular fashion such that variants on outlet nozzle design can be explored, to include alternative outlet shapes such as high aspect ratio rectangular jets. To quantify differences in the jet dynamics produced by each of the different geometries, surface fluctuations and droplet production are measured using a backlit illumination set-up. A uniform background illumination is created using a high-power LED array and a diffuser screen. The jet is imaged with a 4.2-megapixel high-speed camera and lens to produce a field of view that extends from the nozzle exit to approximately 20 jet diameters downstream. An image segmentation methodology is implemented to identify the jet and any droplets produced. Basic statistical quantities of interest include the average and standard deviation in jet diameter as a function of downstream distance. Higher-order statistical measures will further quantify disturbance growth rates, such as surface fluctuation length and timescales derived from two-point two-time correlation functions. The outcome of this experiment will allow the quantitative description of surface fluctuations and droplet production with respect to the upstream flow conditioning elements for use in an IFE reactor. 

Presenting Author: Christopher Tamer United States Military Academy

Presenting Author Biography: CDT Christopher Tamer is a mechanical engineering student at the United States Military Academy with a research focus on free-falling liquid jets and an academic focus in aeronautical engineering.

Authors:

Christopher Tamer United States Military Academy
Wyatt Cyprow United States Military Academy
Jack Maraziti United States Military Academy
Megan Cho United States Military Academy
Andrew Banko United States Military Academy