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Scientific Data in Subproject B2

Description

General Information on the Datasets

The experiments aim to improve the understanding of two phase evaporation effects and phenomena under elevated pressures and temperatures. The corresponding setup uses a pressure cell with multiple inlets, for gaseous and liquid phases, respectively, to produce falling liquid droplets in a pressure and temperature controlled gaseous environment. The cell is a so called ``flown'' cell, which means that there is a steady gaseous volume flow to prevent a saturated atmosphere during droplet evaporation. There are four optical fused silica windows placed at 90° to each other around a core cylindrical plenum to allow for optical access with lasers and cameras. The gaseous phase can be a premixed or a single carrier-gas-less evaporated fluid before it enters the plenum. The liquid phase is brought to target pressure with a double piston high pressure dosing pump. It is then led into through a thermos-oil temperature controlled inlet with a capillary injection pointing into the main plenum of the pressure cell. The droplet can be detached using high voltage electrostatics by modified epoxy cast spark plugs around the capillary. The efficacy of the detachment depends on the nature of the fluid i.e. its polarity and conductivity.

A new iteration of this cell is currently build at ITLR Stuttgart. The new cell will allow pressures of up to 80 bar and 700 Kelvin compared to 60 bar and 570 Kelvin that are currently possible.

Two dimensional Raman scattering experiments have been carried out with a n-heptane nitrogen system. The objective was to determine quantitative mixture fraction properties of the falling, evaporating droplet. To this end, a 532 nm Nd:YAG laser is formed into a lightsheet of 80 µm thickness and shot over the droplet as it falls. The resulting Raman scattering is divided into two processing channels by spectral filtering, the heptane and nitrogen channel. They are recorded by two cameras, respectively. By using a ratiometric calibration prior to the droplet measurements, calibrations constants are determined and then used to recalculate local concentration from the droplet images. The nitrogen channel also serves as a local reference for the laser energy and number density. For more information on this measurement we refer to dx.doi.org/10.1016/j.proci.2016.07.037.

Front lighted shadowgraphy, an overlay of a diffuse lighted image with a shadowgram directly in the optical setup, was applied to an n-pentane nitrogen system. The objective was to simultaneously detect the presence of a material surface of the droplet as well as changes in density gradients in the surrounding atmosphere. The material surface of the droplet is identified by reflections and refractions on the droplet interface caused by diffuse ambient illumination. Changes in the density gradients around the droplet are visualized by direct shadowgraphy in parallel light. For more information on this measurement we refer to dx.doi.org/10.4995/ILASS2017.2017.4635.

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Sonntag, Dezember 15, 2019