About the Morphology of Flash Boiling Liquid Nitrogen Sprays

Rees, Andreas; Salzmann, Heiko; Sender, Joachim; Oschwald, Michael

doi:10.1615/atomizspr.2020035265

Cited by 16 publications

(27 citation statements)

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“…A subsequent in-depth data analysis of this measurement campaign showed, that the droplet velocity and diameter distributions of flash boiling LN2 sprays have a sufficient degree of similarity with data of storable fluids from literature [14]. In a former study [15], the characteristic morphology like break-up patterns and spray angles of flash boiling LN2 sprays was determined by means of high-speed shadowgraphy in dependence on the injection parameters and derived dimensionless quantities. Similar to storable fluids, increasing degrees of superheat lead to a growing dominance of flash boiling on the break-up of the liquid nitrogen jet.…”

Section: State Of Researchmentioning

confidence: 76%

“…Since the dominating parameters for flash boiling are the injection temperature T inj and the back pressure p ch , it is important for an experimental investigation to make them adjustable, to keep them constant during the injection period and to make them reproducible. This is why the new test bench M3.3 with a temperature-controlled injection system was built at DLR Lampoldshausen for a detailed experimental investigation of cryogenic flash boiling processes [12,13,14,15,16].…”

Section: Experimental Set-upmentioning

confidence: 99%

“…The test fluid nitrogen gets liquefied during the chill-down process of the test bench. Further details about the test bench M3.3 and its possible range of injection conditions can be found in references [12,13,14,15].…”

Section: Cryogenic Test Bench M33mentioning

confidence: 99%

“…In this study, we are using the four LN2 sprays #1, #6, #9 and #14 which were generated by a single sharp-edged injector with a diameter of D inj = 1 mm and a length-to-diameter ratio of L /D = 2.9. For further injector details we refer to former works [12,13,14,15,16]. The injection conditions in terms of the injection temperature T inj , the injection pressure p inj , the chamber pressure p ch , the mass flowṁ, the degrees of superheat R p and ∆T * as well as the dimensionless numbers like the gaseous and liquid Weber numbers W e g and W e l , respectively, the Jacob number Ja, the Reynolds number Re and the Ohnesorge number Oh of the sprays #1, #6, #9 and #14 are summarized in Table 1.…”

Section: Injection Conditionsmentioning

confidence: 99%

“…The injection conditions in terms of the injection temperature T inj , the injection pressure p inj , the chamber pressure p ch , the mass flowṁ, the degrees of superheat R p and ∆T * as well as the dimensionless numbers like the gaseous and liquid Weber numbers W e g and W e l , respectively, the Jacob number Ja, the Reynolds number Re and the Ohnesorge number Oh of the sprays #1, #6, #9 and #14 are summarized in Table 1. Detailed definitions of these numbers as well as their confidence intervals can be found in reference [15].…”

Section: Injection Conditionsmentioning

confidence: 99%

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Difficulties in Defining the Degree of Superheat in Flash Boiling Liquid Nitrogen Sprays

Rees

Oschwald

Gärtner

et al. 2021

ICLASS

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Technology development for propulsion systems of upper stages and reaction control thrusters is driven by green propellants to substitute hydrazine. At high-altitude conditions prior to ignition the liquid propellants are injected into the combustor at near-vacuum. Due to the sudden pressure drop the liquid is in a superheated thermodynamic state resulting in an eruptive evaporation and fast expansion, a process called flash boiling. To know the composition related to phase and atomization is important for both to determine the probability of a successful ignition and to avoid destructive pressure peaks. Hence, we visualized flash boiling liquid nitrogen (LN2) sprays by means of shadowgraphy at the cryogenic test bench M3.3 at DLR. The data analysis of these sprays revealed that the commonly used degree of superheat Rp on its own is not sufficient to describe the flash boiling process. This paper focuses on the description of this issue by comparing shadowgraph images of different LN2 sprays to each other and by the discussion of the kinetics of the sprays in terms of velocity and pressure distributions obtained by numerical simulation. Despite similar degrees of superheat Rp, the spray morphology as well as the spray kinetics show serious deviations from each other.

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Section: State Of Researchmentioning

confidence: 76%

Section: Experimental Set-upmentioning

confidence: 99%

Section: Cryogenic Test Bench M33mentioning

confidence: 99%

Section: Injection Conditionsmentioning

confidence: 99%

Section: Injection Conditionsmentioning

confidence: 99%

See 3 more Smart Citations

Difficulties in Defining the Degree of Superheat in Flash Boiling Liquid Nitrogen Sprays

Rees

Oschwald

Gärtner

et al. 2021

ICLASS

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Collaborative Research on Droplet Dynamics Under Extreme Ambient Conditions

Schulte

Dreizler

Munz

et al. 2022

Fluid Mechanics and Its Applications

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A fundamental understanding of droplet dynamics is important for the prediction and optimization of technical systems involving drops and sprays. The Collaborative Research Center (CRC) SFB-TRR 75 was established in January 2010 to focus on the dynamics of basic drop processes, and in particular on processes involving extreme ambient conditions, for example near thermodynamic critical conditions, at very low temperatures, under the influence of strong electric fields, or in situations involving extreme gradients of the boundary conditions. The goal of the CRC was to gain a profound physical understanding of the essential processes, which is the basis for new analytical and numerical descriptions as well as for improved predictive capabilities. This joint initiative involved scientists at the University of Stuttgart, the TU Darmstadt, the TU Berlin, and the German Aerospace Center (DLR) in Lampoldshausen. This first chapter provides a brief overview of the overall structure of this CRC as well as a summary of some selected scientific achievements of the subprojects involved. For further details the reader is referred to the subsequent chapters of this book related to the individual subprojects.

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Experimental Investigation of Transient Injection Phenomena in Rocket Combusters at Vacuum with Cryogenic Flash Boiling

Rees

Oschwald

2022

Fluid Mechanics and Its Applications

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The substitution of the toxic hydrazine in current high-altitude rocket engines like upper stages or reaction control thrusters by green propellants is a major key driver in the current technology development of rocket propulsion systems. Operating these kind of rocket engines at high-altitude leads to a sudden pressure drop in the liquid propellants during their injection into the combustion chamber with a near-vacuum atmosphere prior to ignition. The resulting superheated thermodynamic state of the liquid causes a fast and eruptive evaporation which is called flash boiling. The degree of atomisation is important for a successful ignition and a secure operation of the rocket engine. The development and operation of a cryogenic high-altitude test bench at DLR Lampoldshausen enables the systematical experimental characterization of cryogenic flash boiling due to its ability to adjust and control the injection parameters like temperature, pressure or geometry. Several test campaigns with liquid nitrogen (LN2) were performed using two optical diagnostic methods: First, flash boiling LN2 spray patterns were visualised by means of high-speed shadowgraphy and, secondly, we determined the droplet size and velocity distributions in strongly superheated LN2 sprays with the help of a laser-based Phase Doppler system (PDA). The experimental data generated within these measurement campaigns provide defined boundary conditions as well as a broad data base for the numerical modelling of cryogenic flash boiling like e.g. the publications [8, 9].

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About the Morphology of Flash Boiling Liquid Nitrogen Sprays

Cited by 16 publications

References 0 publications

Difficulties in Defining the Degree of Superheat in Flash Boiling Liquid Nitrogen Sprays

Difficulties in Defining the Degree of Superheat in Flash Boiling Liquid Nitrogen Sprays

Collaborative Research on Droplet Dynamics Under Extreme Ambient Conditions

Experimental Investigation of Transient Injection Phenomena in Rocket Combusters at Vacuum with Cryogenic Flash Boiling

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