UNTERSUCHUNG DES STRÖMUNGSWIDERSTANDS AN METALLISCHEN SIEBGEWEBEN IN KRYOGENEN FLÜSSIGKEITEN

Dieser Artikel beschäftigt sich mit theoretischen Ansätzen zur Vorhersage von Strömungswiderständen metallischer Siebe und deren Anwendbarkeit für die Auslegung von realen Tanksystemen. Es werden Ergebnisse vorgestellt von Druckverlustmessungen, die am DLR Bremen mit flüssigem Stickstoff durchgeführt wurden. Die Ergebnisse werden verglichen mit Literaturdaten und zeigen generell eine gute Übereinstimmung. Bedingt durch die geringen Viskositäten kryogener Fluide ist der Einfluss des turbulenten Anteils am Druckverlust sehr hoch. Korrelationen, wie z.B. von Cady [1] und Armour [2], basieren jedoch hauptsächlich auf Daten mit geringerem turbulenten Einfluss und kleinen Re- Zahlen. Die neuen experimentellen Daten bieten eine genauere Vorhersagemöglichkeit bezüglich des Druckverlustes für Siebdurchströmungen im hohen Re- Bereich

Termination of atrial flutter by directed transesophageal atrial pacing during transesophageal echocardiography: Terminierung von Vorhofflattern mit gerichteter transösophagealer Vorhofstimulation bei transösophagealer Echokardiographie

Introduction: The purpose of this study was to evaluate termination of atrial flutter (AFL) by directed rapid transesophageal atrial pacing (TAP) with and without simultaneous transesophageal echocardiography (TEE) performed using a novel TEE tube electrode. Materials and methods, and Results: A total of 16 AFL patients (age 63"12 years; 13 males) with mean AFL cycle length of 224"24 ms (ns12) and mean ventricular cycle length of 448"47 ms (ns12) were analyzed using either an esophageal TO electrode (ns10) or a novel TEE tube electrode consisting of a tube with four hemispherical electrodes that is pulled over the echo probe (ns6). AFL could be terminated by directed rapid TAP using an esophageal TO electrode, leading to induction of atrial fibrillation (AF) (ns6), induction of AF and spontaneous conversion to sinus rhythm (SR) (ns3), and with conversion to SR (ns1). AFL could also be terminated by directed rapid TAP using the TEE tube electrode, with induction of AF (ns3) or induction of AF and pontaneous conversion to SR (ns3). Conclusion: AFL can be terminated by directed rapid TAP with hemispherical electrodes with and without simultaneous TEE. TAP with the directed TEE tube electrode is a safe, simple, and useful method for terminating AFL

Numerical Investigations on Fluid Flow through Metallic Screens

Metallic screens have important functions in tank systems and feedline systems of spacecraft’s due to their filtering capabilities and capillary features. The screen resistance upon flow through is significant influenced by the individual mesh and pore geometry of the individual screen. In this paper the screens are numerical investigated by using the commercial solver ANSYS Fluent 13.0. Calculations for low to medium screen Reynolds numbers with the different fluids water, liquid hydrogen and IPA are carried out. The results show good agreement with experimental and analytical data. Furthermore the streamlines, the local velocity and pressure field are investigated

Flow Resistance of Metallic Screens in Liquid, Gaseous and Cryogenic Flow

Fine metallic screens are important sub-systems in propellant tank systems of spacecrafts due to their application as filter devices. The flow resistance has to be known for a proper design of tank and feed line systems. In this paper the flow resistance of application-relevant metallic screens is investigated experimentally. The weave types “dutch twilled weave” (DTW) and “broad mesh” (BM) were studied. The description of BM geometry in literature is improper and a screen geometry model is developed, which is suitable for DTW and BM. The experimental data show good agreement with the literature

Study on the gas retention capability of metallic screens

In tank systems of spacecraft’s and satellites, metallic screens are found to provide the possibility besides filtering to retain liquid and prevent gas breakthrough by capillary. For determining the maximum retention capability at screens, the so called bubble point, in this study experimental setups are developed to measure the bubble point pressure for metallic screens of type twilled dutch 165 x 1400, 200 x 1400 and 325 x 2300 with isopropyl alcohol, silicon oil and liquid nitrogen. The results are found to follow a linear fit within the investigated regime of fluid properties and are compared with literature values

Advanced Technology Upper Stages for Future Launchers

The paper describes two different preliminary system designs for stages employing advanced technologies: 1. An experimental micro-stage with a very small storable propellant engine for LEO applications. This vehicle is part of the multinational (France, Spain, Germany) cooperation Aldébaran investigating future options of micro-launchers. 2. An advanced small TSTO rocket with a payload capability in the range of 2000+ kg in SSO and more than 1200 kg in higher energy orbits like MTO. The first stage consists of a high pressure solid motor with a fiber casing while the upper stage is using cryogenic propellants. Synergies with other ongoing European development programs are to be exploited. In its second part the paper gives an overview on advanced cryogenic upper-stage technologies presently under investigation in Germany

Cryo-Laboratories for Test and Development of Propellant Storage and Management Technologies

The paper gives an overview on the test possibilities of the Cryogenic Laboratories in BREMEN and TRAUEN of the DLR Institute of Space Systems with regard to the research and development of propellant management and storage technologies for successful future launcher and advanced cryogenic upper stage systems. To satisfy the current and future need for testing and research, different test facilities have been built up and are available in the labs. In particular a hexapod system and a cryogenic tank demonstrator, provided by Astrium ST, are useable for testing. The test possibilities of the cryogenic laboratories and the available test facilities will be presented

Heat and mass transfer in a cryogenic tank in case of active-pressurization

Predicting the pressurant requirements is one of the key challenges for cryogenic propulsion systems. In this context, a numerical model to simulate the tank pressurization that considers evaporation and condensation phenomena was developed and applied. The novel solver combines a gradient-based phase change model with a weakly compressible multiphase solver of OpenFOAM based on the pressure implicit method with splitting of operator (PISO) algorithm. To maintain a sharp interface the mass source terms are applied to the cells adjacent to the interface. First, the model is validated against two analytical solutions: the one-dimensional phase change problem and secondly, the growth of a vapor bubble in a superheated liquid in the absence of gravity. In a second step, the validated model was applied to a cryogenic pressurization experiment. The measured pressure behavior could be confirmed with the numerical model being in a good approximation. With the numerical model further insights into the physical behavior could be achieved. The condensation and evaporation effects have a significant impact on the pressure development during and after the pressurization. The mass flows due to phase change occurring at the vapor-liquid interface depend on interface location and time. Directly at the wall, evaporation becomes dominant while condensation occurs at the center area of the liquid surface

Experimental investigation on the draining behavior in scaled models of the new A5ME upper stage propellant compartments with respect to different flight conditions

The maximum possible mass, launched to orbit by a rocket, depends on the launcher performance and the desired target orbit. To provide as much capacity to the payload as possible, the total mass of the launchers upper stage has to be minimized. Intelligent propellant management can contribute significantly to increase the performance of the launcher. To optimize the flight missions the tank outlet design is required, to achieve that a maximum of the propellant is available for the mission and a minimum of propellant loading remains as unused residual

D34 Test report sloshing/pressure development

The DLR Bremen with the Kryo Lab as testing facility provides the service of both static and dynamic cryogenic tests with the cryogenic test demonstrator (CTD). These tests are part of the FLPP3 program and have to be made with liquid nitrogen (LN2) as testing fluid and both gaseous nitrogen (GN2) and gaseous helium (GHE) as pressure gas. The former test campaigns estimated the damping and frequency characteristic of the cryogenic liquid in WP31320 [RD2] as well as the cryogenic static behavior during filling, draining and stratification conditions in WP31330 [RD3]. Being the last part of FLPP3 the actual test report within WP31340 finally deals with the pressure development during sloshing. In this context test aim of this test campaign is to analyze the pressure development inside the test vessel with respect to different levels of dynamic excitation and ullage gas mixture. All tests were performed with a thermally chilled tank. During testing pressure level, gaseous flow rates, wall- and fluid temperatures, liquid fill levels, gaseous helium concentration in the ullage and tank acceleration are recorded. Additionally the tank camera system provides an overview video of each test