Dynamic scaling for the growth of non-equilibrium fluctuations during thermophoretic diffusion in microgravity

Diffusion processes are widespread in biological and chemical systems, where they play a fundamental role in the exchange of substances at the cellular level and in determining the rate of chemical reactions. Recently, the classical picture that portrays diffusion as random uncorrelated motion of molecules has been revised, when it was shown that giant non-equilibrium fluctuations develop during diffusion processes. Under microgravity conditions and at steady-state, non-equilibrium fluctuations exhibit scale invariance and their size is only limited by the boundaries of the system. In this work, we investigate the onset of non-equilibrium concentration fluctuations induced by thermophoretic diffusion in microgravity, a regime not accessible to analytical calculations but of great relevance for the understanding of several natural and technological processes. A combination of state of the art simulations and experiments allows us to attain a fully quantitative description of the development of fluctuations during transient diffusion in microgravity. Both experiments and simulations show that during the onset the fluctuations exhibit scale invariance at large wave vectors. In a broader range of wave vectors simulations predict a spinodal-like growth of fluctuations, where the amplitude and length-scale of the dominant mode are determined by the thickness of the diffuse layer.Comment: To appear in Scientific Report

The Borexino Thermal Monitoring & Management System and simulations of the fluid-dynamics of the Borexino detector under asymmetrical, changing boundary conditions

A comprehensive monitoring system for the thermal environment inside the Borexino neutrino detector was developed and installed in order to reduce uncertainties in determining temperatures throughout the detector. A complementary thermal management system limits undesirable thermal couplings between the environment and Borexino's active sections. This strategy is bringing improved radioactive background conditions to the region of interest for the physics signal thanks to reduced fluid mixing induced in the liquid scintillator. Although fluid-dynamical equilibrium has not yet been fully reached, and thermal fine-tuning is possible, the system has proven extremely effective at stabilizing the detector's thermal conditions while offering precise insights into its mechanisms of internal thermal transport. Furthermore, a Computational Fluid-Dynamics analysis has been performed, based on the empirical measurements provided by the thermal monitoring system, and providing information into present and future thermal trends. A two-dimensional modeling approach was implemented in order to achieve a proper understanding of the thermal and fluid-dynamics in Borexino. It was optimized for different regions and periods of interest, focusing on the most critical effects that were identified as influencing background concentrations. Literature experimental case studies were reproduced to benchmark the method and settings, and a Borexino-specific benchmark was implemented in order to validate the modeling approach for thermal transport. Finally, fully-convective models were applied to understand general and specific fluid motions impacting the detector's Active Volume.Comment: arXiv admin note: substantial text overlap with arXiv:1705.09078, arXiv:1705.0965

An experimental correlation of the nonreactive properties of injection schemes and combustion effects in a liquid-propellant rocket engine. Part II. Instrumentation, experimental apparatus, and experimental techniques

Apparatus, techniques, and instrumentation for experimental correlation of nonreactive injection schemes and combustion effects in liquid propellant rocket engin

Experimental Investigation of Hydraulic Effects on Unsaturated Soils Behaviors

Geo-structures are frequently constructed in or on soils with unsaturated conditions and are subjected to variations of moisture contents due to seasonal changes. Even though unsaturated soil mechanics have been established for several decades, it has not been fully implemented in practice today because of a lack of understanding of the interaction between the soil, water, and air phases. Many experimental research studies have been conducted to improve the understanding of unsaturated behavior but these studies are typically limited to small soil elements tested under fully drained conditions. The goal of this research is to evaluate the effect of hydraulics on the mechanical behavior of unsaturated soils by performing soil element testing and centrifuge modeling with a focus on undrained conditions. The research begins by evaluating the hysteretic effects on the soil water characteristic curve (SWCC), the relationship between soil moisture content and matric suction, using the automated Tempe cell systems. Results show that hydraulic hysteresis increases as the clay content increases and also increases as the flow rate increases. The second part of the research focuses on the hysteresis effects on the mechanical behavior observed in constant water content (CW) triaxial testing. Results show that matric suction decreases during shearing for all of the drying path tests, while results from the drying- wetting path tests show increases in matric suction. Results of the drying path tests for clayey sand exhibit strain-hardening behavior while those for silty soil exhibit a strain- hardening/softening behavior. The shear strength found in drying-wetting path tests is higher than that for drying tests performed at the same initial matric suction due to the effect of matric suction history. This effect causes the increase and decrease of matric suction during shearing for the drying path and the drying-wetting path, respectively. To account for the hysteretic effect, the shear strength can be estimated based on the matric suction at failure. The third part of the research focuses on the investigation of unsaturated soil behavior using a geotechnical centrifuge model testing. The research involves the development of a miniature sensor to investigate the hydraulic effects on the mechanical behavior of unsaturated soils. A modified heat dissipation sensor (HDS) is tested in a geotechnical centrifuge to evaluate its performance at different centrifuge g- levels. Results show that the HDS can be used to measure in-flight water content, while the SWCC for each soil type can be used to estimate soil matric suction. The fourth part of the research focuses on the characterization of unsaturated soil using the cone penetration test (CPT) and HDS for centrifuge modeling tests to investigate the hydraulic effects on the cone tip resistance, qc. Results show that the qc increases as the degree of saturation decreases for the as-compacted condition or after the evaporation process. The degree of saturation also decreases significantly when the model is subjected to rainfall events. There is no hysteresis effect on qc. Thus, a single relationship between the qc and the degree of saturation can be developed for the clayey sand tested in this study. Moreover, the centrifuge CPT can be used to evaluate relative change in the shear strength of the soil due to the change in hydraulic conditions. The CPT results from the centrifuge model study are comparable with the predictions based on the cavity expansion theory

A preliminary study of a cryogenic equivalence principle experiment on Shuttle

The Weak Equivalence Principle is the hypothesis that all test bodies fall with the same acceleration in the same gravitational field. The current limit on violations of the Weak Equivalence Principle, measured by the ratio of the difference in acceleration of two test masses to their average acceleration, is about 3 parts in one-hundred billion. It is anticipated that this can be improved in a shuttle experiment to a part in one quadrillion. Topics covered include: (1) studies of the shuttle environment, including interference with the experiment, interfacing to the experiment, and possible alternatives; (2) numerical simulations of the proposed experiment, including analytic solutions for special cases of the mass motion and preliminary estimates of sensitivity and time required; (3) error analysis of several noise sources such as thermal distortion, gas and radiation pressure effects, and mechanical distortion; and (4) development and performance tests of a laboratory version of the instrument

Study Of Periodical Flow Heat Transfer In An Internal Combustion Engine

In-cylinder heat transfer is one of the most critical physical behaviors which has a direct influence on engine out emission and thermal efficiency for IC engine. In-cylinder wall temperature has to be precisely controlled to achieve high efficiency and low emission. However, this cannot be done without knowing gas-to-wall heat flux. This study reports on the development of a technique suitable for engine in-cylinder surface temperature measurement, as the traditional method is “hard to reach.” A laser induced phosphorescence technique was used to study in-cylinder wall temperature effects on engine out unburned hydrocarbons during the engine transitional period (warm up). A linear correlation was found between the cylinder wall surface temperature and the unburned hydrocarbons at mediate and high charge densities. At low charge density, no clear correlation was observed because of miss-fire events. A new auto background correction infrared (IR) diagnostic was developed to measure the instantaneous in-cylinder surface temperature at 0.1 CAD resolution. A numerical mechanism was designed to suppress relatively low-frequency background noise and provide an accurate in-cylinder surface temperature measurements with an error of less than 1.4% inside the IC engine. In addition, a proposed optical coating reduced time delay errors by 50% compared to more conventional thermocouple techniques. A new cycle-averaged (〖Re〗_s ) ̅ number was developed for an IC engine to capture the characteristics of engine flow. Comparison and scaling between different engine flow parameters are available by matching the averaged (〖Re〗_s ) ̅ number. From experimental results, the engine flow motion was classified as intermittently turbulent, and it is different from the original fully developed turbulent assumption, which has previously been used in almost all engine simulations. The intermittent turbulence could have a great impact on engine heat transfer because of the transitional turbulence effect. Engine 3D CFD model further proves the existence of transitional turbulence flow. A new multi zone heat transfer model is proposed for IC engines only. The model includes pressure work effects and improved heat transfer prediction compared to the standard Law of the wall model

Turbine blade and vane heat flux sensor development, phase 2

The development of heat flux sensors for gas turbine blades and vanes and the demonstration of heat transfer measurement methods are reported. The performance of the heat flux sensors was evaluated in a cylinder in cross flow experiment and compared with two other heat flux measurement methods, the slug calorimeter and a dynamic method based on fluctuating gas and surface temperature. Two cylinders, each instrumented with an embedded thermocouple sensor, a Gardon gauge, and a slug calorimeter, were fabricated. Each sensor type was calibrated using a quartz lamp bank facility. The instrumented cylinders were then tested in an atmospheric pressure combustor rig at conditions up to gas stream temperatures of 1700K and velocities to Mach 0.74. The test data are compared to other measurements and analytical prediction

Bidirectional flow measurement based on the differential pressure method for surge analysis on a small centrifugal compressor

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.To obtain a high temporal resolution of mass flow data, a flowmeter based on the differential pressure method has been developed. It is capable of detecting negative flow for investigations of dynamic effects in small centrifugal compressors used for turbocharging automotive internal combustion engines. Experiments were performed at a hot gas test bench focusing on the surge characteristics at different turbocharger speeds and the influence of volume modifications downstream of the compressor. Instantaneous operating points could be traced in the compressor map including the typical orbits at deep surge resulting from the cyclic character of the phenomenon