Altitude Test Facility Humidity Control to Generate Defined Icing Conditions

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Felix M. Barth ◽  
Stephan Staudacher ◽  
Constanze Schiewe
Keyword(s):  
Optical Measurements ◽  
Nucleation Theory ◽  
Test Facility ◽  
Classical Nucleation Theory ◽  
Model Parameters ◽  
Fundamental Part ◽  
Aerosol Particle Size ◽  
The University ◽  
Ingested Nanoparticles

Abstract In altitude test facility (ATF) operation, the requirements to control humidity to generate defined icing conditions are gaining more and more importance. In this context, the ability to predict humidity and condensation becomes a fundamental part of ATF control. For this purpose, classical nucleation theory has been applied in combination with in situ measurements to derive a model suitable to predict the onset of condensation during very low temperature ATF operation. The model parameters have been acquired inside the ATF of the University of Stuttgart downstream of its air coolers. This makes the application or assumption of generalized atmospheric aerosol data unnecessary. Polydisperse nano aerosol distributions were measured and statistically evaluated, showing that a constant distribution of nano aerosol particle size can be assumed. The composition of the ingested nanoparticles was analyzed and Arizona test dust was chosen as a valid substitute material for the application in the prediction model leading to a conservative prediction. The approach has been successfully verified using optical measurements during ATF testing. Its prediction accuracy fulfills the requirements of ATF control for a variety of icing conditions in component and engine altitude testing.

scholarly journals The Effect of Hydrogen on Pore Formation in Aluminum Alloy Castings: Myth Versus Reality

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 368 ◽  
Author(s):  
Murat Tiryakioğlu
Keyword(s):  
Pore Formation ◽  
Liquid Aluminum ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Fundamental Change ◽  
Aluminum Casting ◽  
Solid Aluminum ◽  
Alloy Castings ◽  
Casting Industry

The solubility of hydrogen in liquid and solid aluminum is reviewed. Based on classical nucleation theory, it is shown that pores cannot nucleate either homogeneously or heterogeneously in liquid aluminum. Results of in situ studies on pore formation show that pores appear at low hydrogen supersaturation levels, bypassing nucleation completely. The results are explained based on the bifilm theory introduced by Prof. John Campbell, as this theory is currently the most appropriate, and most likely, the only mechanism for pores to form. Examples for the effect of hydrogen on pore formation are given by using extreme data from the literature. It is concluded that a fundamental change in how hydrogen is viewed is needed in aluminum casting industry.

scholarly journals Reversible disorder-order transitions in atomic crystal nucleation

Science ◽  
2021 ◽  
Vol 371 (6528) ◽  
pp. 498-503
Author(s):  
Sungho Jeon ◽  
Taeyeong Heo ◽  
Sang-Yeon Hwang ◽  
Jim Ciston ◽  
Karen C. Bustillo ◽  
...  
Keyword(s):  
Early Stage ◽  
Nucleation Theory ◽  
Crystal Nucleation ◽  
Classical Nucleation Theory ◽  
Gold Nanocrystals ◽  
Size Dependent ◽  
In Situ Electron Microscopy ◽  
Nucleation Mechanisms ◽  
Structural Fluctuations

Nucleation in atomic crystallization remains poorly understood, despite advances in classical nucleation theory. The nucleation process has been described to involve a nonclassical mechanism that includes a spontaneous transition from disordered to crystalline states, but a detailed understanding of dynamics requires further investigation. In situ electron microscopy of heterogeneous nucleation of individual gold nanocrystals with millisecond temporal resolution shows that the early stage of atomic crystallization proceeds through dynamic structural fluctuations between disordered and crystalline states, rather than through a single irreversible transition. Our experimental and theoretical analyses support the idea that structural fluctuations originate from size-dependent thermodynamic stability of the two states in atomic clusters. These findings, based on dynamics in a real atomic system, reshape and improve our understanding of nucleation mechanisms in atomic crystallization.

scholarly journals An aerosol chamber investigation of the heterogeneous ice nucleating potential of refractory nanoparticles

2010 ◽  
Vol 10 (3) ◽  
pp. 1227-1247 ◽  
Author(s):  
R. W. Saunders ◽  
O. Möhler ◽  
M. Schnaiter ◽  
S. Benz ◽  
R. Wagner ◽  
...  
Keyword(s):  
Silicon Oxide ◽  
Cloud Model ◽  
Active Surface ◽  
Accommodation Coefficient ◽  
Contact Angles ◽  
Nucleation Theory ◽  
Cloud Formation ◽  
Classical Nucleation Theory ◽  
Ice Nuclei

Abstract. Nanoparticles of iron oxide (crystalline and amorphous), silicon oxide and magnesium oxide were investigated for their propensity to nucleate ice over the temperature range 180–250 K, using the AIDA chamber in Karlsruhe, Germany. All samples were observed to initiate ice formation via the deposition mode at threshold ice super-saturations (RHithresh) ranging from 105% to 140% for temperatures below 220 K. Approximately 10% of amorphous Fe2O3 particles (modal diameter = 30 nm) generated in situ from a photochemical aerosol reactor, led to ice nucleation at RHithresh = 140% at an initial chamber temperature of 182 K. Quantitative analysis using a singular hypothesis treatment provided a fitted function [ns(190 K)=10(3.33×sice)+8.16] for the variation in ice-active surface site density (ns:m−2) with ice saturation (sice) for Fe2O3 nanoparticles. This was implemented in an aerosol-cloud model to determine a predicted deposition (mass accommodation) coefficient for water vapour on ice of 0.1 at temperatures appropriate for the upper atmosphere. Classical nucleation theory was used to determine representative contact angles (θ) for the different particle compositions. For the in situ generated Fe2O3 particles, a slight inverse temperature dependence was observed with θ = 10.5° at 182 K, decreasing to 9.0° at 200 K (compared with 10.2° and 11.4° respectively for the SiO2 and MgO particle samples at the higher temperature). These observations indicate that such refractory nanoparticles are relatively efficient materials for the nucleation of ice under the conditions studied in the chamber which correspond to cirrus cloud formation in the upper troposphere. The results also show that Fe2O3 particles do not act as ice nuclei under conditions pertinent for tropospheric mixed phase clouds, which necessarily form above ~233 K. At the lower temperatures (<150 K) where noctilucent clouds form during summer months in the high latitude mesosphere, higher contact angles would be expected, which may reduce the effectiveness of these particles as ice nuclei in this part of the atmosphere.

Study Of Nucleation And Growth Ev Al-Zn Alloys Using TEM

1993 ◽  
Vol 321 ◽  
Author(s):  
G. Sundar ◽  
E. A. Kenik ◽  
J. J. Hoyt ◽  
S. Spooner
Keyword(s):  
Completion Time ◽  
Nucleation And Growth ◽  
Nucleation Theory ◽  
Classical Nucleation Theory ◽  
Initial Value ◽  
Two Phase ◽  
Transmission Electron ◽  
Time Required ◽  
Zn Alloys

ABSTRACTNucleation and growth studies were conducted on Al-Zn alloys at several temperatures using transmission electron Microscopy (TEM) with an in-situ furnace. The value of the critical undercooling was established by noting the lowest temperature at which precipitates were no longer observed, following a quench into the two-phase metastable region. These results were compared with the Langer-Schwartz Model of nucleation and growth in which it is predicted that the half-completion time (i.e, the time required for the supersaturation to reach half its initial value) diverges for initial supersaturations which are higher than those predicted by the classical nucleation theory.

scholarly journals Development and Assessment of Coatings for Future Power Generation Turbines

2012 ◽  
Author(s):  
M. A. Alvin ◽  
D. Zhu ◽  
K. Klotz ◽  
B. McMordie ◽  
B. Warnes ◽  
...  
Keyword(s):  
Single Crystal ◽  
Technology Development ◽  
Extreme Temperature ◽  
Test Facility ◽  
West Virginia University ◽  
University Of Pittsburgh ◽  
Barrier Coating ◽  
Regional University ◽  
The University

The NETL-Regional University Alliance (RUA) continues to advance technology development critical to turbine manufacturer efforts for achieving DOE Fossil Energy (FE’s) Advanced Turbine Program Goals. In conjunction with NETL, Coatings for Industry (CFI), the University of Pittsburgh, NASA GRC, and Corrosion Control Inc., efforts have been focused on development of composite thermal barrier coating (TBC) architectures that consist of an extreme temperature coating, a commercially applied 7-8 YSZ TBC, a reduced cost bond coat, and a diffusion barrier coating that are applied to nickel-based superalloys or single crystal airfoil substrate materials for use at temperatures ≥1450°C (≥ 2640°F). Additionally, construction of a unique, high temperature (∼1100°C; ∼2010°F), bench-scale, micro-indentation, nondestructive (NDE) test facility at West Virginia University (WVU) was completed to experimentally address in-situ changes in TBC stiffness during extended cyclic oxidation exposure of coated single crystal coupons in air or steam-containing environments. The efforts and technical accomplishments in these areas are presented in the following sections of this paper.

An in Situ Hrem Study of Crystal Nucleation in Amorphous Silicon thin Films

1990 ◽  
Vol 202 ◽  
Author(s):  
A. S. Kirtikar ◽  
J. Morgiel ◽  
R. Sinclair ◽  
I-W. Wu ◽  
A. Chiang
Keyword(s):  
Thin Films ◽  
Solid Phase ◽  
High Resolution Electron Microscopy ◽  
Nucleation Theory ◽  
Crystal Nucleation ◽  
Classical Nucleation Theory ◽  
Interface Reactions ◽  
Silicon Thin Films ◽  
Resolution Electron

ABSTRACTIn Situ high resolution electron microscopy has proved to be a valuable tool in investigations involving interface reactions in a number of thin film systems. We have applied this technique to dynamically record nucleation and growth sequences during the amorphous (a-) to crystalline (c-) phase transformation in silicon thin films. Interpretation of the recordings has yielded a wealth of information on the mechanisms and to some extent the kinetics of solid phase crystallization. In our recordings, we have been able to capture the critical nucleus at the a-Si-SiO2 interface. Incorporating this into classical nucleation theory enables us to make an estimate of the a-Si-c-Si interfacial energy.

Development and Experimental Validation of a Compressor Dynamic Model

2004 ◽  
Author(s):  
M. Venturini
Keyword(s):  
Experimental Validation ◽  
Test Facility ◽  
Response Analysis ◽  
Model Parameters ◽  
Modular Model ◽  
Multi Stage ◽  
Model Response ◽  
Dynamic Analyses ◽  
The University ◽  
And Control

In recent years, transient response analysis of energy systems is becoming more and more important in optimizing plant operation and control. Furthermore, dynamic analyses are also used to integrate steady-state diagnostic analyses, since they allow the detection of malfunctions characterized by time-dependent effects. The paper deals with the development of a non-linear modular model for compressor dynamic simulation. After developing the compressor mathematical model through a physics-based approach (laws of conservation and thermal balances), the model is implemented through the Matlab® Simulink tool. Then, a sensitivity analysis is carried out to evaluate the influence of model parameters on the model response. Finally, the model is calibrated on a multi-stage axial-centrifugal small size compressor running in the test facility of the University of Ferrara (Italy) and validated through experimental data taken on the compressor under investigation.

scholarly journals A comparative study of K-rich and Na/Ca-rich feldspar ice-nucleating particles in a nanoliter droplet freezing assay

2016 ◽  
Vol 16 (18) ◽  
pp. 11477-11496 ◽  
Author(s):  
Andreas Peckhaus ◽  
Alexei Kiselev ◽  
Thibault Hiron ◽  
Martin Ebert ◽  
Thomas Leisner
Keyword(s):  
High Temperature ◽  
Surface Density ◽  
Active Sites ◽  
Nucleation Theory ◽  
High Mass ◽  
Classical Nucleation Theory ◽  
Model Parameters ◽  
Freeze Thaw ◽  
Lower Temperature ◽  
Heating Up

Abstract. A recently designed droplet freezing assay was used to study the freezing of up to 1500 identical 0.2 nL water droplets containing suspensions of one Na/Ca-rich feldspar and three K-rich and one Na/Ca-rich feldspar particles. Three types of experiments have been conducted: cooling ramp, isothermal freezing at a constant temperature, and freeze–thaw cycles. The observed freezing behavior has been interpreted with the help of a model based on the classical nucleation theory (soccer ball model (SBM); Niedermeier et al., 2015). By applying the model to the different freezing experiments conducted with the same ice-nucleating material, the unique sets of model parameters for specific feldspar suspensions could be derived. The SBM was shown to adequately describe the observed cooling rate dependence, the ice-nucleating active sites (INAS) surface density ns(T) in a wide temperature range, and the shift of the freezing curves towards lower temperature with dilution. Moreover, the SBM was capable of reproducing the variation of INAS surface density ns(T) with concentration of ice-nucleating particles in the suspension droplets and correctly predicting the leveling-off of ns(T) at low temperature. The freeze–thaw experiments have clearly shown that the heterogeneous freezing induced even by very active ice-nucleating species still possesses a stochastic nature, with the degree of randomness increasing towards homogeneous nucleation. A population of the high-temperature INAS has been identified in one of the K-rich feldspar samples. The freezing of 0.8 wt % suspension droplets of this particular feldspar was observed already at −5 °C. These high-temperature active sites could be deactivated by treating the sample with hydrogen peroxide but survived heating up to 90 °C. Given a high mass concentration of these high-temperature active sites (2.9 × 108 g−1) and a very low value of contact angle (0.56 rad) the possibility of biological contamination of the sample was concluded to be unlikely but could not be completely ruled out. The freezing efficacy of all feldspar samples has been shown to reduce only slightly after suspension in water for over 5 months.

Studies on nucleation phenomena occurring in aqueous solutions supersaturated with calcium sulfate

1978 ◽  
Vol 56 (6) ◽  
pp. 831-838 ◽  
Author(s):  
D. M. Keller ◽  
Ronald E. Massey ◽  
O. E. Hileman Jr.
Keyword(s):  
Aqueous Solutions ◽  
Nucleation Rate ◽  
Calcium Sulfate ◽  
Nucleation Theory ◽  
Critical Parameters ◽  
Classical Nucleation Theory ◽  
In Situ Generation ◽  
Temperature Surface

The results of a set of experiments designed to delineate the nucleation rate, supersaturation, temperature surface for the system CaSO4•2H2O/H2O are reported. The data were obtained using the droplet technique coupled with in situ generation of SO42− under the conditions that dS/dt was large during the early part of the induction period and it was zero during the actual nucleation events. The observed shape of the surface is compared with that suggested by the classical theory of nucleation and differences are commented on. The critical parameters important in classical nucleation theory are reported.

Development and Experimental Validation of a Compressor Dynamic Model

2004 ◽  
Vol 127 (3) ◽  
pp. 599-608 ◽  
Author(s):  
M. Venturini
Keyword(s):  
Experimental Validation ◽  
Energy Systems ◽  
Test Facility ◽  
Response Analysis ◽  
Model Parameters ◽  
Modular Model ◽  
Model Response ◽  
Dynamic Analyses ◽  
The University ◽  
And Control

In recent years, transient response analysis of energy systems is becoming more and more important in optimizing plant operation and control. Furthermore, dynamic analyses are also used to integrate steady-state diagnostic analyses, since they allow the detection of malfunctions characterized by time-dependent effects. The paper deals with the development of a nonlinear modular model for compressor dynamic simulation. After developing the compressor mathematical model through a physics-based approach (laws of conservation and thermal balances), the model is implemented through the MATLAB® SIMULINK® tool. Then, a sensitivity analysis is carried out to evaluate the influence of model parameters on the model response. Finally, the model is calibrated on a multistage axial-centrifugal small size compressor running in the test facility of the University of Ferrara (Italy) and validated through experimental data taken on the compressor under investigation.

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