Adrian Stefan Sabau

Adrian Stefan Sabau
Oak Ridge National Laboratory | ORNL · Computational Sciences and Engineering Division

PhD

About

166
Publications
45,597
Reads
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1,425
Citations
Additional affiliations
October 2018 - present
Oak Ridge National Laboratory
Position
  • Researcher
March 2014 - May 2019
University of Tennessee
Position
  • Joint ORNL-UT faculty
Description
  • 0% MABE
October 1999 - September 2018
Oak Ridge National Laboratory
Position
  • Senior R&D Staff Member
Education
August 1992 - June 1996
Southern Methodist University
Field of study
  • Mechanical Engineering

Publications

Publications (166)
Article
Although vacuum-insulated glazing (VIG) has been proposed as a promising solution towards developing energy-efficient buildings, VIGs have not become popular in the market due to several technical challenges including the complexity of the fabrication process. In particular, the edge-seal is a key component that significantly affects the thermal in...
Article
Supercritical CO2 (sCO2) power cycles are being developed due to their potential for high efficiency and reduced capital cost. It is necessary that these recuperators operate at high pressures and temperatures, up to 30 MPa and 900 K, with effectiveness values > 95% and pressure drops <1% to achieve high cycle efficiencies. Moreover, it is also nec...
Preprint
Full-text available
Modern heat recovery steam generators (HRSGs) operate at elevated temperatures, leading to the formation of oxides inside the tubes of heat exchangers (HXs). This oxide growth reduces the heat recovery efficiency. Moreover, after reaching a certain critical thickness, some oxide scales detach from the tube surface (exfoliation), causing erosion dam...
Article
Additive manufacturing (AM), or 3D printing, of metals is transforming the fabrication of components, in part by dramatically expanding the design space, allowing optimization of shape and topology. However, although the physical processes involved in AM are similar to those of welding, a field with decades of experimental, modeling, simulation, an...
Article
Full-text available
Adhesive bonding requires adequate surface preparation for ensuring an appropriate joint quality. The interest in adhesive joining has recently expanded to thermal systems having a large number of joints employed for manufacturing and assembly. This study presents surface topology of copper 110 produced by a laser-interference setup that would theo...
Article
Ti6Al4V specimens were exposed to high-energy laser pulses, of 1.24 J/cm² fluences per pulse, using a laser-interference using a two-beam optical configuration. In addition to the formation of periodic surface textures by laser-interference, scanning electron microscope (SEM) images demonstrated several microstructural changes on the surface proces...
Article
In this study, corrosion behavior of laser-interference treated Al20204-T3 specimens, which were coated with a primer, is presented. The surface of as-received Al2024-T3 specimens were laser-interference structured by splitting the primary beam of a Q-switched Nd:YAG pulsed nanosecond laser into two beams and focusing them to the same spot on the s...
Article
The laser-based treatment of a metal surface is an intrinsically non-chemical technique that can alter both the topology and chemistry of surfaces. A laser-based treatment for coating and joining applications can offer alternative surface preparations to the chemically-based surface preparation techniques, which are subject to severe environmental...
Article
This paper describes the measurement of convective heat transfer coefficients and friction factors for sCO2 flowing in additively manufactured tubes with internal pin fins at the US DOE’s National Energy Technology Laboratory in Morgantown, WV. The measurement procedures were validated by conducting benchmark tests with smooth stainless-steel tube...
Article
Full-text available
The results obtained from a drying experiment using infrared heating are compared to those obtained from an analytical model based on correlations for the mass transfer coefficients, which are commonly used to obtain evaporation rates for drying applications. It was shown that the mass transfer coefficients calculated by natural convection correlat...
Article
To understand the process-microstructure relationships in additive manufacturing (AM), it is necessary to predict the solidification characteristics in the melt pool. The present study investigates the influence of Marangoni driven fluid flow on the predicted melt pool geometry and solidification dynamics using a continuum finite volume model (FVM)...
Article
Full-text available
A novel heat exchanger architecture was investigated in which each fluid transitions partway through the heat exchanger from tube-flow to shell-flow, or from shell-flow to tube-flow. The heat exchangers (HX) consisted of two plenums filled with tube bundles and a solid core of Counterflow channels Sandwiched between the Plenums (CSP). To allow a hi...
Article
Full-text available
In laser powder bed fusion additive manufacturing (LPBFAM), different solidification conditions, e.g., thermal gradient and cooling rate, can be achieved by controlling the process parameters, such as laser power and laser speed. Tailoring the behaviour of the columnar to equiaxed transition (CET) of the printed alloy during fabrication can facilit...
Conference Paper
Published under licence by IOP Publishing Ltd. In laser powder bed fusion additive manufacturing (LPBFAM), different solidification conditions, e.g., thermal gradient and cooling rate, can be achieved by controlling the process parameters, such as laser power and laser speed. Tailoring the behaviour of the columnar to equiaxed transition (CET) of t...
Article
In this study, the coating adhesion test results are presented for a primer that was coated on laser-interference structured surfaces of as-received Al2024-T3 specimens, i.e., without employing any polishing, cleaning, or any other surface alteration techniques. All of the laser-interference processing was performed by splitting the primary beam of...
Article
Full-text available
The hot-tearing resistance of Al-Cu-Mn-Zr (ACMZ) alloys was investigated as a steptoward introducing these new cast alloys for severe duty, higher-temperature applications, such ascylinder heads for down-sized, turbocharged automotive engines. Alloy Cu compositions werevaried from 5 to 8 wt.%. Targeted Ti levels were 0.02, 0.1, and 0.2 wt.% via add...
Article
Full-text available
Single-track laser fusion were simulated using a heat-transfer-solidification-only (HTS) model and its extension with fluid dynamics (HTS_FD) model using a parallel open-source code, which included laminar fluid dynamics, flat-free surface of the molten alloy, heat transfer, phase-change, evaporation, and surface tension phenomena. The results illu...
Article
Assessing the effect of neutron irradiation of plasma-facing materials has been challenging due to both the technical and radiological challenges involved. In an effort to address the radiological challenges, a facility was developed to conduct high heat flux testing (HHFT) of inherently small samples of neutron-irradiated materials. A new line-foc...
Article
A key limitation for the use of aluminum alloys in multi-material structural components is effective surface cleaning and texturing techniques to improve the quality of structural joints. In this study, the surface and sub-surface chemistries are investigated for a novel surface treatment method using laser interferometry produced by two beams of a...
Article
Full-text available
With recent advancements in advanced manufacturing techniques, it is now possible to fabricate complex geometries that take advantage of well known principles of heat transfer. Therefore, unconventional configurations to enhance effectiveness beyond conventional designs can now be considered for practical application. Thermal performance and overal...
Article
Full-text available
F82H reduced activation steel coated with vacuum plasma sprayed (VPS) tungsten is a candidate as a plasma facing material for main chamber components in future fusion reactors. Due to different coefficients of thermal expansion (CTE), significant thermal stresses are expected in these bimetallic materials. Thus, a major uncertainty in the performan...
Article
In this paper, a novel geometry is proposed for evaporators that are used in Supercritical Organic Rankine Cycles. The proposed geometry consists of successive plenums at several length-scale levels, creating a multi-scale heat exchanger (HX). The channels at the lowest length-scale levels were considered to have their length determined by the ther...
Article
The hot-tearing resistance of multicomponent Al-Cu alloys during permanent mold casting was investigated using a constrained permanent mold in which the load and temperature were measured. The nominal Cu composition was varied from 5 to 8 wt pct. Casting experiments were conducted without adding any grain-refining inoculants. The following variable...
Book
This book contains the proceedings of the symposium “CFD Modeling and Simulation in Materials Processing” held at the TMS 2018 Annual Meeting & Exhibition in Phoenix, Arizona, USA, March 11–15, 2018. This symposium dealt with computational fluid dynamics (CFD) modeling and simulation of engineering processes. The papers published in this book were...
Article
The PHENIX Project is a 6-year U.S./Japan bilateral, multi-institutional collaboration program for the Technological Assessment of Plasma Facing Components for DEMO Reactors. The goal is to address the technical feasibility of helium-cooled divertor concepts using tungsten as the armor material in fusion power reactors. The project specifically att...
Article
Here we explore the idea that the highest heat transfer rate between two fluids in a given volume is achieved when plate channel lengths are given by the thermal entrance length, i.e., when the thermal boundary layers meet at the exit of each channel. The overall design can be thought of an elemental construct of a dendritic heat exchanger, which c...
Chapter
Hot-tearing is a major casting defect that is often difficult to characterize, especially for multicomponent Al alloys used for cylinder head castings. The susceptibility of multicomponent Al-Cu alloys to hot-tearing during permanent mold casting were investigated using a constrained permanent mold in which the load and displacement were measured....
Conference Paper
In this paper, a novel geometry is proposed for evaporators that are used in Organic Rankine Cycles. The proposed geometry consists of employing successive plenums at several length-scale levels, creating a multi-scale heat exchanger. The channels at the lowest length-scale levels were considered to have their length given by the thermal entrance-l...
Article
Here we illustrate the free search for the optimal geometry of flow channel cross-sections that meet two objectives simultaneously: reduced resistances to heat transfer and fluid flow. The element cross section and the wall material are fixed, while the shape of the fluid flow opening, or the wetted perimeter is free to vary. Two element cross sect...
Article
This paper illustrates the morphing of flow architecture toward greater performance in a counterflow heat exchanger. The architecture consists of two plenums with a core of counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the heat exchange...
Article
The increasing use of carbon fiber-reinforced polymer matrix composites (CFPC) and aluminum alloys as lightweight materials in the automotive and aerospace industries demands enhanced surface preparation and control of surface morphology prior to joining. In this study, surfaces of both composite and aluminum were prepared for joining using an Nd:Y...
Article
Modelling and simulation of multiphysical phenomena need to be considered in the design and optimisation of mechanical properties of cast components in order to accelerate the introduction of new cast alloys. The data on casting defects, including microstructure features, are crucial for evaluating the final performance-related properties of the co...
Conference Paper
In this paper, novel geometries of heat exchanger architectures are proposed for evaporators that are used in Organic Rankine Cycles. A multi-scale heat exchanger concept was developed by employing successive plenums at several length-scale levels. Flow passages contain features at both macro-scale and micro-scale, which are designed from Construct...
Book
This collection encompasses the following four areas: (1) Solidification processing: theoretical and experimental investigations of solidification processes including castings solidification, directional solidification of alloys, electromagnetic stirring, ultrasonic cavitation, mechanical vibration, active cooling and heating, powder bed-electron b...
Article
To accelerate the introduction of new cast alloys, the modeling and simulation of multiphysical phenomena needs to be considered in the design and optimization of mechanical properties of cast components. The required models related to casting defects, such as microporosity and hot tears, are reviewed. Three aluminum alloys are considered A356, 356...
Article
The increasing use of lightweight materials, such as aluminum alloys, in auto body struchires requires more effective surface cleaning and texturing techniques to improve the quality of the structural components. The present work introduces a novel surface treatment method using laser interferometry produced by two beams of a pulsed Nd:YAG laser op...
Chapter
Introduction Materials and Optical Properties Experimental Procedures Microstructure Analysis of the Laser Ablation and Structuring Conclusions Acknowledgments
Chapter
The increasing use of Carbon Fiber-reinforced Polymer matrix Composites (CFPC) as a lightweight material in automotive and aerospace industries requires the control of surface morphology. In this study, the composites surface was prepared by ablating the resin on the top fiber layer of the composite using an Nd:YAG laser. The CFPC specimens with T7...
Chapter
To accelerate the introduction of new cast alloys the modeling and simulation of multiphysical phenomena needs to be considered in the design and optimization of mechanical properties of cast components. The required models related to casting defects, such as microporosity and hot tears are reviewed. Three aluminum alloys are considered A356, 356 a...
Chapter
The increasing use of lightweight materials, such as aluminum alloys, in auto body structures requires more effective surface cleaning and texturing techniques to improve the quality of the structural components. The present work introduces a novel surface treatment method using laser interferometry produced by two beams of a pulsed Nd:YAG laser op...
Article
To accelerate the introduction of new materials and components, the development of metal casting processes requires the teaming between different disciplines, as multiphysical phenomena have to be considered simultaneously for the process design and optimization for mechanical properties. The required models for physical phenomena as well as their...
Article
Testing of advanced materials and component mock-ups under prototypical fusion high-heat-flux conditions, while historically a mainstay of fusion research, has proved challenging, especially for irradiated materials. A new high-heat-flux-testing (HHFT) facility based on water-wall plasma arc lamps (PALs) is now introduced for materials and small-co...
Article
Full-text available
A new high-heat flux testing (HHFT) facility using water-wall stabilized high-power high-pressure argon plasma arc lamps (PALs) has been developed for fusion applications. It can accommodate irradiated plasma facing component materials and sub-size mock-up divertor components. Two PALs currently available at Oak Ridge National Laboratory can provid...
Article
Full-text available
Researchers share their views on efforts being made to develop algorithms in computational materials science. The development of solution algorithms will enable the treatment of increasingly complex systems and materials over longer spans of simulated time in an acceptable amount of computational time. The complexity of multiscale and multiphysics...
Article
A model based on a concept of "fraction of exfoliated area" as a function of oxide scale strain energy was developed to predict the extent of exfoliation of steam-side scale from boiler tube superheater loops. As compared with the Armitt diagram, which can be used to predict when scale damage and exfoliation would be likely to occur, a "fraction of...
Article
This paper presents a performance analysis of a supercritical organic Rankine cycle (SORC) with various working fluids with thermal energy provided from a geothermal energy source. In the present study, a number of pure fluids (R23, R32, R125, R143a, R134a, R218, and R170) are analyzed to identify the most suitable fluids for different operating co...
Article
Effective conductivity and mechanical properties of composite polymer electrolytes, in which the reinforcement phase is a sintered packed bed of Li-ion conductive ceramics particles, were estimated using Finite Element Analyses. The computations targeted estimation of the effect of sintering degree, i.e. size of the inter-particle connective necks,...
Article
In this paper, supercritical/transcritical thermodynamic cycles using mixtures of SF6 CO2 as working fluids were investigated for geothermal power plants. The system of equations that described the thermodynamic cycle was solved using a Newton-Raphson method. This approach allows a high computational efficiency even when thermophysical properties o...
Conference Paper
A constitutive model has been developed to predict the yield strength aging curves for aluminum casting alloys during non-isothermal age-hardening processes. The model provides the specific relationship between the process variables and yield strength. Several aging heat treatment scenarios have been investigated using the proposed model, including...
Conference Paper
The microstructure evolution during solution treatment plays an important role in mechanical properties of heat-treated aluminum alloys. In this paper, models were reviewed that can predict the microstructure evolution during the solutionizing process of the aging heat treatment of aluminum alloys. The dissolution of Mg2Si particles has been modele...
Article
The article briefly describes some of the characteristics of oxide growth and exfoliation, the impact of these oxides in modern power plants, and highlights findings from the workshop and requirements for additional research. Superheaters (SH) and reheaters (RH) in modern supercritical (SC) and ultrasupercritical (USC) coal-fired steam power plants...
Article
This paper provides an introduction to a comprehensive model being developed to predict and control oxide scale exfoliation from the steam-side of superheater and reheater tubes in steam boilers. The model deals with the main phenomena involved in scale growth and failure in steam, and incorporates major variables related to boiler design and opera...
Conference Paper
Full-text available
Utilization of titanium components made by powder metallurgy methods has had limited acceptance largely due to the high cost of titanium (Ti) powder. There has been renewed interest in lower cost economical powders and several Ti reduction methods that produce a particulate product show promise. This talk summarizes work done at Oak Ridge National...
Conference Paper
This paper reports on the performance of various organic refrigerants and their mixtures as working fluids for power generation in a supercritical Rankine cycle (SRC) from geothermal sources. Organic fluids that have zero or very low ozone depletion potential and are environmentally safe are selected for this study. Geothermal source temperature is...
Conference Paper
Numerical simulation results for the cold pressing of Armstrong CP-Ti powder are presented. The computational model was implemented in the commercial finite element program ABAQUS. Several simulation cases were conducted for cylindrical samples with different friction coefficients and different compaction pressures, under both single-action and dua...
Article
Mechanical properties and conductivity were computed for several composite polymer electrolyte structures. A multi-phase effective medium approach was used to estimate effective conductivity. The Mori-Tanaka approach was applied for calculating the effective stiffness tensor of the composites. An analysis of effective mechanical properties was perf...
Book
Proceedings of a symposium sponsored by Association for Iron and Steel Technology and the Process Technology and Modeling Committee of the Extraction and Processing Division and the Solidification Committee of the Materials Processing and Manufacturing Division of TMS (The Minerals, Metals & Materials Society) Held during the TMS 2012 Annual Meetin...
Article
The Armstrong Process® developed by Cristal US, Inc./International Titanium Powder, is an innovative, low-cost technology for producing Ti and Ti alloy powders in a one-step, continuous process. In this work, Armstrong Ti–6Al–4V powders were characterized and the cold compaction behavior of the powders were investigated in detail. As-received as we...
Article
The effective DC conductivity of particulate composite electrolytes was obtained by solving electrostatics equations using random resistors network method in three dimensions. The composite structure was considered to consist of three phases: matrix, particulate filler, and conductive shell that surrounded each particle; each phase possessing a dif...
Article
Covering a light-emitting diode (LED) with quantum dots (QDs) can produce a broad spectrum of white light. However, current techniques for applying QDs to LEDs suffer from a high density of defects and a non-uniform distribution of QDs, which, respectively, diminish the efficiency and quality of emitted light. Oak Ridge National Laboratory (ORNL) h...
Article
Research on supercritical carbon dioxide power cycles has been mainly focused on high temperature applications, such as Brayton cycle in a nuclear power plant. This paper conducts a comprehensive study on the feasibility of a CO2-based supercritical power cycle for low-grade heat conversion. Energy and exergy analyses of the cycle were conducted to...
Chapter
A computational methodology is presented for the process simulation of cold pressing and sintering of Armstrong CP-Ti powders. Since the powder consolidation is governed by specific pressure-dependent constitutive equations, solution algorithms were developed for the ABAQUS user material subroutine, UMAT, for computing the plastic strain increments...