Y. A. Hassan

Texas A&M University | TAMU · Department of Nuclear Engineering

This study advances the understanding of temporal dynamics in flow over a sphere in the near-wake by applying spectral proper orthogonal decomposition (SPOD) to time resolved particle image velocimetry experimental data collected at elevated pressures (3–6 MPa) over a wide range of Reynolds numbers (19 200–49 500). From the acquired velocity vector...

Packed beds are commonly found in many engineering systems and have been widely studied for decades. A relatively new packed bed system is the Pebble Bed Reactor, a type of generation-IV nuclear reactor. Unlike many of the packed beds encountered in chemical and process engineering applications, Pebble Bed Reactors are larger and operate at signifi...

The development of fluoride-cooled high-temperature reactors has greatly heightened the need for a thorough comprehension of heat transfer in packed beds that are cooled by liquid salts. The presence of restricting walls has a significant impact on the arrangement and movement of particles in packed beds with modest D/dp ratios (3.75–6). This study...

Diverse applications require us to know the value of a given physical quantity in real time. For many applications, we can rely on probes to fulfill this task. However, this approach can be challenging when we need to know these quantities in many locations over a given domain due to the spatial limitation involved. In this context, using Convoluti...

This file contains supplementary material related to the article titled "Surrogate-Based Multi-Objective Design Optimization of Tree-Shaped Fins with Uniform Branch End Distribution for Latent Heat Thermal Energy Storage," published in Physics of Fluids (Volume 36, Issue 7, Article 077160). https://doi.org/10.1063/5.0213318 https://doi.org/10.6089...

The enhancement of latent heat thermal energy storage (LHTES) systems through fin geometry optimization remains a critical challenge for leveraging the full potential of renewable energy sources. This study focuses on optimizing the geometries of tree-shaped fins to enhance power and energy densities in LHTES systems. The goal is to find branch des...

Heat pipe micro reactors are compact, innovative nuclear reactors that utilize heat pipe technology to manage heat transfer efficiently. The advantage of heat pipe micro reactors lies in their reduced complexity, high efficiency, and ability to provide stable power in various scenarios where traditional, larger reactors are not feasible or practica...

This study presents a comprehensive analysis of the flow behavior in packed pebble-bed reactors using computational fluid dynamics (CFD) simulations. The pebble-bed geometry corresponds to an experimental facility located at the Texas A&M Thermal-Hydraulics Research Laboratory. The unsteady Reynolds-averaged Navier–Stokes (URANS) k − ω shear stress...

Flow-Induced Vibrations (FIVs) have been of the upmost interest in the engineering community due to their large role in safety and reliability design in heat exchangers. This has especially been true in the nuclear sector as focuses have shifted to Small Modular Reactors (SMRs). These reactors aim to decrease the volumetric footprint of reactors, w...

SCOPE (Saudi International Conference On Nuclear Power Engineering) is a first-of-a-kind technical conference in the kingdom of Saudi Arabia. The conference aims to bring together world-renowned researchers and scientists to exchange their research and ideas and foster nuclear research and development. We are now accepting abstract submissions...

Comprehending and counteracting accident conditions presented by impedances of flow in diminutive subchannels of a Liquid Metal Fast Reactor (LMFR) hexagonal rod bundle are imperative toward their development and safety. Scarce experimental research currently exists in the literature to characterize the pressure and friction factor for partial bloc...

Heat pipe micro reactors are drawing a lot of interest lately due to their distinct features, including the elimination of moving parts required for transferring the heat, as they do so passively through heat pipes, combined with the ability of such reactors to provide energy to remote locations. This present study introduces a proposed design for...

The main contribution of this study is the effects of the operating conditions on the internal vapor pressure and temperature in an annular screen wick heat pipe, using distilled water as the working fluid. High-resolution pressure transducers, optical fiber distributed temperature sensors, and K-type thermocouples were employed to measure the inte...

Liquid metal fast reactors assemblies with wire spacers present a compact rod pitch to diameter ratio. Therefore, a typical off-normal condition that may occur is the blockage accident, caused by the accumulation of corrosion products or due to the detachment of broken wires. Blockage accidents may threaten the safety performance, leading to fuel r...

One of the most promising nuclear reactor designs is the Liquid-Metal Fast Reactor (LMFR). Its fuel bundle rods are separated with wire spacers that are helically wrapped around each fuel pin. Since this bundle presents a tight rod pitch to diameter ratio, accumulation of debris, cladding deformation or detachment of the wires may generate the form...

Mixing in large enclosures and thermal stratification play an important role in several advanced reactor designs, including liquid metal cooled reactors and high temperature gas reactors. Lessons learned from a recent international benchmark [1] using system-level codes for the simulations of Sodium-Cooled Fast Reactors (SFRs) have pointed out that...

Wall channeling is a phenomena of interest for Pebble Bed Reactors (PBRs) where flow is diverted into high-porosity regions near the wall. This diversion of flow can have a significant impact on maximum fuel temperatures and core bypass flow. Porous media models that are currently used to model PBRs for design scoping and transient simulation are l...

Thermal hydraulic CATHARE V1.3U code has been used to simulate an International Standard Problem (ISP38) experiment conducted at BETHSY Integral Test Facility located in Grenoble, France. This experiment dealt with simulation of the loss of Residual Heat Removal System (RHRS) during midloop operation. It involved opening of the pressurizer manway a...

Particle Image Velocimetry (PIV) is a non-intrusive measurement technique, which can be used to study the structure of various fluid flows. PIV is a very efficient measurement technique since it can obtain both qualitative and quantitative spatial information about the flow field being studied. This information can be further processed into informa...

Particle Image Velocimetry (PIV) is a non-intrusive measurement technique, which can be used to study the structure of various fluid flows. PIV is used to measure the time varying full field velocity data of a particle-seeded flow field within either a two-dimensional plane or three-dimensional volume. PIV is a very efficient measurement technique...

The dynamic subgrid scale closure model of Germano et. al (1991) is used in the large eddy simulation computer program, GUST, for incompressible isothermal flows. The advantage of the dynamic subgrid scale model is the exclusion of a model coefficient. This model coefficient is evaluated dynamically at each nodal location for a given timestep by fi...

A determination of nominal flow phenomena in liquid metal fast reactor (LMFR) fuel assemblies is critical toward generation-IV reactor development. Axially positioned spacer grids are used to maintain the geometry of hexagonal rod bundles and simultaneously introduce perturbations in the flow. Three-dimensional (3D) printed asymmetric honeycomb spa...

The airfoil-fin, Printed Circuit Heat eXchanger (PCHX) has been considered a key candidate for nuclear energy, Concentrated Solar Power (CSP), and several power conversion cycle applications, using different heat transfer fluids like molten salts, supercritical 𝐶𝑂2, and helium gas among others. In this study, differential pressure and flow rate mea...

This study used optical fiber-distributed temperature sensors to measure the internal and external temperature distributions of a water-cooled heat pipe. The sensor technology used in this study is fiber optical distributed temperature sensing, a distributed sensing technique based on the naturally occurring Rayleigh backscatter in optical fibers....

The scaled water-cooled Reactor Cavity Cooling System (RCCS) experimental facility reproduces a passive safety feature to be implemented in Generation IV nuclear reactors. It keeps the reactor cavity and other internal structures in operational conditions by removing heat leakage from the reactor pressure vessel. The present work uses Flownex one-d...

Potential accumulation of undesirable debris in a subchannel of a Liquid Metal Fast Reactor (LMFR) hexagonal fuel bundle presents accident conditions, which are crucial to investigate. Very limited experimental research persists in literature to understand the fluid dynamics effects of partially blocked subchannels, due to the presence of porous bl...

The objective of this study is to evaluate the capabilities of the Partially Averaged Navier–Stokes (PANS) method in simulations of the flow through a rod bundle representative of a nuclear fuel assembly with a channel-type spacer grid. In the PANS bridging turbulence model, filters can be applied to obtain any level of resolution from Reynolds Ave...

A 50 MWe helium-cooled fast modular reactor (FMR) is under development, and as part of the Department of Energy Integrated Research Project (IRP), Texas A&M University is conducting the thermal-hydraulic characterization of its baseline core configuration. We experimentally investigated the axial and cross flow fields characteristics in the hexagon...

Micro reactors are gaining substantial interest worldwide due to their capabilities to deliver power to remote and decentralized areas and their long fuel cycles, making them more attractive than other energy sources. This paper presents a conceptual design and steady-state neutronics and thermal-hydraulics analyses results for a heat pipe cooled y...

One of the most promising nuclear reactor designs is the Liquid-Metal Fast Reactor (LMFR). Its fuel assembly consists of rods containing the fuel material, arranged in a triangular lattice and covered by a hexagonal duct. The rods are separated with wire spacers that are helically wrapped around each fuel pin. Because this geometry is tight and com...

A Computational Fluid Dynamics (CFD) model is presented to simulate an isothermal flow within a 61-pin wire-wrapped fuel assembly, typically employed in Liquid Metal Nuclear Reactors. A methodology is proposed to compute subchannels friction factors and split parameters, which are relevant variables for reactor licensing calculations and safety eva...

The objective of this study is to assess the predictive capabilities of low and high-fidelity turbulence models for low-Prflows. For this purpose, predictions by two-equation (k-ε) Reynolds-Averaged Navier Stokes (RANS), partially-averaged Navier Stokes (PANS) hybrid RANS/Large Eddy Simulation (LES), and DSM, WALE, filtered LES models are compared...

The verification and validation of Pronghorn is imperative for predicting the fluid velocity, pressure, and temperature in advanced reactors, specifically high-temperature gas-cooled reactors. Pronghorn is a coarse-mesh, intermediate-fidelity, multidimensional thermal-hydraulic code developed by Idaho National Laboratory. The Pronghorn incompressib...

Packed beds play an important role in many engineering fields, with their applications in nuclear energy being driven by the development of next-generation reactors utilizing pebble fuel. The random nature of a packed pebble bed creates a flow field that is complex and difficult to predict. Porous media models are an attractive option for modeling...

This study used an artificial neural network (ANN) regression model in wire-wrapped fuel assemblies to estimate the transition-to-turbulence flow regime boundary (RebT) and friction factor. The ANN models were trained and validated using existing experimental datasets. The bundle dataset comprised several design parameters, such as the number of ro...

In this study, the experimental results of the flow behavior of a non-isothermal confined impinging single plume were analyzed. Experimental measurements were performed in the upper plenum of a high-temperature gas-cooled reactor (HTGR) that was scaled, designed, and assembled at Texas A&M University. The goal was to investigate flow mixing, therma...

A model to predict the pressure drops in a hexagonal wire-wrapped rod bundle with blockage is developed. The model is based on the Upgraded Cheng and Todreas Detailed (UCTD) correlation. Two series of experiments from Texas A&M University (TAMU) and Karlsruhe Institute of Technology (KIT) are used for calibration and validation. The UCTD correlatio...

This report conducts a preliminary investigation of the available literature and summarizes some potential advanced measurement and visualization techniques for operating high-temperature heat pipe (HP) that can be implemented to support the United States (U.S.) Department of Energy (DOE) Microreactor Program (MRP). The primary objective of the ext...

An integrated effort by the Versatile Test Reactor (VTR) Gas-Cooled Fast Reactor (GFR) Team to develop an experiment vehicle or extended-length test assembly for the VTR experiments is led by Idaho National Laboratory and supported by an industrial partner, General Atomics, and university partners, including Texas A&M University, University of Mich...

An integrated effort by the Versatile Test Reactor (VTR) Gas-Cooled Fast Reactor (GFR) Team to develop an experiment vehicle or extended-length test assembly for the VTR experiments is led by the Idaho National Laboratory and supported by an industrial partner, General Atomics, and university partners, including Texas A&M University, University of...

This study aims at investigating the inlet flow conditions of flow through an axisymmetric sudden expansion with an expansion ratio (ER) of 2.0. A series of large eddy simulations (LES) with WALE model were conducted for different inlet Reynolds numbers ( Re) and turbulence intensities ( u rms /Ū m ). The reattachment length, defined as the length...

The helically-coiled heat exchanger (HCSG) offers advantages over straight tubes such as compactness in geometry, increased heat transfer coefficients, and capability to absorb thermal expansion. In this study, the time-resolved velocity field data of shell-side crossflow over a five-layer helically coiled steam generator geometry was obtained usin...

A direct numerical simulation (DNS) database is presented for turbulent flow and heat transfer in a vertical channel for Reynolds number Reτ = 150 and 640, Prandtl number Pr = 0.004, 0.025 and 0.71, with and without buoyancy forcing (Ri = 0 and 0.15 or 0.21). The effects of Pr on mean and turbulent flow and thermal transport in mixed convective con...

In this study, an experimental investigation was conducted on the rising height and contact angle of fluid in an annular wick-type heat pipe. The annular wick-type heat pipe was characterized by a small gap between the wick structure and tube wall, which compensated for the pressure drop along with the porous media and created additional capillary...

This paper presents a direct numerical simulation (DNS) and proper orthogonal decomposition (POD) of the flow in a randomly packed pebble bed. Nek5000, a spectral-element computational fluid dynamics code, was used to develop the DNS fluid flow data, including first- and second-order statistics for an experimental randomly packed pebble bed. Turbul...

Hexagonal rod bundles arranged in a tightly packed triangular lattice are extensively used for heat transfer and energy generation applications. Staggered spacer grids are used to maintain the structural integrity of gas-cooled fast reactor (GFR) fuel assemblies, while inducing localized turbulence in flow. Damage to these spacer grids results in a...

An experimental investigation has been conducted on the hydraulic characteristics of annular type wick structures for heat pipes. An experimental facility which can measure porosity, permeability, and effective pore radius of the wick structures in a vacuum condition is established. Nine different types of multi-layered (6 layers in total) composit...

The development of nuclear reactors that utilize pebble fuel has drastically increased the demand for improving the capabilities to simulate the packed beds found in these reactors. The complex flow fields found in a pebble bed make computational fluid dynamics (CFD) simulations time consuming and costly. Intermediate fidelity porous media models,...

The verification and validation of Pronghorn is imperative to assert its accuracy when predicting the fluid velocity, temperature, and pressure in high-temperature gas-cooled reactors. Pronghorn is a coarse-mesh, intermediate-fidelity, and multidimensional thermal-hydraulics code developed by the Idaho National Laboratory. The Pronghorn porous medi...

Linear eddy viscosity-based Reynolds-averaged Navier-Stokes (RANS), hybrid RANS/Large Eddy Simulation (LES), and LES models are applied for simulations of plane channel flow at Reynolds number Reτ = 150 and 640. Results are obtained for fluids with Prandtl number (Pr) of 0.025 and 0.71, for cases without buoyancy (Gr = 0) and for a vertical channel...

Recent interest for the development of high-temperature gas reactors has increased the need for more advanced understanding of flow characteristics in randomly packed pebble beds. A proper understanding of these flow characteristics can provide a better idea of the cooling capabilities of the system in both normal operation and accident scenarios....

One of the fuel assembly designs considered for liquid metal-cooled fast reactors (LMFR) uses wires helically wrapped around fuel pins as spacers. The understanding of the coolant behavior in LMFR fuels under the influence of a partially blocked flow area is required for a correct safety assessment. Accumulation of debris or cladding deformation ma...

An experimental investigation of single helium bubbles rising in a stagnant molten fluoride salt mixture was conducted in a 25.4 mm quartz tube at 600 °C and atmospheric pressure. The fluoride salt chosen for this research was the eutectic mixture of LiF-NaF-KF (46.5–11.5–42%), also known as FLiNaK. The images obtained using a high-speed camera wer...

Laser Induced Fluorescence (LIF) was investigated for the potential use of full-field temperature measurements in high-temperature molten salt applications. The fluorescent spectra of Tb³⁺, Eu³⁺, and Dy³⁺ were measured using fiber optic spectroscopy in order to study the temperature dependence of lanthanides in the molten LiF-NaF-KF (FLiNaK) salt....

This research work seeks to investigate the influence of spacing and heat transfer on the wake behavior of a triangular arrangement of spheres. Four experimental configurations have been investigated at three Reynolds numbers, Re1 = 350, Re2 = 700, and Re3 = 1050. Two isothermal cases were investigated with spacing between the spheres of zero and o...

Generalizability of machine-learning (ML) based turbulence closures to accurately predict unseen practical flows remains an important challenge. It is well recognized that the neural network (NN) architecture and training protocol profoundly influence the generalizability characteristics. At the Reynolds-averaged Navier–Stokes level, NN–based turbu...

The predictive capability of RANS, hybrid RANS/LES and LES turbulence models are assessed for low-Pr flows involving complex flow features expected in engineering applications, such as forced convection, buoyancy, shear, reattachment, and recirculation. The models are tested for three test case vertical channel, vertical backward facing step with h...

Recent interest for the development of high-temperature gas reactors has increased the need for more advanced understanding of flow characteristics in randomly packed pebble beds. A proper understanding of these flow characteristics can provide a better idea of the cooling capabilities of the system in both normal operation and accident scenarios....

Wire-wrapped hexagonal fuel bundles have been extensively investigated due to their enhanced heat transfer and flow characteristics. Experimental measurements are important to study the thermal-hydraulic behavior of such assemblies and to validate and improve the predicting capabilities of specialized correlations and computational tools. Presently...

The elevated temperatures and corrosive environment typical of molten salt reactors’ operating conditions may pose challenges to flow and temperature measurements. Experimental measurements of these thermal–hydraulic parameters are paramount to advance the knowledge and understanding of the molten salts’ behavior, and are necessary for the validati...

In this study, an artificial neural network (ANN) model was utilized to predict the friction factor for wire-wrapped rod assemblies. The 80 experimental data sets from UCTD correlations (Chen et al., 2018) were used to train and validate the ANN models. Three ANN models were introduced for laminar, transition, and turbulence flow conditions, respec...

We present results for a direct numerical simulation study of isothermal incompressible flow in a regularly packed pebble-bed domain with a bounding wall. We focus specifically on the near-wall behavior of the flow. Our simulation is carried out at a Reynolds number of 9308 to facilitate cross verification with available high-fidelity data. To redu...

Recent interest for the development of high-temperature gas reactors has increased the need for more advanced understanding of flow characteristics in randomly packed pebble beds. A proper understanding of these flow characteristics can provide a better idea of the cooling capabilities of the system in both normal operation and accident scenarios....

In flow boiling systems, bubbles tend to slide along the wall as they depart from nucleation sites where they originate. This behavior has a profound impact on the wall heat transfer as evidenced in previous experiments. As a result, the heat transfer modeling associated with sliding bubbles has gained great attention within the CFD boiling heat tr...

Internal flows through rod assemblies are commonly found in heat exchangers, steam generators, and nuclear reactors. One of the fuel assembly designs considered for liquid metal-cooled reactors utilizes wires helically wrapped around each fuel rod as spacers. The wires keep the fuel pins separated, enhancing the turbulent mixing, and heat transfer,...