bluuebunny/crossref_metadata_2025 huggingface dataset:
Falling Film Evaporation of Pure Refrigerant HCFC123 in a Vertical Rectangular Channel With Serrated-Fins
Authors: Koyama Shigeru , Ohara Junichi , Kuwahara Ken , Masaki Kenichi
Published: January 2022

In the present study, the characteristics of heat transfer and flow patterns are experimentally investigated on the falling film evaporation of pure refrigerant HCFC123 in a vertical rectangular channel with serrated-fins. The experimental ranges are as follows: the mass velocity G = 28∼70 kg/(m2 s), the heat flux q = 30,50 kW/m2 and the pressure 100 kPa. It is clarified that the heat transfer coefficient α depends on G and q in the region of vapor quality x ≥ 0.3, while there is little influence of G and q in the region x ≥ 0.3. From the direct observation, flow patterns are classified into five typical ones : plane liquid film, wavy liquid film, liquid film accompanied with dry patch, liquid film accompanied with dripping and liquid film accompanied with mist. An empirical correlation equation for evaporation heat transfer coefficient in a falling film plate-fin evaporator is also proposed, taking fin efficiency into consideration.
Simulation of Vertical Swirling Flows in a Model Furnace With a High Performance Numerical Method
Authors: de Lemos Marcelo J. S. , Assato Marcelo
Published: January 2022

This work reports numerical results for the case of incompressible laminar heated flow with a swirl in a vertical cylindrical chamber. Computations are obtained with a point-wise block-implicit scheme. Flow governing equations are written in terms of the so-called primitive variables and are recast into a general form. The discretized momentum equations are applied to each cell face and then, together with the mass-continuity, tangential velocity and energy equations, are solved directly in each computational node. The effects of Rayleigh, Reynolds and Swirl numbers on the temperature field are discussed upon. Flow pattern and scalar residual history are reported. Further, it is expected that more advanced parallel computer architectures can benefit from the error smoothing operator here described.
A Study of the Effects of Air-Preheat on the Structure of Methane-Air Counterflow Diffusion Flames
Authors: Lim Jongmook , Gore Jay P. , Viskanta Raymond
Published: January 2022

The effects of air-preheat on flame structure are studied in counter-flow methane-air diffusion flames, considering air temperatures in the range 300 to 560 K. Species concentrations for H2, O2, N2, CH4, CO, CO2, C2H2 and C2H4 were measured using sampling and gas chromatography. Concentrations of NO were measured using sampling and a chemiluminescence analyzer. Results of numerical calculations using detailed chemistry were compared with the measurements. The numerical calculations and measurements show good agreement for major species. Independent of temperature in the range 300 to 560 K, measured and predicted concentrations of CH4, CO2, O2 and N2 collapse reasonably well when plotted against mixture fraction. However, the peak CO and H2 concentrations increase with increasing air-preheat. The peak CO concentrations increased by dissociation of CO2. However, the dissociation causes relatively small scatter in the CO2 state relationship. The peak H2 concentrations increase because of an increase in H atom concentrations causing enhanced CH4 dissociation. Both the measured and predicted NO profiles show approximately 70% increase in peak mole fractions with increasing air-preheat. The predictions of peak NO mole fractions are lower by about 10% than the data for TAIR = 300 K and 560 K. However, in the fuel-rich region, the predicted mole fractions are approximately 40% of the data. The increase in peak NO concentration occurs primarily through an enhanced rate of N2 + CH → HCN + N and subsequent oxidation of the N atoms by the OH radical.
Radiative Properties and Pre-Melting Phase Transition of Uranium Dioxide at High Temperatures
Authors: Salikhov T. P. , Kan V. V. , Ronchi C.
Published: January 2022

A new method for measuring radiative properties of nuclear fuel materials at high temperatures has been developed. The method is based on the pulsed-diffuse optical probing of the flat surface heated by a powerful laser beam and on multiwavelength pyroreflectometry.

Such an approach enables one to measure spectral reflectivity and emissivity of the nuclear fuel material with diffuse, specular or mixed specular-diffuse reflection surface at high temperatures. Moreover, this method permits reflectivity and emissivity measurements to be performed near the melting point of the material being investigated with a high resolution, despite the sharp change in the reflection indicatrix at melting temperature. The described technique was successfully applied up to 4000 K in the spectral range 0.4-1.1 μm at different wavelengths. The reflectivity and emissivity measurement uncertainty does not exceed 3%. The potential of the method developed has been demonstrated in measuring radiative properties of uranium dioxide at high temperatures. The experimental data on radiative properties of uranium dioxide in the spectral range 0.4-1.1 μm and in the temperature interval 2000–3500 K are presented in the paper. Direct measurements of the spectral reflectivity near the premelting point and investigation of the complex behavior of the emissivity during solidification of uranium dioxide have been performed for the first time.
Multiple-Ray Tracing Scheme for a Packed Bed of Non-Specular Spheres
Authors: Wu A. K. C. , Lee S. H.-K.
Published: January 2022

Radiative heat transfer in a system of packed particles is important for numerous industrial processes. Most of the existing numerical work have focused on specular spheres. There has been relatively less numerical work on a packing of diffuse spheres. There are some numerical studies on diffuse spheres, but their foci were not on the adequacy of the Monte-Carlo ray-tracing scheme. This study examines this issue and presents a modified ray-tracing scheme in which multiple rays are utilized. The results show this scheme to be more accurate for certain porous medium.
Developing Real-World, Hands-On, Low Cost, Multi-Disciplinary Experiences for Undergradute Students
Authors: Nasr Karim J. , Jordan Colin
Published: January 2022

This paper presents the use of a vehicle and its components to convey various principles in the area of thermal sciences. The experiences were designed to provide students with hands-on exposure to real systems, develop innovative laboratory experiments and incorporate multi-disciplinary projects in thermal sciences. A total of about ten experiments were derived from the donated vehicle, they included a coast down test, a fuel system test stand, a HVAC unit, and a mechanism experiment, just to name a few. Students explored with the components of the vehicle to develop several laboratory experiments, reverse engineering, and set-up experimental apparatuses for research. This paper describes one laboratory setup, the HVAC system, presents its classroom implementation and related educational objectives, and documents student feedback and faculty reflections on the experiences.
Thermocapillary-Coriolis Instabilities in Liquid Bridges
Authors: Cunff Cédric Le , Zebib Abdelfattah
Published: January 2022

Coriolis effects on thermocapillary instabilities in a liquid bridge of infinite length are investigated. The flow is driven by an imposed temperature gradient along the z-direction in a (r, θ, z) rotating frame of reference. When the rotation vector is parallel to the z-axis the base return flow with no rotation is not modified. In this case, rotation is stabilizing with traveling waves preferred. If the rotation is orthogonal to the z-axis, the base flow is modified and is no longer one-dimensional. Asymptotic methods valid for small rotation are used to calculate the base flow which may become multicellular, both in the radial and azimuthal directions, depending on the Prandtl, Marangoni, and Diot numbers. Linear stability analysis of the new base flow indicates that this type of rotation can be destabilizing while traveling azimuthal waves continue to be the prefered form of convection. Finally, the effect of rotation is studied in a finite length cylinder by direct numerical simulation.
A Numerical Study of Directional Solidification and Melting in Microgravity
Authors: Chen P. Y. P. , Timchenko V. , Leonardi E. , de Vahl Davis G. , de Groh H. C.
Published: January 2022

A computational model is presented for the study of the solidification and melting of a pure substance and of a binary alloy. The enthalpy method has been used, and incorporated into a commercial CFD code. Three examples of the use of the model are described: the three-dimensional solidification of a pure substance (succinonitrile), the results of which are compared with experiment; an example of the solidification of a bismuth-tin alloy; and a simulation of a solidification and melting experiment done in space known as the MEPHISTO program.
Numerical Analysis of Unsteady Marangoni Flow in a Square Cavity Under Reduced Gravity
Authors: Torii Shuichi , Yano Toshiaki , Tsuchino Fumihiro
Published: January 2022

A numerical study is performed on unsteady natural convection heat transfer and fluid flow in a cavity under reduced gravity. Consideration is given to the influences of Marangoni and buoyancy convections on the thermal and velocity fields in a two-dimensional square cell. Here, it consists of two opposing vertical side walls held at constant but different temperature with the horizontal lower wall insulated and the upper face treated as non-deformable adiabatic free surface. The governing equations are discretized by means of a finite-difference technique and numerically solved. If only the buoyancy convection is taken into account, the fluid temperature gradient in the cavity under the reduced gravity is substantially decreased near the hot and cold vertical walls and the dominant heat transfer mechanism switches from convection into conduction, as time progresses. In other words, the heat transfer performance is substantially attenuated due to the absence of buoyancy. On the contrary, the corresponding flow pattern is similar to that under normal gravity condition, resulting in a slight deterioration of the heat transfer performance, if both Marangoni and buoyancy convections interact. Therefore, this is found to be the dominance of Marangoni flow over natural convection in the system considered.
Design and Development of a Sidewall Vent System for Airflow Distribution and Decompression Protection in Commercial Aircraft
Authors: Petersen Brian J. , Buzza Timothy G. , Shim Hyo S.
Published: January 2022

In existing commercial aircraft the air conditioning system delivers air to the cabin for temperature control and cabin pressurization. The conditioned air introduced into the passenger cabin flows down to the utility tunnels under the floor through the sidewall vents and to an outflow valve or valves located on the fuselage of the aircraft and eventually to the ambient pressure. The function of the vent system is to provide cabin air distribution flow control and also to provide decompression protection. In the event of a fuselage decompression the pressure differential between the upper and lower compartments must not exceed the structural limits of the cabin floor. The cabin vent system is designed to limit this pressure differential by increasing the flow area between the upper and lower compartments in the event of a rapid decompression. The differential pressure loads on the floors were analyzed using a rapid decompression computer code.

Lab testing was performed to verify the differential pressure at which the mylar panel ruptures. This testing used a vacuum chamber test setup. The sidewall vent system was exposed to ambient air pressure on one side and quickly exposed to the vacuum system pressure on the other side. These test results were used in the rapid decompression analysis. There are multiple sidewall vents along the length of an aircraft cabin. Therefore aircraft testing was utilized to verify airflow distribution in the aircraft.
An Experimental Investigation of Steam Injection in Fractured Porous Media
Authors: McCreery Glenn. E. , Martineau Richard C.
Published: January 2022

Experiments were conducted which model steam condensation front propagation during the Steam Enhanced Extraction (SEE) process of removing liquid contaminants in fractured porous media*. The process is being considered for implementation for removal of contaminants in the basalt flows which lie above the Snake River aquifer at the Idaho National Engineering and Environmental Laboratory (INEEL). The SEE process consists of steam injection into porous media which is unsaturated, or partially or completely saturated with water and contains (typically) organic contaminants. The steam condenses and sweeps the contaminant along with the condensate toward a low pressure region established by a vacuum (and water) pump. The experiments described are the first in a series to compare and extend results obtained by others for homogeneous porous media, and layers of homogeneous porous media to fractured porous media. Experiment results and thermal analysis are presented.
Modeling Regional Climate Impacts of a Proposed Hydroelectric Project
Authors: Sailor David J. , Rosen Jesse N.
Published: January 2022

This paper is a preliminary analysis of the potential for atmospheric thermal pollution from a man-made reservoir. The specific site for the study is a proposed hydroelectric project on the Sogamoso River in Colombia, S.A. The region is agricultural with the two staple crops being coffee and cocoa. These two crops are sensitive to both high temperatures and more dramatically to high humidity levels. Farmers from the region are concerned that the construction of the reservoir will negatively impact crop yield. We have used a numerical atmospheric model to simulate weather from the region both without and with the proposed reservoir. Simulations show the magnitude of the impact is too small to be of consequence to crop yield. With these results we draw conclusions about the potential impact of the reservoir on climate. This paper provides a brief introduction to the theory behind the climatic consequences of a large lake. Results are then discussed for two time periods, one during the rainy growing season and one during the dry season. One of the biggest uncertainties in the model boundary conditions arises from the specification of the lake temperature, so the sensitivity of the model to lake temperature is analyzed for one of the study dates. Finally it is shown how a small set of weather simulations are used to draw climatic conclusions.
Neck Down and Thermally Induced Defects in High Speed Optical Fiber Drawing
Authors: Yin Z. , Jaluria Y.
Published: January 2022

The drawing speeds employed in the manufacturing of optical fibers have been rising in recent years due to the growing worldwide demand. However, increasing speeds have placed stringent demands on the manufacturing process, mainly because of large temperature gradients that can generate thermally induced defects and undesirable variations in fiber characteristics. Heat transfer and glass flow that arise in drawing fibers of diameters 100–125 microns from cylindrical silica preforms of diameters 5–10 cm play a critical role in the success of the process and in the maintenance of fiber quality. This paper presents an analytical and numerical study of the optical fiber drawing process for relatively large diameter preforms and draw speeds as high as 20 m/s. The free surface which defines the neck-down profile is determined by a force balance and an iterative numerical scheme is employed to obtain the profile under steady conditions. The transport in the glass is calculated to obtain the temperature, velocity and defect distributions. The problem is complicated because of combined radiation, convection and conduction mechanisms that govern this important manufacturing process. A zone radiation model is used for calculating radiative transport within the glass. Because of the large reduction in the diameter of the preform/fiber, the velocity level increases dramatically and the geometry becomes complicated. A coordinate transformation is used to convert the domain to a cylindrical one. Wherever possible, the numerical results are compared with experimental and numerical results in the literature for smaller draw speeds for validation. The effects of high draw speeds and of other physical variables on defects generated in the fiber, on the neck-down profile, and on the relevant transport processes are determined.
Continuously Moving Finite Thickness Susceptor in CVD Processing
Authors: Chiu Wilson K. S. , Jaluria Yogesh
Published: January 2022

Chemical Vapor Deposition (CVD) of thin films onto a moving surface is presented in this study. Conjugate heat and mass transfer processes with surface reactions and conduction effects in the susceptor are numerically investigated. The numerical model is validated for silicon deposition through comparisons with analytical results and experimental data. Results show that a moving susceptor with finite thickness can have a significant effect on deposition rates. Films produced by continuous CVD processing are shown to have a strong dependence on several operational parameters. Increasing susceptor speed and susceptor thickness results in lower deposition rates, thereby decreasing the final film thickness. Enhanced film deposition is obtained by the use of low thermal diffusivity material or by increasing the heating zone size. The governing parameters are correlated to include these effects under typical operating conditions. The results and correlations may be used as guidelines for future CVD reactor design.
Thermal and Carrier Transport in Laser Photo-Etching of n-GaAs Semiconductor Thin Films
Authors: Zhang X. , Wen J.
Published: January 2022

Coupled thermal and carrier transport (electron/hole generation, recombination, diffusion and drifting) in laser photo-etching of GaAs thin film is investigated. A new volumetric heating mechanism originated from SRH (Shockley-Read-Hall) non-radiative recombination and photon recycling is proposed and modeled based on recent experimental findings. Both volumetric SRH heating and Joule heating are found to be important in the carrier transport as well as the etching process. SRH heating and Joule heating are primarily confined within the space charge region which is about 20 nm from the GaAs surface. Surface temperature rises rapidly as the laser intensity exceeds 105 (W/m2). Below a laser intensity of 105 (W/m2), thermal effect is negligible. The etch rate is found to depend on the competition between photo-voltaic and photo-thermal effects on surface potential. At high laser intensity, etch rate is increased by more than 100% due to the SRH and Joule heating.
Modeling Issues for Reactive Spray Atomization and Deposition Processes
Authors: Delplanque Jean-Pierre , Rangel Roger H.
Published: January 2022

The primary goal of the present work is to define a model to predict the characteristics of materials processed using reactive spray atomization and deposition. The materials considered are aluminum alloys while target dispersoids are primarily oxides. These may be obtained by the reaction of oxygen-containing atomization gas mixtures with molten alloy droplets. Droplet position and velocity histories are obtained from the numerical solution of the one-dimensional equation of motion. The energy equation inside the droplet is solved numerically using finite-differences to predict the spatially resolved temperature field. The solid/liquid interface progression rate is estimated using a power law while an oxidation rate expression based on the Mott-Cabrera theory is used for the oxide thickness. Such a model can then be used to determine the parameters controlling the volume fraction and the size distribution of the dispersoids for various systems.
A Multigrid Simulation of the Rapid Solidification of a Pendent Molten Ball
Authors: Sripada Srinivas S. , Cohen I. M. , Ayyaswamy P. S.
Published: January 2022

We consider the solidification of a molten ball pendent at the end of a metallic wire. The melting is caused by the heat from a weakly ionized plasma (dominated by charge-neutral collisions). The low current plasma discharge supplies energy to the wire whose tip subsequently melts. The melt so formed rolls up due to surface tension into a pendent spherical segment at the bottom of the wire. The electric discharge is then extinguished and the melt is allowed to rapidly solidify in the ambient atmosphere. We numerically simulate this solidification process by using a body-fitted adaptive grid scheme. An energy balance at the interface between the solid and molten phases is used to track the motion of the melt interface as the molten segment solidifies. The equivalent heat capacity method is used to account for the latent heat and the “mushy” layer. The set of governing equations is discretized using a finite-volume method, and a multigrid iterative solver is used to solve the system. We evaluate the transient temperature distribution in the layer. Such an evaluation has important applications both in microelectronic packaging and in plasma processing. Results from a simulation of the electronic flame off discharge process employed in micro-electronic packaging (wire bonding) are presented.
Analysis of Heat Transfer to a Spectrum of Particles in Plasma Spray Coating Process
Authors: Verma Alok , Jog Milind A.
Published: January 2022

In plasma spray coating process, ceramic/metallic particles are introduced in a flow of thermal plasma. The heat transfer from the plasma to the particles results in heating and melting of the particles. The molten particles then impinge on a substrate to be coated. The impacting particles spread on the substrate due to their high velocities forming a thin layer. Heat transfer from the particles to the substrate results in rapid solidification and formation of a thin protective coat on the substrate. The heat transfer to/from particles affects the quality of the coatings. It is therefore important to predict and control the particle heat transport. In this paper, we have considered a spectrum of particles moving in thermal plasma. The particle spectrum is represented by a regular array of identical particles. The particle longitudinal and lateral spacing is varied independently to study the effect of particle spacing on the flow and heat transport. The Reynolds number based on the particle diameter is in the intermediate regime (Re ∼ 20–100). The background gas, argon, is at atmospheric pressure and the flow is considered steady. The flow and transport is analyzed by a cylindrical-cell numerical model. An orthogonal adaptive grid is generated to body-fit the particle surface as well as the cylindrical outer boundary of the cell envelop. The grid near the surfaces of the particles is very fine and resembles spherical co-ordinates. The conservation equations for mass, momentum, and energy are solved in the plasma by a finite volume numerical method. The flow field and the temperature distribution are calculated in the plasma for various combinations of lateral and longitudinal particle spacings. The local variations of the viscous and pressure forces acting on the particle surface as well as the local Nusselt number variations are calculated. The overall Nusselt number and the drag force acting on each particle are determined. Results indicate that the flow and transport around a given particle is significantly influenced by the presence of the adjacent particles.

The heat transport and drag force results for a particle in a spray are substantially different from those available for an isolated particle at the same Reynolds number. An increase in the lateral spacing between particles results in a decrease in the Nusselt number as well as the drag coefficient. In contrast, increasing longitudinal particle spacing leads to an increase in both the Nusselt number and the drag coefficient. At lateral spacings greater than about four diameters, the effect of side particles becomes negligible. However, the influence of upstream particles remains significant even at longitudinal particle spacing of five diameters. Simple correlations for the overall Nusselt number and drag coefficient have been proposed to incorporate the effect of inter-particle interactions.
Multi-Spatial-Temporal Grids for Three Dimensional Transient Conduction Problem
Authors: Siu W. W. M. , Lee S. H.-K.
Published: January 2022

Computationally intensive problems are often encountered in numerical heat transfer studies. One of the major cause is the small time steps brought forth by the fine spatial grid required at critical regions. Consequently, computational efficiency becomes one of the key issue in such numerical studies. By and large, the existing methods for enhancing computational efficiency either are only applicable for iterative operations, or provide limited speed-up because the solutions at the certain regions within the domain are marching with an unnecessary small time step. This work presents the development of a new method which achieves a higher computational efficiency. This method is herein referred to as the Multi-Spatial-Temporal Grid (MSTG) method, and it provides a significant speed-up by simultaneously implementing grid reduction and multiple timesteps. This method has been tested to be effective in improving the computational efficiency of conduction problem in transient multi-dimensional orthogonal coordinates. Current benchmarking showed the solution obtained from this method to be within 0.04% of those obtained from a uniform grid. In addition, the speed-up of this scheme was found to be significantly higher than most existing methods.
Control of Convergence of a Computational Fluid Dynamics Algorithm Using Fuzzy Logic
Authors: Dragojlovic Zoran , Kaminski Deborah A. , Ryoo Juntaek
Published: January 2022

Relaxation factors in an iterative fluid flow solver are adjusted by fuzzy logic to achieve automatic convergence of the solution. Three benchmark problems are considered, including a lid-driven cavity, free convection in a square enclosure, and flow in a channel with a backward-facing step. The SIMPLER algorithm with simple substitution is used to solve the incompressible Newtonian conservation equations. The relaxation factors for u and v velocities and temperatures are adjusted on each iteration according to a specified rule set. The control logic allows the algorithm to restart automatically if divergence is imminent. Convergence was achieved in all cases and the CPU time required for convergence with fuzzy control is not far from optimum, compared to that required using conventional constant relaxation factors.
Numerical Bifurcation and Chaos in a One-Dimensional Nonlinear Combined Mode Problem and the Inverse Application
Authors: Lan Chao-Ho , Howell John R.
Published: January 2022

Radiative heat transfer coupled with the other modes is described by highly nonlinear integro-differential equations. Due to the existence and uniqueness of a real positive temperature distribution, numerical solutions should be obtainable. However, experience shows that the solutions usually present convergence difficulties unless we carefully vary parameters and iterate numerous times, depending on the numerical method chosen for solution. In nonlinear analysis, the main objective of bifurcation and chaos theory is to study how the solutions of equations vary as the parameters are varied. This work presents a computational study of bifurcation and chaotic behavior in numerical solutions of combined-mode problems and how that behavior changes with different values of the parameters. Then, maps of the limits of bifurcation and chaos are made, which show the region of convergence. These should be beneficial to the researchers who attempt to program combined mode problems. Finally, a 1-D inverse combined mode problem is investigated to demonstrate the efficiency of the map.
New Objective Approaches for Characterization of Interfacial Structures in Two-Phase Flow
Authors: Ishii M. , Mi Y. , Tsoukalas L. H. , Kim S.
Published: January 2022

Two objective approaches for characterizing the interfacial structures and identifying flow regimes in two-phase flow are presented. The first approach is based on the use of a multi-sensor probe technique to get detailed local information. Performance of a newly designed four-sensor conductivity probe was investigated in a vertical test section with 50.8 mm i.d. The experimental data is categorized into two groups in view of their interfacial structures. Local information on the void fraction, interfacial area concentration, Sauter mean diameter, interface velocity, etc., was obtained successfully. The experimental data demonstrate well the characteristics of the two groups of bubbles.

The second approach is based on the application of a non-intrusive impedance void-meter and neural networks. An advanced non-intrusive impedance void-meter provides input signals to neural networks which are used to identify vertical flow regimes. Both supervised and self-organizing neural network learning paradigms performed flow regime identification successfully. The methodology presented holds considerable promise for multiphase flow diagnostic and measurement applications.
Identification of Flow Pattern Transitions for Horizontal Two-Phase Flows
Authors: Hervieu Eric , Seleghim Paulo
Published: January 2022

This work concerns the development of a methodology the objective of which is to characterize and diagnose two-phase flow regime transitions. The approach is based on the fundamental assumption that a transition flow is less stationary than a flow with an established regime.

In a first time, the efforts focused on:

the design and construction of an experimental loop, allowing to reproduce the main horizontal two-phase flow patterns, in a stable and controlled way,

the design and construction of an electrical impedance probe, providing an imaged information of the spatial phase distribution in the pipe,

the systematic study of the joint time-frequency and time-scale analysis methods, which permitted to define an adequate parameter quantifying the unstationarity degree.

In a second time, in order to verify the fundamental assumption, a series of experiments were conducted, the objective of which was to demonstrate the correlation between unstationarity and regime transition. The unstationarity degree was quantified by calculating the Gabor’s transform time-frequency covariance of the impedance probe signals. Furthermore, the phenomenology of each transition was characterized by the joint moments and entropy.

The results clearly show that the regime transitions are correlated with local time-frequency covariance peaks, which demonstrates that these regime transitions are characterized by a loss of stationarity. Consequently, the time-frequency covariance constitutes an objective two-phase flow regime transition indicator.
Void Fraction Distribution Patterns of Steady Air-Water Two-Phase Flow in a Rod Bundle With a Spacer
Authors: Takenaka N. , Asano H. , Fujii T. , Yoshii K. , Matsubayashi M.
Published: January 2022

Void fraction distributions of a steady air-water two-phase flow in a 4 × 4 rod-bundle with circular ferrule type spacers were visualized by neutron radiography. A high flux thermal neutron radiography system at JRR-3M in Japan Atomic Energy Research Institute and a fast neutron radiography system at Yayoi reactor in the University of Tokyo were used. Thermal neutron radiography was suitable for high void fraction two-phase flow and fast neutron radiography was suitable for low void fraction two-phase flow. Visualization with high spatial resolution up to 0.1 mm was carried out by using a cooled Charge Coupled Device (CCD) camera. The Computed Tomography (CT) reconstruction was carried out to obtain three-dimensional (3-D) void fraction distributions by a filtered back projection method. Cross-sectional averaged one-dimensional (1-D) void fraction distributions were also calculated for many experimental conditions by image processing methods. The 1-D and 3-D void fraction distributions were clearly visualized by neutron radiography. The void fraction distribution patterns in the rod bundle were discussed.
Unsteady Behavior of the Adiabatic Two-Phase Flow in Parallel Vertical Channels
Authors: Jović Valerije D. , Jović Larisa A. , Afgan Naim H.
Published: January 2022

Unsteady behavior of two phase mixture is very complex phenomena which depending on the characteristic of the system and range of the working parameters, will appear in the form of the deformed or selfsustanable flow rate oscillations, pressure, temperature and other parameters. In this paper results of the experimental and analytical study devoted to the investigation of unsteady regimes in air-water adiabatic two phase flow in the system three parallel hydrodinamicaly not identical vertical channels are presented. The onset of oscillatory instability parallel channel two phase flow in time and complex domain is analysed. Using experimentally determined transfer function of the system the criterion’s for the determination of the linearity or nonlinearity was defined. Obtained results show that dynamic equilibrium of conservative forces in two phase system do not ensure stable flow in all its parts. For the regimes when friction forces in two phase part of the channel are dominant over the dissipation and inertial forces, appearance of the unstable pulsation of pressure drop in one, two or all three parallel channels under stable system characteristics is possible.
Auto-Regressive Modeling for Flow Pattern Characterisation
Authors: Legius Erik J. W. M. , Mudde Robert F. , Van Den Akker Harry E. A.
Published: January 2022

The two-phase flow of air/water has been investigated in two ‘complex’ geometries: a vertical pipe with contraction and a line/riser system with a bend. Pressure recordings and optical fiber measurements have been analysed using Auto-Regressive modeling. This type of modeling describes the data as a linear combination of previous data. It is discussed how the transition from one flow regime to an other is influenced by the flow obstructions. The Auto-Regressive modeling provides a quantitative measure of the similarity between two flow realisations. It is found that identification of flow regimes based on this measure coincides with visual observation. With the Auto-Regressive technique the width of the transition could also be quantified. Furthermore it is shown, that the upward bend stabilises the slug flow in the vertical part downstream of the bend: the transition towards churn flow is postponed.
Flow Regime Map for Two-Phase Cocurrent Downflow in a Porous Medium
Authors: Revankar Shripad T.
Published: January 2022

Several flow regimes exist in a gas-liquid cocurrent downflow in a packed bed (trickle bed). These are given descriptive names such as trickle, pulsing, spray and bubble. The hydrodynamic and transport properties of trickle bed are dependent on these flow regimes. The hydrodynamic modeling of gas-liquid cocurrent downflow through a packed bed based on pore scale is presented. The pore scale hydrodynamic is related to the macroscopic scale flow parameters. The two-phase flow at pore level channel is modeled similar to annular two-phase flow in tubes. Using the film instability due to shear by the gas at the pore level channel, the transition criterion for the trickle flow to pulse flow regime is obtained. The model predictions agree with the published data. A model for transition from partial wetting to complete wetting in trickling flow was presented. The model predictions are in agreement with previous models. The model indicates better wetting of the smaller size packing for the same liquid mass flux.
Symbol-Sequence Statistics for Monitoring Fluidization
Authors: Finney C. E. A. , Nguyen K. , Daw C. S. , Halow J. S.
Published: January 2022

We propose that data-symbolization methods derived from nonlinear dynamics and chaos theory can be useful for characterizing and monitoring patterns in fluidized-bed measurement signals. Data symbolization involves the discretization of a measurement signal into a limited set of values. In this discretized form, the measurements can be processed very efficiently to detect dynamic patterns that signify various types of physical phenomena, including bubbling, slugging, and transitions between fluidization states. Besides computational efficiency, symbolic methods are also robust when noise is present. Using various types of measurements from experimental beds, we illustrate specific examples of how symbolization can be applied to fluidization diagnostics. We also suggest directions for future research.
Attenuation of Sound Waves in Liquids With Gas Bubbles in the Presence of a Combustible Gas Component
Authors: Khabeev Nail S. , Zolovkin N. A.
Published: January 2022

The effect of the combustible gas component on the propagation and damping of perturbations in bubbly mixtures is analyzed. For describing the propagation of acoustic perturbations in a liquid with bubbles containing combustible gas component it is possible to employ a one-velocity, two-pressure model of the medium that takes into account the radial inertia of the liquid with change in the voulume of the medium. The liquid carrier phase is assumed to be compressible, and the changes in bubble volume are described within the framework of a spherically symmetric model using the equation of the radial pulsations of the bubble. For simplification we introduced effective viscosity for taking into account heat dissipation. It is shown considerable effect of admixtures, such as chemical energy release due to the presence of a combustible gas component, on the interphase heat exchange in gas-liquid media, as well as on the phase velocity and attenuation of sound in bubbly mixtures.
Hybrid Approach to Tomographic Reconstruction of Bubbles in Two-Phase Flows Using Genetic Algorithm
Authors: Rajesh A. , Ko H. S. , Kihm Ken D.
Published: January 2022

Main hurdles in the application of genetic algorithms to complex problems are two folds. One is the high computational cost due to their slow convergence rate. The other is to reduce the input parameters of a conventional genetic algorithm as in the case of tomographic reconstruction of bubbles. In our present work great strides have been made to alleviate both the problems by using a Hybrid model of Algebraic Reconstruction Technique (ART), Simplex Method and Genetic Algorithm (GA).
Transient Three-Dimensional Density Distribution Reconstructed From Limited Interferogram Images
Authors: Okamoto Koji , Tsuru Daigo
Published: January 2022

Measurement of three-dimensional density distributions in a transient unstable stratified flow is important for the safety analysis on the advanced type nuclear power plant. Three-dimensional density distribution can be reconstructed using computer tomography technique from interferogram images. However, in the experiment, only a few interferogram images could be taken. Conventional tomography techniques have low accuracy with the limited interferogram images, since the information of the projection is not enough for the reconstruction.

While, the transient interferogram images can be easily taken using the real-time holographic interferometer and/or Mach-Zehnder interferometer. That is, there are enough information for the temporal domain. In this study, a transient three-dimensional (4D) reconstruction technique was proposed. The four-dimensional density distribution was assumed to be expressed as the summation of Elementary Distribution Functions (EDFs). The EDFs were distributed not only in the spatial domain, but also in the temporal domain. The tomography was carried out as the optimization of the arrangement for EDFs, using the temporal projection information.
Three-Dimensional Tomography of Thermal Flows for Limited Angle of View
Authors: Likhachov Alexey V. , Pickalov Valery V.
Published: January 2022

The paper is devoted to the study of 3D-tomography problems of flows with the numerical simulations, when the data being measured in the narrow angle range. The algebraic algorithms and ones based on the Fourier transform properties seem to be more appropriate for the considered case. The following of them have been investigated: ART, MART, MENT, Gerchberg-Papoulis type algorithm (mGP3D), combined algorithms cART and cMART.
Application of Transient Heat Flux Sensors to Resolve Time-Dependent Convective Heat Transfer From Wall-Mounted Cubes
Authors: Meinders E. R. , Geuzebroek M. J. , Hanjalić K. , Ortega A.
Published: January 2022

The application of an active fast-responding heat flux sensor to time-dependent heat flux measurements was studied for two aero-dynamically interfering wall-mounted cubes. This sensor was in-house made and it consisted of a heated thin platinum film deposited on an insulating substrate of glass. The frequency response of the sensor was determined from a calibration with chopped laser beams and with responses to on forehand known periodic oscillations in the flow. The purpose of the study was to measure possible correlation between the vortex shedding, induced at the upstream cube in the tandem, and the convective heat flux from the side faces of the downstream cube. This implied that we were mainly interested in detecting possible characteristic frequencies carried by the time-dependent heat flux signal rather than determining the absolute value of the time-dependent convective heat flux. The results showed maxima in the power density spectra of the heat flux signal at frequencies which were in good agreement with the shedding frequencies found in the corresponding velocity spectra.
Evaluation of an Insert Heat Flux Gage in a Transonic Turbine Cascade
Authors: Peabody Hume L. , Diller Thomas E.
Published: January 2022

The effects of using an insert Heat Flux Microsensor (HFM) versus an HFM deposited directly on a turbine blade to measure heat flux in a transonic cascade are investigated. The HFM is a thin-film sensor, 6.35 mm (0.250 in.) in diameter (for an insert gage, including the housing) which measures heat flux and surface temperature. The effects of physical gage offset from the blade surface were measured with an insert HFM in the high acceleration region of the suction side of the blade. This region of high convex curvature and thin boundary layer on a 5 cm (0.197 in.) chord blade makes exact matching of the flat-faced insert sensor with the surface difficult. For comparison, an identical thin-film sensor was deposited directly onto an identical blade surface at the same location, providing a minimal surface disruption on the order of the surface roughness of the blade itself.

The average heat transfer coefficients were compared for intentional offsets of ± 0.25 mm (0.01 in.) with the baseline cases. Turbulence grids were also used to study how the offset affects the heat transfer coefficient with freestream turbulence added to the flow. At the gage location the estimated laminar boundary layer thickness was 0.10 mm (0.004 in.). Both positive and negative offsets produced a higher average heat transfer coefficient than the zero offset case. Using an insert HFM reduced the effects of freestream turbulence and resulted in a substantially higher average heat transfer coefficient relative to the directly deposited gage, even for the zero offset case. Consequently, to accurately measure heat transfer coefficients and the effects of freestream turbulence for transonic turbine blades, the disruption of the flow caused by a gage must be minimized.
Equivalency of Counter-Current Vessel Heat Transfer Formulations
Authors: Roemer Robert B.
Published: January 2022

Models of counter-current blood vessel heat transfer have used one of two, different, previously unreconciled formulations, based either on: 1) an average vessel wall temperature difference, or 2) a bulk mean blood temperature difference. This paper shows that these two formulations are only equivalent when the four, previously undefined, “convective heat transfer coefficients” that are used in the bulk mean temperature difference formulation (two each for the artery and vein) have very specific, problem dependent relationships to the standard convective heat transfer coefficients. These bulk mean temperature difference formulation “convective heat transfer coefficients” are shown to be either: 1) arbitrary, user defined values, or 2) specific functions of a) the tissue conduction resistances, b) the standard convective heat transfer coefficients, and c) the independently specified bulk mean arterial, bulk mean venous and tissue temperatures. Thus, they are not true convective heat transfer coefficients, and must change values dependent on the blood and tissue temperatures, a dependence which significantly limits their usefulness.
A Semi-Infinite Model of Diffusion-Limited Water Transport During Osmotic Cell Dehydration
Authors: Kasharin Alexander V. , Karlsson Jens O. M.
Published: January 2022

A model of diffusive mass transport in a semi-infinite binary liquid solution with a moving semipermeable membrane is developed, in order to analyze dehydration of cells during cryopreservation. An analytic solution is obtained for the water concentration near the membrane, and a characteristic time-scale for cell dehydration is identified.
Mass Transfer Performance Evaluations of an Intravenous Membrane Oxygenator
Authors: Guzmán Amador M. , Amon Cristina H.
Published: January 2022

The mass transfer performance of an Intravenous Membrane Oxygenator is investigated by computational simulations of the conservation of mass, momentum and species equations. The Intravenous Membrane Oxygenator (IMO), is a device developed experimentally to provide consistent and reproducible oxygen and carbon dioxide exchange. The IMO is composed by an elastic and non-permeable pulsating balloon positioned within the vena cava, and micro-porous-membrane fibers that transport oxygen and carbon dioxide, located longitudinally between the balloon and vena cava. During the operation regime, the blood flow motion is originated by a blood pressure gradient and a pulsating balloon motion. A three-dimensional physical-computational model consisting of equally-spaced fibers and a Newtonian and time-dependent incompressible flow is used for the simulations. The numerical simulation results for the stationary balloon configuration, obtained using the spectral element method, demonstrate that the flow remains parallel, laminar and with absence of secondary flows in the whole domain. Evaluations of the mass transfer characteristics and parameters, such as the oxygen concentration profile around the fiber and the Sherwood number, for increasing Reynolds numbers, indicate that the parabolic flow regime increase the oxygen transfer rate until an asymptotic limit in the oxygen transfer capability is reached. A further increase in the Reynolds number beyond this asymptotic limit does not increase the oxygen transfer rate.