bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis on the Stability of Steady-State Responses of an Over-Hung Rotor With Two Disks Supported on Squeeze Film Damper
Authors: Nan Xia , Guang Meng , Tong Fang 
Published: January 2022

Abstract
The stability characteristics of steady-state circular responses of an over-hung rotor with two disks supported on centralized squeeze film damper (SFD) are analyzed in this paper by means of Lyapunov approximation criterion. The eigen-values of the characteristic matrix of variational equations for perturbed motion are solved and the four steps Runge-Kutta integration method is used to evaluate the rotor orbit. It is shown that the unstable response region is greatly influenced by system parameters. With appropriate parameters, die system will have totally stable response and small vibration amplitude. It is also found that the unstable response often appears before the response peak and the system may have three steady-state circular responses. The middle solution is usually unstable and the large solution may also unstable in some cases. There exist other kinds of stable steady-state responses, like non-synchronous responses. Only in very few special cases, the system response is numerically divergent.
Progress in the Analytical Modeling of Stochastic Layers
Authors: Luo Albert C. J. , Han Ray P. S. 
Published: January 2022

Abstract
The exponentially small splitting of separatrix, standard and whisker map approaches. Chirikov overlap criterion, renormalization group technique, incremental energy method are surveyed herein for the analytic modeling of stochastic layers caused by the interaction of nonlinear resonance in nonlinear dynamics. For verification of the analytic modeling, the numerical method to predict the onset of resonance in the stochastic layer through its minimum and maximum energy spectra is also presented. Illustrations of stochastic layers are given by the Poincare mapping section of the Duffing oscillator and periodically-driven pendulum.
Limit Cycles in Ballooning Strings
Authors: Zhu Fang , Rahn Christopher D. 
Published: January 2022

Abstract
This paper uses the Hopf bifurcation theorem to predict the limit cycles of ballooning strings observed in many textile manufacturing processes. The steady state and linearized solutions of the nonlinear governing equations are reviewed. The nonlinear dynamic equations are discretized and projected to a finite dimensional linear normal mode space, resulting in a set of nonlinearly coupled but linearly uncoupled ordinary differential equations. The first two equations, corresponding to the lowest normal mode, are analyzed using the Hopf bifurcation theorem. The first Lyapunov coefficient is calculated to prove the existence of stable limit cycles for double loop balloons with small string length. The bifurcation theorem, however, fails to apply to the large string length Hopf bifurcation point because the first Lyapunov coefficient is indeterminable. Numerical simulation of the nonlinear two-dimensional equations agrees with experimental results quantitatively for small string length and qualitatively for large string length.
Boiling-Induced Two-Phase Natural Convection in an Annular Channel Heated on the Downward Facing Side
Authors: Liu Y. C. , Cheung F. B. 
Published: January 2022

Abstract
The process of two-phase natural convection in an annular channel formed between a heated hemispherical vessel and a surrounding thermal insulation structure is studied theoretically and experimentally. The flow, being driven by buoyancy, is induced entirely by the boiling process taking place on the downward-facing side of the channel, i.e., on the outer surface of the heated vessel. Results of the flow analysis and the experimental observations indicate that there is a strong interaction between the induced two-phase motion and the boiling process. While the mass flow rate of the induced flow is a strong function of the wall heat flux, the rate of boiling is significant affected by the resulting flow. Relative to the case without thermal insulation, a higher boiling heat transfer is obtained in the present case, evidently due to an enhanced mass flow rate induced by the boiling process with the presence of a thermal insulation structure.
Natural Convection From Vertically Stacked Inclined Cylinders
Authors: Clark M. C. , Stewart J. C. , Gir S. 
Published: January 2022

Abstract
While there are published correlations dealing with average natural convection coefficients from a single horizontal, vertical, or inclined cylinder, there do not appear to be any for vertically stacked inclined cylinders. This study investigates natural convection from parallel inclined cylinders spaced two diameters apart in a low Rayleigh number range and Nusselt-Rayleigh number correlations are presented for this case. Convection coefficients generally decreased for both rods as the angle of inclination increased (from horizontal to vertical) and were consistently higher for the bottom rod in all configurations except vertical. Convection from the top cylinder appears to be impaired at this close spacing. Comparisons of the data to modified versions of various horizontal and one inclined cylinder formulation show that while predicted Nusselt numbers have similar trends, no single equation is a good predictor for both rods in this Rayleigh number range.
The Influence of Sun Patches on Buoyancy-Driven Air Movement and Heat Transfer Within a Passive Solar Test Cell
Authors: Arnold’ Peter D. , Hammond Geoffrey P. , Irving Andrew D. , Martin Christopher J. 
Published: January 2022

Abstract
The dynamic (time-varying) behaviour of buoyancy-driven air movement and heat transfer has been examined for a thermally lightweight, low energy test cell subject to external climatic variations. Measurements include heat transfer from a sun patch induced by solar gain through a south-facing, glazed façade This data was analysed by two different methods; simple single-sample thermo-fluid experiments and time-series analysis techniques. These were in turn compared with computational fluid dynamics simulations and recent correlating equations. The results provide insights into the physics of buoyancy-driven convective flows within, and the thermal design requirements for, passive solar buildings.
Turbulent Heat Transfer to Near-Critical Water in a Heated Curved Pipe Under the Conditions of Mixed Convection
Authors: Li L. J. , Lin C. X. , Ebadian M. A. 
Published: January 2022

Abstract
Numerical modeling was performed to investigate the developing turbulent flow and heat transfer characteristics of water near the critical point in a curved pipe. The renormalization group κ-ε model was used to account for the turbulent flow and heat transfer in the curved pipe at a constant wall temperature with or without buoyancy force effect. A control volume finite element method was used to numerically solve the three-dimensional fully elliptic governing equations for the problem. Due to the great variations in physical properties of water near the critical point, the turbulent structure can be significantly altered compared with the pure forced convection in the curved pipe. This study explored the influence of the near-critical pressure and wall temperature on the development of fluid and heat transfer along the pipe.
On Computations of Complex Turbulent Flow by Using Non-Linear K-ω Model
Authors: Song B. , Liu G. R. , Lam K. Y. , Amano R. S. 
Published: January 2022

Abstract
This paper presents the performance of a new non-linear k-ω model for computations of turbulent flows and heat transfer in several different flow types. This model is developed by incorporating cubic terms that take into account the anisotropy of the Reynolds stresses, and the effects of extra strain rates due to a streamline curvature and the rotation of the flow passages. Five cases of turbulent flows are numerically simulated: fully developed turbulent flows in a channel without rotation, in a curved channel, in a rotating channel, and the flow over a two-dimensional blunt rectangular section. Both flow and heat transfer characteristics were examined for the above mentioned flow passages. The governing equations are discretized using a non-staggered finite-volume formulation employing a bounded higher-order differencing scheme. The comparisons are made among the experimental data and the results obtained by DNS, linear and nonlinear k-ω models. It is shown that the non-linear k-ω model generally gives superior results over the existing linear k-ω model by demonstrating better agreement with the data for both flow and heat transfer computations.
Evaluation of Several Typical Correlations for Upward Flow Boiling Heat Transfer of Kerosene in Smooth Tube
Authors: Cheng Lixin , Chen Tingkuan 
Published: January 2022

Abstract
Experiment of upward flow boiling heal transfer with kerosene in vertical smooth tube was conducted. The length of the test section is 2.5m and the size of the tube is Φ19 × 2mm. The test is performed at an absolute pressure of 3 bar. The heat flux ranges from 28.5 to 93.75kW/m2 and the mass flux ranges from 410 to 810kg/m2s. The experimental results are used to evaluate six typical correlations. The selected correlations include Chen correlation, Shah correlation, the correlation of Gungor and Winterton, the correlation of Liu and Winterton, Klimenko correlation and Kandilar correlation. By comparison, the most suitable correlations are recommended for the calculation of flow boiling heal transfer coefficient of kerosene in smooth tube.
Effect of Surface Finish on Flow Boiling Heat Transfer
Authors: Kandlikar Satish G. , Spiesman Paul H. 
Published: January 2022

Abstract
It is well known that the surface structure affects the pool boiling heat transfer from a heater surface. The number and size distribution of cavities present on a heater surface affect the nucleation characteristics. This fact is utilized in developing structured and sintered surfaces for enhanced boiling performance. The nucleate boiling component in flow boiling is also expected to exhibit a somewhat similar dependence.
The present study investigates the flow boiling heat transfer of subcooled water over heater surfaces prepared with different roughness characteristics. The setup consists of a 9.5 mm diameter circular heater placed on the lower wall of a 3 mm × 40 mm horizontal channel. Four different surface finishes are tested on the same heater unit. Each surface is observed under a microscope, and analyzed with an image processing software to obtain the cavity size distribution. Relationships between the cavity size distribution and the heat transfer are then compared for the four surfaces.
The results indicate that the wall superheats for the four surfaces tested were within 0–30 percent of each other for a given heat flux. Although the roughest surface generally performed the best, no definite trend could be observed. It is also noted that the cavity size distribution of a surface is not significantly affected by simple polishing techniques. A commercially prepared sintered surface is also tested. Its performance was markedly above the four roughened surfaces. However, the sintered surface exhibited a large hysteresis effect, while the four roughened surfaces showed little hysteresis under the test conditions.
CHF Enhancement by Modulated Porous-Layer Coating
Authors: Liter Scott G. , Kaviany Massoud 
Published: January 2022

Abstract
The effect of structural modulation of porous-layer coating on the qCHF for horizontal surfaces is examined experimentally. The surface consists of a copper substrate coated with spherical copper particles which are diffusion sintered into modulated structures inside graphite molds. Results are reported for pentane boiling on four different surfaces; a plain uncoated surface, a surface with a porous-layer coating of uniform thickness, and two surfaces with different modulated porous-layer coatings. A two-fold increase in the critical heat flux (qCHF) is found for one of the modulated porous-layer coatings. A brief explanation of the hydrodynamic theory for the qCHF is then given in which it is postulated that the qCHF occurs when columnar, vapor-escape passages through the liquid become unstable and collapse. It is then hypothesized that the enhancement of the modulated coating results from surface-induced changes in the characteristic interfacial wavelengths that stabilize the liquid-vapor interfaces, delaying the collapse of these vapor escape paths, and ultimately increasing qCHF.
Turbulent Heat Transfer in Single Phase Jet Impingement Flow Over a Flat Circular Disk
Authors: Siba Erick A. , Ganesa-Pillai M. , Harris Kendall T. , Haji-Sheikh A. 
Published: January 2022

Abstract
The flow and heat transfer characteristics of a turbulent submerged air jet impinging on a horizontal flat surface is studied. The primary aerodynamics that influence the heat transfer are shown to be the turbulent fluctuations of the free stream velocity. Two regions with distinct flow characteristics are observed, the impingement or stagnation region, and the wall-jet region. Heat transfer relations are derived for each region, based on the assumption that the sum of the laminar and turbulent component of heat flux approximates the total wall heat flux. The laminar component, hlam, of the heat transfer coefficient agrees well with published data. The turbulent component, htur, in the stagnation and wall-jet region are shown to vary linearly with the root mean square value of the fluctuating component of velocity, u’. Unlike the stagnation region, htur in the wall-jet region shows dependence on the Nozzle Reynolds Number, ReD.
The Effect of Geometrical Arrangement on the Transient Temperature Computation of Contacting Spheres
Authors: Siu W. W. M. , Lee S. H.-K. 
Published: January 2022

Abstract
Among engineering systems requiring heat transfer analyses, spheres in a packing structure is one of the more common configuration. A porous medium approach is often used to solve such a complicated system. In fact, it is a useful tool for solving a system involving a large number of spheres, such as in a geothermal system. However for systems containing less spheres, such as in a sintering application, this approach may not be accurate. Recently, a method was developed to solve the mean temperature of contacting spheres in 180 degree orientation. This method used thermal constriction resistances and was able to provide much finer resolution, but contact angles of 180 degree are not a realistic arrangement for spheres in a packing. The present study seeks to extend the earlier formulation to accommodate spheres with varying contact angles. A finite volume formulation was developed using non-uniform grids. Since the grid size must necessarily be small at the contact surfaces, the computation time was significant. To alleviate this, a Multi-Spatial-Temporal Grid Scheme was utilized. A new governing equation has been formulated and verified for packed spheres with varying contact angles. In addition, correlations for the corresponding constriction resistance and the characteristic time parameter have also been developed.
Mixed Convection in Flow Past a Porous Cavity: Application of the UNIFAES Discretization Scheme
Authors: Llagostera Jorge , Figueiredo José R. 
Published: January 2022

Abstract
Combined natural and forced convection occurring in saturated porous media is an important subject in several engineering fields, including design of high performance thermal insulation systems, packed beds, contaminants flow, and the development of geothermal resources.
The paper presents numerical simulation results on mixed convection flow past a porous cavity located in a porous layer. The steady-state regime is studied for several intensities of the buoyancy effects due to temperature variations. The influences of Péclet and Rayleigh numbers on flow pattern and temperature distributions are examined. Local and global Nusselt numbers are reported for the heated wall.
The differential equations were approximated numerically, being discretized by integration over finite volumes. The fluxes at the volume boundaries were represented using the UNIFAES discretization scheme. The UNIFAES, unified finite approaches exponential scheme for convective-diffusive fluid transport equations, has shown excellent accuracy and stability with irregular grids.
Experimental Study of Solids Conveying in Single-Screw Food Extrusion
Authors: Zhang Shibo , Sernas Valentinas 
Published: January 2022

Abstract
Up to now, all the theories on solids conveying in single-screw extruders (Darnell and Mol, 1956; Broyer and Tadmor, 1972; Campbell and Dontula, 1995; Hyun and Spalding, 1997) considered the solids to move as a plug flow (i.e., there is no relative movement in the granular solid, the velocity of the granules is constant in time and uniform in space). Therefore, the solids were treated as a rigid body which never experienced any deformation. But our experiments have shown that in corn meal extrusion, the solids move as a plug only in the loose powder region. After the start of compaction, there is a helical flow in the extruder channel. The flow in this region is not a plug flow at all, and the convective heat transfer is not negligible. Based on our experiments, the whole extrusion process can be divided into four zones, each one having different characteristics. Each zone should be treated with different motion models.
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.